ESA’s EnVision Mission Doesn’t Have a lot of Fuel, so it’s Going to Aerobrake in the Atmosphere of Venus

Venus has almost been “the forgotten planet,” with only one space mission going there in the past 30 years. But the recent resurgence of interest in Earth’s closest neighbor has NASA and ESA committing to three new missions to Venus, all due to launch by the early 2030s.

ESA’s EnVision mission Venus is slated to take high-resolution optical, spectral and radar images of the planet’s surface. But to do so, the van-sized spacecraft will need to perform a special maneuver called aerobraking to gradually slow down and lower its orbit through the planet’s hot, thick atmosphere. Aerobraking uses atmospheric drag to slow down a spacecraft and EnVision will make thousands of passages through Venus’ atmosphere for about two years.

The aerobraking maneuver is a necessity for the mission.

“EnVision as currently conceived cannot take place without this lengthy phase of aerobraking,” said  EnVision study manager Thomas Voirin. “The spacecraft will be injected into Venus orbit at a very high altitude, at approximately 250,000 km, then we need to get down to a 500 km altitude polar orbit for science operations. Flying on an Ariane 62, we cannot afford all the extra propellant it would take to lower our orbit. Instead, we will slow ourselves down through repeated passes through the upper atmosphere of Venus, coming as low as 130 km from the surface.”

Aerobraking has been performed by several spacecraft at Mars, such as the Mars Reconnaissance Orbiter and ExoMars Trace Gas Orbiter, to gradually slow the spacecraft down to place the spacecraft in the correct orbit for the mission parameters. But because of Venus’ ultra-thick atmosphere, ESA said that they are currently testing candidate spacecraft materials to “check they can safely withstand this challenging process of atmospheric surfing.”

However, this won’t be the first time a spacecraft has used aerobraking at Venus. ESA’s Venus Express, performed experimental aerobraking during the final months of its mission in 2014, gathering valuable data on the technique. The Venus Express mission was supposed to last 500 days, but the robust spacecraft ultimately spent eight years orbiting Venus before running out of fuel. It began a controlled descent, dipping further and further into Venus’s atmosphere, while using onboard accelerometers to measure its own deceleration.

Voirin said aerobraking around Venus is a challenge because the gravity of Venus is about 10 times higher than that of Mars. This means velocities are about two times higher than at Mars the spacecraft passes through the atmosphere – and heat is generated as a cube of velocity. Accordingly, EnVision has to target a lower aerobraking regime, resulting in an aerobraking phase twice as long.

Artist impression of ESA’s EnVision mission at Venus. Credit: ESA/VR2Planets/Damia Bouic

“On top of that, we are also going to be much closer to the Sun, experiencing around double the solar intensity of Earth’s, with the thick white clouds of the atmosphere reflecting a lot of sunlight straight back to space, which additionally needs to be taken into account,” Voirin said. “Then on top of all that, we realized we had to reckon with another factor over the thousands of orbits we envisage, previously only experienced in low Earth orbit: highly-erosive atomic oxygen.”

This is a phenomenon that remained unknown during the first decades of the space age. It was only when early Space Shuttle flights returned from low orbit in the early 1980s that engineers received a shock: the spacecraft’s thermal blankets had been severely eroded.

The culprit turned out to be highly reactive atomic oxygen – individual atoms of oxygen at the fringes of the atmosphere, the result of standard oxygen molecules of the kind found just above the ground being broken apart by powerful ultraviolet radiation from the Sun. Today, all missions below about 1,000 km need to be designed to resist atomic oxygen.

Space Shuttle Endeavour’s tail aglow with atomic oxygen, as seen during the STS-99 mission in February 2000. Highly erosive atomic oxygen turned out to eat away at unprotected thermal blankets during early Shuttle missions, until countermeasures were put in place. Credit: NASA

Spectral observations by past Venus orbiters of airglow above the planet confirm that atomic oxygen is widespread at the top of the Venusian atmosphere too, which is more than 90 times thicker than Earth’s.

Thomas says: “The concentration is quite high, with one pass it doesn’t matter so much but over thousands of times it starts to accumulate and ends up with a level of atomic oxygen fluence we have to take account of, equivalent to what we experience in low-Earth orbit, but at higher temperatures.”

