The GALAH Fourth Data Release Provides Vital Data on One Million Stars in the Milky Way.

For the past ten years, Australia’s ARC Centre of Excellence in All Sky Astrophysics in 3 Dimensions (ASTRO 3D) has been investigating star formation, chemical enrichment, migration, and mergers in the Milky Way with the Anglo-Australian Telescope (AAT). Their work is part of the GALactic Archaeology with HERMES (GALAH) project, an international collaboration of more than 100 scientists from institutes and universities worldwide. These observations have led to the highest spectral resolution multi-dimensional datasets for over a million stars in the Milky Way.

Previous GALAH data releases have led to many significant discoveries about the evolution of the Milky Way, the existence of exoplanets, hidden star clusters, and many more. In the fourth data release (DR4), the GALAH team released the chemical fingerprints (spectra) for almost 1 million stars. This data is the pinnacle of the 10-year project and was released during the 50th anniversary celebration of the AAT. According to the study that accompanied the release, the data will inform decades of research into the formation and evolution of our galaxy.

The study was led by Sven Buder, a research fellow at ASTRO 3D and the Australian National University (ANU). He was joined by an international team of researchers from ANU’s Research School of Astronomy and Astrophysics, ASTRO 3D, ACCESS-NRI, the UNSW Data Science Hub, the Sydney Institute for Astronomy, Astrophysics and Space Technologies Research Centre, Space Telescope Science Institute (STScI), the Stellar Astrophysics Centre, the International Space Science Institute, and multiple universities. The paper describing the data release recently appeared in the Publications of the Astronomical Society of Australia.

The GALAH survey relies on the High Efficiency and Resolution Multi-Element Spectrograph (HERMES) working in conjunction with the 2-degree field (2dF) positioner. Both instruments are part of the Anglo-Australian Telescope (AAT) located at the Siding Spring Observatory in Coonabarabran, New South Wales. The 2dF positioner places a fiber at a star’s location in order for the light to pass to the HERMES instrument, which obtains detailed spectra of 392 objects at a time over two degrees of the sky. As Dr. Buder explained in a recent Science in Public news release:

“Our work is focused on collecting as much quality data as we can,” said ASTRO 3D’s Sven Buder, a research fellow at the Australian National University. GALAH has shown us which chemical elements make up the stars of the Milky Way. This dataset now helps further our ability to accurately age the stars in our neighborhood and understand where they came from. This data becomes a powerful tool for astronomers to test new theories and make new scientific discoveries about the Universe.”

The project scientists also rely on data from the Gaia, Kepler, and CoRoT missions, which have gathered optical data on countless stars in our galaxy. The GALAH project aims to determine the ages of these stars via their chemical signatures to get a clearer picture of the assembly of the Milky Way. This will allow astronomers to estimate a timeline of the Galaxy’s chemical and dynamical evolution and to investigate changes in the rate of star formation rate over time.

“We have measured the elements within these stars, like carbon, nitrogen, oxygen, as well as heavy elements found in our smartphones and electric vehicles,” added Dr. Buder. “This data will help us figure out how these elements are produced in stars, which is fundamental to explaining the origins of the building blocks of life.”

The spectral data consists of the visible spectrum with overlapping barcodes that indicate at which wavelengths light is being absorbed. These are the “chemical fingerprints” of the star, revealing their overall composition. This data will also help astronomers understand how the elements were formed and distributed throughout the Universe, offering hints about cosmic evolution. As if that wasn’t enough, the spectra can also be used for potentially detecting signatures of planetary systems.

The colorful spectra taken at Siding Spring Observatory with the element barcode of the pointer stars alpha Centauri, our Sun, and stars with very little elements. Credit: Sven Buder, ANU/ASTRO 3D

In the past, GALAH data has shown stars that may have consumed planets as the Milky Way developed. Said co-author Professor Daniel Zucker of Macquarie University:

“The GALAH survey has detected signs that some stars may have ‘eaten’ planets that were orbiting them. This can be observed by looking at the chemical composition of the star, as the elements from the consumed planet would show up as markers in the star’s spectrum.”

The GALAH datasets have had a profound impact on the global astronomical community and led to 290 scientific studies to date. The previous data release (DR3) paper covered 300,000 stars and became the most cited work of the year for the journal responsible. With data on almost 1,000,000 stars, the scientific impact of this latest release is expected to be tremendous. The GALAH dataset is also expected to play a vital role in training the next generation of machine-learning tools, which are increasingly important to astronomy.

“We are really looking towards an incredibly exciting period over the next few years where all of these discoveries about what’s happening in our Universe are going to flow from the data that we’ve collected right here in Australia using Australian telescopes and building on Australian research,” said Associate Professor Sarah Martell of UNSW, a key member of the project. Professor Emma Ryan-Weber, the Director of ASTRO 3D, added that the GALAH project is directly aligned with ASTRO 3D’s mission:

“It helps us understand how galaxies build mass over time. The chemical information the research team has gathered is like stellar DNA – we can use it to tell where each star has come from. We can also determine their ages and movements and gain a deeper understanding of how the Milky Way and other galaxies formed and have evolved. What’s more, as the ASTRO 3D mission comes to a close, the GALAH project will leave a lasting legacy of Australian science informing astronomical discoveries about the Universe’s origins and development for decades to come.”

The DR4 release can be found here, while the entire list of GALAH datasets can be found here.

Further Reading: Science in Public

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The Sun Unleashes its Strongest Flare This Cycle

Yesterday the Sun released a huge solar flare, and it’s heading toward Earth! It’s nothing to worry about since it’s nowhere near as large as the Carrington Event of 1859, but it is large enough to give us some amazing aurora.

