New Simulation Recreates an Early Time in the Universe That Still Hasn't Been Seen Directly

The fields of astronomy and astrophysics are poised for a revolution in the coming years. Thanks to next-generation observatories like the James Webb Space Telescope (JWST), scientists will finally be able to witness the formation of the first stars and galaxies in the Universe. In effect, they will be able to pierce the veil of the Cosmic Dark Ages, which lasted from roughly 370,000 years to 1 billion years after the Big Bang.

During this period, the Universe was filled with clouds of neutral hydrogen and decoupled photons that were not visible to astronomers. In anticipation of what astronomers will see, researchers from the Harvard & Smithsonian Center for Astrophysics (CfA), the Massachusetts Institute of Technology (MIT), and the Max Planck Institute for Astrophysics (MPIA) created a new simulation suite called Thesan that simulates the earliest period of galaxy formation.

The creation of the Thesan suite and the results the team obtained are described in a series of three papers that were recently accepted to the Monthly Notices of the Royal Astronomical Society. The simulations were created using the SuperMUC-NG supercomputer located at the Leibniz Supercomputing Centre of the Bavarian Academy of Sciences. The process took over 30 million CPU hours and would have required more than 3,500 years to complete on a conventional computer.

An illustration of cosmic expansion. Credit: NASA’s Goddard Space Flight Center Conceptual Image Lab

The simulations cover the Epoch of Reionization (ca. 13 billion years ago). In this cosmic period, neutral hydrogen atoms were ionized to form positive hydrogen atoms, allowing light to spread throughout the Universe. Simulating this period was no easy task, as it involved recreating some immensely complicated and chaotic interactions between gravity, gas, radiation, and more. It also meant capturing physics down to scales a million times smaller than the simulated regions.

The team accomplished this by combining realistic models of galaxy formation and cosmic dust with a new algorithm that tracks how light interacts with gas. Through this, they were able to resolve interactions in the early Universe in unprecedented detail and over the largest volume of any previous simulation. As Rahul Kannan, an astrophysicist at the CfA and the lead author of the first paper in the series, explained:

“Most astronomers don’t have labs to conduct experiments in. The scales of space and time are too large, so the only way we can do experiments is on computers. We are able to take basic physics equations and governing theoretical models to simulate what happened in the early universe.”

“A lot of telescopes coming online, like the JWST, are specifically designed to study this epoch. That’s where our simulations come in; they are going to help us interpret real observations of this period and understand what we’re seeing.”

Image of the Universe’s large-scale structure, showing filaments and voids within the cosmic structure. Credit: Millennium Simulation Project

With this new simulation suite, researchers can simulate a piece of our Universe spanning 300 million light-years in diameter. They can then run it forward in time to track and visualize the formation of the first galaxies in this space, beginning around 400,000 years after the Big Bang, and watch how they evolved during the first billion years. When the team ran the simulations, they found that the transition from complete darkness to light was gradual.

Said study co-author Aaron Smith, a NASA Einstein Fellow in MIT’s Kavli Institute for Astrophysics and Space Research:

“It’s a bit like water in ice cube trays; when you put it in the freezer, it does take time, but after a while it starts to freeze on the edges and then slowly creeps in. This was the same situation in the early Universe — it was a neutral, dark cosmos that became bright and ionized as light began to emerge from the first galaxies.”

The simulations were created to prepare for observations from next-generation telescopes like James Webb, Nancy Grace Roman, and Origins space telescopes. Along with ground-based telescopes like the Extremely Large Telescope (ELT) and the Giant Magellan Telescope (GMT), these observatories will be able to see deeper into space and (hence) farther back in time than their predecessors. In fact, it is estimated that James Webb will be able to see the Universe as it was 13.5 billion years ago.

Right now, the record for the most distant single object ever seen goes to Earendel, a star located about 12.9 billion light-years from Earth. In terms of galaxies, that record goes to GN-z11, located about 13.39 billion light-years from Earth in the constellation Ursa Major. What’s especially exciting is that the astronomical community won’t have to wait long for real telescope observations and data to be compared to Thesan simulations.

A visualization of what the Universe looked like when it was going through its last major transformative era: the epoch of reionization. Credit: Paul Geil & Simon Mutch/The University of Melbourne

“And that’s the interesting part,” said co-author Mark Vogelsberger, an associate professor of physics at MIT. “Either our Thesan simulations and model will agree with what JWST finds, which would confirm our picture of the universe, or there will be a significant disagreement showing that our understanding of the early universe is wrong.”

However, the team won’t know how their model stacks up against the real thing until the first observations become available. Once they do, they will attempt to match various aspects of their model to the observations, including the properties of early galaxies and the absorption and escape of light in the early Universe. From this, we will finally know how and when the Dark Ages were dispelled.

“We have developed simulations based on what we know,” Kannan says. “But while the scientific community has learned a lot in recent years, there is still quite a bit of uncertainty, especially in these early times when the universe was very young.”

For generations, astronomers have waited for the day when it would be possible to view the earliest periods of the Universe and see how it all began. When paired with observations of how the cosmos has evolved since scientists will finally be able to address some of the deepest mysteries of the cosmos. To know that such a day is right around the corner is nothing short of exciting!

And be sure to check out this 3D view of the Thesan simulation. Check out more simulations on their Youtube page!

Further Reading: Harvard-Smithsonian Center for Astrophysics

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Europa Could be Pulling Oxygen Down Below the Ice to Feed Life

Jupiter’s moon Europa is a prime candidate in the search for life. The frozen moon has a subsurface ocean, and evidence indicates it’s warm, salty, and rich in life-enabling chemistry.

New research shows that the moon is pulling oxygen down below its icy shell, where it could be feeding simple life.

Whether or not Europa can sustain life in its subsurface ocean is highly debatable, and the debate is essentially stuck in neutral until NASA sends the Europa Clipper there. The mission to Europa has to be meticulously designed, and NASA bases part of the design on what specific questions scientists want the Clipper to address. We can’t send a spacecraft to Europa and tell it to find life.

NASA designs missions with big questions in mind, but they can only answer smaller, specific questions. So scientists are studying different aspects of Europa and performing simulations to fine-tune the questions they need the mission to ask.

Oxygen is at the heart of one of those questions. It might be the final piece in understanding Europa’s habitability.

Europa has, or we think it has, most of what life needs to sustain itself. Water is the prime ingredient, and it has an abundance of water in its subsurface ocean. Europa has more water than Earth’s oceans. It also has the required chemical nutrients. Life needs energy, and Europa’s energy source is tidal flexing from Jupiter, which heats its interior and stops the ocean from freezing solid. These are pretty well-established facts to most scientists.

The frozen moon also has oxygen at its surface, another intriguing hint of habitability. The oxygen is generated when sunlight and charged particles from Jupiter strike the moon’s surface. But there’s a problem: Europa’s thick ice sheet is a barrier between oxygen and the ocean. Europa’s surface is frozen solid, so any life would have to be in its vast ocean.

How can oxygen make its way from the surface to the ocean?

When charged particles strike Europa’s surface, they split water molecules apart. The lighter hydrogen floats away into space, but the oxygen stays behind. If the oxygen somehow makes its way to the ocean, it could provide chemical energy for microbial life. Image Credit: NASA

According to a new research letter, pools of saltwater in Europa’s icy shell could be transporting the oxygen from the surface to the ocean. The research letter is “Downward Oxidant Transport Through Europa’s Ice Shell by Density-Driven Brine Percolation,” published in the journal Geophysical Research Letters. The lead author is Marc Hesse, a professor at the UT Jackson School of Geosciences Department of Geological Sciences.

