A recent study published in The Astrophysical Journal Letters examines a rare alloy molecule known as chromium hydride (CrH) and its first-time confirmation on an exoplanet, in this case, WASP-31 b. Traditionally, CrH is only found in large quantities between 1,200 to 2,000 degrees Kelvin (926.85 to 1,726.85 degrees Celsius/1700 to 3,140 degrees Fahrenheit), and used to ascertain the temperature of cool stars and brown dwarfs. Therefore, astronomers like Dr. Laura Flagg in the Department of Astronomy and Carl Sagan Institute at Cornell University refer to CrH as a “thermometer for stars”.
For the study, the researchers analyzed the transmission spectrum of WASP-31 b using a combination of data from March 2022 and archival data from 2017 to ascertain that WASP-31 b possessed CrH within its atmosphere. The reason why the 2017 data was included in this current study was because it was initially not used to identify metal hydrides.
“Part of our data for this paper was old data that was on the very edge of the data set. You wouldn’t have looked for it,” said Dr. Flagg, who is lead author of the study.
For context within our own solar system, CrH has only been identified within sunspots on our Sun, with Dr. Flagg noting that the Sun is too hot (surface temperatures of approximately 6,000 degrees Kelvin (5,726.85 degrees Celsius)), and all remaining objects within the solar system are below 1,200 degrees Kelvin.
Discovered in 2010 using transit photometry by the WASP project, WASP-31 b is located approximately 1,252 light-years from Earth with a radius just over 1.5 times larger than Jupiter and a mass just under half of it, as well. Its orbital period around its F5V main-sequence star is 3.4 days, making WASP-31 b a “hot Jupiter”. For context, our Sun is designated as a G-type main-sequence star, with F-type main-sequence stars being slightly larger along with exhibiting slightly higher surface temperatures (~6,300 degrees Kelvin). That WASP-31 b is as cool as it is despite its parent star being hotter than our own Sun makes this finding all the more intriguing.
Artist impression of “hot Jupiter” exoplanet, WASP-31 b. (Credit: ESA/Hubble & NASA)
Dr. Flagg specializes in using high-resolution spectroscopy to identify and study the atmospheres of exoplanets, while also studying the formation and evolution of exoplanets orbiting young stars, as well. Spectroscopy involves using light to determine what elements might be present based on their color within the electromagnetic spectrum. For astronomy, this means using spectroscopy to study exoplanet atmospheres by measuring the parent star’s light passing through it. In the case of WASP-31 b, spectroscopy was used to measure the light from its parent star to identify CrH within WASP-31 b’s atmosphere.
“High spectral resolution means we have very precise wavelength information,” said Dr. Flagg. “We can get thousands of different lines. We combine them using various statistical methods, using a template – an approximate idea of what the spectrum looks like – and we compare it to the data, and we match it up. If it matches well, there’s a signal. We try all the different templates, and in this case the chromium hydride template produced a signal.” Dr. Flagg notes that sensitive instruments and telescopes are required to identify CrH due to its rarity, even at the current temperature.
While the research team states this is the first confirmed detection of CrH on an exoplanet, this research builds on a 2021 study which reported the first evidence for CrH in the atmosphere of WASP-31 b, but those researchers stopped short of calling it a confirmed finding based on their data at the time.
With this new confirmation of CrH, the team notes this could open doors for using high-resolution observations for studying exoplanet atmospheres, going as far as saying WASP-31 b will not be the last exoplanet where the presence of CrH will be confirmed.
How many more exoplanets will astronomers confirm the presence of CrH throughout the cosmos, and what can CrH teach us about exoplanet atmospheres in the coming years and decades? Only time will tell, and this is why we science!
The Pentagon has opened up a new portal on the internet for professionals to submit reports about UFOs — now officially known as unidentified anomalous phenomena, or UAPs — and for the rest of us to find out about the reports that have been released.
AARO.mil, the website for the All-domain Anomaly Resolution Office, is still a work in progress. For example, a promised online form for contacting the AARO is labeled as “Coming Soon.” But the version unveiled today offers eight videos showing UAPs, plus archives for congressional reports and briefings, press releases and links to other resources.
“The website will serve as a one-stop shop for all publicly available information related to AARO and UAP,” Air Force Brig. Gen. Pat Ryder, the Department of Defense’s press secretary, said today during a briefing.
That move was aimed at speeding up AARO’s development and the website’s launch. “I believe that transparency is a critical component of AARO’s work, and I am committed to sharing AARO’s discoveries with Congress and the public, consistent with our responsibility to protect critical national defense and intelligence capabilities,” Hicks, who played a lead role in establishing AARO last year, told DefenseScoop.
When the website is fully ready for prime time, it will serve as the secure channel for current or former government employees, military personnel and contractors to register UAP reports. In a news release, the Defense Department said that the secure reporting tool will be launched this fall. “A mechanism for members of the general public to make reports will be announced in coming months,” the Pentagon said.
Civilian pilots were encouraged to report UAP sightings to air traffic controllers. AARO said it would receive UAP-related pilot reports, known as PIREPs, from the Federal Aviation Administration.
AARO lists three UAP categories:
Airborne objects that are not immediately identifiable.
Transmedium objects or devices.
Submerged objects or devices that are not immediately identifiable and that display behavior or performance characteristics suggesting that the objects or devices may be related to objects or devices in the first two categories.
AARO says the Defense Department considers UAPs to be “sources of anomalous detections in one or more domains (i.e., airborne, seaborne, spaceborne and/or transmedium) that are not yet attributable to known actors and that demonstrate behaviors that are not readily understood by sensors or observers.”
The website doesn’t explicitly mention possible extraterrestrial origins for UAPs. One of the reasons why government officials and lawmakers are becoming more concerned about UAPs is because they may represent intrusions by the likes of Russia or China. A prime example would be the Chinese spy balloon that floated across the United States before it was shot down by an Air Force fighter jet.
All supernovae are exploding stars. But the nature of a supernova explosion varies quite a bit. One type, named Type 1a supernovae, involves a binary star where one of the pair is a white dwarf. And while supernovae of all types usually involve a single explosion, astronomers have found something that breaks that mould: A Type 1a supernova that may have detonated twice.