Large solar flares happen periodically. Quite literally, because the Sun goes through an 11-year cycle of lower and higher activity. Right now the Sun is near the maximum of a cycle, so we see lots of sunspots and flares. When astronomers first studied the cycle they could only measure the number of sunspots at a given time. Solar flares were largely invisible to early telescopes. But now with orbiting observatories such as the Solar Dynamics Observatory, we can capture images of solar flares in real time. Astronomers now categorize the strength of solar flares by the intensity of x-rays they emit, known as their x-class. The categories are numbered by power level, with each category double the previous one. So, for example, an X2 flare is twice as powerful as an X1 and half as strong as an X3.

This latest flare is rated as X9, which is much stronger than most solar flares. But stronger events have reached Earth before. In 1989 an X15 event triggered a regional blackout event in Quebec. In November of 2003 the Sun released an X28 solar flare, but most of it missed Earth. The 1859 Carrington Event occurred before astronomers developed the x-class rating, but it’s estimated to have been around X45. So this flare is huge, but it won’t put our electrical infrastructure at serious risk.

What it will provide, however, is an auroral light show. As the charged particles released by the flare reach Earth’s magnetosphere, many of them will be caught by our magnetic field and spiral along the field lines to strike Earth’s atmosphere in the polar regions. The impact will trigger the subtle and beautiful light shows known as aurora. If you happen to live far enough from the equator you might be able to see them in the next few days. To find out your chances, you can check out the National Oceanic and Atmospheric Administration’s Space Weather Prediction Center.

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What Does a Trip to Mars Do to the Brain?

It’s not long before a conversation about space travel is likely to turn to the impact on the human body. Our bodies have evolved to exist on Earth with a constant force of 1G acting upon them but up in orbit, all of a sudden that force is apparently lacking. The impact of this is well known; muscle loss and reduction in bone density but there are effects of spaceflight. Cosmic radiation from the Galaxy has an impact on cognition too, an effect that has recently been studied in mice!

When an object like the space station is in orbit around the Earth it is in a state known as freefall. This means it is constantly falling to Earth but the curvature of the Earth is constantly falling away from it. In other words, it is constantly falling but never reaches the ground. This state means anyone or anything inside the space station would also fall at the same rate but this would be experienced as floating. Muscle loss and reduction in bone density are the well known impacts of such an environment but there are more that await a space traveller. 

ESA astronaut Alexander Gerst spent six hours and 13 minutes outside the International Space Station with NASA astronaut Reid Wiseman on Tuesday, 7 October 2014. This was the first spacewalk for both astronauts but they performed well in the weightlessness of orbit. Credit: NASA/ESA

Galactic cosmic radiation (GCR) is made up of energy originating from sources outside of our Solar System. These tend to be from supernova explosions and other energetic events in deep space. The particles from GCR are mostly protons and electrons along with some heavier nuclei. They can penetrate our atmosphere but the Earth’s magnetic field offers some protection to those on the surface. To those venturing out into space, things are a little less rosey for GCR can have quite an impact on astronauts. 

Sources of Ionizing Radiation in Interplanetary Space. The Radiation Assessment Detector (RAD) on NASA’s Curiosity Mars rover monitors high-energy atomic and subatomic particles coming from the sun, distant supernovae and other sources. The two types of radiation are known as Galactic Cosmic Rays and Solar Energetic Particles. RAD measured the flux of this energetic-particle radiation while shielded inside the Mars Science Laboratory spacecraft on the flight delivering Curiosity from Earth to Mars, and continues to monitor the flux on the surface of Mars. Credit: NASA/JPL-Caltech/SwRI

GCR is a real problem for longer duration space exploration like trips to Mars since currently, the radiation can penetrate spacecraft shielding and be a real threat to human health. Studies to date have shown that GCR can have an effect cognitive abilities on mice in the short term however a new study paints a rather more bleak picture. The paper published in the Journal of Neurochemistry reports that GCR exposure can have long lasting effects too. 

Surprisingly, the team studied the impact on both male and female mice by subjecting them to a multi-particle spectrum GCR similar to the radiation that would be experienced on a deep space mission. The experiment was undertaken at Brookhaven National Laboratory where a 33-ion beam was used to simulate radiation from space. The team found that the radiation impaired numerous central nervous system functions from memory, pattern separation (when the brain minimises overlap between patterns of neuronal activity that represents similar experiences), anxiety, vigilance, social novelty (tendency to spend time with a previously unknown mouse rather than a familiar mouse!) and motor controls.

The discovery that the impact on females was more pronounced was unexpected but the team also established that mice which were fed an antioxidant and anti-inflammatory drugs known as CDDO-EA were less effected. The findings will be of immediate benefit to space exploration but will also help us to understand the long term impact on our cognition from radiation.

Source : Can cosmic radiation in outer space affect astronauts’ long-term cognition?

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Could a New Sungrazer Comet Put on a Show at the End of October?

Could this be the next great comet? To be sure, these words have been said lots of times before. In a clockwork sky, how comets will perform is always the great wildcard. Comets from Kohoutek to ISON have failed to live up to expectations, while others like W3 Lovejoy took us all by surprise. But a discovery this past weekend has message boards abuzz, as an incoming sungrazer could put on a show right around Halloween.