These briny pools exist in places in the shell where some ice melts due to convection currents in the ocean. Europa’s famous and photogenic chaos terrain forms above these pools.

Chaos terrain covers about 25% of Europa’s frozen surface. Chaos terrain is where ridges, cracks, faults, and plains are jumbled together. There’s no clear understanding of the exact causes of chaos terrain, though it’s likely related to uneven subsurface heating and melting. Some of Europa’s most iconic images highlight this strangely beautiful feature.

Image of Europa’s ice shell, taken by the Galileo spacecraft, of fractured “chaos terrain.” Saltwater pools below chaos terrain may be transporting oxygen to the moon’s ocean. Image Credit: NASA/JPL-Caltech

Scientists think Europa’s ice sheet is about 15 to 25 km (10 to 15 miles) thick. A 2011 study found that chaos terrain on Europa may be located above vast lakes of liquid water as little as 3 km (1.9 miles) below the ice. These lakes aren’t directly connected to the subsurface ocean but can drain into them. According to this new study, the briny lakes can mix with surface oxygen and over time, can deliver large quantities of oxygen to the deeper subsurface ocean.

This figure from the study shows how oxidants are generated and distributed in Europa’s surface ice. Radiolysis sputters H2O into H2 and O, with O recombining into O2. Some of the O2 is released into the moon’s atmosphere, but most of it returns to the icy regolith and is trapped in bubbles. The bubbles are the dominant near-surface reservoir for oxidants. Over thousands of years, the bubbles can make their way down to the ocean. Image Credit: Hesse et al. 2022.

“Our research puts this process into the realm of the possible,” said Hesse. “It provides a solution to what is considered one of the outstanding problems of the habitability of the Europa subsurface ocean.”

The researchers showed how oxygen is transported through the ice in their simulation. The oxygen-laden brine moves to the subsurface ocean in a porosity wave. A porosity wave transports the brine through the ice by momentarily widening the pores in the ice before quickly sealing up again. Over thousands of years, these porosity waves transport the oxygen-rich brine to the ocean.

The physics-based model built by the researchers shows a porosity wave (spherical shape) carrying brine and oxygen at Europa’s surface through the moon’s ice shell to the liquid water ocean below. The chart shows time (in thousands of years) and ice shell depth (in kilometres). Red indicates higher levels of oxygen. Blue represents lower levels of oxygen. Credit: Hesse et al. 2022

The relationship between chaos terrain and oxygen transport is not completely clear. But scientists think that convective upwellings caused by tidal heating partially melt the ice, manifesting as the jumbled chaos terrain on the surface. The ice under the brine must be molten or partially molten for the oxygen-rich brine to drain into the ocean. “For these brines to drain, the underlying ice must be permeable and thus partially molten. Previous studies show that tidal heating increases the temperature of upwellings in the convecting portion of Europa’s ice shell to the melting point of pure ice,” the authors write.

“Given that chaotic terrains likely form over diapiric upwellings, it is plausible that the underlying ice is partially molten,” the letter says. The presence of NaCl in the connecting ice likely increases the melt.

Europa’s surface is bitterly cold but not cold enough to refreeze so quickly that oxygen can’t be transported in brines. At the moon’s poles, the temperature never rises above minus 220 C (370 F.) But the model’s results “… demonstrate that refreezing at the surface is too slow to arrest the drainage of the brine and prevent oxidant delivery to the internal ocean.” Though Europa’s surface ice is frozen solid, the ice under it is convective, which delays freezing. And some research shows that the seafloor may be volcanic.

This illustration shows how volcanism in Europa’s interior might work to maintain a liquid ocean. Credit: NASA/JPL-Caltech/Michael Carroll

The study says that about 86% of the oxygen taken up at Europa’s surface makes it to the ocean. Over the moon’s history, that percentage could have shifted widely. But the highest estimate produced by the researchers’ model creates an oxygen-rich ocean very similar to Earth’s. Could something be living under the ice?

Artist’s impression of a hypothetical ocean cryobot (a robot capable of penetrating water ice) in Europa. Credit: NASA

“It’s enticing to think of some kind of aerobic organisms living just under the ice,” said co-author Steven Vance, a research scientist at NASA’s Jet Propulsion Laboratory (JPL) and the supervisor of its Planetary Interiors and Geophysics Group.

Kevin Hand is one of the many scientists keenly interested in Europa, its potential for life, and the upcoming Europa Clipper mission. Hand is a NASA/JPL scientist whose work focuses on Europa. He’s hopeful that Hesse and his fellow researchers have solved the problem of oxygen in the frozen moon’s oceans.

“We know that Europa has useful compounds like oxygen on its surface, but do those make it down into the ocean below, where life can use them?” he asked. “In the work by Hesse and his collaborators, the answer seems to be yes.”

What questions can the Europa Clipper ask that might confirm these findings?

The Clipper is the first mission dedicated to Europa. We think we know many things about Europa that we haven’t been able to confirm. The Clipper is designed to address three larger objectives:

• Investigate the ocean’s composition to determine if it has the necessary components to sustain life.
• Investigate the moon’s geology to understand how the surface formed, including the chaos terrain.
• Determine the ice shell’s thickness and if there’s liquid water within and beneath it. They also will determine how the ocean interacts with the surface: Does anything in the ocean rise through the shell to the top? Does any material from the surface work its way down into the ocean?

That last point speaks to the potential transport of oxygen from the surface to the ocean. The Europa Clipper will carry ten instruments that will work together to address these questions.

The MAss SPectrometer for Planetary EXploration/Europa (MASPEX) is particularly interesting when it comes to oxygen transport on Europa.

“MASPEX will gain crucial answers from gases near Europa, such as the chemistry of Europa’s surface, atmosphere, and suspected ocean,” the instrument’s web page explains. “MASPEX will study how Jupiter’s radiation alters Europa’s surface compounds and how the surface and ocean exchange material.”

MASPEX, and the rest of Europa Clipper’s instruments, might confirm oxygen transport from the surface to the ocean, where life could use it if life exists there. But we’ll have to wait a while. Europa Clipper is scheduled to launch in October 2024 and won’t reach the Jupiter system until 5.5 years later. Once there, its science phase is expected to last four years. So it could be 2034 before we have all the data.

In the meantime, research like this will whet our appetites.

More:

• Press Release: On Jupiter’s Moon Europa, ‘Chaos Terrains’ Could be Shuttling Oxygen to Ocean
• Research Letter: Downward Oxidant Transport Through Europa’s Ice Shell by Density-Driven Brine Percolation
• Universe Today: If There are Water Plumes on Europa, Here’s how Europa Clipper Will Study Them

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It’s Not Conclusive, But Methane is Probably the Best Sign of Life on Exoplanets

When the James Webb Space Telescope aims at exoplanet atmospheres, it’ll use spectroscopy to identify chemical elements. One of the things it’s looking for is methane, a chemical compound that can indicate the presence of life.

Methane is a compelling biosignature. Finding a large amount of methane in an exoplanet’s atmosphere might be our most reliable indication that life’s at work there. There are abiotic sources of methane, but for the most part, methane comes from life.

But to understand methane as a potential biosignature, we need to understand it in a planetary context. A new research letter aims to do that.