Type 1A supernovae occur in binary stars where one star is a white dwarf, and the other star is anything from a massive star to another white dwarf. As the primary white dwarf siphons material away from its secondary companion, it eventually gathers enough mass and exceeds the Chandrasekhar limit. When that happens, it triggers a cataclysmic explosion.
But a Type 1a supernova named SN 2022joj is exhibiting some peculiar behaviour. This led the authors of a new paper to consider that the supernova may have exploded twice. Moreover, it didn’t have to exceed the Chandrasekhar limit to detonate.
This artist’s illustration shows a white dwarf accreting material from its companion star. When enough mass has accumulated, it triggers an explosion: A type 1a supernova. Image Credit: NASA/CXC/M.Weiss
The paper is “SN 2022joj: A Potential Double Detonation with a Thin Helium Shell.” It hasn’t been published yet and is available on the pre-press site arxiv.org. The lead author is Estefania Padilla Gonzalez from the Department of Physics at UC Santa Barbara and the Las Cumbres Observatory.
Double-detonation stars are rare but not unheard of. They happen when the white dwarf accretes a layer of helium that ignites. In these types of explosions, the white dwarf doesn’t exceed the Chandrasekhar limit, and the explosion is relatively dim. These types of twice-exploding supernovae are called sub-luminous supernovae.
But it’s not just the dimness that signals a double-detonation supernova. It has an unusual light curve where red light manifests 11 days prior to its maximum brightness. After that peak, it resembles a more typical Type 1a supernova. That, combined with other aspects of its spectroscopy, led the authors of the new paper to consider that Sn 2202joj might have experienced a double detonation.
At different stages of their evolution, different types of stars can have layers or shells of different chemical elements. White dwarfs are no different and can have outer shells of either helium or hydrogen. The large majority of white dwarfs have a hydrogen shell or atmosphere.
It’s not to scale, but this schematic shows the onion-like layers of a massive evolved star just before it collapses. Each concentric shell of plasma is burning inside the star. Image Credit: By User: Rursus – R. J. Hall, CC BY 2.5, https://ift.tt/Hqc45ek
The authors of this study suggest that Sn 2202joj has an outer shell of helium. In this case, the white dwarf’s companion star has an outer shell of helium and 2202joj has siphoned off some of that helium to form its own helium shell. That can trigger a helium detonation, even though the star hasn’t exceeded the well-known Chandrasekhar limit. An important point is that this helium explosion creates another element: an isotope of Nickel called 56Ni. All that nickel is visible in the star’s spectrometry.
When the helium shell detonates, it not only synthesizes 56Ni. It drives a powerful shock wave into the white dwarf. That shock can trigger another detonation inside the star, and that’s how nature creates a double-detonation supernova.
The spectroscopy from the supernova supports this explanation, according to the authors. “Spectroscopically, we find strong agreement between SN 2022joj and double-detonation models with white dwarf masses around 1 M? and thin He-shell between 0.01 and 0.02 M?,” they write.
Light curves tell astrophysicists a lot about what’s going on with a star. This one is no different, and SN 2202joj’s light curve revealed a lot to the team of astronomers who studied it. Typically, a Type 1a supernova’s light curve looks like this.
This light curve is typical of Type 1a supernova. The nickel produced by the explosion decays rapidly and creates a peak in brightness, then the luminosity decreases and is dominated by the decay of Cobalt. Image Credit: The Astrophysical Journal 547 (2): 988. DOI:10.1086/318428., CC BY-SA 3.0, https://ift.tt/HDfndNK
But SN 2202joj’s light curve is different than a regular Type 1a SN. It has two separate peaks, and the first one is exceedingly red before quickly declining and shifting toward blue.
The following image compares SN 2202joj’s light curve with light curves from other SNe as well as different models of double detonation SNe. There’s a lot of data in this image, but it’s worth a look.
This figure from the study shows the colour evolution of SN 2022joj plotted against other SNe and Sne models in colour and time since explosion. Dashed lines are what different models of double detonation SNe predict. Black is 2202joj, while the other colours are other stars that astrophysicists have studied. Notice that the magenta and the blue stars are both other double detonation SN, while 2202joj is a thin helium shell double detonation SN. It’s particularly interesting that 2202joj is much redder in its early phases than the other supernovae. Image Credit: Gonzalez et al. 2023.
The researchers aren’t 100% certain that this is a double detonation SN. The early red colours indicated that two explosions occurred, but other evidence doesn’t agree. “However, the nebular spectra composition in SN 2022joj deviates from expectations for double detonation,” they write. The nebular spectra contain strong Fe III emissions, which a double detonation can’t explain.
“More detailed modelling, e.g., including viewing angle effects, is required to test if double detonation models can explain the nebular spectra,” they conclude.
Supernovae, though rare, play an important role in nature. They synthesize metals and spread them out into space when they explode. Without them, there would be no rocky planets like ours. Type 1a supernovae are important because of the specific role they play in the Universe. Scientists think that they synthesize the majority of the elements in the iron group, from titanium to zinc.
Nature creates all kinds of fascinating things in space, and exploding stars are some of the most awe-inspiring. Stars contain an enormous amount of matter, and when one explodes, the supernova releases a massive amount of energy in a short period of time. It’s only natural that these objects attract our attention.
There’s an odd exoplanet out there posing a challenge to planetary scientists. It’s a hot Neptune denser than steel. The big question is: how did it form?
The planet is TOI-1538b and it orbits its parent dwarf star every 1.24 days. It’s classified by planetary scientists as a world in the “Hot Neptune Desert”. That means there aren’t as many of these close-in hot Neptunes as scientists expect. There are a few others like it, although not as dense.
The stats on this world are impressive. It has the equivalent of ~75 Earth masses and is about 3.5 Earth radii. At a density of ~9.7 gm/cm3, that implies the interior contains a lot more rocky stuff than expected. (For reference, steel can be as much as 8.0 gm/cm3.) And, that makes this place a puzzling find because its evolution doesn’t seem to fit conventional planetary formation theories.
Could Massive Collisions Be the Answer?
A team of scientists led by Luca Naponiello of Rome Tor Vergata suspected that multiple catastrophic planetary collisions shaped TOI-1538b. Those impacts removed lighter atmospheric gases and water, leaving behind a rocky core. It’s not a surprising conclusion, since planetary formation involves lots of smaller worlds smacking together to make bigger ones. So, why not big ones slamming into each other?
