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THE SOCIETY FOR POPULAR ASTRONOMY Electronic News Bulletin No. 561 2022 March 13

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THE SOCIETY FOR POPULAR ASTRONOMY Electronic News Bulletin No. 561 2022 March 13
We're delighted that the Society for Popular Astronomy's free Electronic News Bulletins have gained many hundreds of subscribers since we first issued them more than 23 years ago!
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And now, here is our latest round-up of news.

FATE OF DINOSAURS SEALED IN SPRING
European Synchrotron Radiation Facility

Scientists have determined when the meteorite crashed onto the Earth, after analysing the remains of fish that died just after the impact. Around 66 million years ago, the so-called Chicxulub meteorite crashed into the Earth, in what today is the Yucatán peninsula in Mexico, marking the demise of dinosaurs and end of the Cretaceous period. This mass extinction still puzzles scientists today, as it was one of the most selective in the history of life: all non-avian dinosaurs, pterosaurs, ammonites, and most marine reptiles disappeared, whilst mammals, birds, crocodiles, and turtles survived. When the meteorite impacted Earth, it rocked the continental plate and caused huge waves in water bodies, such as rivers and lakes. These moved enormous volumes of sediment that engulfed fish and buried them alive, while impact spherules (glass beads of Earth rock) rained down from the sky, less than an hour after impact. Today, the event deposit of Tanis in North Dakota (United States) preserves a fossilised ecosystem that includes paddlefishes and sturgeons, which were direct casualties of the event. The fossil fish were exceptionally preserved, with their bones showing almost no signs of geochemical alteration. Researchers went onsite to excavate the precious specimens. The team came to the ESRF, a particle accelerator that produces the world's brightest x-rays, with a partial fish specimen and representative sections of the bones and carried out high-resolution synchrotron X-ray tomography. The ESRF is the perfect tool to research these kind of samples and the facility has developed unique expertise in palaeontology over the last two decades.
The X-ray scans showed the distribution, shapes, and sizes of the bone cells, which are known to fluctuate with the seasons as well. In all studied fish, bone cell density and volumes can be traced over multiple years and they indicate whether it was spring, summer, autumn, or winter. Researchers saw that both cell density and volumes were on the rise but had not yet peaked during the year of death, which implies that growth abruptly stopped spring. In parallel to synchrotron radiation studies, the team carried out carbon isotope analysis to reveal the annual feeding pattern of a fish. The availability of zooplankton, its prey of choice, oscillated seasonally and peaked in summer. This temporary increase of ingested zooplankton enriched the skeleton of the fish with the heavier 13C carbon isotope relative to the lighter 12C carbon isotope. The carbon isotope signal across the growth record of this unfortunate paddlefish confirms that the feeding season had not yet climaxed -- death came in spring. The findings will aid future research into the selectivity of the mass extinction: in the Northern Hemisphere, it was spring and therefore the reproduction cycles of organisms were starting, only to be abruptly stopped. Meanwhile, it was autumn in the Southern Hemisphere, where many organisms were likely preparing for winter. In general, it is well understood that organisms who were exposed died virtually immediately. So those sheltering in caves or burrows because they were hibernating were far more likely to survive into the Paleogene. The results will help to uncover why most of the dinosaurs died out while birds and early mammals managed to evade extinction.