Methane is interesting because it doesn’t last long in an atmosphere. Photochemical reactions destroy it, so detecting a lot of it means something is constantly replenishing it. There has to be a large and prominent source. “Terrestrial planets, which are the focus of this study, require significant methane surface fluxes to sustain high atmospheric abundances,” the study says. “On Earth, life sustains large methane surface fluxes, and so methane has long been regarded as a potential biosignature gas for terrestrial exoplanets.”

But not all methane detections will mean life. Scientists need a way to work through any future methane detections in exoplanet atmospheres. The researchers wanted to create a “…dedicated assessment of the planetary conditions needed for methane to be a good biosignature.”

“We wanted to provide a framework for interpreting observations, so if we see a rocky planet with methane, we know what other observations are needed for it to be a persuasive biosignature.”

Maggie Thompson, lead author, UC Santa Cruz.

The new research letter is titled “The case and context for atmospheric methane as an exoplanet biosignature.” It’s available online at the Proceedings of the National Academy of Sciences (PNAS.) The lead author is Maggie Thompson, a graduate student in astronomy and astrophysics at UC Santa Cruz.

Part of methane’s status as a reliable biosignature is its detectability. Oxygen is a good biosignature, and for some of the same reasons methane is. Like methane, it’s also unstable in an atmosphere, so finding a large quantity of it means a significant source is replenishing it.

The James Webb Space Telescope will be operating soon, and one of its jobs is to examine exoplanet atmospheres spectroscopically. It’ll be characterizing exoplanet atmospheres, and detecting biosignatures is part of that work. But while Webb will detect methane relatively easily in a terrestrial atmosphere, oxygen is more difficult to detect. “Given the imminent feasibility of observing methane with JWST, it is imperative to determine the planetary conditions where methane is a compelling biosignature,” the authors write.

This research letter wants to put scientists in a stronger position to interpret methane’s presence in an exoplanet atmosphere. The idea is to identify what other questions researchers need to ask when they detect methane. What other indications will support the conclusion that methane is a biosignature? What will contradict that?

“We wanted to provide a framework for interpreting observations, so if we see a rocky planet with methane, we know what other observations are needed for it to be a persuasive biosignature,” lead author Thompson said in a press release.

The team examined abiotic methane sources to understand how they might account for methane in an exoplanet atmosphere. Volcanoes are one abiotic source of methane. Methane also comes from reactions in places like mid-ocean ridges, hydrothermal vents, and tectonic subduction zones. Comet and asteroid impacts can also produce methane. Researchers can look for evidence of these sources on an exoplanet where they detect methane.

<Click Image to Enlarge> This figure from the study compares methane sources on Earth. The top row shows biogenic methane flux; all other rows show abiogenic methane flux from other sources. No abiotic source can produce the same methane flux as life can. Image Credit: Thompson et al. 2022.

In planetary atmospheres, methane exists in relation to other gases. So identifying abiotic methane sources is only part of the picture. How do other gases like carbon monoxide and carbon dioxide fit into a methane-rich atmosphere? How do they affect one another?

“Methane is one piece of the puzzle, but to determine if there is life on a planet you have to consider its geochemistry, how it’s interacting with its star and the many processes that can affect a planet’s atmosphere on geologic timescales.”

Maggie Thompson, lead author, UC Santa Cruz.

From the research letter:

“While methane can be produced by a variety of abiotic mechanisms such as outgassing, serpentinizing reactions, and impacts, we argue that—in contrast to an Earth-like biosphere—known abiotic processes cannot easily generate atmospheres rich in CH4 and CO2 with limited CO…” the authors explain in their paper.

Earth’s history provides some clues to methane in exoplanet atmospheres. We know that in the past, Earth had an even more methane-rich atmosphere than it does now. And we know what the source was: life.

“If you detect a lot of methane on a rocky planet, you typically need a massive source to explain that,” said co-author Joshua Krissansen-Totton, a Sagan Fellow at UCSC. “We know biological activity creates large amounts of methane on Earth, and probably did on the early Earth as well because making methane is a fairly easy thing to do metabolically.”

Methane-producing microorganisms called methanogens were one of Earth’s earliest lifeforms, originating between 4.11 and 3.78 billion years ago. They were so effective at producing methane that at several times early Earth likely had a hazy, methane-filled atmosphere similar to Saturn’s moon Titan. Maybe we’ll find an exoplanet with a methane-rich atmosphere similar to early Earth’s one day. If that happens, we’ll likely detect it from a great distance, making it challenging to determine if the source is biotic.

But detecting abiotic sources of methane is potentially much more straightforward. Volcanoes, for example, provide other clues that methane is from a non-living source. Volcanoes not only inject methane into the atmosphere but also carbon monoxide. On the other hand, biological activity is likely to consume carbon monoxide. The researchers found that nonbiological processes cannot readily produce habitable planet atmospheres rich in methane and carbon dioxide and with little to no carbon monoxide.

This diagram shows the geological process of subduction, where a heavier tectonic plate sinks under a lighter one. Alteration of ultramafic rocks in subduction zones plays a major role in methane production via abiotic processes on Earth and beyond. Image Credit: By KDS4444 – Own work, CC BY-SA 4.0, https://ift.tt/OiKfCEx.

“One molecule is not going to give you the answer—you have to take into account the planet’s full context,” Thompson said. “Methane is one piece of the puzzle, but to determine if there is life on a planet, you have to consider its geochemistry, how it’s interacting with its star and the many processes that can affect a planet’s atmosphere on geologic timescales.”

The authors point out that the detection of methane in an exoplanet’s atmosphere is just the beginning. They found that detecting methane is a strong indicator of life for a rocky planet orbiting a Sun-like star if the atmosphere also contains carbon dioxide. If methane is more abundant than carbon dioxide, that’s also a more robust indicator of life, as long as the planet isn’t too water-rich.

This image is a summary of known abiotic sources of methane on Earth. (©2022 Elena Hartley)

The James Webb Space Telescope is extraordinarily powerful. But no observing tool or method is error-free, even the long-awaited Webb. False positives are an issue in scientific endeavours like the search for biosignatures. The researchers looked at the role false positives play in biosignatures and gave some guidelines for handling methane detections.

“The atmospheres of rocky exoplanets are probably going to surprise us, and we will need to be cautious in our interpretations.”

Joshua Krissansen-Totton, co-author, UCSC.

“There are two things that could go wrong—you could misinterpret something as a biosignature and get a false positive, or you could overlook something that’s a real biosignature,” Krissansen-Totton said. “With this paper, we wanted to develop a framework to help avoid both of those potential errors with methane.”

“With the upcoming technological advancements in exoplanet observations enabling the characterization of potentially habitable exoplanets, it is important to consider possible biosignature gases and the sources of false-positive detections,” the research letter says. “This is particularly urgent for methane since biogenic methane is likely detectable for some terrestrial exoplanets with JWST.”

The researchers acknowledge that various abiotic sources could replenish atmospheric methane in diverse planetary environments. But for a planet to produce a methane flux comparable to Earth’s, the same abiotic sources would also generate “observable contextual clues” that would indicate a false positive. “In every case, abiotic processes cannot easily produce atmospheres rich in CH4 and CO2 with negligible CO…” Life would readily consume the CO.

“Clearly, the mere detection of methane in an exoplanet’s atmosphere is not sufficient evidence to indicate the presence of life given the variety of abiotic methane-production mechanisms. Instead, the entire planetary and astrophysical context must be taken into account to interpret atmospheric methane.”

The hunt for biosignatures in exoplanet atmospheres is a relatively new scientific undertaking. Researchers need to do a lot of groundwork before they can have confidence in detecting things like methane. The recent detection, or non-detection, of methane on Mars, shows how incomplete our understanding of other planets is and how the detection of methane may only be a starting point in painting a complete picture of a planet.