Senior Research Associate and study co-author Dr Phil Carter from the University of Bristol’s School of Physics explained the idea. “We have strong evidence for highly energetic collisions between planetary bodies in our solar system, such as the existence of Earth’s Moon, and good evidence from a small number of exoplanets,” he said. “We know that there is a huge diversity of planets in exoplanetary systems; many have no analog in our solar system but often have masses and compositions between that of the rocky planets and Neptune/Uranus (the ice giants).”
Collisions in Exoplanet Formation
Our own solar system provides a good model for the formation of exoplanet systems. Some 4.5 billion years ago, the proto-Sun began coalescing in a cloud of gas and dust. That nebula was rich with heavier elements useful for planetary formation. Smaller particles—planetesimals—slammed together in the resulting protoplanetary disk to make larger and larger bodies. The result was four small rocky bodies plus four gas- and ice-rich giant worlds. In addition, the solar system has dwarf planets, comets, asteroids, and moons.
Artist’s conception of a solar system in formation. It’s likely that exoplanet formation around other stars proceeded similarly. Credit: NASA/FUSE/Lynette Cook
Bombardment of these infant worlds continued, scarring some with craters (like Mercury), and flipping at least one (Uranus) on its side. Planetary scientists look to that formation history to understand how similar processes played out around other stars. Spacecraft such as the Kepler and TESS missions discovered more than 5,000 candidate worlds. Astronomers suspect the galaxy teems with millions of planets. Most systems appear to have similar collections of exoplanets to ours, although not always in the sizes and masses that match our own.
Collisions remain an important part of how this exoplanet and other worlds formed. “Our contribution to the study [of TOI-1853b] was to model extreme giant impacts that could potentially remove the lighter atmosphere and water/ice from the original larger planet in order to produce the extreme density measured,” said Carter. If those happen frequently, that opens up new avenues of study for planetary formation specialists.
Modeling a Steely Exoworld
To understand its formation history, a science team led by essentially modeled extreme giant impacts that could strip away atmospheric elements. They found that the proto-Neptune would have once been a very wet exoplanet. In order to lose all that material, an impactor had to slam into it at a speed of more than 75 meters per second. Given those conditions, they could model a planet very similar to TOI-1853b. According to team member Zoë Leinhardt, the type of planetary impact that created this exoplanet wasn’t something they’d thought about. “We had not previously investigated such extreme giant impacts as they are not something we had expected. There is much work to be done to improve the material models that underlie our simulations, and to extend the range of extreme giant impacts modeled,” she said.
A simulation of an impact that might have created TOI-1538b. Courtesy: Jingyao Dou.
The next step is to do follow-up observations of the planet. It’s important to find out what’s left of its atmosphere and the composition of its gases. With a “real-world” example of what the planetary scientists modeled, it seems likely others could exist. TOI-1853b provides new evidence for the prevalence of giant impacts in the formation of planets throughout the galaxy. This discovery helps to connect theories for planet formation based on the solar system to the formation of exoplanets.
Adrift in a great sea of stars, we must surely not be alone.
It’s hard not to look at the night sky and think about the possibility of other civilizations out there. From the philosophical speculations of Giordano Bruno to the statistical estimations of Frank Drake, the more we’ve learned about the universe, the more likely alien life seems to be. And yet, in our search for this life, we have heard nothing but silence.
It’s always possible that we are the only living things in the cosmos, just as it is possible other civilizations keep to themselves or use communication technology invisible to us. But radio communication is both powerful and cheap, and we use it extensively. Our radio signals have been beaming from Earth for decades. So why shouldn’t other civilizations use radio as well?
There are some who feel we’re being too optimistic. Although we do emit plenty of radio signals into space, the power of radio light fades with distance as it fills an ever-expanding sphere. Combined with interference from the dust and gas of interstellar space, it is likely our signals could only be heard within a few light years of Earth using radio receivers we currently have today. We have directly transmitted powerful radio messages into space a few times, such as the Arecibo message beamed to the Hercules cluster in 1974. But even these would be terribly faint by the time they travel 22,000 light-years to their destination.
A color-coded version of the Arecibo message. Credit: Arecibo Observatory
Of course, we are a young and simple species. Perhaps an ancient, hyper-advanced species could pull our messages out of the cosmic dust. But could they do it across hundreds or thousands of light-years? That’s the question examined in a new arXiv paper.
The author starts with the Kardashev scale for advanced civilizations. First proposed in 1964, the scale ranks civilizations based on their ability to tap energy resources. A Type I civilization can access energy on a planetary scale, Type II on the scale of a star system, and Type III on a galactic scale. Carl Sagan and others have generalized this to a sliding scale and estimated humans are around 0.73. Based on this, the author asks what scale a civilization needs to be in order to detect relics of human civilization, and what distance would this be possible?
Given that our artificial radio signals only penetrate a hundred light-years of space, a species would have a better chance of trying to resolve artificial features on Earth. Things on the scale of cities or major earthworks. As an example, consider the pyramids of Giza. They have been around for thousands of years, and the Great Pyramid has a base of about 230 meters.
Given the amount of light reaching the Earth, the pyramids wouldn’t be visible beyond a few thousand light years or so, regardless of the power of your telescope. Not enough photons would reach beyond that distance to resolve anything. Taking the middle range of visible light (about 550nm) and a resolution of 10 meters, the maximum distance comes out to about 3,000 light-years.
To resolve pyramid-scale features at this distance you would need an optical telescope with a diameter of about 10 AU. That’s a bit larger than the orbit of Saturn. A telescope on that scale could in principle be constructed using an optical telescope array with millions of satellites across Saturn’s orbit. Of course, this is far beyond our current ability, or that of any planet-scale civilization. You would at least need to be masters of your star system.
So the upshot of all this is that a Type II civilization could see our great works of humanity within 3,000 light years. A great alien species might know that we’re here after all. But it will be thousands of years before we reach level 2 and are able to see them in return.
The last place to look for windstorms is on the Moon. Yet, it has swirls on its surface that look like the wind put them there. Since there’s no atmosphere on the Moon, planetary scientists had to look for another cause. It turns out there’s a connection to local magnetic anomalies and an interplay with lunar topography.