UNUSUAL GLASS BEADS ON FAR SIDE OF MOON
GIZMODO

A pair of translucent glass spheres, each measuring over a half-inch thick, have been observed in an impact crater near the lunar south pole. They're the first of their kind to ever be discovered on the Moon. The beads likely formed from the heat generated by a violent impact or possibly from early volcanic activity. The finding is significant, as glass spheres record important information about the mantle composition and the history of lunar volcanism and impact cratering. The "translucent glass globules," as the scientists describe them, were spotted by the eight-wheeled Yutu-2 rover. The rover, as part of China's Chang'e 4 mission, is currently investigating selenological (the lunar equivalent of "geological") and chemical differences between the near and far sides of the Moon. The tiny rover landed in the 186-kilometre Von Kármán Crater on January 3, 2019. This large crater is situated within the much larger Aitken Basin--the Moon's biggest impact basin--near the lunar south pole. That Yutu-2 stumbled upon glass is hardly special, as the stuff is strewn across much of the Moon's surface. What makes these particular objects unique is their large size and translucent nature. Lunar glass tends to be small, measuring less than 1 mm, but Apollo astronauts did manage to spot some beads as large as these. The two globules in Von Kármán Crater are estimated to be between 0.5 and 1 inches (1.5 cm-2.5 cm) in diameter, hence their description as being "macroscopic" in size. But whereas the Apollo samples were dark and dull, the newly discovered beads are translucent or semi-transparent and they exhibit a vitreous lustre. Four other similar objects were found by Yutu-2's panoramic camera, but the image resolution wasn't clear enough for the scientists to identify them as being glass spheres. The shape and location of these spherules suggest they're impact glasses, other than objects delivered from other planetary bodies or products of volcanic activity.
Glass globules form from the intense heat produced by large impacts, in which silicates liquify and assume a spherical shape when airborne. Tossed into the sky, the liquid balls cool rapidly, returning to the surface as glass. Volcanic eruptions can do the same, but volcanoes haven't been active on the Moon in quite some time. What's more, the characteristics of these beads aren't really consistent with volcanism, the scientists say, arguing that they're impact glasses produced by "anorthositic melt." Lunar anorthosite is a type of igneous rock that's common in the lunar highlands near the south pole. A limitation of the paper is that the exact composition of the beads could not be determined. The scientists say the glass beads formed recently or were only recently exposed. The top inch of the lunar regolith gets covered in less than 100,000 years, indicating the globules might be extremely young. It's likely that a recent impact event kicked up the beads, depositing them onto the surface. Similar objects have been found on Earth, and they're called tektites. The scientists suspect that these macroscopic objects are a common feature of the Moon and that other spherules should "be abundant across the lunar highland. Yutu-2 made headlines in December 2021 when it spotted a strange shape on the lunar horizon. Dubbed the "mystery hut," the object turned out to be an irregularly shaped rock.

LASERS COULD HELP PROBES SAIL TO OUTER PLANETS
American Chemical Society

Space travel can be agonizingly slow: For example, the New Horizons probe took almost 10 years to reach Pluto. Traveling to Proxima Centauri b, the closest habitable planet to Earth, would require thousands of years with even the biggest rockets. Now, researchers calculate that low-power lasers on Earth could launch and manoeuvre small probes equipped with silicon or boron nitride sails, propelling them to much faster speeds than rocket engines. Instead of catching wind, like the sails on boats, "laser sails" would catch laser beams and could, in principle, push spacecraft to nearly the speed of light. Scientists have been working on this concept for a while. For example, one privately funded project called the Breakthrough Starshot initiative aims to send a small, sailed probe weighing about a gram to Proxima Centauri b with a flight taking only 20 years. It would be propelled to 20% of light speed by a 100 GW, kilometre-square laser array. Scientists wondered if much lower-power, smaller laser arrays could find use in applications where conventional electric and chemical rockets are now used. The lasers might someday be able to adjust the orbit of satellites after launch or propel tiny sailed probes on interplanetary or interstellar missions, without requiring large amounts of fuel. The researchers performed calculations to show that even lasers with powers of about 100 kW and array sizes of about a metre could power a 1-gram probe at velocities far exceeding the current record, with only minutes to hours of laser illumination. According to their calculations, the lasers could manoeuvre small probes between different Earth orbits in only a day, which is not possible with current electrical and chemical rockets. The team determined that the best materials for the laser sails, which allowed high reflectivity and rapid cooling, were silicon nitride and boron nitride structured at the nanoscale. Finally, the researchers calculated that these tiny laser-propelled probes could travel fast enough to escape the solar system, reaching 5 times higher velocities than the New Horizons probe. These prototype sailed spacecraft, driven by low-power lasers, could pave the wave for fast space exploration and future interstellar flight, the researchers say.