Anatomy of a Sungrazer

The discovery comes to us from the prolific Asteroid Terrestrial-impact Last Alert System (ATLAS), which first spotted the comet on the night of September 27^th. The initial designation of the comet was A11bP7I. The comet now has an official designation: C/2024 S1 ATLAS. This was announced on October 1^st, in the International Astronomical Union’s Central Bureau for Astronomical Telegram’s message 5453.

The orbit of Comet C/2024 S1 ATLAS. Credit: NASA/JPL.

The highly eccentric hyperbolic orbit of the comet suggests it’s a member of the Kreutz family group of sungrazer comets. Most of these comets are doomed for destruction at perihelion, but there have been a few exceptions over the years. Those sungrazers that have survived have gone on to become great comets.

Could C/2024 S1 ATLAS do the same?

Comet Caveats

Now, a few caveats are in order. Astronomers found S1 ATLAS at +12^th magnitude, 1.094 Astronomical Units (AU) from the Sun. It could well be the case that it simply had an outburst right when it was first spotted, and could in fact be smaller and less energetic than it seems. What we need are more observations over the next few weeks.

Comet C/2024 ATLAS imaged shortly after discovery. Credit: Michael Jaeger.

“It’s early days, so I think the prudent approach is to moderate our expectations and then be ‘pleasantly surprised’ later,” astronomer Karl Battams (U.S. Naval Research Laboratory) told Universe Today. “That said, there’s clearly the potential for this to be a very exciting comet. The best analog we have is comet Lovejoy in 2011, which was discovered just a couple of weeks from perihelion, versus this one which is nearly a month away.”

Comet S1 ATLAS imaged on September 28th. Credit: Filipp Romanov.

The comet reaches perihelion on October 28^th, 0.0082 AU from the Sun. That’s 762,600 miles from solar center, just 330,600 miles from the surface of the Sun. The solar radius is about 432,000 miles. As always seems to be the case, southern hemisphere observers will get a better view of the comet leading up to perihelion in mid-October as it approaches the Sun through the constellation Hydra. The comet will be visible low to the east at dawn, and ‘could’ break +6^th magnitude in the final week of October. The comet passes 0.306 AU from the Earth on October 23^rd after which, things could start to get interesting.

Prospects for Sungrazer A1 ATLAS

As of writing this, best estimates for peak magnitudes for comet S1 ATLAS top out at -7—think a bright daytime comet, but very close to the Sun—though -1^st magnitude or so is probably more conservative.

Northern hemisphere viewers might get best views of the comet low to the east at dawn after perihelion… if it survives.

Looking low to the east at dawn on Halloween morning. Credit: Starry Night.

“This Kreutz-group comet won’t pass quite as close to the Sun as W3 Lovejoy, so it’s not unreasonable to guess that it will aid its survival potential.” Says Battams. “Assuming so, it might be briefly visible to northern hemisphere observers very low in the early morning (in) southeast skies after perihelion, but it would require good viewing circumstances (a clear, low horizon)… and won’t hang around there for long.”

A simulation of Comet A1 ATLAS in SOHO’s field of view. Credit: Starry Night.

The comet enters the Solar Heliospheric Observatory (SOHO’s) LASCO C2/C3 field of view on October 26^th, and exits on the 29^th. It’s strange to think: prior to SOHO’s launch in 1995, astronomers knew of less than a handful of sungrazer comets. Now, thanks to the mission, we know of 5,065 sungrazing comets and counting.

New sticky: I rarely tweet these days, mainly b/c most of the fun people have left. ? But I still pop in from time-to-time, and will post about exciting comet or Sun stuff.
As always, any images/data I post are from 100% public sources, and all opinions are solely mine. pic.twitter.com/OeQRia2ppU

— Karl Battams (@SungrazerComets) October 2, 2024

Classic Sungrazers of Yore

2011’s sungrazer W3 Lovejoy survived a passage just 87,000 miles from the surface of the Sun… Comet ISON, however, did not survive a 0.001244 AU, 116,000 mile surface pass at perihelion on U.S. Thanksgiving Day 2013.

Long-time comet watchers will remember sungrazer Ikeya-Seki, which survived a 280,000 mile pass (just a little over the Earth-Moon distance) from the surface of the Sun. That comet went on to dazzle observers in 1965.

Comet Ikeya-Seki. Credit: James W. Young/TMO/JPL/NASA.

“What I will say is that I am very excited at the ‘prospect,’ and will be watching the evolution of this extremely closely over the next couple of weeks.” says Battams. “I think by mid-October we’ll be able to state some facts with a lot more certainty.”

It seems like good comets always come in pairs…remember Hale-Bopp and Hyakutake in the late 90s? We (finally) caught sight of comet C/2023 A3 Tsuchinshan-ATLAS this morning from here in Bristol, Tennessee, looking like a fuzzy ‘star’ with a short tail in the brightening twilight low to the east, peeking out between pine trees.

We’re cautious for now when it comes to S1 ATLAS. But remember: comets never read predictions… and S1 ATLAS could well surprise us.

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Gravitational Lens Confirms the Hubble Tension

We’ve known the Universe is expanding for a long time. The first solid paper demonstrating cosmic expansion was published by Edwin Hubble in 1929, based on observations made by Vesto Slipher, Milton Humason, and Henrietta Leavitt. Because of this, the rate of cosmic expansion is known as the Hubble constant, or Hubble parameter, H₀. From this parameter, you can calculate things such as the age of the Universe since the Big Bang, so knowing the value of H₀ is central to our understanding of modern cosmology.