ESA says the results of a test of materials are expected at the end of this year.

EnVision will use an array of instruments to perform comprehensive observations of Venus from its inner core to upper atmosphere to better understand how Venus and Earth evolved so differently.

The other upcoming Venus missions are DAVINCI+, a mission to understand the atmospheric evolution of Venus, and VERITAS, a mission to better map the Venusian surface and subsurface. Those two missions are aiming for launch between 2028 and 2030.

Further reading: ESA press release
EnVision mission factsheet

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Jupiter's Giant Moons Prevent it From Having Rings Like Saturn

When the name Saturn is uttered, what comes to mind? For most people, the answer would probably be, “its fabulous system of rings.” There’s no doubt they are iconic, but what is perhaps lesser-known is that Jupiter, Uranus, and Neptune all have ring systems of their own. However, whereas Saturn’s rings are composed mainly of ice particles (making them highly reflective), Jupiter’s rings are composed mainly of dust grains. Meanwhile, Uranus and Neptune have rings of extremely dark particles known as tholins that are very hard to see. For this reason, none of the other gas giants get much recognition for their rings.

However, the question of why Jupiter doesn’t have larger, more spectacular rings than Saturn has been bothering astronomers for quite some time. As the larger and more massive of the two bodies, Jupiter should have rings that would dwarf Saturn’s by comparison. This mystery may have finally been resolved thanks to new research by a team from UC Riverside. According to their study, Jupiter’s massive moons (aka. Jupiter’s Galilean Moons) prevented it from developing a big, bright, beautiful ring system that would put Saturn’s to shame.

The research was conducted by Stephen R. Kane, a professor of astronomy and planetary astrophysics with the Department of Earth and Planetary Sciences at UC Riverside, and his graduate student Zhexing Li. The paper that describes their work, “The Dynamical Viability of an Extended Jupiter Ring System,” recently appeared online and is soon to be published in the Planetary Science Journal. As Kane stated in a recent article with UC Riverside News, the mystery of Jupiter’s missing rings is one he and Li were highly motivated to address.

Illustration of Jupiter and the Galilean satellites. Credit: NASA

“It’s long bothered me why Jupiter doesn’t have even more amazing rings that would put Saturn’s to shame,” he said. “If Jupiter did have them, they’d appear even brighter to us because the planet is so much closer than Saturn.” For their study, the team ran a series of dynamical N-body simulations that accounted for the orbits of Jupiter’s Galilean Moons (Io, Europa, Ganymede, and Callisto) and the availability of ring material.

Their results indicate that some of the icy material for Saturn’s rings may have come from comets, which were also responsible for distributing water to the planets of the inner Solar System billions of years ago. Jupiter would have been subject to the same level of comet activity in its early history, but the gravity of its massive moons was strong enough that they might have pushed this ice out of Jupiter’s orbit (or changed the orbit of the ice enough so that it collided with its moons). As Kane explained:

“Massive planets form massive moons, which prevents them from having substantial rings. We didn’t know these ephemeral rings existed until the Voyager spacecraft went past because we couldn’t see them. For us astronomers, they are the blood spatter on the walls of a crime scene. When we look at the rings of giant planets, it’s evidence something catastrophic happened to put that material there.”

While Saturn has many prominent moons of its own, only Titan rivals the Galileans in terms of mass. Eventhough that Saturn has 82 moons in orbit around it (that we know of), Titan accounts for 96% of their collective mass. While the gravitational interaction of these moons was enough to give Saturn its axial tilt (26.73° relative to the Sun’s ecliptic), their combined gravitational force was not strong enough to prevent Saturn from accumulating icy material into a series of bright rings.

Jupiter and its moon Europa are seen through the James Webb Space Telescope’s NIRCam instrument 2.12-micron filter. Credits: NASA, ESA, CSA, and B. Holler and J. Stansberry (STScI)

Among the images recently released by the JWST, some showed Jupiter and its faint rings, which are more prominent when seen in infrared wavelengths. This is one of many objectives of the Webb mission, which is to study the planets and moons of the outer Solar System. Using its advanced infrared cameras, Webb can spot faint ring structures and small objects around the gas giants that are hard to see in visible light. This is expected to yield valuable scientific returns, like telling us more about how planets in our Solar System formed and evolved.