LARGEST MOLECULE EVER FOUND IN PLANET FORMING DISC
ESO

Using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, researchers at Leiden Observatory in the Netherlands have for the first time detected dimethyl ether in a planet-forming disc. With nine atoms, this is the largest molecule identified in such a disc to date. It is also a precursor of larger organic molecules that can lead to the emergence of life. Dimethyl ether is an organic molecule commonly seen in star-forming clouds, but had never before been found in a planet-forming disc. The researchers also made a tentative detection of methyl formate, a complex molecule similar to dimethyl ether that is also a building block for even larger organic molecules. The molecules were found in the planet-forming disc around the young star IRS 48 (also known as Oph-IRS 48), located 444 light-years away in the constellation Ophiuchus, has been the subject of numerous studies because its disc contains an asymmetric, cashew-nut-shaped "dust trap". This region, which likely formed as a result of a newly born planet or small companion star located between the star and the dust trap, retains large numbers of millimetre-sized dust grains that can come together and grow into kilometre-sized objects like comets, asteroids and potentially even planets. Many complex organic molecules, such as dimethyl ether, are thought to arise in star-forming clouds, even before the stars themselves are born. In these cold environments, atoms and simple molecules like carbon monoxide stick to dust grains, forming an ice layer and undergoing chemical reactions, which result in more complex molecules.
Researchers recently discovered that the dust trap in the IRS 48 disc is also an ice reservoir, harbouring dust grains covered with this ice rich in complex molecules. It was in this region of the disc that ALMA has now spotted signs of the dimethyl ether molecule: as heating from IRS 48 sublimates the ice into gas, the trapped molecules inherited from the cold clouds are freed and become detectable. The discovery of dimethyl ether suggests that many other complex molecules that are commonly detected in star-forming regions may also be lurking on icy structures in planet-forming discs. These molecules are the precursors of prebiotic molecules such as amino acids and sugars, which are some of the basic building blocks of life. By studying their formation and evolution, researchers can therefore gain a better understanding of how prebiotic molecules end up on planets, including our own. Future studies of IRS 48 with ESO's Extremely Large Telescope (ELT), currently under construction in Chile and set to start operations later this decade, will allow the team to study the chemistry of the very inner regions of the disc, where planets like Earth may be forming.

ERROR OF "CLOSEST BLACK HOLE"
ESO

In 2020 a team led by European Southern Observatory (ESO) astronomers reported the closest black hole to Earth, located just 1000 light-years away in the HR 6819 system. But the results of their study were contested by other researchers, including by an international team based at KU Leuven, Belgium. In a new, these two teams have united to report that there is in fact no black hole in HR 6819, which is instead a "vampire" two-star system in a rare and short-lived stage of its evolution. The original study on HR 6819 received significant attention from both the press and scientists. Astronomers were convinced that the best explanation for the data they had, obtained with the MPG/ESO 2.2-metre telescope, was that HR 6819 was a triple system, with one star orbiting a black hole every 40 days and a second star in a much wider orbit. But a Belgian study proposed a different explanation for the same data: HR 6819 could also be a system with only two stars on a 40-day orbit and no black hole at all. This alternative scenario would require one of the stars to be "stripped", meaning that, at an earlier time, it had lost a large fraction of its mass to the other star. To solve the mystery, the two teams worked together to obtain new, sharper data of HR 6819 using ESO's Very Large Telescope (VLT) and Very Large Telescope Interferometer (VLTI). To distinguish between the two proposals, the astronomers used both the VLTI's GRAVITY instrument and the Multi Unit Spectroscopic Explorer (MUSE) instrument on ESO's VLT.
MUSE confirmed that there was no bright companion in a wider orbit, while GRAVITY's high spatial resolution was able to resolve two bright sources separated by only one-third of the distance between the Earth and the Sun. These data proved to be the final piece of the puzzle, and allowed us to conclude that HR 6819 is a binary system with no black hole. The best interpretation so far is that astronomers caught this binary system in a moment shortly after one of the stars had sucked the atmosphere off its companion star. This is a common phenomenon in close binary systems, sometimes referred to as "stellar vampirism" in the press. Catching such a post-interaction phase is extremely difficult as it is so short. This makes the findings for HR 6819 very exciting, as it presents a perfect candidate to study how this vampirism affects the evolution of massive stars, and in turn the formation of their associated phenomena including gravitational waves and violent supernova explosions. The newly formed Leuven-ESO joint team now plans to monitor HR 6819 more closely using the VLTI's GRAVITY instrument. The researchers will conduct a joint study of the system over time, to better understand its evolution, constrain its properties, and use that knowledge to learn more about other binary systems.