Early on, the measured value of the Hubble parameter varied widely. Hubble’s initial value was on the order of 500 (km/s)/Mpc. By the 1960s, the value settled down to between 50 and 90 (km/s)/Mpc, where it stayed for most of the 20th century. It was difficult to get more precise because our methods of calculating it were limited. All of these were based on the cosmic distance ladder, which uses a series of observations to calculate ever greater cosmic distances, each building on the previous method. But in the past few decades we got pretty good at it, and the Hubble value seemed to settle around 70 (km/s)/Mpc. After that, things started to get…problematic.

With satellites such as WMAP and Planck we started to get high-resolution maps of the cosmic microwave background. From fluctuations in this background we have a new way to measure H₀ and get a value of 67 – 68 (km/s)/Mpc. At the same time, observations of distant supernovae and the cosmic distance ladder pin down the value to 73 – 75 (km/s)/Mpc. Both methods are quite precise, and yet they entirely disagree. This disagreement is now known as the Hubble tension problem, and it is the most bothersome mystery in cosmology.

Hubble tension between methods. Credit: Wikipedia user Primefac

We aren’t sure what causes the Hubble tension. It might mean that one or more of our observation methods are fundamentally flawed, or it might mean there is something about dark energy and cosmic expansion that we really don’t understand. But astronomers generally agree that one way to address this mystery is to look for ways to measure H₀ that are independent of both the cosmic background and the cosmic distance ladder. One such method involves gravitational lensing.

Gravitational lensing occurs because gravity warps space, meaning that the path of light can be deflected by the presence of a large mass. So, for example, if a distant galaxy happens to be behind a closer galaxy from our vantage point, we see a gravitationally distorted view of the distant galaxy or even multiple images of the galaxy. The interesting thing about the multiple image effect is that the light from each image travels a different path around the closer galaxy, each with a different distance. Since the speed of light is finite this means each image gives us a view of the galaxy at different times in history.

This doesn’t matter much for galaxies, but for supernovae it means gravitational lensing can let us observe the same supernova multiple times. By calculating the path of each supernova image we can determine the relative distance of each path, and by timing the appearance of each image we can determine the actual distance. This gives us a measurement that is independent of the cosmic distance ladder, giving us a new way to measure the Hubble parameter. This method has been used a couple of times, but the uncertainties of their Hubble values weren’t small enough to address the Hubble tension. However, a new study using this method is precise enough.

The study is based on JWST images of a Type Ia supernova named SN H0pe. It is one of the most distant supernovae ever observed, and thanks to the less-distant galaxy cluster G165, the team captured three lensed images of SN H0pe. With their timing, observed brightness, and calculated paths, the team calculated H₀ to be 70 – 83 (km/s)/Mpc. This still has a higher uncertainty than other methods, but it agrees with the usual distance ladder method. It also clearly disagrees with the cosmic microwave background method.

Despite H0pe, the Hubble tension is very real. If anything, this new result makes the issue even more troublesome. There is something about cosmic expansion we don’t understand, and it’s now clear that better observations will not solve this mystery on their own.

Reference: Pascale, Massimo, et al. “SN H0pe: The First Measurement of H₀ from a Multiply-Imaged Type Ia Supernova, Discovered by JWST.” arXiv preprint arXiv:2403.18902 (2024).

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Jets From Supermassive Black Holes Create New Stars Along Their Trajectory

Since the 1970s, astronomers have observed that supermassive black holes (SMBHs) reside at the centers of most massive galaxies. In some cases, these black holes accelerate gas and dust from their poles, forming relativistic jets that can extend for thousands of light-years. Using the NASA/ESA Hubble Space Telescope, a team of astronomers observed the jet emanating from the center of M87, the supermassive galaxy located 53.5 million light-years away. To their surprise, the team observed nova erupting along the jet’s trajectory, twice as many as they observed in M87 itself.

The team was led by Alec M. Lessing, a Stanford University astronomer, and included researchers from the American Museum of Natural History, the University of Maryland Baltimore, Columbia University, Yale University, the SETI Institute, and NASA’s Goddard Space Flight Center. The paper detailing their findings recently appeared in The Astrophysical Journal. Their research was part of a 9-month survey of the M87 galaxy using Hubble’s near-UV Cosmic Origins Spectrograph (COS).

To date, all novae have been observed in double-star systems consisting of a red giant star and a white dwarf companion. In these systems, the outer layers of the red giant are siphoned away by the white dwarf and accreted onto its surface. When the white dwarf has accumulated enough hydrogen, the layer explodes in a “nova eruption,” and the cycle begins again. When the team observed M87 using Hubble’s COS, they found twice as many novae eruptions near the 3000-light-year-long jet than in the galaxy itself during the surveyed period.

A Hubble image of M87 shows a 3,000-light-year-long jet of plasma blasting from the galaxy’s 6.5-billion-solar-mass central black hole. Credit: NASA/ESA/STScI/A. Lessing et al. (2004).

These findings imply that there are twice as many nova-forming double-star systems near the jet or that these systems erupt twice as often as similar systems elsewhere in the galaxy. Another possibility is that the jet is heating the red giant stars in these binary systems, causing them to overflow further and dump more hydrogen onto the dwarf companion. However, the researchers determined that this heating is not significant enough to have this effect. As Lessing explained in an ESA press release:

“We don’t know what’s going on, but it’s just a very exciting finding. This means there’s something missing from our understanding of how black hole jets interact with their surroundings… There’s something that the jet is doing to the star systems that wander into the surrounding neighborhood.