Herein lies the value of studying planetary rings, where astronomers can learn more about the history of a planet because they are potential evidence of collisions with moons or comets that happened in the past. Their shape, size, and composition are all indications of events that might have led to their formation. Looking ahead, Kane plans to run simulations that address Uranus’ ring structure (smaller but more substantial than Saturn’s) to learn more about their history. A popular theory is that the same impact that is believed to have knocked Uranus on its side led to these rings.

The answer to this and other mysteries of planet formation and evolution will be the subject of considerable research in the coming years. The implications of these studies will go far beyond our Solar System and extend to the study of exoplanets, many of which are sure to have ring systems! For these distant worlds, the presence, size, and composition will provide clues about their formation and evolution.

Further Reading: UCR Riverside

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When Stars eat Their Planets, the Carnage can be Seen Billions of Years Later

The vast majority of stars have planets. We know that from observations of exoplanetary systems. We also know some stars don’t have planets, and perhaps they never had planets. This raises an interesting question. Suppose we see an old star that has no planets. How do we know if ever did? Maybe the star lost its planets during a close approach by another star, or maybe the planets spiraled inward and were consumed like Chronos eating his children. How could we possibly tell? A recent study on the arXiv answers half that question.

It all comes down to an odd little element known as lithium.

Lithium is the third element on the periodic table. Although most of the atoms formed during the big bang were hydrogen and helium, trace amounts of lithium were formed from the big bang. About one atom in ten billion so the current model goes. But it turns out there is less lithium in the universe than you’d expect. That’s because while other elements such as carbon, oxygen, and iron are created in the hearts of large stars, lithium is destroyed. It’s an effect known as lithium burning, and it means older stars typically don’t have much lithium present in their atmosphere.

Astronomers use this effect to distinguish between high-mass brown dwarfs and low-mass stars. If there is plenty of lithium present in the atmosphere, then fusion isn’t happening, and it’s a brown dwarf. Not much lithium and you have a star. But some stars have atmospheric lithium. They are clearly large enough and hot enough to undergo fusion, and they haven’t burned lithium out of their atmosphere. So what gives?

Modeled abundances for a star that consumes a planet vs one that does not. Credit: Savilla, J., et al

The common hypothesis has been that these unusual stars must undergo some unusual internal mixing that somehow prevents lithium from being cycled into the star’s interior where it can be consumed. This latest study proposes an alternative. Perhaps these stars happened to consume their young planets instead.

Since planets don’t burn lithium when a planet is eaten by a star its lithium is added into the star’s mix. The team simulated how that added lithium would behave in a star’s interior, and how long it would take to fade from the star’s upper layers. They found that smaller red dwarf stars are fairly effective in burning the new lithium. Because a small star has large convection zones that mix its interior really well, within a few hundred million years the new lithium is depleted. But for larger, more Sun-like stars, lithium can hang around for billions of years. Long after a planet is consumed, its lithium is still present in the stellar atmosphere.

So if we see an old Sun-like star with lithium in its atmosphere, it’s quite possible it once had planets. Stellar lithium seems to be a good sign of a sated star after a planetary meal.

Reference: Savilla, J., et al. “Long-Term Lithium Abundance Signatures following Planetary Engulfment.” arXiv preprint arXiv:2207.13232 (2022).

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JWST Damage, New Mars Helicopters, Teaching Robots to Die

JWST is doing after its micrometeorite strike, two more helicopters are flying to Mars, China will drop a 50+ meter booster… somewhere, and how do you stop the Milky Way from turning into self-replicating robot probes.

This week brought us many exciting and sometimes even scary space news. If you’re in the mood to relax and consume them in a convenient bite-size video format, you’re in luck! Because this is exactly what we have for you here:

How Bad the JWST Damage Is

A few weeks ago, we reported that JWST had taken a surprisingly large micrometeorite hit on one of its mirror segments. A new image released from NASA shows the extent of the damage. The telescope has been hit six times so far, with 5 of the 6 causing negligible damage to its optics, but the strike in May on the C3 mirror segment caused a “significant uncorrectable change.” After the strike, Webb’s operators could realign the segment to minimize the effect on its image quality.

