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Author Topic: Mid October Astronomy Bulletin  (Read 263 times)

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Mid October Astronomy Bulletin
« on: October 18, 2020, 10:18 »
STELLAR EXPLOSION NEAR EARTH EONS AGO
Technical University of Munich (TUM)

When the brightness of the star Betelgeuse dropped dramatically a few months ago, some observers suspected an impending supernova -- a stellar explosion that could also cause damage on Earth. While Betelgeuse has returned to normal, physicists have found evidence of a supernova that exploded near the Earth around 2.5 million years ago. The life of stars with a mass more than ten times that of our Sun ends in stellar explosion. This explosion leads to the formation of iron, manganese and other heavy elements. In layers of a manganese crust that are around two and a half million years old a research team has now confirmed the existence of both iron-60 and manganese-53. The increased concentrations of manganese-53 can be taken as the "smoking gun" -- the ultimate proof that this supernova really did take place. While a very close supernova could inflict massive harm to life on Earth, this one was far enough away. It only caused a boost in cosmic rays over several thousand years. However, this can lead to increased cloud formation, perhaps linking to the Pleistocene epoch, the period of the Ice Ages, which began 2.6 million years ago.

Typically, manganese occurs on Earth as manganese-55. Manganese-53, on the other hand, usually stems from cosmic dust, like that found in the asteroid belt of our solar system. This dust rains down onto the Earth continuously; but only rarely do we perceive larger specks of dust that glow as meteorites. New sediment layers that accumulate year for year on the sea floor preserve the distribution of the elements in manganese crusts and sediment samples. Using accelerator mass spectrometry, the team of scientists has now detected both iron-60 and increased levels of manganese-53 in layers that were deposited about two and a half million years ago. Researchers say this is investigative ultra-trace analysis - merely a few atoms. But accelerator mass spectrometry is so sensitive that it even allows us to calculate from our measurements that the star that exploded must have had around 11 to 25 times the size of the Sun. The researchers were also able to determine the half-life of manganese-53 from comparisons to other nuclides and the age of the samples. The result: 3.7 million years. To date, there has only been a single measurement to this end worldwide.


SURFACE OF NEAR-EARTH ASTEROID BENNU STUDIED
Southwest Research Institute

As the days count down to NASA's OSIRIS-REx spacecraft's Touch-And-Go asteroid sample collection attempt, scientists have helped determine what the spacecraft can expect to return from the near-Earth asteroid Bennu's surface. On October 20, the spacecraft will descend to the asteroid's boulder-strewn surface, touch the ground with its robotic arm for a few seconds and collect a sample of rocks and dust -- marking the first time NASA has grabbed pieces of an asteroid for return to Earth. The first attempt will be made at Nightingale, a rocky area 66 feet in diameter in Bennu's northern hemisphere. Since the spacecraft arrived at Bennu in 2018, scientists have been characterizing the asteroid's composition and comparing it to other asteroids and meteorites. The mission discovered carbon-bearing compounds on Bennu's surface, a first for a near-Earth asteroid, as well as minerals containing or formed by water. Scientists also studied the distribution of these materials, globally and at the sample sites. Asteroid Bennu is a dark, rubble pile held together by gravity and thought to be the collisional remnant of a much larger main-belt object. Its rubble-pile nature and heavily cratered surface indicates that it has had a rough-and-tumble life since being liberated from its much larger parent asteroid millions or even billions of years ago. The boulders on Bennu have diverse textures and colours, which may provide information about their variable exposure to micrometeorite bombardment and the solar wind over time. Studying
colour and reflectance data provide information about the geologic history of planetary surfaces. The OSIRIS-REx team is also comparing Bennu to Ryugu, another near-Earth asteroid. Both asteroids are thought to have originated from primitive asteroid families in the inner main belt. The Japan Aerospace Exploration Agency launched Hayabusa2 in 2014 and rendezvoused with near-Earth asteroid Ryugu in 2018. After surveying the asteroid for a year and a half, the spacecraft collected samples and is expected to return to Earth December 6, 2020. The sample returned by OSIRIS-REx, combined with the surface context maps OSIRIS-REx has collected, will improve interpretations of available ground and space telescope data for other primitive dark asteroids. Comparing returned Bennu samples with those of Ryugu will be instrumental for understanding the diversity within, and history of, asteroid families and the entire asteroid belt.