“Maybe the jet somehow snowplows hydrogen fuel onto the white dwarfs, causing them to erupt more frequently. But it’s not clear that it’s a physical pushing. It could be the effect of the pressure of the light emanating from the jet. When you deliver hydrogen faster, you get eruptions faster. Something might be doubling the mass transfer rate onto the white dwarfs near the jet.”

This is not the first time astronomers have noticed increased levels of activity around the M87 jet. Shortly after Hubble launched in 1990, astronomers observed the galaxy’s SMBH using its first-generation Faint Object Camera (FOC). These observations revealed “transient events” that could be evidence of novae, but the FOC’s view was too narrow to compare what was happening between the jet and in the near-jet region. Thanks to the nine-month campaign that relied on Hubble’s upgraded cameras (which have a wider view) and viewed the jet’s environment every five days, the team was able to count the novae along the jet’s trajectory.

Sag A* compared to M87* and the orbit of Mercury. Credit: EHT collaboration

The observations, which were the deepest images of M87 ever taken, revealed 94 novae within the M87 galaxy’s inner region. Said co-author Michael Shara, the Curator of Astrophysics at the American Museum of Natural History:

“The jet was not the only thing that we were looking at — we were looking at the entire inner galaxy. Once you plotted all known novae on top of M87 you didn’t need statistics to convince yourself that there is an excess of novae along the jet. This is not rocket science. We made the discovery simply by looking at the images. And while we were really surprised, our statistical analyses of the data confirmed what we clearly saw.”

These observations confirm that the venerable Hubble still has the capability to reveal new and interesting things about the Universe. In addition, these findings provide an opportunity for follow-up studies to learn more about how relativistic jets could influence star systems extending well beyond their galaxies.

Further Reading: ESA Hubble, The Astrophysical Journal

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NASA Turns Off One of Voyager 2's Science Instruments

The two Voyager spacecraft have been speeding through space since 1977, powered by decaying chunks of plutonium that produce less and less energy every year. With less electricity available, NASA has decided to shut down one experiment on Voyager 2, the plasma science instrument. This device measures the quantity and direction of ionized particles passing the spacecraft. While Voyager 2 still has enough electricity to support its four other operational instruments, it will likely be down to just one by the 2030s.

NASA said that over the past several years, engineers for the mission have taken steps to avoid turning off any science instruments for as long as possible since the science data collected by the two Voyager probes is unique. As the first spacecraft to reach interstellar space — the region outside the heliosphere – this is currently our only chance to study this region. However, this particular instrument has been collecting limited data in recent years due to its orientation relative to the direction that plasma is flowing in interstellar space.

The 47-year old Voyager 2 is traveling at about 15 km/second (35,000 miles per hour) and is currently more than 20.5 billion km (12.8 billion miles) from Earth. The four remaining science instruments are studying the region outside our heliosphere and include a magnetometer to study the interplanetary magnetic field, a charged particle instrument that measures the distributions of ions and electrons, a cosmic ray system that determines the origin of interstellar cosmic rays, and a plasma wave detector.

The Grand Tour

The Grand Tour ‘poster.’ Image: NASA/JPL

The two Voyagers both launched in 1977 (August and September), and their different trajectories were designed to take advantage of a rare geometric arrangement of the outer planets in the late 1970s and the 1980s which allowed for a four-planet tour for a minimum of propellant and trip time. The positions of those planets — which only occurs about every 175 years — took Voyager 2 (which launched first) past the gas giants Jupiter and Saturn, and then its flight path allowed for encounters with the ice giants Uranus and Neptune. It remains the only spacecraft to have visited either of the ice giant planets.

Voyager 1 made flybys of Jupiter, Saturn, and Saturn’s largest moon, Titan. Both spacecraft made incredible discoveries at the distant planets, and the astounding imagery sent back to Earth opened a whole new way of looking at the outer Solar System.

Europa seen during Voyager 2 Closest Approach. Credit: NASA/JPL

Now, they’re in the Voyager Interstellar Mission phase, where their data helped characterize and study the regions and boundaries of the outer heliosphere, and now explores the interstellar medium. Voyager 1 crossed the heliopause and entered interstellar space on August 25, 2012. Voyager 2 entered interstellar space on November 5, 2018, at a distance of 119.7 AU. Both communicate with Earth via the Deep Space Network. It takes nearly a day for one-way communications to reach each spacecraft and another day for data to be sent back to Earth.

Dwindling Power

Pellet of Pu-238. RTGs are constructed using marshmallow-sized pellets of Pu-238. As it decays, interactions between the alpha particles and the shielding material produce heat that can be converted into electricity.

Each Voyager 2 is powered by three multihundred-watt radioisotope thermoelectric generators (RTG). At launch, each RTG provided enough heat to generate approximately 157 watts of electrical power, and so collectively, the RTGs supplied the spacecraft with 470 watts at launch, and their power halves every 87.7 years. They were predicted to allow operations to continue until at least 2020, but are still providing enough energy for some data collection and communications. NASA estimates they lose about 4 watts of power each year.

After the twin Voyagers completed their exploration of the giant planets in the 1980s, the mission team turned off several science instruments that would not be used to study of interstellar space. That gave the spacecraft plenty of extra power until a few years ago. Since then, the team has turned off all onboard systems not essential for keeping the probes working, including some heaters. In order to postpone having to shut off another science instrument, they also adjusted how Voyager 2’s voltage is monitored.

The device that was recently turned off, the plasma science instrument, measured the amount of plasma (electrically charged atoms) and the direction it is flowing. In 2018, the plasma science instrument helped determine that Voyager 2 left the heliosphere. Inside the heliosphere, particles from the Sun flow outward, away from our parent star. Since the heliosphere is moving through interstellar space, the plasma flows in almost the opposite direction of the solar particles.