This image illustrates possible ways methane might get into Mars’ atmosphere and be removed from it: microbes (left) under the surface that release the gas into the atmosphere, weathering of rock (right), and stored methane ice called a clathrate. Ultraviolet light can work on surface materials to produce methane and break it apart into other molecules (formaldehyde and methanol) to produce carbon dioxide. Credit: NASA/JPL-Caltech/SAM-GSFC/Univ. of Michigan

“This study is focused on the most obvious false positives for methane as a biosignature,” Krissansen-Totton said. “The atmospheres of rocky exoplanets are probably going to surprise us, and we will need to be cautious in our interpretations. Future work should try to anticipate and quantify more unusual mechanisms for nonbiological methane production.”

“With these results, we provide a tentative framework for assessing methane biosignatures,” the authors write. “If life is abundant in the Universe, then with the correct planetary context, atmospheric methane may be the first detectable indication of life beyond Earth.”

More:

• Press Release: Methane could be the first detectable indication of life beyond Earth
• Research Letter: The case and context for atmospheric methane as an exoplanet biosignature
• Universe Today: If a Planet Has a Lot of Methane in its Atmosphere, Life is the Most Likely Cause

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Supermassive Black Holes Shut Down Star Formation

One of the key aspects of galactic evolution is star production. On a basic level, stars form within a galaxy’s gas and dust all the time, and where they form can help determine a galaxy’s shape and size. But there seems to be a sweet point when star production in a galaxy is particularly strong. Galaxies often have a period of rapid star production which then drops off. Astronomers are still trying to understand what causes this drop-off.

One idea is that galaxies simply run out of the gas and dust needed to form stars. Stars consume gas and dust to form, and since stars can last for billions of years, there’s increasingly less material available. Another idea is that supernovae clear a galaxy of gas and dust. The earliest stars of a galaxy are often incredibly massive, living short lives and exploding as supernovae. The shock waves from these supernovae could quench star production by ripping apart star-forming regions. But a new study suggests the main cause is the supermassive black hole that lurks in the heart of a galaxy.

In the study, the team took data from the Sloan Digital Sky Survey (SDSS) and applied machine learning to categorize galaxies into active galaxies where star formation is high and quiescent galaxies where star production is low. They then correlated these with three parameters: the mass of a galaxy’s dark matter halo, the total mass of stars in the galaxy, and the mass of the galaxy’s supermassive black hole. They found that black hole mass was the strongest factor in determining whether a galaxy is active or quiescent.

Artist’s representation of an active galactic nucleus (AGN) at the center of a galaxy. Credit: NASA/CXC/M.Weiss

But why would this be? To answer this question, the team used computer simulations to model various possibilities for quenching star production. By comparing their simulations with the observed distribution of galaxies, they found the strongest model was one where a supermassive black hole injects energy into the surrounding galaxy. As a galaxy’s black hole grows, it becomes an active galactic nucleus (AGN), which can create powerful jets and push gas and dust away from the center of the galaxy. The larger the black hole, the more powerful that push can be.

Galaxies with lots of gas and dust in their central region are ripe for star production. But they are also the perfect setting for supermassive black holes to grow larger. So, a galaxy can be active for a time, until the black hole becomes active itself and kills off star production.

Reference: Piotrowska, Joanna M., et al. “On the quenching of star formation in observed and simulated central galaxies: Evidence for the role of integrated AGN feedback.” Monthly Notices of the Royal Astronomical Society 512.1 (2022): 1052-1090.

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NASA Astronaut and Cosmonauts Land Safely Together in Kazakhstan

After much speculation and concern the past month whether Russia would allow a US astronaut to ride back to Earth in a Soyuz spacecraft, Mark Vande Hei and two cosmonauts landed safely in Kazakhstan on March 30.  

Mostly lost amid the political tensions due to Russia’s invasion of Ukraine, Vande Hei quietly set a record for the longest single spaceflight by an American, at 355 days. Vande Hei eclipsed astronaut Scott Kelly’s seemingly more heralded long-duration mission on the International Space Station in 2015, when he and Cosmonaut Mikhail Kornienko spent 340 days in space. Cosmonaut Pyotr Dubrov also spent 355 days on his first spaceflight, along with Vande Hei.

Vande Hei, Dubrov and Anton Shkaplerov landed under parachute at 7:28 a.m. (5:28 p.m. Kazakhstan time) southeast of the remote town of Dzhezkazgan, Kazakhstan. Vande Hei tweeted that he was thrilled to be “back on Mother Earth.”

Fantastic place, occupied by amazing people, working for all of humanity. I’ll forever cherish the memories of serving on the International Space Station. Now, though, I’m thrilled to be back on Mother Earth! pic.twitter.com/pv0V2DqkXZ

— Mark T. Vande Hei (@Astro_Sabot) March 30, 2022

The crew was taken for post-landing checkups in nearby Karaganda, Kazakhstan, aboard Russian helicopters. Vande Hei then boarded a NASA plane, which stopped in Germany for refueling before returning to the US. The plane reached Ellington Field in Houston this morning, March 31.

Russian Search and Rescue teams arrive at the Soyuz MS-19 spacecraft shortly after it landed in a remote area near the town of Zhezkazgan, Kazakhstan with Expedition 66 crew members Mark Vande Hei of NASA, and cosmonauts Pyotr Dubrov, and Anton Shkaplerov of Roscosmos, Wednesday, March 30, 2022. Credit: NASA/Bill Ingalls.

The landing and departure came without tensions or any show of political propaganda. However, NASA avoided Russian airspace when it flew to Kazakhstan for the landing.

Looks like NASA5 completely avoided Russian airspace. Apparently no diplomatic exemption for NASA. pic.twitter.com/x1kGJ64Im7

— Pete ? ? ?? (@Space_Pete) March 27, 2022

NASA said that Vande Hei’s extended mission will provide researchers the opportunity to observe the effects of long-duration spaceflight on humans as the agency plans to return to the Moon under the Artemis program and prepare for exploration of Mars.

“Mark’s mission is not only record-breaking, but also paving the way for future human explorers on the Moon, Mars, and beyond,” said NASA Administrator Bill Nelson, in a press release. “Our astronauts make incredible sacrifices in the name of science, exploration, and cutting-edge technology development, not least among them time away from loved ones. NASA and the nation are proud to welcome Mark home and grateful for his incredible contributions throughout his year-long stay on the International Space Station.”

NASA astronaut Mark Vande Hei takes in the view from the International Space Statio’s multi-window cupola compartment in February. The Soyuz spacecraft that will carry him back to Earth on March 30 after a 355-day stay in space is visible out the center window. Credit: NASA

Vande Hei launched April 9, 2021, alongside cosmonauts Dubrov and Oleg Novitskiy.  Vande Hei completed approximately 5,680 orbits of the Earth and a journey of more than 150 million miles, roughly the equivalent of 312 trips to the Moon and back. He witnessed the arrival of 15 visiting spacecraft and new modules, and the departure of 14 visiting spacecraft.

You can see a detailed list here of the experiments Vande Hei worked on during his time on the ISS, which covered Expeditions 64-66.

With the departure of this crew, Expedition 67 officially began aboard the station. NASA astronaut Tom Marshburn recently took over as station commander, and is joined by NASA astronauts Raja Chari and Kayla Barron, ESA (European Space Agency) astronaut Matthias Maurer, and Roscosmos cosmonauts Oleg Artemyev, Denis Matveev, and Sergey Korsakov.