SNOWCAPPED MOUNTAINS OF PLUTO
CNRS

In 2015, the New Horizons space probe discovered spectacular snowcapped mountains on Pluto, which are strikingly similar to mountains on Earth. Such a landscape had never before been observed elsewhere in the Solar System. However, as atmospheric temperatures on our planet decrease at altitude, on Pluto they heat up at altitude as a result of solar radiation. So where does this ice come from? An international team has determined that the "snow" on Pluto's mountains actually consists of frozen methane, with traces of this gas being present in Pluto's atmosphere, just like water vapour on Earth. Then, to understand how the same landscape could be produced in such different conditions, they used a climate model for the dwarf planet, which revealed that due to its particular dynamics, Pluto's atmosphere is rich in gaseous methane at altitudes. As a result, it is only at the peaks of mountains high enough to reach this enriched zone that the air contains enough methane for it to condense. At lower altitudes the air is too low in methane for ice to form. This research could also explain why the thick glaciers consisting of methane observed elsewhere on Pluto bristle with spectacular craggy ridges, unlike Earth's flat glaciers, which consist of water.


ARROKOTHN CHANGED SHAPE IN 100 MILLION YEARS
by Max Planck Society

The trans-Neptunian object Arrokoth, also known as Ultima Thule, which NASA's space probe New Horizons passed on New Year's Day 2019, may have changed its shape significantly in the first 100 million years since its formation. Astronomers suggest that the current shape of Arrokoth, which resembles a flattened snowman, could be of evolutionary origin due to volatile outgassing. Their calculations help to understand what the current state of bodies from the edge of the Solar System may teach us about their original properties. The many millions of bodies populating the Kuiper Belt beyond Neptune's orbit are yet to reveal many of their secrets. In the 1980s, the space probes Pioneer 1 and 2 as well as Voyager 1 and 2 crossed this region but without cameras on board. NASA's spacecraft New Horizons sent the first images from the outermost edge of the solar system to Earth: in the summer of
2015 of dwarf planet Pluto and three and a half years later of the trans-Neptunian object Arrokoth, about 30 kilometres in size. Not yet officially named, the body was nicknamed Ultima Thule at the time, in reference to the northernmost land point on Earth. After all, the trans-Neptunian object is the body furthest away from the Sun that has ever been visited and imaged by a man-made probe. Especially Arrokoth's strange shape caused a sensation in the days after the fly-by. The body is a contact binary, believed to be a result of low velocity merging of two separate bodies that formed close together. It is composed of two connected lobes, of which the smaller one is slightly flattened, the larger one strongly so, creating the impression of a squashed snowman. In their current publication, the researchers investigate how this shape came to be. A pronounced bi-lobed shape is also known from some comets. However, there is no other known body that is as flat as Arrokoth. Did Arrokoth already look like this when it was created? Or did its shape develop gradually?

Astronomers like to think of the Kuiper Belt as a region where time has more or less stood still since the birth of the Solar System. More than four billion kilometres away from the Sun, the bodies of the Kuiper Belt have remained frozen and unchanged, so is the common belief. New Horizon's images of Arrokoth challenge this idea by its apparently smooth surface without signs of frequent cratering events and by its peculiar, flattened shape. Scientists assume that the Solar System was formed 4.6 billion years ago from a disk of dust: the particles from this nebula agglomerated into ever larger clumps; these clumps collided and merged into even larger bodies. There is as yet no explanation as to how a body as flat as Arrokoth could emerge from this process. Another possibility would be that Arrokoth had a more ordinary shape to begin with. It may have started as a merger between a spherical and an oblate body at the time of its creation and only gradually become flattened. Earlier studies suggest that during the formation of the Solar System, the region where Arrrokoth is located could have been a distinct environment in the cold, dust-shaded mid-plane of the outer nebula. The low temperatures enabled volatiles such as carbon monoxide and methane to freeze onto dust grains and compose planetesimals. When the nebular dust cleared after Arrokoth's formation, solar illumination would have raised its temperature and hence rapidly driven off the condensed volatiles. Arrokoth's strange shape would then be a natural outcome due to a favourable combination of its large obliquity, small eccentricity and mass-loss rate variation with solar flux, resulting in nearly symmetric erosion between north and south hemispheres. For a body to change its shape as extremely as Arrokoth, its rotational axis needs to be oriented in a special way. Unlike Earth's rotational axis, Arrokoth's is almost parallel to the orbital plane. During its 298 year orbit around the Sun, one polar region of Arrokoth faces the Sun continuously for nearly half the time while the other faces away. Regions at equator and lower latitudes are dominated by diurnal variations year round. This causes the poles to heat up the most, so that frozen gases escape from there most efficiently resulting in a strong mass loss.  The flattening process most likely occurred early in the evolution history of the body and proceeded rather quickly on a timescale of about one to 100 million years during the presence of super volatile ices in the near subsurface layers. In addition, the scientists self-consistently demonstrated that the induced torques would play a negligible role in the planetesimal's spin state change during the mass loss phase.


