Topic: Late May Astronomy Bulletin

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LUNAR SOIL MIGHT GENERATE OXYGEN AND FUEL
Cell Press

Soil on the Moon contains active compounds that can convert carbon dioxide into oxygen and fuels, scientists in China report. They are now exploring whether lunar resources can be used to facilitate human exploration on the Moon or beyond. Nanjing University material scientists hope to design a system that takes advantage of lunar soil and solar radiation, the two most abundant resources on the Moon. After analyzing the lunar soil brought back by China's Chang'e 5 spacecraft, their team found the sample contains compounds -- including iron-rich and titanium-rich substances -- that could work as a catalyst to make desired products such as oxygen using sunlight and carbon dioxide. Based on the observation, the team proposed an "extraterrestrial photosynthesis" strategy. Mainly, the system uses lunar soil to electrolyze water extracted from the moon and in astronauts' breathing exhaust into oxygen and hydrogen powered by sunlight. The carbon dioxide exhaled by moon inhabitants is also collected and combined with hydrogen from water electrolysis during a hydrogenation process catalyzed by lunar soil. The process yields hydrocarbons such as methane, which could be used as fuel. The strategy uses no external energy but sunlight to produce a variety of desirable products such as water, oxygen, and fuel that could support life on a moonbase, the researchers say. The team is looking for an opportunity to test the system in space, likely with China's future crewed lunar missions.

While the catalytic efficiency of lunar soil is less than catalysts available on Earth, the team is testing different approaches to improve the design, such as melting the lunar soil into a nanostructured high-entropy material, which is a better catalyst. Previously, scientists have proposed many strategies for extraterrestrial survival. But most designs require energy sources from Earth. For example, NASA's Perseverance Mars rover brought an instrument that can use carbon dioxide in the planet's atmosphere to make oxygen, but it's powered by a nuclear battery onboard. In the near future, China claims we will see the crewed spaceflight industry developing rapidly. Just like the 'Age of Sail' in the 1600s when hundreds of ships head to the sea, we will enter an 'Age of Space.' But if we want to carry out large-scale exploration of the extraterrestrial world, we will need to think of ways to reduce payload, meaning relying on as little supplies from Earth as possible and using extraterrestrial resources instead.


LIMITED WATER CIRCULATION LATE IN MARTIAN HISTORY
Lund University


A Swedish research team has investigated a meteorite from Mars using neutron and X-ray tomography. The technology, which will probably be used when NASA examines samples from the Red Planet in 2030, showed that the meteorite had limited exposure to water, thus making life at that specific time and place unlikely. In a cloud of smoke, NASA's spacecraft Perseverance parachuted onto the dusty surface of Mars in February 2021. For several years, the vehicle will skid around and take samples to try to answer the question posed by David Bowie in Life on Mars in 1971. It isn't until around 2030 that Nasa actually intends to send the samples back to Earth, but material from Mars is already being studied -- in the form of meteorites. In a new study published in Science Advances, an international research team has studied an approximately 1.3 billion-year-old meteorite using advanced scanning. Since water is central to the question of whether life ever existed on Mars, researchers wanted to investigate how much of the meteorite reacted with water when it was still part of the Mars bedrock. To answer the question of whether there was any major hydrothermal system, which is generally a favourable environment for life to occur, the researchers used neutron and X-ray tomography. X-ray tomography is a common method of examining an object without damaging it. Neutron tomography was used because neutrons are very sensitive to hydrogen. This means that if a mineral contains hydrogen, it is possible to study it in three dimensions and see where in the meteorite the hydrogen is located. Hydrogen (H) is always of interest when scientists study material from Mars, because water (H2O) is a prerequisite for life as we know it. The results show that a fairly small part of the sample seems to have reacted with water, and that it therefore probably wasn't a large hydrothermal system that gave rise to the alteration.

A more probable explanation is that the reaction took place after small accumulations of underground ice melted during a meteorite impact about 630 million years ago. Of course, that doesn't mean that life couldn't have existed in other places on Mars, or that there couldn't have been life at other times. The researchers hope that the results of their study will be helpful when NASA brings back the first samples from Mars around 2030, and there are many reasons to believe that the current technology with neutron and X-ray tomography will be useful when this happens.