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A New Record! Hubble Detects an Individual Star From a Time When the Universe Was Less Than a Billion Years Old

A star that sounds as if it came from “The Lord of the Rings” now marks one of the Hubble Space Telescope’s farthest frontiers: The fuzzy point of light, known as Earendel, has been dated to a mere 900 million years after the big bang and appears to represent the farthest-out individual star seen to date.

Based on its redshift value of 6.2, Earendel’s light has taken 12.9 billion years to reach Earth, astronomers report in this week’s issue of the journal Nature. That distance mark outshines Hubble’s previous record-holder for a single star, which registered a redshift of 1.5 and is thought to have existed when the universe was 4 billion years old.

The newly reported record comes with caveats. First of all, we’re talking here about a single star rather than star clusters or galaxies. Hubble has seen agglomerations of stars that go back farther in time.

“Normally at these distances, entire galaxies look like small smudges, with the light from millions of stars blending together,” lead author Brian Welch, an astronomer at Johns Hopkins University, said today in a news release. “The galaxy hosting this star has been magnified and distorted by gravitational lensing into a long crescent that we named the Sunrise Arc.”

A close look at the arc turned up several bright spots, but the characteristics of the light coming from Earendel pointed to a high redshift, which translates into extreme distance. The higher the redshift, the faster the source of the light is receding from us in an ever-more-quickly expanding universe.

The observations were made as part of a Hubble program known as the Reionization Lensing Cluster Survey, or RELICS, led by study co-author Dan Coe at the Space Telescope Science Institute.

RELICS’ astronomers made use of gravitational lensing, a weird phenomenon in which a massive object such as a galaxy cluster bends and focuses the light coming from even more distant objects. The lensing effect results in magnified, arc-like images of far-flung stars, clusters and galaxies.

In the case of the Sunrise Arc, the lensing object is WHL 0137-08, a galaxy cluster that’s roughly 6 million light-years away in the constellation Cetus.

One fuzzy spot in the Sunrise Arc stuck out. The nickname that Welch and his colleagues gave to that spot, Earendel, comes from the Old English word for “morning star.” (It also evokes the name of Eärendil, who was a fictional half-elven mariner mentioned in J.R.R. Tolkien’s “Lord of the Rings” and “The Silmarillion.”)

Astronomers determined that Earendel was most likely an individual star system rather than, say, a star cluster. “We almost didn’t believe it at first, it was so much farther than the previous most-distant, highest-redshift star,” Welch said.

The research team estimates that Earendel is at least 50 times the mass of our sun and puts out millions of times more light. But plenty of mysteries remain to be resolved. For example, is it truly a single star, or is it actually a multiple-star system? And does it contain the same stuff that closer-in stars are made of?

If Earendel contains only the primordial elements of hydrogen and helium, it just might be the first known example of the first generation of stars born after the big bang.

Solving such mysteries is beyond the capabilities of the 32-year-old Hubble Space Telescope, but the recently launched James Webb Space Telescope could crack the case.

“With Webb, we expect to confirm Earendel is indeed a star, as well as measure its brightness and temperature,” Coe said. “We also expect to find the Sunrise Arc galaxy is lacking in heavy elements that form in subsequent generations of stars. This would suggest Earendel is a rare, massive metal-poor star.”

The research team has already booked time on the new space telescope, which is expected to begin science observations within the next couple of months.

What they find could take some of the shine off Earendel’s fame.

“We may see stars even farther than Earendel, which would be incredibly exciting,” Welch said. “We’ll go as far back as we can. I would love to see Webb break Earendel’s distance record.” 

#ICYMI, Hubble just spotted the farthest individual star ever seen! ?

Want to know more? Join us here tomorrow at 2 p.m. ET for a live Q&A with @NASA scientists. pic.twitter.com/DAjg6QTKoT

— Hubble (@NASAHubble) March 30, 2022

Welch and Coe are among 29 authors of the paper published by Nature, “A Highly Magnified Star at Redshift 6.2.”

Lead image: The star nicknamed Earendel, indicated by the white arrow, is positioned along a ripple in spacetime that gives the image extreme magnification. Source: Hubblesite.org. Credit: NASA / ESA / Brian Welch (JHU) / Dan Coe (STScI) / Alyssa Pagan (STScI).

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ESA’s Solar Orbiter Takes a Ludicrously High Resolution Image of the Sun

The European Space Agency’s Solar Orbiter snaps an amazing image, en route to its first close pass near the Sun.

You’ve never seen the Sun like this. Earlier this month, the European Space Agency’s Solar Orbiter captured an amazing view of our host star.

The images were snapped on March 7^th, as Solar Orbiter passed directly between the Earth and the Sun. There was an explicit reason for this, as the science team wanted to calibrate and compare the images with Earth-based and missions in Earth orbit, to include the Inouye solar observatory, NASA’s Solar Dynamics Observatory and the joint ESA/NASA Solar Heliospheric Observatory (SOHO), located at the Lagrange (L1) Sun-Earth point.

“From this point on-wards, we are ‘entering the unknown,’ as far as Solar Orbiter’s observations of the Sun are concerned,” says Solar Orbiter Project Scientist Daniel Müller in a recent press release.

The instruments used aboard the spacecraft included the Extreme Ultraviolet Imager (EUI) and the Spectral Imaging of the Coronal Environment (SPICE) imager. The EUI image alone represents the highest full disk resolution image of the Sun, looking right down through and capturing the corona and outer solar atmosphere. It’s definitely worth a scroll through and zoom in:

EUI full disc image of the Sun. Credit: ESA/Solar Orbiter Team. Click here for a full resolution zoomable view.

The full disk SPICE image captures the Sun at the Lyman-beta wavelength in the ultraviolet, and represents one of the first images of its kind taken in 50 years, since the solar observation experiments aboard Skylab.

Solar Orbiter snapped these images over a 4-hour session, while the probe was 75 million kilometers from the Sun, interior to the orbit of Venus. The Sun was large enough (two degrees across) from that distance that EUI needed a mosaic of 25 images to cover the entire disc of the Sun. The final result is laid out in a 9148 by 9112 grid of 83 million pixels, with a resolution 10 times better than your 4K TV screen.

The image includes filaments, nano-flares and spicules seen across the roiling surface of the Sun. Solar Orbiter observations will address the key question of how eruptions are born on the surface of the Sun, by characterizing the temperature of the Sun seen through successive layers.

You’d think that the Sun gets cooler, out through successive layers farther out… but the reverse is actually the case, as the outer corona reaches a million degrees versus the surface of the photosphere, at a relatively cool 5,000 degrees Celsius.

SPICE’s temperature view of the Sun: one layer at a time. Credit: ESA

The SPICE sequence in particular shows temperature layers in color versus elemental composition: yellow (neon) at 630,000 degrees Celsius, green (oxygen) at 320,000 degrees Celsius, blue (carbon) 32,000 degrees Celsius, and purple (hydrogen) at a ‘cool’ 10,000 degrees Celsius.

Solar Orbiter: taking the temperature of the Sun. Credit: ESA

Launched on February 10^th, 2020 atop an Atlas V rocket from Cape Canaveral Space Force (at the time, Air Force) Station, Solar Orbiter has a primary seven year mission to study the Sun. The mission comes at an auspicious time, as Solar Cycle 25 gets underway in earnest this year, en route to its peak around 2025, which may be one of the most powerful in decades.