Swirls are albedo patterns on the Moon’s surface and they’ve kept planetary scientists debating their cause for years. They’re visible from Earth, although it wasn’t until 1966 that the NASA Lunar Orbiter II managed to get a clear image of one. One of the largest, Reiner Gamma, is visible through an amateur telescope.
A new study by scientists at the Planetary Science Institute, led by planetary scientist Deborah Domingue, examined the texture of the surface where these swirls appear. They looked at a spot in Mare Ingenii using photometric analysis to determine the cause. That technique takes into account how material scatters light and how those scattering properties change as the illumination (angle of the sunlight to the surface) and viewing (position of your spacecraft) geometries change.
Closeups in Mare Ingenii of topology where lunar swirls are created by highly mobile regolith, deposited by more than one process. Courtesy PSI.
Changing Ideas about Lunar Swirls
Over the years, lunar observers have come up with several explanations for these weird markings. Cometary impacts might send swirls of dust across the surface. Such collisions might also explain the magnetic anomalies associated with the swirls.
It’s also highly likely that the solar wind plays a role. It’s a frequent occurrence and could explain why some swirls seem to change more quickly over time. In this case, a magnetic anomaly protects light-colored regolith (lunar surface materials), which could be exposed silicates. This explains the swirling pattern, as shielded material would be brighter than materials outside the magnetic field. However, the spectral properties don’t always match those of shielded materials.
A reprocessed Lunar Orbiter II image of Mare Ingenii. Courtesy James Stuby, CC0.
It could be that magnetic fields segregate and trap electrostatically levitated dust. It’s the smallest size of all lunar dust and made of minerals brighter than the larger sizes of dust grains. Those bigger ones are more difficult to move electrostatically. The darker dust includes small inclusions of nanometer-scale iron. It’s more likely to get magnetically separated and deposited in the dark areas of the swirls. Ironically, one way to produce this nanometer-scale iron is by solar wind radiation.
Related to that is an idea that says weak electric fields created by interactions with the magnetic anomalies and solar wind plasma could attract or repel fine dust particles. Another theory, proposed by scientists in 2022 says that topography may also play a role in the placement of the swirls.
Lunar swirl region near Firsov Crater, as seen from Apollo 10. Courtesy NASA.
Using Photometric Analysis
What the team found with their photometric analysis study is that the grain-to-grain roughness was similar across the swirl region. However, the soil in the dark lanes has grains with a more complicated structure. In addition, they found that the composition between the bright and dark areas is different, following the expectations from dust collection and segregation.
Domingue thinks they may have a better feel for the origins of these strange swirls now. “The evidence, which includes recent correlation of topographic lows with the bright areas of the swirls, tells a story that more than one process is involved in their formation”, she said. “We definitely see evidence that the bright areas are less radiated, but this doesn’t explain all the properties of the swirls. Something else is operating, and the textures suggest dust collection and segregation are part of the tale.”
In an age of increasing “stuff” orbiting Earth one big concern is what happens if one satellite hits another. The result could be an explosion, or a chain reaction of collisions, or the closure of an orbit. That would be catastrophic. However, a small satellite called SBUDNIC just sent itself back to Earth earlier than expected. It’s goal: to demonstrate a low-cost way to take care of space debris.
SBUDNIC was the brainchild of a group of students at Brown University who were in a “Design of Space Systems” class taught by engineering Professor Rick Fleeter. It was a 3U CubeSat made of off-the-shelf components (including 48 Energizer batteries), a small camera, and a plastic drag sail. It joins a host of other CubeSats used (or proposed for use) at Earth and throughout the Solar System.
The team launched it aboard a SpaceX rocket on May 25, 2022. They communicated with it through a Ham radio-based Arduino prototyping platform. These are commonly used aboard 3U Cubesats due to their light weight and dependability. The idea was to show an affordable deorbit method.
A typical type of CubeSat on orbit like the one used by the Brown students for their orbital experiment in de-orbiting a satellite. Courtesy NASA.
“We were trying to prove that there are ways of deorbiting space junk after mission life has ended that are not super costly,” said Selia Jindal, who graduated from Brown in May and was one of the project leads. “This showed that we can do that. We were successfully able to deorbit our satellite so that it’s no longer taking up space in Earth’s orbit. More importantly, the project really helped show there are significant plans we can put in place to combat the space junk problem that are cost-effective.”
Gradually Leaving Orbit
Once in orbit at an altitude of 520 kilometers, the spacecraft’s sail popped open. Think of its drag sail almost like a drogue chute that slows down the spacecraft. That helped push the tiny spacecraft gradually back into Earth’s atmosphere. It turns out the sail was pretty efficient, which helped the satellite lose altitude. By March of this year, it had slipped to 470 kilometers. Later, on August 8, 2023, it had fallen to 147 kilometers, its last known position. Shortly after that, it burned up over Turkey due to the heat of re-entry.
This is a pretty quick re-entry and demonstrates a useful technology for other satellites. It used to be that these objects could stay in orbit for up to 25 years. But, in 2022, the Federal Communications Commission created a new 5-year rule for deorbiting satellites. It states that spacecraft ending up at altitudes less than kilometers must deorbit as soon as possible and no more than five years after the end of their missions.
One other thing to consider is solar activity. It causes Earth’s atmosphere to “puff up” during periods of solar maximum. That increases the drag on low-orbiting satellites. It’s a known problem that satellite operators face. The low-cost, off-the-shelf technology demonstrated by the Brown student SBUDNIC project offers a useful solution for unanticipated deorbits.
Avoiding Catastrophe through a Classroom Project
The idea of sudden deorbits and other catastrophes in near-Earth space is something that all satellite operators dread. That’s what inspired the student project in the first place. “These are horrible scenarios but unfortunately the numbers dictate probability-wise that this will happen eventually, so we need to be prepared,” said Marco Cross, who graduated from Brown last year with a master’s degree in biomedical engineering and served as chief engineer for SBUDNIC.
Creating the test satellite using a CubeSat as part of a class project provided a perfect chance for engineering students to put theory into practice. The project cost about $10,000 and allowed the students to practice fast “sketch to launch” turnarounds. “This was an unusual circumstance and we took advantage of it,” said Fleeter.