More about JWST’s damage.

Another Great Processed Picture from James Webb

Feast your eyes on another incredible image from the James Webb Space Telescope. This time you’re looking at galaxy IC 5332, located about 30 million light-years away. The image processing was done by Judy Schmidt, who downloaded Webb’s data in four different wavelengths and then combined them into a single image with colors that the human eye can see. You can see regions of dense star formation in the galaxy’s spiral arms, which are highlighted in the infrared spectrum.

More about IC 5332.

China Adds New Module to Its Space Station

China continues the construction of its Tiangong 3 space station, this week adding a new science module called Wentian. The new lab launched on July 23rd and was docked with the station on July 25th. One final laboratory module will be attached to the station in October called Mengtian. Once it’s complete, the station will have about 1/5th the internal volume of the International Space Station, with three crew members on board.

More about China’s new module.

How Likely It Is To Die From Space Debris

Satellites and space junk are always falling back to Earth, burning up in the atmosphere. Some debris is so large, however, that it can survive the trip through the atmosphere, crashing onto the surface of the Earth. Could one of these chunks kill a person? According to a new estimate, there’s a 6-10% chance that someone somewhere will die from falling space junk in the next decade. For comparison, 13 people are killed yearly by falling vending machines.

More about space debris risks.

Two More Helicopters To Mars

After the obvious success of the Ingenuity helicopter, which went to Mars with the Perseverance rover, NASA is planning to send more of them. It will be a part of the Sample Return Mission and there will be two helicopters. One of their tasks will be collecting samples, so they might be equipped with wheels and robotic hands. That makes future Mars missions even more exciting!

More about future Mars helicopters.

We Need To Teach Robots To Die

Sending swarms of self-replicating robots to explore the Universe isn’t a new idea. It’s called Von Neumann probes. It’s actually quite clever. You can explore an entire galaxy in just several million years. But there’s a challenge that we need to solve first before we should build those. It’s teaching robots to die.

More on Von Neumann probes.

Most Sensitive Dark Matter Detector Goes Online

The hunt for dark matter continues, with astronomers scanning the skies with telescopes, physicists generating exotic particles in the Large Hadron Collider, and new experiments watching for particle collisions. A new experiment deep underground in South Dakota has come online called LUX-Zeplin. It contains a vast volume of xenon gas surrounded by detectors. If a particle of dark matter happens to collide with xenon gas, it should generate a cascade of particles that would be detectable.

More about LUX-Zeplin.

NASA Needs Your Help

Compared to stars, planets are very dim. If we wanted to observe an Earth-sized world orbiting a sunlike star, we’d need to be able to block the light from the star to reveal a planet that’s a million million times less bright. An exciting solution to this problem is a starshade, a flower-like spacecraft that flies thousands of kilometres away from a telescope, blocking the light from the star, but letting the planet’s light through. NASA is looking for the public’s help to design a starshade that could fly in orbit, allowing ground-based observatories to see planets.

More about NASA’s starshade call for help.

Surprisingly Comfy Moon Lava Tubes

The surface of the Moon experiences severe temperature changes. In the daytime, the surface can heat up to 127 C and cool to -173 C at night. But new observations from NASA’s Lunar Reconnaissance Orbiter show that inside collapsed lava tubes on the Moon, the temperature always remains a comfortable 17 C. You could wear a short-sleeved shirt (inside a pressurized space suit) and wouldn’t need complex and power-hungry heaters and coolers. In the low gravity of Mars, these lava tubes can be hundreds or even thousands of meters tall, allowing room for enormous lunar bases.

More about lava tubes on the Moon.

Stay On Top Of More Space News

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The Mars Sample Return Mission Will Take Two Helicopters to the Red Planet to Help Retrieve Samples

NASA’s upcoming Mars Sample Return mission plan just received a glow-up: it will now carry a pair of twin helicopters, each capable of retrieving samples and delivering them to the ascent vehicle for return to Earth.

The helicopters take the place of a previously planned fetch rover, which has now been ditched from the plan altogether. The fetch rover would have required a second lander, while the helicopters can fit alongside the ascent vehicle, simplifying the mission and reducing its overall cost and complexity.

