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Late April Astronomy Bulletin

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Clive:
VENUS IS VOLCANICALLY ACTIVE
University of Alaska Fairbanks

Venus appears to have volcanic activity, according to a new research paper that offers strong evidence to answer the lingering question about whether Earth's sister planet currently has eruptions and lava flows. Venus, although similar to Earth in size and mass, differs markedly in that it does not have plate tectonics. The boundaries of Earth's moving surface plates are the primary locations of volcanic activity. New research revealed a nearly 1-square-mile volcanic vent that changed in shape and grew over eight months in 1991. Changes on such a scale on Earth are associated with volcanic activity, whether through an eruption at the vent or movement of magma beneath the vent that causes the vent walls to collapse and the vent to expand. Researchers studied images taken in the early 1990s during the first two imaging cycles of NASA's Magellan space probe. Until recently, comparing digital images to find new lava flows took too much time, the paper notes. As a result, few scientists have searched Magellan data for feature formation. The new research focused on an area containing two of Venus' largest volcanoes, Ozza and Maat Mons which are comparable in volume to Earth's largest volcanoes but have lower slopes and thus are more spread out. Maat Mons contains the expanded vent that indicates volcanic activity. A Magellan image from mid-February 1991 was compared with a mid-October 1991 image and noticed a change to a vent on the north side of a domed shield volcano that is part of the Maat Mons volcano. The vent had grown from a circular formation of just under 1 square mile to an irregular shape of about 1.5 square miles. The later image indicates that the vent's walls became shorter, perhaps only a few hundred feet high, and that the vent was nearly filled to its rim. The researchers speculate that a lava lake formed in the vent during the eight months between the images, though whether the contents were liquid or cooled and solidified isn't known.

The researchers offer one caveat: a nonvolcanic, earthquake-triggered collapse of the vent's walls might have caused the expansion. They note, however, that vent collapses of this scale on Earth's volcanoes have always been accompanied by nearby volcanic eruptions; magma withdraws from beneath the vent because it is going somewhere else. The surface of Venus is geologically young, especially compared to all the other rocky bodies except Earth an Jupiter's moon Io. However, the estimates of how often eruptions might occur on Venus have been speculative, ranging from several large eruptions per year to one such eruption every several or even tens of years. Researchers contrast the lack of information about Venusian volcanism with what is known about Jupiter's moon Io and about Mars. Io is so active that multiple ongoing eruptions have been imaged every time the team observed it. On a geological time scale, relatively young lava flows indicate Mars remains volcanically active. However, nothing has occurred in the 45 years that the team has been observing Mars, and most scientists would say that you'd probably need to watch the surface for a few million years to have a reasonable chance of seeing a new lava flow. The research adds Venus to the small pool of volcanically active bodies in our solar system.


FLATTEST EXPLOSION EVER SEEN IN SPACE
University of Sheffield

An explosion the size of our solar system puzzled scientists, as part of its shape -- similar to that of an extremely flat disc -- challenges everything we know about explosions in space. The explosion observed was a bright Fast Blue Optical Transient (FBOT) -- an extremely rare class of explosion which is much less common than other explosions, such as supernovas. The first bright FBOT was discovered in 2018 and given the nickname "the cow." Explosions of stars in the Universe are almost always spherical in shape, as the stars themselves are spherical. However, this explosion, which occurred 180 million light years away, is the most aspherical ever seen in space, with a shape like a disc emerging a few days after it was discovered. This section of the explosion may have come from material shed by the star just before it exploded. It's still unclear how bright FBOT explosions occur, but it's hoped that this observation will bring us closer to understanding them. Very little is known about FBOT explosions -- they just don't behave like exploding stars should, they are too bright and they evolve too quickly. Put simply, they are weird, and this new observation makes them even weirder. Scientists never thought that explosions could be this aspherical. There are a few potential explanations for it: the stars involved may have created a disc just before they died or these could be failed supernovas, where the core of the star collapses to a black hole or neutron star which then eats the rest of the star.