LARGEST MARTIAN EARTHQUAKE DETECTED
NASA


NASA’s InSight Mars lander has detected the largest quake ever observed on another planet: an estimated magnitude 5 temblor that occurred on May 4, 2022, the 1,222nd Martian day, or sol, of the mission. This adds to the catalogue of more than 1,313 quakes InSight has detected since landing on Mars in November 2018. The largest previously recorded quake was an estimated magnitude 4.2 detected Aug. 25, 2021. InSight was sent to Mars with a highly sensitive seismometer to study the deep interior of the planet. As seismic waves pass through or reflect off material in Mars’ crust, mantle, and core, they change in ways that seismologists can study to determine the depth and composition of these layers. What scientists learn about the structure of Mars can help them better understand the formation of all rocky worlds, including Earth and its Moon.

A magnitude 5 quake is a medium-size quake compared to those felt on Earth, but it’s close to the upper limit of what scientists hoped to see on Mars during InSight’s mission. The science team will need to study this new quake further before being able to provide details such as its location, the nature of its source, and what it might tell us about the interior of Mars. The large quake comes as InSight is facing new challenges with its solar panels, which power the mission. As InSight’s location on Mars enters winter, there’s more dust in the air, reducing available sunlight. On May 7, 2022, the lander’s available energy fell just below the limit that triggers safe mode, where the spacecraft suspends all but the most essential functions. This reaction is designed to protect the lander and may occur again as available power slowly decreases. After the lander completed its prime mission at the end of 2020, meeting its original science goals, NASA extended the mission until December 2022.


MILKY WAY STAR CONTAINS 65 ELEMENTS OF PERIODIC TABLE
University of Michigan

In our Sun's neighbourhood of the Milky Way Galaxy is a relatively bright star, and in it, astronomers have been able to identify the widest range of elements in a star beyond our solar system yet. The study has identified 65 elements in the star, HD 222925. Forty-two of the elements identified are heavy elements that are listed along the bottom of the periodic table of elements. Identifying these elements in a single star will help astronomers understand what's called the "rapid neutron capture process," or one of the major ways by which heavy elements in the Universe were created. The process, also called the "r-process," begins with the presence of lighter elements such as iron. Then, rapidly -- on the order of a second -- neutrons are added to the nuclei of the lighter elements. This creates heavier elements such as selenium, silver, tellurium, platinum, gold and thorium, the kind found in HD 222925, and all of which are rarely detected in stars, according to the astronomers.  One of these environments has been confirmed: the merging of neutron stars. Neutron stars are the collapsed cores of supergiant stars, and are the smallest and densest known celestial objects. The collision of neutron star pairs causes gravitational waves and in 2017, astronomers first detected gravitational waves from merging neutron stars. Another way the r-process might occur is after the explosive death of massive stars. The elements the team identified in HD 222925 were produced in either a massive supernovae or a merger of neutron stars very early in the Universe. The material was ejected and thrown back into space, where it later reformed into the star HD 222925.

This star can then be used as a proxy for what one of those events would have produced. Any model developed in the future that demonstrates how the r-process or nature produces elements on the bottom two-thirds of the periodic table must have the same signature as HD 222925. Crucially, the astronomers used an instrument on the Hubble Space Telescope that can collect ultraviolet spectra. This instrument was key in allowing the astronomers to collect light in the ultraviolet part of the light spectrum -- light that is faint, coming from a cool star such as HD 222925. The astronomers also used one of the Magellan telescopes in Chile to collect light from HD 222925 in the optical part of the light spectrum. These spectra encode the "chemical fingerprint" of elements within stars, and reading these spectra allows the astronomers not only to identify the elements contained in the star, but also how much of an element the star contains. Many of the study co-authors are part of a group called the R-Process Alliance, a group of astrophysicists dedicated to solving the big questions of the r-process. This project marks one of the team's key goals: identifying which elements, and in what amounts, were produced in the r-process in an unprecedented level of detail.