The decision was announced in a press release earlier this week, which indicated that NASA had finished the system requirements review for the Sample Return mission.

Sample return efforts are already in progress, as the Perseverance Rover is actively collecting samples from scientifically important sites in Jezero Crater on Mars, and has been since early 2021. The original plan was for Perseverance to cache the sample tubes for the fetch rover to collect at a later date. However, Perseverance is still going strong, and NASA expects that it will last long enough to deliver the samples to the ascent vehicle itself. The two helicopters will provide redundant delivery capabilities, should Perseverance fail.

Several recent developments made the updated plan possible. Perseverance’s longevity is one of these. The other is the unadulterated success of Ingenuity, Perseverance’s companion helicopter, which made the first-ever powered flight on Mars back in 2021. It has now lasted over a year longer than its expected operational lifetime, having performed 29 flights in that time. More than just a proof of concept, Ingenuity has demonstrated that powered flight vehicles can be adept, versatile workhorses for a variety of tasks on Mars.

At a media press conference on July 27, Richard Cook, Mars Sample Return Program Manager at the Jet Propulsion Laboratory, indicated that the new helicopters will be distinct from Ingenuity in two ways. The first is that they will feature a set of small wheels rather than landing legs “that allow the helicopters to traverse across the surface on the ground as well as fly…and secondly, each of the helicopters will have a little arm that can reach down and grab onto the…sample tubes.” These capabilities will only be necessary if Perseverance itself cannot deliver the samples, but their presence is a comforting insurance policy in case things go south with the rover.

Jezero Crater on Mars, where Perseverance and Ingenuity are collecting rock samples. They will be joined in 2028 by an ascent vehicle and two new drone helicopters to help return the samples to Earth. Image Credit: NASA/JPL/JHUAPL/MSSS/Brown University

The helicopters, along with the lander carrying the ascent stage, are expected to launch from Earth in 2028 (an orbiter built by the European Space Agency [ESA] will precede them in 2027). After Perseverance and/or the helicopters retrieve the samples, the ascent stage will carry them to Mars orbit and rendezvous with the orbiter, before returning the precious core samples to Earth in 2033.

The changes to the Mars Sample Return Program bear out the recommendations of the Planetary Science Decadal Survey, released back in April 2022. The survey indicated that a successful Mars sample return ought to be the highest scientific priority for NASA’s robotic exploration efforts this decade, but not at the expense of other missions. “Its cost should not be allowed to undermine the long-term programmatic balance of the planetary portfolio,” the survey cautioned. Restructuring the mission to make a second rover and lander unnecessary should help keep costs manageable, while Ingenuity’s success offers compelling evidence that the new plan ought to be feasible.

If all goes well, scientists may soon be spoiled with riches of Martian dust and rock. Alongside NASA’s and ESA’s efforts, a Chinese sample return mission is slated to return Martian soil to Earth by 2031, and a Japanese mission plans to bring samples back from Mars’ largest moon Phobos in 2029.

While in-situ geology performed by rovers like Perseverance and its predecessor Curiosity can tell us a lot about conditions on Mars, there are investigative tools and techniques possible in laboratories back on Earth that no rover can match. Sample return missions will allow scientists to study the minerals in more detail, uncovering the history of the Red Planet and, potentially, its ecosystems (if it ever had any).

The funding for the project is falling into place too. Yesterday, the US Senate released its FY23 draft spending bill, proposing to give NASA the funds it requested for the next year to move the project forward.

You can read more about the sample return mission here: https://www.nasa.gov/press-release/nasa-will-inspire-world-when-it-returns-mars-samples-to-earth-in-2033

Featured Image: artist’s rendering of the Mars Sample Return Program infrastructure. Credit: NASA/JPL-Caltech.

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The James Webb is Measuring Distant Galaxies 5-10 Times Better Than any Other Telescope

On December 25th, 2021, after many years of waiting, the James Webb Space Telescope (JWST) finally launched to space. In the sixth-month period that followed, this next-generation observatory unfurled its Sunshield, deployed its primary and secondary mirrors, aligned its mirror segments, and flew to its current position at the Earth-Sun Lagrange 2 (L2) Point. On July 12th, 2022, the first images were released and presented the most-detailed views of the Universe. Shortly thereafter, NASA released an image of the most distant galaxy ever observed (which existed just 300 million years after the Big Bang).