The successful proof of concept was supported by such industry partners as D-Orbit, AMSAT-Italy, as well as La Sapienza-University of Rome, and NASA Rhode Island Space Grant. The results could have a positive impact on efforts to cut down on space debris. “There are companies that are trying to solve this problem of space junk with concepts like space tow trucks or nets in space that will capture space junk and take them out of orbit,” said Dheraj Ganjikunta, who graduated from Brown in 2022 and was SBUDNIC’s lead program manager. “What’s amazing about SBUDNIC is that it’s magnitudes less cost than any of those solutions. Rather than taking junk out of space as it after it becomes a problem, we have this $30 drag device you can just throw onto satellites and radically reduce how long they’re in space.”
What’s true for optical astronomy is also true for gravitational wave astronomy: the more observatories you have, the better your view of the sky. This is why the list of active gravitational wave observatories is growing. But so far they are all in the Northern Hemisphere. As a recent article on the arXiv points out, that means we are missing out on a good number of gravitational events.
To its credit, gravitational wave astronomy is still in its youth. In the early days of large optical telescopes, there was also a northern bias to their locations. Part of this was based on the technical challenges of constructing telescopes in the global south, but there was also a cultural bias that is still with us today. We would do well to be mindful of this bias and try to correct it.
But this latest work shows that building a gravitational wave observatory in the southern hemisphere wouldn’t simply be an act of broadening global participation, it would gain us significantly more observational data. This is particularly true given that the dense central region of our galaxy is in the Southern sky.
As a basic case, the authors consider adding a LIGO-like observatory in Australia. Currently, there are two LIGO detectors in the United States and the Virgo detector in Italy. Together they detect around 3 events a year, though that number is rising as techniques improve. The addition of an Australian detector would double that count to more than 6 events. With three source detections, we could triangulate the event in the sky, allowing optical telescopes to gather data for multi-messenger astronomy.
Sensitivity of Cosmic Explorer and current observatories. Credit: Evan D. Hall
Of course, by the time an observatory can be constructed in the global south, gravitational wave detectors will be significantly improved. So the authors look at a more realistic case of building a third-generation advanced detector in Australia. This could operate in tandem with an American-based Cosmic Explorer and a European-based Einstein Telescope. Where LIGO uses detector arms 4 kilometers long, these new detectors would use 20-kilometer arms or even 40-kilometer arms. They will be able to detect gravitational sources we can currently only dream of seeing.
In this case, adding an Australian detector would not significantly increase the number of observed events, raising the number from an estimated 40 a year to 44 a year. But as you can imagine, these new observatories will be so cutting edge that downtimes will be inevitable. In this case, an Australian observatory would give us a significant edge. With only Einstein and Cosmic Explorer, if one goes down for maintenance, the detection rate drops to a few a year. But with two observatories still active, the rate stays around 40 a year.
As we get better at gravitational wave astronomy, there will eventually be detectors all over the world, and even in space. Gravitational wave astronomy will come to the global south. But as this study shows, the time for that is sooner, not later.
The two most powerful space telescopes ever built, NASA’s James Webb Space Telescope (JWST) and Hubble Space Telescope, are about to gather data about the most volcanically body in the entire solar system, Jupiter’s first Galilean Moon, Io. This data will be used in combination with upcoming flybys of Io by NASA’s Juno spacecraft, which is currently surveying the Jupiter system and is slated to conduct these flybys later this year and early 2024. The purpose of examining this small, volcanic moon with these two powerful telescopes and one orbiting spacecraft is for scientists to gain a better understanding of how Io’s escaping atmosphere interacts with Jupiter’s surrounding magnetic and plasma environment.
“The timing of this project is critical,” said Dr. Kurt Retherford, who is a researcher at the Southwest Research Institute (SwRI) and principal investigator of this elaborate science campaign. “Over the next year, Juno will buzz past Io several times, offering rare opportunities to combine in situ and remote observations of this complex system. We hope to gain new insights into Io’s dramatic volcanism, plasma-moon interactions and the neutral gas and plasma populations that propagate through Jupiter’s vast magnetosphere and trigger intense Jovian auroral emissions.”
Requesting observing time on Hubble is done through NASA’s Hubble Space Telescope Observing Program and is allocated based on the number of orbits that Hubble will be asked to complete around the Earth for a science campaign to complete its research, with each orbit taking approximately 90 minutes. Typically, large observing projects request 75 or more orbits. This will not be the first time Hubble has examined Jupiter, as it has an extensive history of studying the largest planet in the solar system.
For this campaign, Dr. Retherford and his team will be using 122 orbits of Hubble around the Earth to gather data on Io for a total time of 183 observing hours, or just over 4.25 complete orbits of Io around Jupiter, with each orbit taking approximately 42.5 hours. Additionally, JWST will gather data on Io over the course of 4.8 hours, or just over 10 percent of one complete orbit of Io around Jupiter.
Jupiter’s massive magnetic field is comprised of a giant bubble of charged particles that encircles and swirls around the largest planet in the solar system, of which is comprised primarily of Io’s escaping atmosphere. What has remained a mystery to scientists is the interaction between Io’s atmosphere, surface volatiles, volcanic eruptions, Io’s extended neutral clouds, Jupiter’s ionosphere, and the Io Plasma Torus (IPT), and specifically how to measure and gain greater insights into it. The IPT is a donut-shaped cloud that encircles Jupiter and is produced from Io’s escaping gases being ionized.
Concept image of the various features within Jupiter’s surrounding environment that this new science campaign will examine, including its massive magnetic field, along with Io’s neutral clouds and plasma torus. (Credit: Southwest Research Institute/John Spencer)
“Most of these materials don’t actually escape straight out of the volcanoes but rather are associated with the sublimation of sulfur dioxide frost from Io’s dayside surface,” said Dr. Katherine de Kleer, who is an assistant professor of planetary science and astronomy at Caltech, an expert in JWST data analysis, and one of several co-investigators on this campaign. “The interaction between Io’s atmosphere and the surrounding plasma provides the escape mechanism for gases released from the moon’s frozen surface.”
After arriving at Jupiter in July 2016, Juno spent its primary science mission studying Jupiter, including its interior, aurorae, and massive magnetosphere. Juno’s extended mission began in August 2021, which is slated to last until September 2025 and has been used to conduct flybys of Jupiter’s Galilean moons, Io, Europa, Ganymede, and Callisto. For Io, Juno has already conducted flybys in 2022 and earlier this year, with the further close flybys for this new campaign being scheduled for December 30, 2023, February 1, 2024, and September 20, 2024.