4.4 MILLION GALAXIES REVEALED IN NEW MAP
Durham University

A team of scientists has mapped more than a quarter of the northern sky using the Low Frequency Array (LOFAR), a pan-European radio telescope. The map reveals an astonishingly detailed radio image of more than 4.4 million objects and a very dynamic picture of our Universe, which now has been made public for the first time. The vast majority of these objects are billions of light years away and are either galaxies that harbour massive black holes or are rapidly growing new stars. Rarer objects that have been discovered include colliding groups of distant galaxies and flaring stars within the Milky Way. To produce the map, scientists deployed state-of-the-art data processing algorithms on high performance computers all over Europe to process 3,500 hours of observations that occupy 8 petabytes of disk space--the equivalent to roughly 20,000 laptops. This data release, which is by far the largest from the LOFAR Two-metre Sky Survey, presents about a million objects that have never been seen before with any telescope and almost four million objects that are new discoveries at radio wavelengths. This release is only 27% of the entire survey and the team anticipates it will lead to many more scientific breakthroughs in the future, including examining how the largest structures in the Universe grow, how black holes form and evolve, the physics governing the formation of stars in distant galaxies and even detailing the most spectacular phases in the life of stars in our own Galaxy. This data presents a major step forward in astrophysics and can be used to search for a wide range of signals, such as those from nearby planets or galaxies right through to faint signatures in the distant Universe.

COLOSSAL BLACK HOLES ORBITING EACH OTHER
California Institute of Technology

Locked in a cosmic waltz 9 billion light years away, two supermassive black holes appear to be orbiting around each other every two years. The two giant bodies each have masses that are hundreds of millions of times larger than that of our Sun, and the objects are separated by a distance roughly 50 times that which separates our Sun and Pluto. When the pair merge in roughly 10,000 years, the titanic collision is expected to shake space and time itself, sending gravitational waves across the Universe. Astronomers discovered evidence for this scenario taking place within a fiercely energetic object known as a quasar. Quasars are active cores of galaxies in which a supermassive black hole is siphoning material from a disk encircling it. In some quasars, the supermassive black hole creates a jet that shoots out at near the speed of light. The quasar observed in the new study, PKS 2131-021, belongs to a subclass of quasars called blazars in which the jet is pointing toward the Earth. Astronomers already knew quasars could possess two orbiting supermassive black holes, but finding direct evidence for this has proved difficult. The researchers argue that PKS 2131-021 is now the second known candidate for a pair of supermassive black holes caught in the act of merging. The first candidate pair, within a quasar called OJ 287, orbit each other at greater distances, circling every nine years versus the two years it takes for the PKS 2131-021 pair to complete an orbit. The telltale evidence came from radio observations of PKS 2131-021 that span 45 years. According to the study, a powerful jet emanating from one of the two black holes within PKS 2131-021 is shifting back and forth due to the pair's orbital motion. This causes periodic changes in the quasar's radio-light brightness. Five different observatories registered these oscillations, including Caltech's Owens Valley Radio Observatory (OVRO), the University of Michigan Radio Astronomy Observatory (UMRAO), MIT's Haystack Observatory, the National Radio Astronomy Observatory (NRAO), Metsähovi Radio Observatory in Finland, and NASA's Wide-field Infrared Survey Explorer (WISE) space satellite. The combination of the radio data yields a nearly perfect sinusoidal light curve unlike anything observed from quasars before.
Most, if not all, galaxies possess monstrous black holes at their cores, including our own Milky Way galaxy. When galaxies merge, their black holes "sink" to the middle of the newly formed galaxy and eventually join together to form an even more massive black hole. As the black holes spiral toward each other, they increasingly disturb the fabric of space and time, sending out gravitational waves, which were first predicted by Albert Einstein more than 100 years ago. The National Science Foundation's LIGO (Laser Interferometer Gravitational-Wave Observatory), which is managed jointly by Caltech and MIT, detects gravitational waves from pairs of black holes up to dozens of times the mass of our Sun. However, the supermassive black holes at the centres of galaxies have millions to billions of times as much mass as our Sun, and give off lower frequencies of gravitational waves than those detected by LIGO. In the future, pulsar timing arrays -- which consist of an array of pulsing dead stars precisely monitored by radio telescopes -- should be able to detect the gravitational waves from supermassive black holes of this heft. (The upcoming Laser Interferometer Space Antenna, or LISA, mission would detect merging black holes whose masses are 1,000 to 10 million times greater than the mass of our Sun.) So far, no gravitational waves have been registered from any of these heavier sources, but PKS 2131-021 provides the most promising target yet. In the meantime, light waves are the best option to detect coalescing supermassive black holes. The first such candidate, OJ 287, also exhibits periodic radio-light variations. These fluctuations are more irregular, and not sinusoidal, but they suggest the black holes orbit each other every nine years. The black holes within the new quasar, PKS 2131-021, orbit each other every two years and are 2,000 astronomical units apart, about 50 times the distance between our Sun and Pluto, or 10 to 100 times closer than the pair in OJ 287.
 