Scientists made the discovery after spotting a flash of polarised light completely by chance. They were able to measure the polarisation of the blast -- using the astronomical equivalent of polaroid sunglasses -- with the Liverpool Telescope (owned by Liverpool John Moores University) located on La Palma. By measuring the polarisation, it allowed them to measure the shape of the explosion, effectively seeing something the size of our Solar System but in a galaxy 180 million light years away. They were then able to use the data to reconstruct the 3D shape of the explosion, and were able to map the edges of the blast -- allowing them to see just how flat it was. The mirror of the Liverpool Telescope is only 2.0m in diameter, but by studying the polarisation the astronomers were able to reconstruct the shape of the explosion as if the telescope had a diameter of about 750km. Researchers will now undertake a new survey with the international Vera Rubin Observatory in Chile, which is expected to help discover more FBOTs and further understand them.


ONE OF THE BIGGEST BLACK HOLES EVER FOUND
RAS

A team of astronomers has discovered one of the biggest black holes ever found, taking advantage of a phenomenon called gravitational lensing. The team used gravitational lensing - where a foreground galaxy bends the light from a more distant object and magnifies it – and supercomputer simulations on the DiRAC HPC facility, enabled the team to closely examine how light is bent by a black hole inside a galaxy hundreds of millions of light years from Earth. It found an ultramassive black hole, an object over 30 billion times the mass of our Sun, in the foreground galaxy – a scale rarely seen by astronomers. 
This is the first black hole found using the technique, whereby the team simulates light travelling through the Universe hundreds of thousands of times. Each simulation includes a different mass black hole, changing light’s journey to Earth. When the researchers included an ultramassive black hole in one of their simulations the path taken by the light from the faraway galaxy to reach Earth matched the path seen in real images captured by the Hubble Space Telescope. A gravitational lens occurs when the gravitational field of a foreground galaxy appears to bend the light of a background galaxy, meaning that we observe it more than once. Like a real lens, this also magnifies the background galaxy, allowing scientists to study it in enhanced detail. The study, which also includes Germany’s Max Planck Institute, opens up the tantalising possibility that astronomers can discover far more inactive and ultramassive black holes than previously thought, and investigate how they grew so large.

The story of this particular discovery started back in 2004 when fellow Durham University astronomer, Professor Alastair Edge, noticed a giant arc of a gravitational lens when reviewing images of a galaxy survey. Fast forward 18 years and with the help of some extremely high-resolution images from NASA’s Hubble telescope and the DiRAC COSMA8 supercomputer facilities at Durham University, Dr Nightingale and his team were able to revisit this and explore it further. The team hopes that this is the first step in enabling a deeper exploration of the mysteries of black holes, and that future large-scale telescopes will help astronomers study even more distant black holes to learn more about their size and scale. This particular black hole, which is roughly 30 billion times the mass of our Sun, is one of the biggest ever detected and on the upper limit of how large we believe black holes can theoretically become, so it is an extremely exciting discovery.
Dr Nightingale said: “Most of the biggest black holes that we know about are in an active state, where matter pulled in close to the black hole heats up and releases energy in the form of light, X-rays, and other radiation. However, gravitational lensing makes it possible to study inactive black holes, something not currently possible in distant galaxies. This approach could let us detect many more black holes beyond our local Universe and reveal how these exotic objects evolved further back in cosmic time.