NASA’s Voyager 2 Probe Enters Interstellar Space This illustration shows the position of NASA’s Voyager 1 and Voyager 2 probes, outside of the heliosphere, a protective bubble created by the Sun that extends well past the orbit of Pluto. Voyager 1 exited the heliosphere in August 2012. Voyager 2 exited at a different location in November 2018. Credit: NASA/JPL-Caltech

When Voyager 2 exited the heliosphere, the flow of plasma into the instrument dropped off dramatically. Most recently, the instrument has been used only once every three months, when the spacecraft does a 360-degree turn on the axis pointed toward the Sun. This limited usage factored into the mission’s decision to turn this instrument off before others.

NASA said the same plasma science instrument on Voyager 1 stopped working in 1980 and was turned off in 2007 to save power.

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Bernard's Star Has a Planet (Again)!

The thing about exoplanets is that astronomers don’t see them the way most people think they do. Part of the reason for that is the way we announce them. Whenever an interesting exoplanet is discovered, the press release usually has colorful artwork showing oceans, mountains, and clouds. Something visually captivating like the image above. But the reality is that we have only imaged a few exoplanets directly, and even then, they appear only as small fuzzy blobs. Most of the known exoplanets were discovered by the transit method, where the star dims slightly as the planet passes in front of it. So what astronomers actually see is a periodic flickering of starlight.

This isn’t a problem for astronomers, since they are interested in data, not pretty pictures. Usually, the data is strong enough to confirm the presence of an exoplanet without directly observing it. But sometimes the observational data can be a bit more fuzzy, and that means we might think a planet is there only for further observations to prove us wrong. So sometimes an exoplanet is announced, only for the discovery to be retracted later. But sometimes a planet is confirmed, then unconfirmed, then confirmed again, as in the case of a recent study of Barnard’s star.

Barnard’s star is a small red dwarf just 6 light-years from Earth. Back in 2018, observations of the star suggested the presence of a Super-Earth sized companion named Barnard b. What’s interesting about this exoplanet is that it wasn’t discovered by the usual transit method but by a different approach known as the radial velocity method. As a planet orbits a star, the gravitational pull of the planet causes the star to wobble slightly toward and away from us. Since the relative motion of the star can cause its spectrum to shift slightly, we can observe the shift to know if the planet is there. But the radial velocity method is more difficult to do than the transit method, which is part of the reason fewer exoplanets have been discovered this way. And in this particular case, the data was fairly tenuous, and so Barnard b was shifted to the unconfirmed category.

Diagram detailing the Radial Velocity method. Credit: Las Cumbres Observatory

This new study finds that the 2018 discovery was a false positive. The data doesn’t support the existence of a super-Earth orbiting Barnard’s star. But the data does confirm the presence of an exoplanet. Barnard b does exist, just not the one we thought. This newly confirmed planet isn’t a super-Earth, but rather has less mass than our world. It orbits the star every 3 days, which is part of the reason it was so difficult to detect.

It took 5 years of observational data to confirm this exoplanet, which just reinforces how difficult it is to find planets this way. But the good news is that the data hints at the presence of other planets as well. It will take more data and study to confirm them, but it’s quite possible that Barnard’s star has a whole system of small worlds, similar to the TRAPPIST-1 system.

Reference: J. I. González Hernández, et al. “A sub-Earth-mass planet orbiting Barnard’s star.” Astronomy & Astrophysics 690 (2024): A79.

Reference: Ribas, Ignasi, et al. “A candidate super-Earth planet orbiting near the snow line of Barnard’s star.” Nature 563.7731 (2018): 365-368.

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An Earth-like Planet Around a Dead Sun Provides Some Reassurance About the Future of Earth

In about five billion years, our Sun will exit its main sequence phase and transition to its red giant phase. At this point, the Sun will expand and consume the planets of the inner Solar System, including Mercury and Venus. What will become of Earth when this happens has been the subject of debate for many decades. But with the recent explosion in exoplanet discoveries, 5,759 confirmed in 4,305 systems so far, astronomers hope to learn more about how planets fare as their stars near the end of their life cycle.

Using the 10-meter telescope at the Keck Observatory in Hawaii, an international team of astronomers discovered an Earth-like planet orbiting a white dwarf star 4,000 light-years from Earth. This planet orbits its star, about half the mass of our Sun, at a distance roughly twice that of the Earth today. The system resembles what is expected to become of our system once the Sun has exhausted the last of its fuel and blows off its outer layers in a supernova. It also offers some assurances that Earth will survive the Sun becoming a red giant and exploding in a supernova.

The team was led by Keming Zhang, a former doctoral student at the University of California, Berkeley, who is now an Eric and Wendy Schmidt AI in Science Postdoctoral fellow at UC San Diego. He was joined by multiple colleagues from UC Berkeley, UC San Diego, Tsinghua University, the Harvard & Smithsonian Center for Astrophysics (CfA), the California Institute of Technology (Caltech), the University of Washington, Ohio State University, the University of Maryland, and the NASA Goddard Space Flight Center. The paper that details their findings recently appeared in the journal Nature Astronomy.