NuSTAR OBSERVATORY MAKES ILLUMINATING DISCOVERIES
NASA

A design quirk in the X-ray observatory has made it possible for astronomers to use previously unwanted light to study even more cosmic objects than before. For almost 10 years, the NuSTAR (Nuclear Spectroscopic Telescope Array) X-ray space observatory has been studying some of the highest-energy objects in the Universe, such as colliding dead stars and enormous black holes feasting on hot gas. During that time, scientists have had to deal with stray light leaking in through the sides of the observatory, which can interfere with observations much like external noise can drown out a phone call. But now team members have figured out how to use that stray X-ray light to learn about objects in NuSTAR's peripheral vision while also performing normal targeted observations. This development has the potential to multiply the insights that NuSTAR provides. A new science paper describes the first use of NuSTAR's stray light observations to learn about a cosmic object - in this case, a neutron star. Nuggets of material left over after a star collapses, neutron stars are some of the densest objects in the Universe, second only to black holes. Their powerful magnetic fields trap gas particles and funnel them toward the neutron star's surface. As the particles are accelerated and energized, they release high-energy X-rays that NuSTAR can detect. The new study describes a system called SMC X-1, which consists of a neutron star orbiting a living star in one of two small galaxies orbiting the Milky Way. The brightness of SMC X-1's X-ray output appears to vary wildly when viewed by telescopes, but decades of direct observations by NuSTAR and other telescopes have revealed a pattern to the fluctuations. Scientists have pinpointed several reasons why SMC X-1 changes in brightness when studied by X-ray telescopes. For example, the X-rays' brightness dims as the neutron star dips behind the living star with each orbit. According to the paper, the stray light data was sensitive enough to pick up on some of those well-documented changes.
The new approach is possible because of NuSTAR's shape, which is similar to dumbbell or dog bone: It has two bulky components at either end of a narrow, 33-foot-long (10-metre-long) structure called a deployable mast, or boom. Typically, researchers point one of the bulky ends - which contains the optics, or the hardware that collects X-rays - at the object they want to study. The light travels along the boom to the detectors, located at the other end of the spacecraft. The distance between the two is necessary to focus the light. But stray light also reaches the detectors by entering through the sides of the boom, bypassing the optics. It appears in NuSTAR's field of view along with light from whatever object the telescope directly observes, and is often fairly easy to identify by eye: It forms a circle of faint light emerging from the sides of the image. (Unsurprisingly, stray light is a problem for many other space- and ground-based telescopes.) A group of NuSTAR team members has spent the last few years separating the stray light from various NuSTAR observations. After identifying bright, known X-ray sources in the periphery of each observation, they used computer models to predict how much stray light should appear based on which bright object was nearby. They also looked at almost every NuSTAR observation to confirm the telltale sign of stray light. The team created a catalogue of about 80 objects for which NuSTAR had collected stray light observations, naming the collection "StrayCats." Of course, the stray light data can't replace direct observations by NuSTAR. Aside from stray light being unfocused, many objects that NuSTAR can observe directly are too faint to appear in the stray light catalogue. But Caltech students have combed through the data and found instances of rapid brightening from peripheral objects, which might be any number of dramatic events, such as thermonuclear explosions on the surfaces of neutron stars. Observing the frequency and intensity of a neutron star's changes in brightness can help scientists decipher what's happening to those objects. NuSTAR launched on June 13, 2012.