BRIGHTEST GAMMA-RAY BURST EVER OBSERVED
Harvard-Smithsonian Center for Astrophysics

On October 9, 2022, an intense pulse of gamma-ray radiation swept through our solar system, overwhelming gamma-ray detectors on numerous orbiting satellites, and sending astronomers on a chase to study the event using the most powerful telescopes in the world. The new source, dubbed GRB 221009A for its discovery date, turned out to be the brightest gamma-ray burst (GRB) ever recorded. In a new study observations of GRB 221009A spanning from radio waves to gamma-rays, including critical millimeter-wave observations with the Center for Astrophysics | Harvard & Smithsonian's Submillimeter Array (SMA) in Hawaii, shed new light on the decades-long quest to understand the origin of these extreme cosmic explosions. The gamma-ray emission from GRB 221009A lasted over 300 seconds. Astronomers think that such "long-duration" GRBs is the birth cry of a black hole, formed as the core of a massive and rapidly spinning star collapses under its own weight. The newborn black hole launches powerful jets of plasma at near the speed of light, which pierce through the collapsing star and shine in gamma-rays. With GRB 221009A being the brightest burst ever recorded, a real mystery lay in what would come after the initial burst of gamma-rays. "As the jets slam into gas surrounding the dying star, they produce a bright `afterglow' of light across the entire spectrum. The afterglow fades quite rapidly, which means we have to be quick in capturing the light before it disappears, taking its secrets with it. This burst, being so bright, provided a unique opportunity to explore the detailed behaviour and evolution of an afterglow with unprecedented detail.

After analyzing and combining the data from the SMA and other telescopes all over the world, the astronomers were flummoxed: the millimeter and radio wave measurements were much brighter than expected based on the visible and X-ray light. This is one of the most detailed datasets ever collected, and it is clear that the millimeter and radio data just don't behave as expected. A few GRBs in the past have shown a brief excess of millimeter and radio emission that is thought to be the signature of a shockwave in the jet itself, but in GRB 221009A the excess emission behaves quite differently than in these past cases. It is likely that a completely new mechanism to produce excess millimeter and radio waves has been discovered. One possibility is that the powerful jet produced by GRB 221009A is more complex than in most GRBs. It is possible that the visible and X-ray light are produced by one portion of the jet, while the early millimeter and radio waves are produced by a different component. Luckily, this afterglow is so bright that we will continue to study its radio emission for months and maybe years to come. With this much longer time span astronomers hope to decipher the mysterious origin of the early excess emission.


HUBBLE FINDS DOUBLE QUASAR IN DISTANT UNIVERSE
NASA/Goddard Space Flight Center

The early Universe was a rambunctious place where galaxies often bumped into each other and even merged together. Using NASA's Hubble Space Telescope and other space and ground-based observatories, astronomers investigating these developments have made an unexpected and rare discovery: a pair of gravitationally bound quasars, both blazing away inside two merging galaxies. They existed when the Universe was just 3 billion years old. Quasars are bright objects powered by voracious, supermassive black holes blasting out ferocious fountains of energy as they engorge themselves on gas, dust, and anything else within their gravitational grasp. We don't see a lot of double quasars at this early time in the Universe which is why this discovery is so exciting. Finding close binary quasars is a relatively new area of research that has just developed in the past 10 to 15 years. Today's powerful new observatories have allowed astronomers to identify instances where two quasars are active at the same time and are close enough that they will eventually merge. There is increasing evidence that large galaxies are built up through mergers. Smaller systems come together to form bigger systems and ever larger structures. During that process there should be pairs of supermassive black holes formed within the merging galaxies. Knowing about the progenitor population of black holes will eventually tell us about the emergence of supermassive black holes in the early Universe, and how frequent those mergers could be. Astronomers are starting to unveil this tip of the iceberg of the early binary quasar population. The uniqueness of this study is that it is actually telling us that this population exists, and now we have a method to identify double quasars that are separated by less than the size of a single galaxy. Hubble shows, unequivocally, that this is indeed a genuine pair of supermassive black holes, rather than two images of the same quasar created by a foreground gravitational lens. And, Hubble shows a tidal feature from the merging of two galaxies, where gravity distorts the shape of the galaxies forming two tails of stars. However, Hubble's sharp resolution alone isn't good enough to go looking for these dual light beacons. The researchers enlisted Gaia, which launched in 2013, to pinpoint potential double-quasar candidates. Gaia measures the positions, distances, and motions of nearby celestial objects very precisely. But in a novel technique, it can be used to explore the distant Universe. Gaia's huge database can be used to search for quasars that mimic the apparent motion of nearby stars. The quasars appear as single objects in the Gaia data because they are so close together.