To break it down, the Sun’s expansion as it becomes a red giant will likely mean the destruction of Mercury and Venus. At the same time, the Sun’s decreasing mass will force the surviving planets to migrate to more distant orbits, which could include Earth. If Earth survives when the Sun finally goes supernova, it will probably end up orbiting the resulting white dwarf remnant at a distance of 2 astronomical units (AUs) – twice its current distance. As Zhang related in a UC Berkeley News release,

“We do not currently have a consensus whether Earth could avoid being engulfed by the red giant sun in 6 billion years. In any case, planet Earth will only be habitable for around another billion years, at which point Earth’s oceans would be vaporized by runaway greenhouse effect — long before the risk of getting swallowed by the red giant.”

This is what astronomers may have found when they observed this planetary system roughly 4,000 light-years away. Located near the bulge at the center of our galaxy, this system was first noticed in 2020 when it passed in front of another star located 25,000 light-years from Earth. This caused a microlensing event, where the powerful gravity of the white dwarf focused and amplified the light of the background star by a factor of 1,000. The event was first detected by the Korea Microlensing Telescope Network (NMTNet) in the Southern Hemisphere, leading the team to designate it KMT-2020-BLG-0414.

The team estimated that the system included a star about half the mass of our Sun, an Earth-sized planet, and a likely brown dwarf with 17 times the mass of Jupiter. The analysis also concluded that the Earth-sized planet orbited its star at a distance of between 1 and 2 AUs. At the time, it was difficult to identify the type of star because neighboring stars and the magnified background star obscured its light. By 2023, the lensing event had passed, which made it possible for the team to examine the lensing system more closely using the Keck II 10-meter telescope in Hawaii.

As Zhang indicated, the team took two separate images but detected nothing. Since the lensing star was dark and low mass, they concluded it could only be a white dwarf. As noted, scientists are unsure what will happen to Earth when it reaches its red giant phase or if it will survive to orbit the white star remnant. This planetary system provides an example of a planet that did survive its sun expanding and exploding in a supernova. However, there is little chance of it being habitable since it orbits beyond the white dwarf’s habitable zone.

The top of Mauna Kea is a prime site for telescopes, as shown in this image. It boasts clear, dry atmospheric conditions. Global climate change could alter that. Credit: Mauna Kea Observatories

What’s more, some research suggests that if the expanding Sun doesn’t engulf our planet, it will eventually blow our atmosphere off and vaporize Earth’s oceans. Said co-author Jessica Lu, an associate professor and chair of astronomy at UC Berkeley:

“Whether life can survive on Earth through that (red giant) period is unknown. But certainly the most important thing is that Earth isn’t swallowed by the Sun when it becomes a red giant. This system that Keming’s found is an example of a planet — probably an Earth-like planet originally on a similar orbit to Earth — that survived its host star’s red giant phase.”

In addition, Zhang and his colleagues resolved an ambiguity regarding the location of the brown dwarf. According to the original analysis, the brown dwarf had a very wide Neptune-like or Mercury-type orbit. In the latter case, this would make it a hot brown dwarf, similar to the many “Hot Jupiters” observed repeatedly beyond our Solar System. Zhang and his colleagues could rule the latter scenario since a closely-orbited brown dwarf would have been consumed once the star entered its red giant phase.

This ambiguity resulted from “microlensing degeneracy,” where two distinct lensing configurations can give rise to the same lensing effect. Luckily, Zhang and co-author Bloom discovered a similar degeneracy in 2022 using a machine-learning algorithm designed to analyze microlensing simulations. When they applied the same technique to KMT-2020-BLG-0414, they were able to rule out alternative models of the planetary system. As Bloom explained:

“Microlensing has turned into a very interesting way of studying other star systems that can’t be observed and detected by the conventional means, i.e. the transit method or the radial velocity method. There is a whole set of worlds that are now opening up to us through the microlensing channel, and what’s exciting is that we’re on the precipice of finding exotic configurations like this.”

A NASA illustration of the giant planet WASP-193b and its star. Credit: NASA/ESA/CSA)

This system offers many opportunities for follow-up observations by next-generation telescopes like the Nancy Grace Roman Space Telescope (RST), scheduled for launch in 2027. One of the main objectives of the RST is to measure light curves from microlensing events to find exoplanets. “What is required is careful follow-up with the world’s best facilities, i.e., adaptive optics and the Keck Observatory, not just a day or a month later, but many, many years into the future, after the lens has moved away from the background star so you can start disambiguating what you’re seeing,” said Bloom.

The findings would seem to confirm another theory about the fate of our Solar System. When the Sun expands, our system’s habitable zone will migrate to the outer Solar System. If humanity is still around at this time, it will need to migrate to the icy satellites that orbit Jupiter and Saturn, which are likely to become planets covered in deep oceans – giving new meaning to the words “Ocean Worlds.”

Further Reading: Berkeley News, Nature Astronomy

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We Don’t See Many Planets in Old Triple Star Systems

Why is it important to search for exoplanets in triple star systems and how many can we find there? This is what a recent study accepted by Astrophysics & Space Science hopes to address as a pair of researchers from the University of Texas at Arlington investigated the statistical likelihood of triple star systems hosting exoplanets. This study holds the potential to help researchers better understand the formation and evolution of triple star systems and whether they are suitable to find life as we know it.

Here, Universe Today discusses this incredible research with Dr. Manfred Cuntz, who is a physics professor at the University of Texas at Arlington and lead author of the study, regarding the motivation behind the study, the most significant results, the importance of studying triple star systems, and the likelihood of finding exolife in triple star systems. Therefore, what was the motivation behind the study?