The United Launch Alliance Atlas V rocket carrying the Solar Orbiter lifts off Space Launch Complex 41 at Cape Canaveral Air Force Station. Credit: NASA

Solar Orbiter just reached its closest perihelion yet this past weekend, passing 50 million kilometers from the Sun interior to the orbit of Mercury. Passages near Venus will gradually change the inclination of Solar Orbiter’s path, gradually giving us views of the elusive polar regions of the Sun.

Get set for more great science, courtesy of Solar Orbiter.

Lead image credit: An artist’s conception of the Solar Orbiter mission. Credit: ESA.

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This is Where the Mars Sample Return Mission Could be Landing

NASA’s Perseverance Rover is busy exploring Jezero Crater on Mars. Part of its mission is to collect samples for retrieval by a future mission. NASA and the ESA haven’t determined where the sample return mission will land yet.

That depends on the Perseverance mission and how it spends the rest of its time on Mars. But we know of one possible—albeit ambitious—landing spot: just west of Jezero Crater.

If intellectual curiosity about nature is one of humanity’s finest traits, then the people associated with the HiRISE camera have a serious case of it. HiRISE is the High-Resolution Imaging Science Experiment camera on NASA’s Mars Reconnaissance Orbiter. A recent HiPOD or HiRISE Picture of the Day shows a possible landing location for the eventual Mars Sample Return mission.

The thing is, it’s well outside of Jezero Crater, and it’s based on a “hopeful scenario” according to the team at HiPOD.

“This image was acquired based on a hopeful scenario in which the Perseverance rover has an extended mission or two and travels outside of Jezero Crater to explore terrains to the west,” the HiPOD post says. “In this scenario, the decision could be made to land the Mars Sample Return (MSR) mission here to pick up samples collected by Perseverance.”

The diverse landforms and colours in the image make the area a tantalizing place for Perseverance to explore. While the HiPOD post talks about this as a potential landing spot for Mars Sample Return, there are no plans to land here. Image Credit: NASA/JPL/UArizona

HiRISE paved the way for the Perseverance Rover. Its high-resolution images were critical to assessing potential landing spots for the mission. The MRO’s Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument also played a critical role in identifying and mapping concentrations of different minerals on the Martian surface.

CRISM identified carbonate minerals in Jezero Crater that are particularly interesting because they form in the presence of water. Initially scientists thought they formed in the ancient paleolake inside Jezero, but recent research suggests the carbonated formed elsewhere and were carried into Jezero by a river. The possible MSR landing spot in the HiPOD image is upstream from Jezero Crater.

Orbital picture of the Jezero crater, showing its fossil river delta. The green regions are carbonate minerals. Credit: NASA/JPL/JHUAPL/MSSS/BROWN UNIVERSITY

Perseverance has been on Mars for over 400 Earth days so far, and it’s planned mission length is 687 Earth days. But Mars rovers have a habit of extending their missions. Perseverance’s RTG should provide enough power for a mission extension, and the rover is in good condition. There’s a possibility it could leave Jezero Crater and head west to explore interesting areas.

This image shows Perseverance’s (and Ingenuity’s) location in Jezero Crater. The region in the HiPOD image is in the black rectangle on the left, south of Angelica Crater. Image Credit:

Perseverance likely won’t exhaust all of the scientific potential in Jezero Crater. Why risk an overland journey?

Perseverance’s entire mission is a series of calculated risks, and so far the calculations have been reliable. If there are compelling enough reasons to leave Jezero behind and explore nearby interesting areas, maybe the mission operators will do it.

In that case, the region highlighted in the HiPOD could very well be in play as a landing site for Mars Sample Return.

More:

• University of Arizona: HiRISE camera page
• MRO: CRISM instrument
• Universe Today: Perseverance has Collected its First Sample of Mars and Prepared it for Return to Earth… Eventually

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Astronomers Come up With a New Message to let the Aliens Know we’re Here

On Nov. 16th, 1974, the most powerful signal ever beamed into space was broadcast from the Arecibo Radio Telescope in Peurto Rico. Designed by famed SETI researcher Frank Drake (creator of the Drake Equation) and famed science communicator Carl Sagan, the broadcast was intended to demonstrate humanity’s level of technological achievement. Forty-eight years later, the Arecibo Message remains the most well-known attempt to Message Extraterrestrial Intelligence (METI).

To mark the occasion, an international team made of researchers led by Jonathan H. Jiang of NASA’s Jet Propulsion Laboratory has come up with a new signal! Known as The Beacon in the Galaxy (BITG) message, this updated signal combines aspects of the original Arecibo Message with every METI attempt made to date – like the Pioneer Plaques, the Voyager Golden Records, and the Evpatoria Transmission Messages (ETMs).

Jiang was joined by researchers from the SETI Institute, the Virginia Polytechnic Institute and State University, the University of Cambridge, the Hanze University of Applied Sciences, the Chevron Energy Technology Company, the School of Physics and Technology at Wuhan University, Beijing Normal University, and the University of California at Los Angeles. The paper that describes their findings recently appeared online.

A team of astronomers from UCLA searched for “technosignatures” in the Kepler field data. Credit and Copyright: Danielle Futselaar

The Original Signal

Audio representation of the Arecibo message sent to space in 1974. Credit: NAIC/UCF

The transmission was part of a ceremony that marked the end of a three-year upgrade to the Arecibo’s 305m (1000 ft) Radio Telescope. This included aluminum panels on the giant spherical reflector antenna to improve accuracy, a high-power S-band radar transmitter, and modifications to the superstructure to accommodate S-band frequencies. The emission was equivalent to a 20 trillion watt broadcast and would be detectable about anywhere in the galaxy if the receiving antenna was similar in size to Arecibo’s.

The message’s destination was M13, a globular star cluster located near the edge of the Milky Way Galaxy (about 22,180 light-years away). This cluster was believed to be a good candidate for finding intelligent civilizations since it is estimated to be 11.66 billion years old and contains approximately three-hundred thousand stars. Drake and Sagan decided to use prime numbers since they believed it would make the message easier for an alien civilization to translate.

“The Arecibo Message was the first carefully designed message into space, encoded in radio waves, hoping to get in touch with alien civilizations,” said Jiang to Universe Today via email. “It pioneered Earth’s first attempt to contact aliens.

The broadcast consisted of a 1,679-binary digit pictogram (210 bytes), which is the product of two prime numbers, arranged rectangularly into 73 lines of 23 characters per line (also prime numbers). The ones and zeroes were simulated by shifting the frequency at a rate of 10 bits per second, and the total broadcast lasted less than three minutes. They conveyed a series of scientific, geographical, biological, and astronomical information in different colors. These included:

• A counting scheme of 1 to 10 (white)
• The atomic numbers for hydrogen, carbon, nitrogen, oxygen, and phosphorus, which make up DNA (purple)
• The chemical formula of the four purines and pyrimidine bases that make up DNA (green)
• An image of the DNA double helix and ab estimate of the number of nucleotides (blue and white, respectively)
• A stick-figure of a human being (red) our average dimensions (blue/white), and the human population of Earth (white)
• A depiction of the Solar System, indicating that the message is coming from the third planet (yellow)
• A schematic of the Arecibo Observatory and its dimensions (purple/white and blue)

Before and Since

Numerous METI attempts have been made since the beginning of the Space Age. The first radio signal deliberately broadcast to space was the Morse Message, which was sent from the Evpatoria Planetary Radar (EPR) in Ukraine in 1962. This broadcast sent a series of brief radio messages to Venus consisting of three words encoded in Morse code: “Mir” (“Peace” or “World” in Russian), “Lenin,” and “USSR.”