However, Gaia can pick up a subtle, unexpected "jiggle" that mimics an apparent change in position of some of the quasars it observes. In reality, the quasars aren't moving through space in any measurable way. Instead, their jiggle could be evidence of random fluctuations of light as each member of the quasar pair varies in brightness on timescales of days to months, depending on their black hole's feeding schedule. This alternating brightness between the quasar pair is similar to seeing a railroad crossing signal from a distance. As the lights on both sides of the stationary signal alternately flash, the sign gives the illusion of "jiggling." Another challenge is that because gravity warps space like a funhouse mirror, a foreground galaxy could split the image of a distant quasar into two, creating the illusion it was really a binary pair. The Keck telescope was used to make sure there's no lensing galaxy in between us and the suspected double quasar. Because Hubble peers into the distant past, this double quasar no longer exists. Over the intervening 10 billion years, their host galaxies have likely settled into a giant elliptical galaxy, like the ones seen in the local Universe today. And, the quasars have merged to become a gargantuan, supermassive black hole at its centre. The nearby giant elliptical galaxy, M87, has a monstrous black hole weighing 6.5 billion times the mass of our Sun. Perhaps this black hole was grown from one or more galaxy mergers over the past billions of years. The upcoming NASA Nancy Grace Roman Space Telescope, having the same visual acuity as Hubble, is ideal for binary quasar hunting. Hubble has been used to painstakingly take data for individual targets. But Roman's very wide-angle infrared view of the Universe is 200 times larger than Hubble's.


PRECURSORS TO LIFE FOUND IN PERSEUS CLOUD
Instituto de Astrofísica de Canarias (IAC)

Scientists have discovered the presence of numerous prebiotic molecules in the star formation region IC348 of the Perseus Molecular Cloud, a young star cluster some 2-3 million years old. Some of these biological molecules are considered essential building bricks for the construction of more complex molecules such as the amino acids, which formed the genetic code of ancient micro-organisms, and brought about the flourishing of life on Earth. Getting to know the distribution and the abundances of these precursor molecules in regions where planets are very probably forming, is an important challenge for astrophysics. The Perseus Cloud is one of the star forming regions closest to the Solar System. Many of its stars are young, and have protoplanetary discs where the physical processes which give rise to planets can take place. "It is an extraordinary laboratory of organic chemistry" explains Iglesias-Groth who in 2019 found fullerenes in the same cloud. These are complex molecules of pure carbon which often occur as building blocks for the key molecules of life. Now new research has detected in the inner part of this region common molecules such as molecular hydrogen (H2), hydroxyl (OH), water (H2O), carbon dioxide (CO2) and ammonia (NH3) as well as several carbon bearing molecules which could play an important role in the production of more complex hydrocarbons and prebiotic molecules, such as hydrogen cyanide (HCN), acetylene (C2H2), diacetylene (C4H2), cyanoacetylene (HC3N), cyanobutadiyne (HC5N), ethane (C2H6), hexatrine (C6H2) and benzene (C6H6). The data also show the presence of more complex molecules such as the polycyclic aromaatic hydrocarbons (PAH) and the fullerenes C60 and C70. "IC 348 seems to be very rich and diverse in its molecular content" states Iglesias-Gorth. "The novelty is that we see the molecules in the diffuse gas from which stars and protoplanetary discs are forming."

The presence of prebiotic molecules at interstellar sites so close to this star clusters suggests the possibility that accretion processes are taking place onto young planets which could contribute to the formation of complex organic molecules. These key molecules could have been supplied to the nascent planets in the protoplanetary discs and could in this way help to produce there a route towards the molecules of life. The detection by the researchers is based on data taken wth NASA's Spitzer satellite. The next step will be to use the powerful James Webb Space Telescope (JWST). "The spectroscopic capacity of the JWST could provide details about the spatial distribution of all these molecules, and extend the present search to others which are more complex, giving higher sensitivity and resolution which are essential to confirm the very probable presence of amino acids in the gas in this and in other star forming regions.