IS DARK ENERGY ONLY AN ILLUSION?
Scuola Internazionale Superiore di Studi Avanzati

A huge amount of mysterious dark energy is necessary to explain cosmological phenomena, such as the accelerated expansion of the Universe, with Einstein's theory. But what if dark energy was just an illusion and general relativity itself had to be modified? A new study offers a new approach to answer this question. Thanks to huge computational and mathematical effort, scientists produced the first simulation ever of merging binary neutron stars in theories beyond general relativity that reproduce a dark- energy like behaviour on cosmological scales. This allows the comparison of Einstein's theory and modified versions of it, and, with sufficiently accurate data, may solve the dark energy mystery. For about 100 years now, general relativity has been very successful at describing gravity on a variety of regimes, passing all experimental tests on Earth and the solar system. However, to explain cosmological observations such as the observed accelerated expansion of the Universe, we need to introduce dark components, such as dark matter and dark energy, which still remain a mystery. Astrophysicists question whether dark energy is real or, instead, it may be interpreted as a breakdown of our understanding of gravity.
The accelerated expansion of the Universe might be caused by some yet unknown modifications of general relativity, a sort of 'dark gravity'. The merger of neutron stars offers a unique situation to test this hypothesis because gravity around them is pushed to the extreme. Neutron stars are the densest stars that exist, typically only 10 kilometres in radius, but with a mass between one or two times the mass of our Sun. This makes gravity and the spacetime around them extreme, allowing for abundant production of gravitational waves when two of them collide. We can use the data acquired during such events to study the workings of gravity and test Einstein's theory in a new window. In this study scientists produced the first simulation of merging binary neutron stars in theories of modified gravity relevant for cosmology: This type of simulations is extremely challenging because of the highly non-linear nature of the problem. It requires a huge computational effort -months of run in supercomputers -- that was made possible also by the agreement between SISSA and CINECA consortium. Thanks to these simulations, researchers are finally able to compare general relativity and modified gravity. Surprisingly, they found that the 'dark gravity' hypothesis is equally good as general relativity at explaining the data acquired by the LIGO and Virgo interferometers during past binary neutron star collisions. Indeed, the differences between the two theories in these systems are quite subtle, but they may be detectable by next-generation gravitational interferometers, such as the Einstein telescope in Europe and Cosmic Explorer in USA. This opens the exciting possibility of using gravitational waves to discriminate between dark energy and 'dark gravity.

EUROPE'S MARS ROVER UNLIKELY TO LAUNCH
BBC Science

It's "very unlikely" the British-built Mars rover, Rosalind Franklin, will launch this year. The European Space Agency (ESA) says the project is now at risk because of the worsening diplomatic crisis over the war in Ukraine. The robot is part of a joint venture with the Russian space agency. It's due to launch on a Russian rocket in September and land eight months later using Russian hardware, but this cooperation may now be hard to justify. The Russian space agency Roscosmos announced it would be suspending flights of its Soyuz rockets from the European Kourou spaceport in French Guiana, as retaliation for EU economic sanctions. It also means the European Union's satellite navigation system, Galileo, was due to launch two satellites on Russian rockets from a spaceport in French Guiana, South America. Roscosmos has now cancelled the launches from the territory. Even more alarming is the Russian's refusal to use their cargo spacecraft to deliver fuel and supplies to the International Space Station. Without regular maintenance the 400 ton ISS would spin out of control and "crash land on Europe or America" according to the head of the Russian Space Agency. It's thought Elon Musk's SpaceX will be able to take over the task of keeping the space station in orbit. Meanwhile, the British backed OneWeb satellite system planned launch of a further 36 communication satellites was aborted by the Russians just three days before take-off and it's not clear what will become of them.
Bulletin compiled by Clive Down
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Geoff