According to a new study by an international team of scientists, the JWST will allow astronomers to obtain accurate mass measurements of early galaxies. Using data from James Webb’s Near-Infrared Camera (NIRCam), which was provided through the GLASS-JWST-Early Release Science (GLASS-ERT) program, the team obtained mass estimates from some of the distant galaxies that were many times more accurate than previous measurements. Their findings illustrate how Webb will revolutionize our understanding of how the earliest galaxies in the Universe grew and evolved.

The research team (led by Paola Santini of the Astronomical Observatory of Rome) included members from the Instituto Nationale di Astrophysica (INAF) in Italy, the ASTRO 3D collaboration (Australia), the National Astronomical Research Institute of Thailand (ARIT), the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC), the Cosmic Dawn Center (DAWN), the Niels Bohr Institute, The Carnegie Institution for Science, the Infrared Processing and Analysis Center at Caltech, and universities and institutes in the U.S., Europe, Australia, and Asia.

As they indicate in their study, stellar mass is one of the most important physical properties (if not the most) for understanding galaxy formation and evolution. It measures the total amount of stars in a galaxy, which are constantly being added through the conversion of gas and dust into new stars. Therefore, it is the most direct means of tracing a galaxy’s growth. By comparing observations of the oldest galaxies in the Universe (those more than 13 billion light years away), astronomers can study how galaxies evolved.

Unfortunately, obtaining accurate measurements of these early galaxies has been an ongoing problem for astronomers. Typically, astronomers will conduct mass-to-light (M/L) ratio measurements – where the light produced by a galaxy is used to estimate the total mass of stars within it – rather than computing the stellar masses on a source-by-source base. To date, studies conducted by Hubble of the most distant galaxies – like GN-z11, which formed about 13.5 billion years ago – were limited to the Ultraviolet (UV) spectrum.

This is because the light from these ancient galaxies experiences significant redshift by the time it reaches us. This means that as the light travels through spacetime, its wavelength is lengthened due to the expansion of the cosmos, effectively shifting it towards the red end of the spectrum. For galaxies whose redshift value (z) is seven or higher – at a distance of 13.46 light-years or more – much of the light will be shifted to the point where it is only visible in the infrared part of the spectrum. As Santini explained to Universe Today via email:

“The bulk of the stars in galaxies, those that mostly contribute to its stellar mass, emit at optical-near infrared (NIR) wavelengths… [B]y the time the light takes to travels from a distant galaxy to our telescopes, the light emitted by its stars is no more in the optical regime. E.g., for a z=7 galaxy, the light originally emitted at 0.6 micron, reaches our telescope with a wavelength of 4.8 micron. The higher the redshift (i.e. the more distant the galaxy), the stronger is this effect.”

“This implies that we need infrared detectors to measure galaxy stellar masses (the light emitted by the bulk of their stars is out of reach of the Hubble Space Telescope). The only IR telescope we had before the advent of JWST was Spitzer Space Telescope, dismissed a few years ago. However, its 85 cm mirror was not comparable with the 6.5 m mirror of JWST. Most of the distant galaxies were out of reach of Spitzer too: due to its limited sensitivity and angular resolution, they were not detected (or affected by high levels of noise) on its images.

A spectral diagram comparing emitted light from an object to the observed redshifted light. As the Universe expands, it stretches light into lower frequencies or towards the red portion of the spectrum. Credit: NASA/ESA/C. Christian/Z. Levay (STScI)

Moreover, previous surveys were likely to miss a large fraction of intrinsically red galaxies that are dust-rich (which obscures light) and faint in the UV spectrum. Consequently, previous estimates of the cosmic star stellar mass density of the early Universe could be off by a factor of up to six. But thanks to its advanced suite of infrared instruments and unparalleled sensitivity, the JWST is poised to open “a new window” (as Santini put it) into studying the oldest and faintest galaxies in the Universe. As Santini expressed, Webb will enable the first-ever precision measurements of galactic masses out to the furthest distances:

“Due to all these limitations in measuring the stellar mass, a commonly used approach before the launch of JWST was to convert the UV light (which is easily measured by HST) into a stellar mass estimate by assuming an average mass-to-UV light ratio. The mass-light relation was calibrated with the few and uncertain measurements we had, and it was representative only of those galaxy populations that were more easily observed (young, dust-free galaxies). Stellar mass measurements were therefore prone to large uncertainties (both when directly measured, and even more when inferred from the UV light).”