BIRTH OF GALAXY CLUSTER FROM EARLY UNIVERSE WITNESSED
ESO

Using the Atacama Large Millimeter/submillimeter Array (ALMA), astronomers have discovered a large reservoir of hot gas in the still-forming galaxy cluster around the Spiderweb galaxy -- the most distant detection of such hot gas yet. Galaxy clusters are some of the largest objects known in the Universe. Galaxy clusters, as the name suggests, host a large number of galaxies -- sometimes even thousands. They also contain a vast "intracluster medium" (ICM) of gas that permeates the space between the galaxies in the cluster. This gas in fact considerably outweighs the galaxies themselves. Much of the physics of galaxy clusters is well understood; however, observations of the earliest phases of formation of the ICM remain scarce. Previously, the ICM had only been studied in fully-formed nearby galaxy clusters. Detecting the ICM in distant protoclusters -- that is, still-forming galaxy clusters -- would allow astronomers to catch these clusters in the early stages of formation. Galaxy clusters are so massive that they can bring together gas that heats up as it falls towards the cluster. Cosmological simulations have predicted the presence of hot gas in protoclusters for over a decade, but observational confirmation has been missing. Pursuing such key observational confirmation led astronomers to carefully select one of the most promising candidate protoclusters. That was the Spiderweb protocluster, located at an epoch when the Universe was only 3 billion years old. Despite being the most intensively studied protocluster, the presence of the ICM has remained elusive. Finding a large reservoir of hot gas in the Spiderweb protocluster would indicate that the system is on its way to becoming a proper, long-lasting galaxy cluster rather than dispersing.

The team detected the ICM of the Spiderweb protocluster through what's known as the thermal Sunyaev-Zeldovich (SZ) effect. This effect happens when light from the cosmic microwave background -- the relic radiation from the Big Bang -- passes through the ICM. When this light interacts with the fast-moving electrons in the hot gas it gains a bit of energy and its colour, or wavelength, changes slightly. At the right wavelengths, the SZ effect thus appears as a shadowing effect of a galaxy cluster on the cosmic microwave background. By measuring these shadows on the cosmic microwave background, astronomers can therefore infer the existence of the hot gas, estimate its mass and map its shape. "Thanks to its unparalleled resolution and sensitivity, ALMA is the only facility currently capable of performing such a measurement for the distant progenitors of massive clusters. They determined that the Spiderweb protocluster contains a vast reservoir of hot gas at a temperature of a few tens of millions of degrees Celsius. Previously, cold gas had been detected in this protocluster, but the mass of the hot gas found in this new study outweighs it by thousands of times. This finding shows that the Spiderweb protocluster is indeed expected to turn into a massive galaxy cluster in around 10 billion years, growing its mass by at least a factor of ten. The hot thermal component will destroy much of the cold component as the system evolves, and we are witnessing a delicate transition. It provides observational confirmation of long-standing theoretical predictions about the formation of the largest gravitationally bound objects in the Universe.


NEW MEASUREMENT COULD CHANGE UNDERSTANDING OF UNIVERSE
Ecole Polytechnique Fédérale de Lausanne