Infrared image from the Juno spacecraft of Jupiter’s moon, Io, taken on July 5, 2022, featuring hotspots that are volcanic features. (Credit: NASA/JPL-Caltech/Southwest Research Institute/ASI/INAF/JIRAM)
“The chance for a holistic approach to Io investigations has not been available since a series of Galileo spacecraft flybys in 1999-2000 were supported by Hubble with a prolific 30-orbit campaign,” said Dr. Retherford. “The combination of Juno’s intensive in situ measurements with our remote-sensing observations will undoubtedly advance our understanding of Io’s role in driving coupled phenomena in the Jupiter system.”
As noted, Io is the most volcanically active body in the entire solar system, boasting hundreds of volcanoes that discharge lava dozens of kilometers (or miles) into space. Its volcanic activity is the result of tidal heating as the small moon is compressed and stretched by the much more massive Jupiter, along with two of the outer moons, Europa and Ganymede. Io’s volcanic activity was first predicted just prior to the arrival of NASA’s Voyager 1 in 1979, which confirmed this activity and imaged the first signs of active volcanism outside the Earth.
What new discoveries will JWST, Hubble, and Juno reveal about the solar system’s most volcanically active planetary body? Only time will tell, and this is why we science!
Ever since the first direct observations of the solar wind in 1959, astronomers have worked to figure out what powers this plasma flow. Now, scientists using the ESA/NASA Solar Orbiter spacecraft think they have an answer: tiny little outbursts called “picoflares” They flash out from the corona at 100 kilometers per second.
The discovery comes from highly detailed extreme ultraviolet studies of a coronal hole at the Sun’s south pole. The observations revealed a collection of short-lived, faint features associated with tiny plasma jets ejected from the Sun. “We could only detect these tiny jets because of the unprecedented high-resolution, high-cadence images produced by EUI,” said Lakshmi Pradeep Chitta, Max Planck Institute for Solar System Research, Germany. In a paper describing the observations, Chitta and colleagues outline the observations and findings.
This movie was created from observations taken by the ESA/NASA Solar Orbiter spacecraft on 30 March 2022 between 04:30 and 04:55 UTC and shows a ‘coronal hole’ near the Sun’s south pole. Tiny jets show up as little flashes of bright light across the image. Each one expels charged particles, known as plasma, into space. These jets could be the source of the solar wind.
Creating the Solar Wind
The solar wind is responsible for a number of phenomena in the Solar System. It impacts magnetic fields around various worlds, including Earth, and plays a role in space weather events like aurorae. It also affects comets, shaping their plasma tails as these icy bodies whip around the Sun.
Although this wind is a fundamental feature of the Sun, solar physicists haven’t always had a definitive explanation for what generates it. They’ve known for quite some time that it’s mostly associated with coronal holes. These are magnetic structures in the corona and appear as dark regions on the solar surface. Essentially, they’re places in the solar atmosphere where the magnetic field doesn’t duck back down into the Sun. Rather, their magnetic field lines extend out from the Sun and through the Solar System. Naturally, plasma can flow along those “exit lines” and that’s what the solar wind is: an escape of plasma from the Sun. But, the big question remains: what launches it in the first place?
Coronal holes can appear nearly anywhere on the Sun, although they occur quite often around the polar regions. They seem to be more common and last longer during the quiet part of the solar cycle (solar minimum). However, they also show up during solar maximum.
Jets and the Solar Wind
The idea of jets and outbursts from the Sun is not new and solar physicists observe a range of them. The largest are coronal mass ejections. These carry huge amounts of energetic particles out through space. There are also events called X-class solar flares. Then, there are the solar nanoflares These are less energetic but still influential. They have about a billion times less energy than the huge solar flares, but they happen nearly constantly. They could well be responsible for heating the corona to its incredibly high 2-million-degree temperatures.
Picoflares carry less power than nanoflares. Those tiny jets discovered by Solar Orbiter show about a thousand times less energy than a nanoflare. However, they seem to pack a mighty punch. Most of their energy gets channeled into ejecting plasma away from the Sun. That contributes to the near-constant flow of the solar wind. They’re ubiquitous enough that they probably eject a larger fraction of the solar wind than expected.
A sequence of Solar Orbiter images showing tiny jets called “picoflares” escaping the Sun and helping to create the solar wind. Courtesy: ESA.
There’s still quite a bit to learn about this process, but ongoing Solar Orbiter studies should help explain the mechanism further. “One of the results here is that to a large extent, this flow is not actually uniform, the ubiquity of the jets suggests that the solar wind from coronal holes might originate as a highly intermittent outflow,” said Andrei Zhukov, Royal Observatory of Belgium, a collaborator on the work who led the Solar Orbiter observing campaign.
Next Steps
Solar Orbiter isn’t done measuring these constant little ejections. It’s actually circling the Sun in the equatorial regions at the moment. Eventually, its orbit will cover the polar areas. Luckily, that change in orbit will also help the spacecraft study changes in the Sun as the current solar cycle progresses. That means it will be able to study these tiny structures in coronal holes that show up at different solar latitudes.
After years of build-up and anticipation, the James Webb Space Telescope finally launched into orbit on December 25th, 2021 (what a Christmas present, huh?). Since then, the stunning images and data it has returned have proven beyond a doubt that it was the best Christmas present ever! After its first year of operations, the JWST has lived up to one of its primary objectives: to observe the first stars and galaxies that populated the Universe. The next-generation observatory has accomplished that by setting new distance records and revealing galaxies that existed less than 1 billion years after the Big Bang!
These studies are essential to charting the evolution of the cosmos and resolving issues with our cosmological models, like the Hubble Tension and the mysteries of Dark Matter and Dark Energy. Well, hang onto your hats because things have reached a new level of awesome! In a recent study, an international team of scientists isolated a well-magnified star candidate in a galaxy that appears as it was almost 12.5 billion years ago. The detection of a star that existed when the Universe was only ~1.2 billion years old showcases the abilities of the JWST and offers a preview of what’s to come!