Dr. Cuntz tells Universe Today, “Ages and metallicity (i.e., the amount of heavy elements = elements other than hydrogen and helium) are fundamental properties of stars – a statement that applies to all stars. Considering that most stars (which however does not apply to the sun) are members of higher order systems – the study of stars in triple stellar systems is a natural extension of research focusing on single stars.”

For the study, the researchers conducted a statistical analysis regarding both the ages and metallicities of triple star systems with a total of 27 confirmed exoplanets based on past research, with the number of exoplanets in each system ranging from 1 to 5. The ages of the triple star system ages, with margins of error, ranged between 20 million years old to 7.2 billion years old. For context, our Sun is estimated to be slightly more than 4.6 billion years old.

The metallicities of the star systems, with margins of error, ranged between -0.59 to +0.56, which is often calculated based on the ratio of iron to hydrogen (Fe/H), and is also calculated with the equation X + Y + Z =1, with X being the fraction of hydrogen, Y being the fraction of helium, and Z being everything else (i.e., carbon, oxygen, silicon, iron, etc.). These values range between -4.5 to +1.0, with stars exhibiting 0, -1, greater than 0, and less than 0 indicating a star is equal in iron abundance to our Sun, one-tenth the iron abundance of our Sun, greater metal content than our Sun, and less metal content than our Sun, respectively. Therefore, what were the most significant results from this study?

“Two highly significant results have been identified,” Dr. Cuntz tells Universe Today. “First, stars in triple stellar systems are on average notably younger than stars situated in the solar neighborhood. The most plausible explanation is a possible double selection effect due to the relatively high mass of planet-hosting stars of those systems (which spend less time on the main-sequence than low-mass stars) and that planets in triple stellar systems may be long-term orbitally unstable. The stellar metallicities of those stars are on average solar-like; however, owing to the limited number of data, this result is not inconsistent with the previous finding that stars with planets tend to be metal-rich as the deduced metallicity distribution is relatively broad.”

The distances to the respective triple star systems range between 4.3 to 1,870 light-years from Earth, but only 6 of the 27 triple star systems reside within 100 light-years away. These six triple star systems include Alpha Centauri (4.3 light-years), Epsilon Indi (11.9 light-years), LTT 1445 (22.4 light-years), Gliese 667 (23.6 light-years), 94 Ceti (73.6 light-years), and Psi¹ Draconis (74.5 light-years), with the number of total exoplanets (with exoplanet candidates) within each system being 3 (2), 1, 1, 2 (1), 1, and 1, respectively. For context, as of September 2024, the total number of confirmed exoplanetary systems within our cosmos is more than 4,300 that encompasses almost 5,800 exoplanets. But despite the small number of triple star systems that host exoplanets, what is the importance of studying triple star systems?

Dr. Cuntz tells Universe Today, “Most stars (which however does not apply to the sun) are members of higher order systems, especially binaries – and in less common cases triple stellar systems, and systems of even higher order. Therefore, the study of planets hosted by triple stellar systems is a natural extension of the standard approach focusing on planets around single stars. The current study focuses on some of the properties of stars in triple stellar systems, which are also known to host (a) planet(s) – a relatively rare setting. The importance of the current study is to expand our general understanding of star-planet systems.”

For Alpha Centauri, the exoplanet, Proxima Centauri b, has been confirmed to be terrestrial (rocky), approximately the size of Earth in both radius and mass, and orbits within the habitable zone (HZ) of Proxima Centauri, one of the stars that comprise the Alpha Centauri triple star system. The only other terrestrial exoplanet orbiting within its star’s HZ is Gliese 667 Cc, whose mass and radius is larger than the Earth, designating it as a super-Earth. Therefore, given the small number of triple star systems that have exoplanets and even fewer that host terrestrial exoplanets orbiting in its HZ, what is the likelihood of finding exolife in triple star systems?

“The only planet where we know for sure that life does exist is Earth,” Dr. Cuntz tells Universe Today. “However, through both observational and theoretical studies during many decades of committed work, scientists are convinced that exolife is almost certainly real. This statement should also apply to planets in triple star systems. However, those planets are typically subject to relatively variable environmental forcings (e.g., variable amounts of radiation received by the stellar components), which is expected to reduce the likelihood of advanced life forms, but should still permit microbial life, especially extremophiles.”

As the number of confirmed exoplanets continues to grow, so should the confirmed number of triple star systems that host exoplanets, as well. When science fiction fans read about multi-star systems, they almost immediately think of the iconic scene in Star Wars: A New Hope of Luke Skywalker watching two stars setting on the horizon. While Tatooine was habitable for humans and other interesting life forms, this might not be the case in the real world, as demonstrated by Proxima Centauri b currently being the only Earth-like exoplanet orbiting in its HZ within 100 light-years from Earth. Therefore, what constraints should scientists put on finding life in triple star systems? Should we instead study their moons, as the film Avatar depicted the semi-habitable moon, Pandora, orbiting a much larger exoplanet within the Alpha Centauri system? Are triple star systems with exoplanets as rare as the statistics show today?

“The search for life outside of planet Earth continues to be a fascinating topic,” Dr. Cuntz tells Universe Today. “Political and societal support for ongoing and future space missions is highly appreciated. We, as scientists, are grateful about the ongoing support by the taxpayers around the world, but especially here in the U.S.”

What new discoveries about triple star systems will researchers make in the coming years and decades? Only time will tell, and this is why we science!

As always, keep doing science & keep looking up!

Reference: Cuntz, Manfred & Patel, Shaan D. “On the Age and Metallicity of Planet-hosting Triple Star Systems.” Astrophysics and Space Science (2024) (accepted)

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