EGYPTIAN STONE BRINGS FIRST SUPERNOVA CLUES TO EARTH
University of Johannesburg

New chemistry 'forensics' indicate that the stone named Hypatia from the Egyptian desert could be the first tangible evidence found on Earth of a supernova type Ia explosion. These rare supernovae are some of the most energetic events in the Universe. Since 2013, researchers have discovered a series of highly unusual chemistry clues in a small fragment of the Hypatia Stone. In the new research, they eliminate 'cosmic suspects' for the origin of the stone in a painstaking process. They have pieced together a timeline stretching back to the early stages of the formation of Earth, our Sun and the other planets in our solar system. Their hypothesis about Hypatia's origin starts with a star: A red giant star collapsed into a white dwarf star. The collapse would have happened inside a gigantic nebula. That white dwarf found itself in a binary system with a second star. The white dwarf star eventually 'ate' the other star. At some point the white dwarf exploded as a supernova type Ia inside the dust cloud. After cooling, the gas atoms which remained of the supernova Ia started sticking to the particles of the dust cloud. A huge 'bubble' of this supernova dust-and-gas-atoms mix never interacted with other dust clouds. Millions of years would pass, and eventually the 'bubble' would slowly become solid. Hypatia's 'parent body' would become a solid rock sometime in the early stages of formation of our solar system. This process probably happened in a cold, uneventful outer part of our solar system -- in the Oort cloud or in the Kuiper belt. At some point, Hypatia's parent rock started hurtling towards Earth. The heat of entry into Earth's atmosphere, combined with the pressure of impact in the Great Sand Sea in south-western Egypt, created micro-diamonds and shattered the parent rock. The Hypatia stone picked up in the desert must be one of many fragments of the original impactor. If this hypothesis is correct, the Hypatia stone would be the first tangible evidence on Earth of a supernova type Ia explosion. Perhaps equally important, it shows that an individual anomalous 'parcel' of dust from outer space could actually be incorporated in the solar nebula that our solar system was formed from, without being fully mixed in. This goes against the conventional view that dust which our solar system was formed from, was thoroughly mixed.

To piece together the timeline of how Hypatia may have formed, the researchers used several techniques to analyse the strange stone. In 2013, a study of the argon isotopes showed the rock was not formed on Earth. It had to be extraterrestrial. A 2015 study of noble gases in the fragment indicated that it may not be from any known type of meteorite or comet. In 2018 the UJ team published various analyses, which included the discovery of a mineral, nickel phosphide, not previously found in any object in our solar system. The team selected 17 targets on the tiny sample for analysis. All were chosen to be well away from the earthly minerals that had formed in the cracks of the original rock after its impact in the desert. 15 different elements were identified in Hypatia with much greater precision and accuracy, with the proton microprobe. This gave the chemical 'ingredients' needed to start the next process of analysing all the data. The first big new clue from the proton beam analyses was the surprisingly low level of silicon in the Hypatia stone targets. The silicon, along with chromium and manganese, were less than 1% to be expected for something formed within our inner solar system. Further, high iron, high sulphur, high phosphorus, high copper and high vanadium were conspicuous and anomalous. A consistent pattern was found of trace element abundances that is completely different from anything in the solar system, primitive or evolved. Objects in the asteroid belt and meteors don't match this either. So next researchers looked outside the solar system and compared the Hypatia element concentration pattern with what one would expect to see in the dust between stars in our solar arm of the Milky Way galaxy. There was no similarity at all. The next simplest possible explanation for the element concentration pattern in Hypatia, would be a red giant star. Red giant stars are common in the Universe. But the proton beam data ruled out mass outflow from a red giant star too: Hypatia had too much iron, too little silicon and too low concentrations of heavy elements heavier than iron.