GALAXIES TRAPPED IN WEB OF BLACK HOLE
ESO

Astronomers have found six galaxies lying around a supermassive black hole when the Universe was less than a billion years old. This is the first time such a close grouping has been seen so soon after the Big Bang and the finding helps us better understand how supermassive black holes, one of which exists at the centre of our Milky Way, formed and grew to their enormous sizes so quickly. It supports the theory that black holes can grow rapidly within large, web-like structures which contain plenty of gas to fuel them. The new observations with the VLT revealed several galaxies surrounding a supermassive black hole, all lying in a cosmic “spider’s web” of gas extending to over 300 times the size of the Milky Way. The light from this large web-like structure, with its black hole of one billion solar masses, has travelled to us from a time when the Universe was only 0.9 billion years old. The very first black holes, thought to have formed from the collapse of the first stars, must have grown very fast to reach masses of a billion suns within the first 0.9 billion years of the Universe’s life. But astronomers have struggled to explain how sufficiently large amounts of “black hole fuel” could have been available to enable these objects to grow to such enormous sizes in such a short time.

The new-found structure offers a likely explanation: the “spider’s web” and the galaxies within it contain enough gas to provide the fuel that the central black hole needs to quickly become a supermassive giant. But how did such large web-like structures form in the first place? Astronomers think giant halos of mysterious dark matter are key. These large regions of invisible matter are thought to attract huge amounts of gas in the early Universe; together, the gas and the invisible dark matter form the web-like structures where galaxies and black holes can evolve. The galaxies now detected are some of the faintest that current telescopes can observe.This discovery required observations over several hours using the largest optical telescopes available, including ESO’s VLT. Using the MUSE and FORS2 instruments at the Paranal Observatory in the Chilean Atacama Desert, the team confirmed the link between four of the six galaxies and the black hole. These results contribute to our understanding of how supermassive black holes and large cosmic structures formed and evolved. ESO’s Extremely Large Telescope, currently under construction in Chile, will be able to build on this research by observing many more fainter galaxies around massive black holes in the early Universe using its
powerful instruments.


DEATH BY SPAGHETTIFICATION
ESO

Using telescopes from the European Southern Observatory and other organisations around the world, astronomers have spotted a rare blast of light from a star being ripped apart by a supermassive black hole. The phenomenon, known as a tidal disruption event, is the closest such flare recorded to date at just over 215 million light-years from Earth, and has been studied in unprecedented detail. The idea of a black hole ‘sucking in’ a nearby star sounds like science fiction. But this is exactly what happens in a tidal disruption event. But these tidal disruption events, where a star experiences what’s known as spaghettification as it’s sucked in by a black hole, are rare and not always easy to study. The team of researchers pointed ESO’s Very Large Telescope (VLT) and ESO’s New Technology Telescope (NTT) at a new flash of light that occurred last year close to a supermassive black hole, to investigate in detail what happens when a star is devoured by such a monster. Astronomers know what should happen in theory. When an unlucky star wanders too close to a supermassive black hole in the centre of a galaxy, the extreme gravitational pull of the black hole shreds the star into thin streams of material. As some of the thin strands of stellar material fall into the black hole during this spaghettification process, a bright flare of energy is released, which astronomers can detect. Although powerful and bright, up to now astronomers have had trouble investigating this burst of light, which is often obscured by a curtain of dust and debris. Only now have astronomers been able to shed light on the origin of this curtain. The discovery was possible because the tidal disruption event the team studied, AT2019qiz, was found just a short time after the star was ripped apart.