Between 1999 to 2016, several more messages were attempted that targeted stars between 17 and 69 light-years from the Earth. In the coming years, Breakthrough Message plans to mount an international competition (with a prize purse of $1,000,000 for winning entries) to create messages broadcast by their participating institutes. As Philip E. Rosen, a retired energy industry engineer and a co-author on the paper, said:

“Following the 1974 Arecibo Message there were two transmissions made from the Evpatoria 70-meter dish located in the Crimea, Ukraine, these occurring in 1999 and 2003. The Evpatoria transmissions were overseen by a pair of Canadian researchers, Dr. Yvan Dutil and Stéphane Dumas, and were beamed at a total of nine relatively nearby stars ranging in distance from Earth of 10.1 to 21.6 parsec. The 2003 transmission utilized a more robust (i.e., distortion/error resistant) version of the message sent in 1999.”

Other messaging attempts include the Pioneer Plaques that adorned the Pioneer 10 and 11 spacecraft, the first robotic missions dispatched to the outer Solar System. These messages were the brainchild of Carl Sagan and constituted the first “message in a bottle” sent by humans to space. They depict the location of Earth in the Galaxy, two circles representing neutral hydrogen, and a naked man and woman drawn in relation to the spacecraft.

This was followed by the Voyager Golden Records, also crafted by Carl Sagan and his colleagues at Cornell University, which were meant as more of a “time capsule.” The cover depicted instructions on how to play the record, which contained sounds and images that portray life and culture on Earth. Also depicted are the same pulsar maps and representation of neutral hydrogen featured on the Pioneer Plaques.

Enter the BITG

The BITG message comprises 13 parts that consist of approximately 204,000 effective binary digits, or 25,500 bytes, overall. Based on the optimal timing during a given calendar year, the team determined that the Five-hundred-meter Aperture Spherical radio Telescope (FAST) in China and the SETI Institute’s Allen Telescope Array in northern California would be well-positioned to send the Beacon.

As for the target of the broadcast, Jiang and his colleagues chose a concentric ring that is 4 kiloparsecs (~13,000 light-years) from the galactic center. In a previous study, Jiang and other co-authors determined that the center of the galaxy is the most likely place for intelligent life to have emerged. This is bolstered by similar research demonstrating how the galactic center is the best place to search for technosignatures.

“Therefore, we choose stars between 2 kpcs and 6 kpcs from the galaxy’s center as the intended destination. We maximize the chances of the message being received by an ETI and maximize the probability of receiving a response in the distant future,” said Jiang.

The message was designed and coded by co-authors Matthew Chong (the University of Cambridge), Hanjie Li (Virginia Polytechnic Institute and State University), and Qitian Jin (Hanze University of Applied Sciences). As they explained, the Beacon Message incorporates elements from all METI attempts to date.

“The main part of the beacon in the Galaxy (BITG) Message contains a new combination of graphical information in the form of images and special “alphabets” to represent numbers, elements, DNA, land, ocean, human, etc., similar to the 1999/2003 Cosmic Call by Stephane Dumas and Yvan Dutil,” said Jiang. As Li added, the Beacon relies on the same mathematical language as Arecibo:

“The BITG message starts and ends with a prime number set (2, 3, 5, 7, 11…) to let itself stand out from the EM waves that can be easily picked up by extraterrestrial intelligent (ETI) civilizations. A new mechanism in message design may help ETI to decode our message:  the Row Length Indicator (RLI), which is a repetition of a designated number of zeros and ones. The original Arecibo message is a rectangular block with the same number of elements per row. With RLI, the message can be made of several matrices of zeros and ones in different sizes that enable more flexibility to the content design and decode by ETIs.”

Allen Telescope Array. Credit: SETI Institute

“The BITG message also contains a Location Stamp and a Time Stamp,” said Jin. “The Location Stamp describes the Solar System’s position in the galaxy by using globular clusters as landmarks. The Time Stamp uses Hydrogen Spin-Flip to estimate the time we create/send the message in respect to the theoretical birth of the universe.”

To Listen or to Message?

The publication of the Beacon message comes at a particularly auspicious time. Thanks to renewed interest in space exploration, there has been a growing movement to revitalize the Search for Extraterrestrial Intelligence (SETI). As a result, there is a growing debate between advocates for “Passive-SETI” (listening) and “Active-SETI” (messaging). Whereas some feel that METI is “more global and unselfish” in focus than conventional SETI (Zaitsev, 2006), others feel it’s unnecessarily risky.

However, Jiang and his colleagues emphasize that no formalized discussion has been made regarding the risks or ethics of broadcasting. In the meantime, Jiang points out that humanity is already transmitting (albeit unintentionally):

“[W]e are aware that there have been calls for discussions on whether it’s safe to broadcast this type of message. It is always worth pointing out that we humans are unintentionally sending out signals about our presence, albeit at a much lower intensity, which signals have not been designed to put us in the best light (e.g. the ongoing war). They likely would have managed their contact better if there had been intentional communication sent out.”

In the end, the team believes that the ongoing development of the Beacon message may help ensure that this conversation takes place. Another benefit of their work is that it is being done in the open, something that is essential to any METI effort. Said Jiang:

“[This] is important because there are concerns that some power could initiate a broadcast without being open to the rest of the world. This is another reason to promote broadcasts with open participation, to avoid there being only secret broadcasts. This is why our BITG message is being finalized and published openly, inviting feedback from all interested parties.”

The Five-hundred-metre Aperture Spherical Telescope (FAST) has just finished construction in the southwestern province of Guizhou. Credit: FAST

“The BITG message should be promoted as a means of inspiring our human civilization to be better at living sustainably,” adds Stuart Taylor, a nuclear physicist with the SETI Institute. “We must consider human survival as a goal more than we do, rather than caring too much about our own separate nations.”

The Arecibo Message was broadcast at the height of the first Space Age and showcased what humanity’s facilities were capable of. For many people worldwide, the loss of the Arecibo Observatory in 2020 felt like the end of an era. As we enter a renewed era of space exploration and astronomy, updating and adding to what was undoubtedly one of our “greatest hits” seems appropriate!

Further Reading: arXiv

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Part of the Milky Way Is Much Older Than Previously Believed

The Milky Way is older than astronomers thought, or part of it is. A newly-published study shows that part of the disk is two billion years older than we thought. The region, called the thick disk, started forming only 0.8 billion years after the Big Bang.

A pair of astronomers pieced together the Milky Way’s history in more detail than ever. Their results are based on detailed data from the ESA’s Gaia mission and China’s Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). The key to this discovery lies in subgiant stars.

The paper is “A time-resolved picture of our Milky Way’s early formation history,” and it’s online in the journal Nature. The authors are Maosheng Xiang and Hans-Walter Rix, both from the Max-Planck Institute for Astronomy (MPIA.)

“Our results provide exquisite details about that part of the Milky Way, such as its birthday, its star-formation rate and metal enrichment history. Putting together these discoveries using Gaia data is revolutionizing our picture of when and how our galaxy was formed.”

Maosheng Xiang, study co-author, MPIA.

One of the most difficult things to determine about a star is its age. A star’s composition, or metallicity, is key to finding its age. The more accurately astronomers can measure metallicity, the more accurately they can determine its age. The early Universe contained hydrogen and helium almost exclusively. Elements heavier than hydrogen and helium are produced in stars and spread out into the Universe when those stars die and explode. Astronomers call every element heavier than the two primordial elements “metals.”