For their study, Santini and his international team of researchers relied on images acquired by NIRCam on June 28th-29th, 2022, as part of its first set of observations. They then measured the stellar mass of 21 distant galaxies (which ranged in redshift from 6.7 to 12.3) by probing their UV emission and redshifted-optical light. As Santini indicated, this allowed them to avoid the large extrapolations and uncertainties of past surveys and increased the accuracy of their mass measurements by a factor of 5 to 10.

“By comparing the stellar masses with the UV light (measured with the bluest NIRCam bands), we found that the M/L ratio is far from approximable with a single, average value,” he said. “It instead spans roughly two orders of magnitude for a given luminosity. From a physical point of view, this finding suggests that the population of early galaxies was largely heterogeneous, with galaxies exhibiting a broad variety of physical conditions.”

The first image taken by the James Webb Space Telescope. Credit: NASA, ESA, CSA, and STScI

These results are part of a growing collection of scientific studies emerging from the earliest James Webb observations, which show just how pivotal the mission will be. In this case, the ability to offer more tightly-constrained estimates of stellar mass in galaxies will greatly assist astronomers engaged in the study of the cosmos on the largest and longest of scales (aka. cosmology). Said Santini:

“The major implication is that previous results regarding the mass growth process in galaxies could be affected by significant systematics. In our work we assess, for example, the level of systematic uncertainty affecting the cosmic stellar mass density. The latter describes the global growth of galaxies in the Universe as a function of time. Its assessment at early epochs is subject to large variance from one work to another. We found that the systematic uncertainty resulting from the assumption of a standard mass-to-light can be as high as a factor of a few, definitely too large compared to the level of precision we aim to reach, and it could at least partly explain the mismatch in the results of the literature.”

So far, Webb has demonstrated its optical capabilities by capturing the clearest and most detailed images of the cosmos, which are already leading to new discoveries. Its spectrometers have obtained spectra from a distant exoplanet, demonstrating how it will assist in the characterization of exoplanet atmospheres and determine if they are truly “habitable.” This latest study shows that it will also play a vital role in determining the characteristics of the earliest galaxies in the Universe, how they have since evolved, and the possible role that Dark Matter and Dark Energy play.

Further Reading: arXiv

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A Black Hole can Tear a Neutron Star Apart in Less Than 2 Seconds

Almost seven years ago (September 14th, 2015), researchers at the Laser Interferometer Gravitational-wave Observatory (LIGO) detected gravitational waves (GWs) for the first time. Their results were shared with the world six months later and earned the discovery team the Noble Prize in Physics the following year. Since then, a total of 90 signals have been observed that were created by binary systems of two black holes, two neutron stars, or one of each. This latter scenario presents some very interesting opportunities for astronomers.

If a merger involves a black hole and neutron star, the event will produce GWs and a serious light display! Using data collected from the three black hole-neutron star mergers we’ve detected so far, a team of astrophysicists from Japan and Germany was able to model the complete process of the collision of a black hole with a neutron star, which included everything from the final orbits of the binary to the merger and post-merger phase. Their results could help inform future surveys that are sensitive enough to study mergers and GW events in much greater detail.

The research team was led by Kota Hayashi, a researcher with Kyoto University’s Yukawa Institute for Theoretical Physics (YITP). He was joined by multiple colleagues from YITP and Toho University in Japan and the Albert Einstein Institute at the Max Planck Institute for Gravitational Physics (MPIGP) in Postdam, Germany. The paper that describes their findings was led by YITP Prof. Koto Hayashi and recently appeared in the scientific journal Physical Review D.