The next 'suspect' to consider was a supernova type II. Supernovae of type II cook up a lot of iron. They are also a relatively common type of supernova. Again, the proton beam data for Hypatia ruled out a promising suspect with 'chemistry forensics'. A supernova type II was highly unlikely as the source of strange minerals like nickel phosphide in the pebble. There was also too much iron in Hypatia compared to silicon and calcium. It was time to closely examine the predicted chemistry of one of the most dramatic explosions in the Universe. A rarer kind of supernova also makes a lot of iron. Supernovas of the type Ia only happen once or twice per galaxy per century. But they manufacture most of the iron (Fe) in the Universe. Also, established science says that some Ia supernovas leave very distinctive 'forensic chemistry' clues behind. This is because of the way some Ia supernovas are set up. First, a red giant star at the end of its life collapses into a very dense white dwarf star. White dwarf stars are usually incredibly stable for very long periods and most unlikely to explode. However, there are exceptions to this. A white dwarf star could start 'pulling' matter off another star in a binary system. Eventually the white dwarf gets so heavy, hot and unstable, it explodes in a supernova Ia. The nuclear fusion during the supernova Ia explosion should create highly unusual element concentration patterns, accepted scientific theoretical models predict. Also, the white dwarf star that explodes in a supernova Ia is not just blown to bits, but literally blown to atoms. The supernova Ia matter is delivered into space as gas atoms. In an extensive literature search of star data and model results, the team could not identify any similar or better chemical fit for the Hypatia stone than a specific set of supernova Ia models. Not all 15 of the analysed elements in Hypatia fit the predictions though. In six of the 15 elements, proportions were between 10 and 100 times higher than the ranges predicted by theoretical models for supernovas of type 1A. These are the elements aluminium, phosphorus, chlorine, potassium, copper and zinc. If this hypothesis is correct, the Hypatia stone would be the first tangible evidence on Earth of a supernova type Ia explosion, one of the most energetic events in the Universe.


EXPLOSION OBSERVED ON WHITE DWARF
Friedrich-Alexander-Universität Erlangen-Nürnberg

When stars like our Sun use up all their fuel, they shrink to form white dwarfs. Sometimes such dead stars flare back to life in a super hot explosion and produce a fireball of X-ray radiation. A research team has now been able to observe such an explosion of X-ray light for the very first time. These X-ray flashes last only a few hours and are almost impossible to predict, but the observational instrument must be pointed directly at the explosion at exactly the right time. The instrument in this case is the eROSITA X-ray telescope, which is currently located one and a half million kilometres from Earth and has been surveying the sky for soft X-rays since 2019. On July 7, 2020 it measured strong X-ray radiation in an area of the sky that had been completely inconspicuous four hours previously. When the X-ray telescope surveyed the same position in the sky four hours later, the radiation had disappeared. It follows that the X-ray flash that had previously completely overexposed the centre of the detector must have lasted less than eight hours. X-ray explosions such as this were predicted by theoretical research more than 30 years ago, but have never been observed directly until now. These fireballs of X-rays occur on the surface of stars that were originally comparable in size to the Sun before using up most of their fuel made of hydrogen and later helium deep inside their cores. These stellar corpses shrink until "white dwarfs" remain, which are similar to Earth in size but contain a mass that can be similar to that of our Sun. One way to picture these proportions is to think of the Sun being the same size as an apple, which means Earth would be the same size as a pin head orbiting around the apple at a distance of 10 metres. On the other hand, if you were to shrink an apple to the size of a pin head, this tiny particle would retain the comparatively large weight of the apple. A teaspoon of matter from the inside of a white dwarf easily has the same mass as a large truck. Since these burned out stars are mainly made up of oxygen and carbon, we can compare them to gigantic diamonds that are the same size as Earth floating around in space. These objects in the form of precious gems are so hot they glow white. However, the radiation is so weak that it is difficult to detect from Earth.

Unless the white dwarf is accompanied by a star that is still burning, that is, and when the enormous gravitational pull of the white dwarf draws hydrogen from the shell of the accompanying star. "In time, this hydrogen can collect to form a layer only a few metres thick on the surface of the white dwarf. In this layer, the huge gravitational pull generates enormous pressure that is so great that it causes the star to reignite. In a chain reaction, it soon comes to a huge explosion during which the layer of hydrogen is blown off. The X-ray radiation of an explosion like this is what hit the detectors of eROSITA on July 7, 2020 producing an overexposed image. Using the model calculations the team originally drew up while supporting the development of the X-ray instrument, researchers were able to analyze the overexposed image in more detail during a complex process to gain a behind the scenes view of an explosion of a white dwarf, or nova. According to the results, the white dwarf has around the mass of our Sun and is therefore relatively large. The explosion generated a fireball with a temperature of around 327,000 degrees, making it around sixty times hotter than the Sun. Since these novae run out of fuel quite quickly, they cool rapidly and the X-ray radiation becomes weaker until it eventually becomes visible light, which reached Earth half a day after the eROSITA detection and was observed by optical telescopes. A seemingly bright star then appeared, which was actually the visible light from the explosion, and so bright that it could be seen on the night sky by the naked eye. Seemingly "new stars" such as this one have been observed in the past and were named "nova stella," or "new star" on account of their unexpected appearance. Since these novae are only visible after the X-ray flash, it is very difficult to predict such outbreaks and it is mainly down to chance when they hit the X-ray detectors.