A trio of faint objects (circled) captured in the James Webb Space Telescope’s deep image of the galaxy cluster SMACS 0723 exhibit properties remarkably similar to rare, small galaxies called “green peas” found much closer to home. Image Credit: NASA/ESA/CSA/STScI
Observations by Hubble and JWST of some of the earliest galaxies in the Universe have provided a wealth of information that challenged and confirmed prevailing models of cosmological evolution. Unfortunately, as the authors indicated in their study, directly observing individual stars at these distances is impossible since they are too dim relative to their surrounding galaxies. However, scientists have demonstrated that stars can be observed using gravitational lensing, a technique where a massive object in the foreground will amplify light from a more distant object.
This effect, predicted by Einstein’s Theory of General Relativity, occurs when the gravitational force of massive objects alters the curvature of spacetime around them. In recent years, this technique has allowed astronomers to identify several dozen stars in strong lensing star cluster fields, and the JWST has detected several already. For the sake of their study, the team consulted images obtained by Webb‘s Near-Infrared Camera (NIRCam), which captured the galaxy cluster MACS0647 during its first year of operations as part of the Cycle 1 General Observers (GO) program 1433.
As Furtak told Universe Today via email, this represented a major accomplishment, as lensed studies traditionally focus on high-redshift galaxies:
“The study of individual lensed stars at cosmological distances is a relatively new field that has gained interest in recent years thanks to the phenomenal capacities of the Hubble and James Webb Space Telescopes. Individual stars can normally only be observed in our Galaxy and its immediate neighbours while at larger cosmological distances we only see whole galaxies.
“However, the gravitational lensing effect, where massive objects such as galaxy clusters deflect the light from background sources and magnify it, can change this if a single star in a lensed background galaxy happens to cross the so-called critical line which is a region where the gravitational magnification reaches extreme values. If the alignment is right, this then enables us to observe single stars in distant galaxies.”
Icarus, the farthest individual star ever seen, is visible only because the gravity of a massive galaxy cluster is magnifying it. Credit: NASA/ESA/Patrick Kelly (UoM)
The gravity of this massive cluster produces a powerful lens that has already been used to identify the triple-lensed JD galaxy, which has a redshift value of z=11. This corresponds to an apparent distance of 13.4 billion light-years ago, which means it appears today as it did when the Universe was less than 500 million years old. Using this same lensing galaxy, the team obtained spectra from an individual star at z=4.76 (MACS0647-star-1) – at an apparent distance of about 12.35 billion years ago – and analyzed it to derive the star’s properties.
The star was first detected in 2022 using data from Webb’s NIRCam, which was reported on in a paper by Dr. Ashish Meena of Ben-Gurion University (a colleague and co-author on this latest paper. Said Furtak:
“[MACS0647-star-1] was identified as such based on its position in a strongly lensed and distorted background galaxy very close or even on top of the critical line, i.e. in a region where the gravitational lensing magnification reaches extreme values. Note that a fainter second star was also detected in the same study, MACS0647-star-2. Based on the photometry in multiple broad-band filters, MACS0647-star-1 was identified as a candidate B-type supergiant star of surface temperature ~10000K.”
A few months later, Furtak and his team obtained the MACS0647-star-1 spectra using Webb’s Near-Infrared Spectrometer (NIRSpec) as part of a larger campaign targeting the whole lensing cluster. The spectra allowed them to precisely measure the redshift to MACSO647-star-1, from which they derived distance estimates that showed the star existed when the Universe was just 1.2 billion years old. As Furtak added, they also found that the spectrum provided a more complex picture than the previous photometric data:
“While the photometric measurement from the imaging was consistent with a single B-type supergiant star, [but] with the spectrum we now see, we must be either looking at two stars – one B-type and one colder F-type – or at a hot B-type star whose light is reddened by dust somewhere along the line of sight. The latter explanation is the more probable one, though. That being said, with the current spectrum – i.e., 1.8h integration time and NIRSpec-prism mode, which has a relatively low resolution – we cannot completely rule out the possibility that this is not actually a whole star-cluster instead of a single star either (i.e., a globular-cluster type object, very dense old stellar population).”
Discovered by Hubble, Earendel is the farthest star ever detected. It existed in the first billion years after the Big Bang! Credit: NASA/ESA/CSA/STScI
To get a better idea of what Webb revealed, follow-up observations of the MACS0647 lensing galaxy are needed. Specifically, Furtak indicated the need for much deeper spectra and much higher spectral resolution to measure absorption lines more clearly. Regardless, these findings are likely to become commonplace soon as Webb continues to study stars and galaxies that existed during the early Universe. To date, several lensed stars at cosmological distances have been observed by Hubble, the first (Icarus) being spotted in 2018 by Hubble, while the latest (Earendel) was detected in 2022.
Based on what Webb has revealed in just its first year of observations, Furtak anticipates that the JWST will find lensed stars at a rate of one per galaxy cluster observed. It has already detected several lensed stars, including MACS0647-star-1, which is the second furthest observed to date. This, said Furtak, offers a tantalizing preview of what lies in store:
“This study definitely shows that JWST has the instrumental capacity to not only detect lensed stars in imaging campaigns but to also obtain their spectra with NIRSpec. This is the second spectrum of a lensed star ever obtained and the first space-based one with JWST. For example, a spectrum for the most distant star Earendel, has also recently been taken and will probably be published soon. In future observation campaigns, we can systematically follow up NIRCam-detected lensed stars, if they are persistent sources, with NIRSpec spectroscopy in order to derive their properties.
“This study is also based on relatively short JWST exposure times of ~2h, whereas JWST is perfectly capable of reaching much higher signal-to-noise ratios through longer exposure times which means that future NIRSpec observations might well be able to detect absorption features in lensed stars at least in the brightest ones. Note that this would also be a compelling science case for the upcoming 30m-class telescopes like ESOs ELT, which will be able to reach similar sensitivities and resolutions as JWST, though be it at slightly lower wavelengths.”
The preprint of their paper recently appeared online and is being reviewed for publication in the Monthly Notices of the Royal Astronomical Society.
When you think of a black hole, you might think its defining feature is its event horizon. That point of no return not even light can escape. While it’s true that all black holes have an event horizon, a more critical feature is the disk of hot gas and dust circling it, known as the accretion disk. And a team of astronomers have made the first direct measure of one.