The mergers of compact objects discovered so far by LIGO and Virgo (in O1, O2, and O3a). Credit: LIGO Virgo Collaboration / Frank Elavsky, Aaron Geller / Northwestern

To recap, GWs are mysterious ripples in spacetime originally predicted by Einstein’s General Theory of Relativity. They are created whenever massive objects merge and create tidal disruptions to the very fabric of the Universe, which can be detected thousands of light-years away. To date, only three mergers have been observed involving a binary system consisting of a black hole and a neutron star. During one of these – GW170817, detected on August 17th, 2017 – astronomers detected an electromagnetic counterpart to the GWs it produced.

In the coming years, telescopes and interferometers of greater sensitivity are expected to see much more from these events. Based on the mechanics involved, scientists anticipate that black hole-neutron star mergers will include matter ejected from the system and a tremendous release of radiation (which might include short gamma-ray bursts). For their study, the team modeled what black hole-neutron star mergers would look like to test these predictions.

They selected two different model systems consisting of a rotating black hole and a neutron star, with the black hole set at 5.4 and 8.1 solar masses and the neutron star at 1.35 solar masses. These parameters were selected so that the neutron star was likely to be torn apart by tidal forces. The merger process was simulated using the computer cluster “Sakura” at the MPIGP’s Department of Computational Relativistic Astrophysics. In an MPIGP press release, Department director and co-author Masaru Shibata explained:

“We get insights into a process that lasts one to two seconds – that sounds short, but in fact a lot happens during that time: from the final orbits and the disruption of the neutron star by the tidal forces, the ejection of matter, to the formation of an accretion disk around the nascent black hole, and further ejection of matter in a jet. This high-energy jet is probably also a reason for short gamma-ray bursts, whose origin is still mysterious. The simulation results also indicate that the ejected matter should synthesize heavy elements such as gold and platinum.”

The team also shared the details of their simulation in an animation (shown above) via the Max Planck Institute for Gravitational Physics’ Youtube Channel. On the left side, the simulation shows the density profile as blue and green contours, the magnetic field lines that penetrate the black hole are shown as pink curves, and the matter ejected from the system as cloudy white masses. On the right side, the magnetic field strength of the merger is depicted in magenta, while the field lines appear as light-blue curves.

In the end, their simulations showed that during the merger process, the neutron star is torn apart by tidal forces in a matter of seconds. About 80% of the neutron star’s matter was consumed by the black hole in the first few milliseconds, increasing the black hole’s mass by an additional solar mass. In the following ten milliseconds, the neutron star formed a one-armed spiral structure, part of the matter was ejected from the system while the rest (02.-0.3 solar masses) formed an accretion disk around the black hole.

After the merger was complete, the accretion disk fell into the black hole, causing a focused jet-like stream of electromagnetic radiation and matter. This jet emanates from the poles, similar to what is often seen with Active Galactic Nuclei (AGNs), and could result in a short gamma-ray burst. What was especially astounding was that while the simulations took two months to generate, the simulated merger lasted about two seconds! Said Dr. Kenta Kiuchi, the group leader in Shibata’s department who developed the simulation code:

“Such general relativistic simulations are very time-consuming. That’s why research groups around the world have so far focused only on short simulations. In contrast, an end-to-end simulation, such as the one we have now performed for the first time, provides a self-consistent picture of the entire process for given binary initial conditions that are defined once at the beginning.”

Artist’s illustration of two merging neutron stars. The narrow beams represent the gamma-ray burst, while the rippling spacetime grid indicates gravitational waves. Credit: National Science Foundation/LIGO/Sonoma State University/A. Simonnet

Long-term simulations also allow astronomers to explore the mechanism behind short-lived gamma-ray bursts (GRBs). In addition to being a transient phenomenon, like Fast Radio Bursts (FRBs) that also last for only seconds or milliseconds, GRBs are the most energetic phenomenon in the Universe, and astronomers are keen to investigate them further. Looking ahead, Shibata and his colleagues are working on more complex numerical simulations to model the merger of neutron stars and what results.

The merger of neutron stars is also expected to include an electromagnetic contribution and short-lived gamma-ray bursts. This study serves to illustrate how the study of GW has advanced by leaps and bounds in recent years and how more sensitive observations and keeping pace with improvements in computing and simulations. The result is breakthroughs in our understanding of the Universe that occur at an ever-increasing rate! Who knows what discoveries might be right around the next corner?

Further Reading: MPIGP, Physical Review D

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