SURVIVING COMPANION IN SUPERNOVA AFTERMATH REVEALED
NASA/Goddard Space Flight Center

It's not unheard of to find a surviving star at the scene of a titanic supernova explosion, which would be expected to obliterate everything around it, but the latest research from the Hubble Space Telescope has provided a long-awaited clue to a specific type of stellar death. In some supernova cases, astronomers find no trace of the former star's outermost layer of hydrogen. What happened to the hydrogen? Suspicions that companion stars are responsible -- siphoning away their partners' outer shell before their death -- are supported by Hubble's identification of a surviving companion star on the scene of supernova 2013ge. The discovery also lends support to the theory that the majority of massive stars form and evolve as binary systems. It could also be the prequel to another cosmic drama: In time, the surviving, massive companion star will also undergo a supernova, and if both the stars' remnant cores are not flung from the system, they will eventually merge and produce gravitational waves, shaking the fabric of space itself. NASA's Hubble Space Telescope has uncovered a witness at the scene of a star's explosive death: a companion star previously hidden in the glare of its partner's supernova. The discovery is a first for a particular type of supernova -- one in which the star was stripped of its entire outer gas envelope before exploding. The finding provides crucial insight into the binary nature of massive stars, as well as the potential prequel to the ultimate merger of the companion stars that would rattle across the Universe as gravitational waves, ripples in the fabric of spacetime itself.

Astronomers detect the signature of various elements in supernova explosions. These elements are layered like an onion pre-supernova. Hydrogen is found in the outermost layer of a star, and if no hydrogen is detected in the aftermath of the supernova, that means it was stripped away before the explosion occurred. The cause of the hydrogen loss had been a mystery, and astronomers have been using Hubble to search for clues and test theories to explain these stripped supernovae. The new Hubble observations provide the best evidence yet to support the theory that an unseen companion star siphons off the gas envelope from its partner star before it explodes. Astronomers used Hubble's Wide Field Camera 3 to study the region of supernova (SN) 2013ge in ultraviolet light, as well as previous Hubble observations in the Barbara A. Mikulski Archive for Space Telescopes. Astronomers saw the light of the supernova fading over time from 2016 to 2020 -- but another nearby source of ultraviolet light at the same position maintained its brightness. This underlying source of ultraviolet emission is what the team proposes is the surviving binary companion to SN 2013ge. Previously, scientists theorized that a massive progenitor star's strong winds could blow away its hydrogen gas envelope, but observational evidence didn't support that. To explain the disconnect, astronomers developed theories and models in which a binary companion siphons off the hydrogen. In prior observations of SN 2013ge, Hubble saw two peaks in the ultraviolet light, rather than just the one typically seen in most supernovae. One explanation for this double brightening was that the second peak shows when the supernova's shock wave hit a companion star, a possibility that now seems much more likely. Hubble's latest observations indicate that while the companion star was significantly jostled, including the hydrogen gas it had siphoned off its partner, it was not destroyed. Researchers liken the effect to a jiggling bowl of jelly, which will eventually settle back to its original form. While additional confirmation and similar supporting discoveries need to be found, the implications of the discovery are still substantial, lending support to theories that the majority of massive stars form and evolve as binary systems.