According to Newton, if you drop an object from rest near a planet or star, the object will fall straight down, tracing a linear path until it strikes the planet or star. Einstein says something slightly different. That straight path is only possible if the planet or star isn’t rotating. If it is rotating, then space near the planet or star is twisted. It’s an effect known as frame dragging, and it means our object will be pulled around an object as it falls. We have measured frame dragging on satellites near Earth, so we know it is a real effect.
Near fast-rotating black holes the frame-dragging effect can be immense. This means as gas and dust start to fall toward the black hole it’s swept out into a disk around the equatorial plane of the black hole. All the gas and dust are superheated, which builds up tremendous pressure. An accretion disk can generate strong magnetic fields, emit powerful X-rays, and even power jets of gas that stream away from the black hole at nearly the speed of light. Most of the black holes we’ve identified in the Universe have been through the high-energy effects of their accretion disks. But the physics of black hole accretion disks are complex, and we don’t yet fully understand their dynamics or even have a precise gauge of their size.
We do have a basic gauge of the size of accretion disks. One of the things we’ve noticed with quasars is that they can fluctuate in brightness. Quasars are supermassive black holes with a radio-bright accretion disk. Given the finite speed of light, the rate of fluctuations gives us an upper bound on the size of the accretion disk. So for example, if a quasar fluctuates on the scale of a year, we know the accretion disk can’t be larger than about a light-year across. The most accurately measured fluctuating quasar is 3C 273, and we know its accretion disk is about 1.5 light-years across, or about 100,000 AU.
But this is only an upper bound, and the accretion disk could be smaller. Without a direct measure of an accretion disk, we rely on computer simulations to estimate its size. But this recent work has measured the accretion disk of a supermassive black hole directly, which gives us a step up in understanding black holes.
The double peak spectra of the oxygen emission line. Credit: dos Santos, et al
To achieve this, the team used a different approach. Rather than using brightness fluctuations, they measured the emission lines of a supermassive black hole at the center of a galaxy known as III Zw 002. Using the Gemini North telescope, they were able to study a particularly bright emission line of hydrogen and one of oxygen. Both of these spectra presented a double peak feature. This double peak is caused by the rotation of the accretion disk. As the disk rotates, light from the portion of the disk rotating toward us is shifted toward the blue spectrum, while light on the portion of the disk rotating away from us is redshifted. The effect is most significant on the outer edges of the disk, hence the appearance of a double peak.
From this spectral data, the team determined that the black hole is about 400 – 900 million solar masses, and its axis of rotation is tilted about 18 degrees relative to our line of sight. The peaks of the hydrogen line are about 16.8 light-days from the black hole, and the peaks of the oxygen line are about 18.9 light-days from the black hole. That means the accretion disk is around 40 light-days across.
This result is just the first step. The team continues to observe III Zw 002 and hopes to be able to study how the accretion disk precesses around the black hole over time, which will tell us about the dynamics between the two.
Europa and other ocean worlds in our solar system have recently attracted much attention. They are thought to be some of the most likely places in our solar system for life to have developed off Earth, given the presence of liquid water under their ice sheathes and our understanding of liquid water as one of the necessities for the development of life. Various missions are planned to these ocean worlds, but many suffer from numerous design constraints. Requirements to break through kilometers of ice on a world far from the Sun will do that to any mission. These design constraints sometimes make it difficult for the missions to achieve one of their most important functions – the search for life. But a team of engineers from NASA’s Jet Propulsion Laboratory think they have a solution – send forth a swarm of swimming microbots to scour the ocean beneath a main “mothership” bot.
One of the most likely forms of the mothership bot for this mission is the Subsurface Access Mechanism for Europa – SESAME. It’s a type of “thermo-mechanical drilling robot” that can tunnel through Europa’s thick ice shell, which measures up to 25 km in some places. It does this by melting, cutting, and burning straight down to reach the interface between Europa’s ice crust and its undersea ocean.
But what happens once the drilling bot gets there? Ideally, the robot itself would explore its immediate surroundings. However, there is a good chance that drilling through the ice crust (thereby disrupting the nearby environment) will limit the usefulness of any data collected nearby. The bot itself could go for a dip, but the power source required to drill through all that ice would likely create a “hot bubble” around the robot, diminishing the usefulness of any science its sensors attempt to do.
Dr. Ethan Scahler, a mechanical engineer at NASA’s JPL who had two separate NIAC grants in 2021, explains SWIM and FLOAT – his two awarded concepts.
Credit – KISSCaltech YouTube Channel
That’s where the Sensing with Independent Microswimmers (SWIM) idea comes in. SWIM bots could deploy from the SESAME bot after it breaches into the ocean from the ice shelf. Once deposited into the water, they can move away autonomously from the mothership and explore distances up to a few hundred meters away.
Doing so with a tether is tricky. If there is more than one microbot nearby, it’s very likely the tether would become ensnared, and mission engineers would end up trying to untie a Gordian knot on another world. Alternatively, not using a tether has its own set of challenges. One is communication.
Water is notoriously difficult to transfer electric signals through. Hence, the JPL engineers suggested using an ultrasonic communication system to send data from the mothership to the microbots and vice versa. Potentially, the SESAME mothership could also power the microbots using an underwater power transfer technique, though there are a lot of ways that can go wrong.
Fraser discusses a more recent NIAC grant to cut through the ice on the way down to Europa’s ocean.
An alternative is to develop a sound enough control system so the bots can return to the mothership to recharge before going out on another mission into the depths. Some of the most exciting environments in the solar system are out in those depths.
In recent decades, scientists have discovered whole ecosystems on Earth that live entirely separately from the Sun by utilizing energy emitted from thermal vents. There is a good chance the Enceladus also has thermal vents in its oceans and a decent chance that the microswimmers can get to them to collect data. While their instrumentation might not be all that capable, especially compared to a larger, single submersible, having many microbots would allow them to spread out. That dramatically increases their chances of coming across one of these underwater vents, if they exist, increasing their chance of finding life on one of these ocean worlds.
That’s still a long way off, though NASA seems supportive of the idea – they granted the team at JPL a NIAC Phase II grant to further flesh out the concept. Hopefully, that’ll provide enough background research to push this idea into a viable state for full-blown mission development. Maybe someday we’ll be able to watch as little microbots explore the ocean of a completely different world.