The Universe is expanding -- but how fast exactly? The answer appears to depend on whether you estimate the cosmic expansion rate -- referred to as the Hubble's constant, or H0 -- based on the echo of the Big Bang (the cosmic microwave background, or CMB) or you measure H0 directly based on today's stars and galaxies. This problem, known as the Hubble tension, has puzzled astrophysicists and cosmologists around the world. A study carried out by the Stellar Standard Candles and Distances research group adds a new piece to the puzzle. Their research achieved the most accurate calibration of Cepheid stars -- a type of variable star whose luminosity fluctuates over a defined period -- for distance measurements to date based on data collected by the European Space Agency's (ESA's) Gaia mission. This new calibration further amplifies the Hubble tension. The Hubble constant (H0) is named after the astrophysicist who, together with Georges Lemaître, discovered the phenomenon in the late 1920s. It's measured in kilometers per second per megaparsec (km/s/Mpc), where 1 Mpc is around 3.26 million light years. The best direct measurement of H0 uses a "cosmic distance ladder," whose first rung is set by the absolute calibration of the brightness of Cepheids, now recalibrated by the EPFL study. In turn, Cepheids calibrate the next rung of the ladder, where supernovae -- powerful explosions of stars at the end of their lives -- trace the expansion of space itself. This distance ladder, measured by the Supernovae, H0, for the Equation of State of dark energy (SH0ES) team led by Adam Riess, winner of the 2011 Nobel Prize in Physics, puts H0 at 73.0 ± 1.0 km/s/Mpc.

H0 can also be determined by interpreting the CMB -- which is the ubiquitous microwave radiation left over from the Big Bang more than 13 billion years ago. However, this "early Universe" measurement method has to assume the most detailed physical understanding of how the Universe evolves, rendering it model dependent. The ESA's Planck satellite has provided the most complete data on the CMB, and according to this method, H0 is 67.4 ± 0.5 km/s/Mpc. The Hubble tension refers to this discrepancy of 5.6 km/s/Mpc, depending on whether the CMB (early Universe) method or the distance ladder (late Universe) method is used. The implication, provided that the measurements performed in both methods are correct, is that there is something wrong in the understanding of the basic physical laws that govern the Universe. Naturally, this major issue underscores how essential it is for astrophysicists' methods to be reliable. The new EPFL study is so important because it strengthens the first rung of the distance ladder by improving the calibration of Cepheids as distance tracers. Indeed, the new calibration allows us to measure astronomical distances to within ± 0.9%, and this lends strong support to the late Universe measurement. Additionally, the results obtained at EPFL, in collaboration with the SH0ES team, helped to refine the H0 measurement, resulting in improved precision and an increased significance of the Hubble tension.

The study confirms the 73 km/s/Mpc expansion rate, but more importantly, it also provides the most precise, reliable calibrations of Cepheids as tools to measure distances to date. Researchers developed a method that searched for Cepheids belonging to star clusters made up of several hundreds of stars by testing whether stars are moving together through the Milky Way. Thanks to this trick, we could take advantage of the best knowledge of Gaia's parallax measurements while benefiting from the gain in precision provided by the many cluster member stars. This has allowed us to push the accuracy of Gaia parallaxes to their limit and provides the firmest basis on which the distance ladder can be rested. Why does a difference of just a few km/s/Mpc matter, given the vast scale of the Universe? "This discrepancy has a huge significance. Suppose you wanted to build a tunnel by digging into two opposite sides of a mountain. If you've understood the type of rock correctly and if your calculations are correct, then the two holes you're digging will meet in the centre. But if they don't, that means you've made a mistake -- either your calculations are wrong or you're wrong about the type of rock. That's what's going on with the Hubble constant. The more confirmation we get that our calculations are accurate, the more we can conclude that the discrepancy means our understanding of the Universe is mistaken, that the Universe isn't quite as we thought. The discrepancy has many other implications. It calls into question the very fundamentals, like the exact nature of dark energy, the time-space continuum, and gravity. "t means we have to rethink the basic concepts that form the foundation of our overall understanding of physics. The research group's study makes an important contribution in other areas, too. Because their measurements are so precise, they give us insight into the geometry of the Milky Way. The highly accurate calibration developed will let us better determine the Milky Way's size and shape as a flat-disk galaxy and its distance from other galaxies, for example. The work also confirmed the reliability of the Gaia data by comparing them with those taken from other telescopes.

Simon:
Do I keep seeing the same one of these, or are they appearing in clusters?   :o:

Clive:
Playing catch-up Simon.  Someone else did them while I was away but I couldn’t post them as I rarely had an internet connection.

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