Unlike supernovae that have a puffy shell of gas to light up, the progenitors of fully stripped-envelope supernovae have proven difficult to identify in pre-explosion images. Now that astronomers have been lucky enough to identify the surviving companion star, they can use it to work backward and determine characteristics of the star that exploded, as well as the unprecedented opportunity to watch the aftermath unfold with the survivor. As a massive star itself, SN 2013ge's companion is also destined to undergo a supernova. Its former partner is now likely a compact object, such as a neutron star or black hole, and the companion will likely go that route as well. The closeness of the original companion stars will determine if they stay together. If the distance is too great, the companion star will be flung out of the system to wander alone across our galaxy, a fate that could explain many seemingly solitary supernovae. However, if the stars were close enough to each other pre-supernova, they will continue orbiting each other as black holes or neutron stars. In that case, they would eventually spiral toward each other and merge, creating gravitational waves in the process. That is an exciting prospect for astronomers, as gravitational waves are a branch of astrophysics that has only begun to be explored. They are waves or ripples in the fabric of spacetime itself, predicted by Albert Einstein in the early 20th century. Gravitational waves were first directly observed by the Laser Interferometer Gravitational-Wave Observatory.


FIRST IMAGE TAKEN OF BLACK HOLE AT CENTRE OF MILKY WAY
ESO

Astronomers have unveiled the first image of the supermassive black hole at the centre of our own Milky Way galaxy. This result provides overwhelming evidence that the object is indeed a black hole and yields valuable clues about the workings of such giants, which are thought to reside at the centre of most galaxies. The image was produced by a global research team called the Event Horizon Telescope (EHT) Collaboration, using observations from a worldwide network of radio telescopes. The image is a long-anticipated look at the massive object that sits at the very centre of our galaxy. Scientists had previously seen stars orbiting around something invisible, compact, and very massive at the centre of the Milky Way. This strongly suggested that this object — known as Sagittarius A* (Sgr A*, pronounced "sadge-ay-star") — is a black hole, and today’s image provides the first direct visual evidence of it. Although we cannot see the black hole itself, because it is completely dark, glowing gas around it reveals a telltale signature: a dark central region (called a shadow) surrounded by a bright ring-like structure. The new view captures light bent by the powerful gravity of the black hole, which is four million times more massive than our Sun. Because the black hole is about 27 000 light-years away from Earth, it appears to us to have about the same size in the sky as a doughnut on the Moon. To image it, the team created the powerful EHT, which linked together eight existing radio observatories across the planet to form a single “Earth-sized” virtual telescope. The EHT observed Sgr A* on multiple nights in 2017, collecting data for many hours in a row, similar to using a long exposure time on a camera. In addition to other facilities, the EHT network of radio observatories includes the Atacama Large Millimeter/submillimeter Array (ALMA) and the Atacama Pathfinder EXperiment (APEX) in the Atacama Desert in Chile, co-owned and co-operated by ESO on behalf of its member states in Europe. Europe also contributes to the EHT observations with other radio observatories — the IRAM 30-meter telescope in Spain and, since 2018, the NOrthern Extended Millimeter Array (NOEMA) in France — as well as a supercomputer to combine EHT data hosted by the Max Planck Institute for Radio Astronomy in Germany. Moreover, Europe contributed with funding to the EHT consortium project through grants by the European Research Council and by the Max Planck Society in Germany.

The EHT achievement follows the collaboration’s 2019 release of the first image of a black hole, called M87*, at the centre of the more distant Messier 87 galaxy. The two black holes look remarkably similar, even though our galaxy’s black hole is more than a thousand times smaller and less massive than M87*. The researchers had to develop sophisticated new tools that accounted for the gas movement around Sgr A*. While M87* was an easier, steadier target, with nearly all images looking the same, that was not the case for Sgr A*. The image of the Sgr A* black hole is an average of the different images the team extracted, finally revealing the giant lurking at the centre of our galaxy for the first time. The effort was made possible through the ingenuity of more than 300 researchers from 80 institutes around the world that together make up the EHT Collaboration. In addition to developing complex tools to overcome the challenges of imaging Sgr A*, the team worked rigorously for five years, using supercomputers to combine and analyse their data, all while compiling an unprecedented library of simulated black holes to compare with the observations. Scientists are particularly excited to finally have images of two black holes of very different sizes, which offers the opportunity to understand how they compare and contrast. They have also begun to use the new data to test theories and models of how gas behaves around supermassive black holes. This process is not yet fully understood but is thought to play a key role in shaping the formation and evolution of galaxies.