Stars with lower metallicity are older because they formed when mostly just hydrogen and helium were available. So when astronomers identify a population of stars mainly containing hydrogen and helium, they know those stars are older. When they find a population of stars with higher proportions of metals, they know those stars must be younger.

Precision age measurements are the holy grail in some aspects of astronomy, which is true in this case. Xiang and Rix used more than just metallicity to determine stellar ages. They focused on a specific type of star: subgiants. The subgiant phase in a star’s life is relatively brief, so astronomers can determine a star’s age most accurately when it’s a subgiant. Subgiants are transitioning to red giants and no longer produce energy in their cores. Instead, fusion has moved into a shell around the core.

This figure from the study shows some of the detail for the 247,000 subgiant stars in the sample. (a) shows the subgiant selection by magnitude and temperature. (b) shows the distribution in the relative age precision as a function of age. Image Credit: Xhiang and Rix 2022.

In this study, the pair of scientists used LAMOST data to determine the metallicity of about 250,000 stars in different parts of the Milky Way. They also used Gaia data which gives the precise position and brightness data for about 1.5 billion stars.

The ESA’s Gaia mission is responsible for increased accuracy in this study and many others. Before Gaia, astronomers routinely worked with stellar age uncertainties between 20% to 40%. That meant that ages could be off by one billion years, which is a lot. But Gaia has changed all this. The current data release from the mission is Gaia EDR 3 or Early Data Release 3, and it’s a vast improvement. EDR3 gives precise 3D positions of over 330,000 stars. It also gives high-precision measurements of the stars’ motions through space.

The researchers used all this data from Gaia and LAMOST and compared it to known models of stellar parameters to determine the subgiants’ ages with greater accuracy. “With Gaia’s brightness data, we are able to determine the age of a subgiant star to a few percent,” said Maosheng. The subgiants are spread throughout the different parts of the Milky Way, allowing the researchers to piece together the ages of the other components and build a timeline of the Milky Way’s history.

The study shows two distinct phases in our galaxy’s history. The first phase started 0.8 billion years ago when the thick disk began forming stars. The galactic halo’s inner regions started to develop too. Two billion years after that, a merger propelled the star formation in the thick disk to completion. A dwarf galaxy named Gaia-Sausage-Enceladus merged with the Milky Way.

An artist’s impression of our Milky Way galaxy, a roughly 13 billion-year-old barred spiral galaxy that is home to a few hundred billion stars. On the right, an edge-on view reveals the flattened shape of the disc. Observations point to a substructure: a thin disc some 700 light-years high embedded in a thick disc, about 3000 light-years high, populated with older stars. The new study shows that the thick disc started forming stars only 0.8 billion years after the Big Bang, about two billion years sooner than thought. Image Credit: NASA/JPL-Caltech; right: ESA; layout: ESA/ATG medialab

The Gaia-Sausage-Enceladus (GSE) dwarf galaxy isn’t shaped like a sausage. It gets its name from plotting its stars on a velocity chart, where their orbits are highly-elongated. When GSE merged with the Milky Way, it helped create the thick disk, and the gas that came with it fuelled the star formation in that part of the galaxy. The merger also filled the Milky Way’s halo with stars. Astronomers think the globular cluster NGC 2808 might be the Gaia Sausage’s remnant core. NGC 2808 is one of the most massive globular clusters in the Milky Way.

The star formation triggered in the thick disk by the GSE lasted for about 4 billion years. About 6 billion years after the Big Bang, the gas was all used up. During that period, the thick disk’s metallicity increased by more than a factor of ten.

The study also found a very tight correlation between the metallicity and the ages of the stars in the entire disk. That means that the gas that came with the GSE must have been turbulent, causing it to mix more thoroughly in the disk.

Astronomers only recently discovered the GSE merger in 2018. Discoveries like it have shaped our understanding of the Milky Way’s history, and the galaxy’s developmental timeline is becoming clearer. This new study is giving us a more detailed account.

The NGC 2808 star cluster might be the remnant of the Gaia-Sausage-Enceladus galaxy that merged with the Milky Way billions of years ago. Credit: NASA, ESA, A. Sarajedini (University of Florida) and G. Piotto (University of Padova)

“Since the discovery of the ancient merger with Gaia-Sausage-Enceladus, in 2018, astronomers have suspected that the Milky Way was already there before the halo formed, but we didn’t have a clear picture of what that Milky Way looked like. Our results provide exquisite details about that part of the Milky Way, such as its birthday, star-formation rate and metal enrichment history. Putting together these discoveries using Gaia data is revolutionizing our picture of when and how our galaxy was formed,” says Maosheng.

In recent years astronomers have discovered more detail about the Milky Way. But it’s challenging to map its structure because we’re in the middle of it. The ESA’s Gaia mission is our best catalogue yet of the stars in the Milky Way. And each data release gets better and better.

“With each new analysis and data release, Gaia allows us to piece together the history of our galaxy in even more unprecedented detail. With the release of Gaia DR3 in June, astronomers will be able to enrich the story with even more details,” says Timo Prusti, Gaia Project Scientist for ESA.

The Gaia mission is essential, but observations of other galaxies like the Milky Way also give astronomers insights into the Milky Way’s structure and history. But observing galaxies only two billion years after the Big Bang is difficult. That requires powerful infrared telescopes. Fortunately, one long-awaited infrared space telescope is about to begin observations soon.

The James Webb Space Telescope (JWST) has the power to look back in time to the Universe’s early years. It’ll be able to see the Universe’s earliest Milky Way-like galaxies. Astronomers want to know more about the GSE merger and how it led to star formation and shaped our galaxy’s thick disk only two billion years after the Big Bang. JWST observations of ancient, high-redshift galaxies similar to the Milky Way could help answer some questions and fill in a more detailed galactic history.

The James Webb Space Telescope was built to answer some of our biggest questions about the early Universe, including how the first galaxies formed. That question directly relates to how the Milky Way began and grew. Image Credit: ESA

And in June, the ESA will release Gaia’s full third data release, called DR3. The DR3 catalogue will contain ages, metallicity, and spectra for over 7 million stars. DR3 and the JWST will be a potent combination.

What will all of that data tell us?

As the Universe evolves, galaxies must either eat or be eaten. Gravity draws galaxies together, but the Universe is also expanding thanks to dark energy, and the dark energy pushes galaxies apart. So galaxies tend to clump together into groups. The Milky Way is part of the Local Group.

The groups stay internally coherent because of the galaxies’ combined gravity, but the groups drift away from one another due to expansion. Eventually, the largest galaxies in a group consume the smaller ones. The Milky Way has consumed the GSE and globular clusters. And it’s consuming the Large Magellanic Cloud, which is consuming its even smaller neighbour, the Small Magellanic Cloud. Eventually, the Milky Way will consume both, and then in about 4.5 billion years, it’ll merge with the even larger Andromeda Galaxy, another member of the Local Group.

It’s an odd situation because the Milky Way’s future might be easier to discern than its past. That’s the conundrum of an expanding Universe: the evidence we seek keeps receding from us, lost to time and distance. But the JWST and the Gaia DR3 have the potential to turn the tables on the expanding Universe. Together they can shed more light on the Milky Way’s history and on the details of galaxy mergers in general. Hopefully, we’ll end up with a much more thorough historical timeline.

More:

• Press Release: Gaia finds parts of the Milky Way much older than expected
• New Research: A time-resolved picture of our Milky Way’s early formation history
• Universe Today: The Milky Way is Already Starting to Digest the Magellanic Clouds, Starting With Their Protective Halos of Hot Gas

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