The team carried out observations of AT2019qiz, located in a spiral galaxy in the constellation of Eridanus, over a 6-month period as the flare grew in luminosity and then faded away. Multiple observations of the event were taken over the following months with facilities that included X-shooter and EFOSC2, powerful instruments on ESO’s VLT and ESO’s NTT, which are situated in Chile. The prompt and extensive observations in ultraviolet, optical, X-ray and radio light revealed, for the first time, a direct connection between the material flowing out from the star and the bright flare emitted as it is devoured by the black hole. The observations showed that the star had roughly the same mass as our own Sun, and that it lost about half of that to the monster black hole, which is over a million times more massive. The research helps us better understand supermassive black holes and how matter
behaves in the extreme gravity environments around them. The team say AT2019qiz could even act as a ‘Rosetta stone’ for interpreting future observations of tidal disruption events. ESO’s Extremely Large Telescope (ELT), planned to start operating this decade, will enable researchers to detect increasingly fainter and faster evolving tidal disruption events, to solve further mysteries of black hole physics.


EINSTEIN’S GRAVITY NOW MUCH HARDER TO BEAT
University of Arizona

Einstein's theory of general relativity -- the idea that gravity is matter warping spacetime -- has withstood over 100 years of scrutiny and testing, including the newest test from the Event Horizon Telescope collaboration. According to the findings, Einstein's theory just got 500 times harder to beat. Despite its successes, Einstein's robust theory remains mathematically irreconcilable with quantum mechanics, the scientific understanding of the subatomic world. Testing general relativity is important because the ultimate theory of the universe must encompass both gravity and quantum mechanics. Scientists expect a complete theory of gravity to be different from general relativity, but there are many ways one can modify it. They found that whatever the correct theory is, it can't be significantly different from general relativity when it comes to black holes. To perform the test, the team used the first image ever taken of the supermassive black hole at the centre of nearby galaxy M87 obtained with the EHT last year. The first results had shown that the size of the black-hole shadow was consistent with the size predicted by general relativity. At that time, researchers were not able to ask the opposite question: How different can a gravity theory be from general relativity and still be consistent with the shadow size? The team did a very broad analysis of many modifications to the theory of general relativity to identify the unique characteristic of a theory of gravity that determines the size of a black hole shadow. In this way, it can now pinpoint whether some alternative to general relativity is in agreement with the Event Horizon Telescope observations, without worrying about any other details.

The team focused on the range of alternatives that had passed all the previous tests in the solar system. Using the gauge it developed, the team showed that the measured size of the black hole shadow in M87 tightens the wiggle room for modifications to Einstein's theory of general relativity by almost a factor of 500, compared to previous tests in the solar system. Many ways to modify general relativity fail at this new and tighter black hole shadow test. Black hole images provide a completely new angle for testing Einstein's theory of general relativity. Together with gravitational wave observations, this marks the beginning of a new era in black hole astrophysics. Next, the EHT team expects higher fidelity images that will be captured by the expanded array of telescopes, which includes the Greenland Telescope, the 12-meter Telescope on Kitt Peak near Tucson, and the Northern Extended Millimeter Array Observatory in France. When we obtain an image of the black hole at the centre of our own galaxy, then we can constrain deviations from general relativity even further.


NOBEL PRIZE IN PHYSICS 2020
Nobel Foundation

Three Laureates share this year's Nobel Prize in Physics for their discoveries about one of the most exotic phenomena in the Universe, the black hole. Roger Penrose showed that the general theory of relativity leads to the formation of black holes. Reinhard Genzel and Andrea Ghez discovered that an invisible and extremely heavy object governs the orbits of stars at the centre of our Galaxy. A supermassive black hole is the only currently known explanation. Roger Penrose used ingenious
mathematical methods in his proof that black holes are a direct consequence of Albert Einstein's general theory of relativity. Einstein did not himself believe that black holes really exist, these super-heavyweight monsters that capture everything that enters them. Nothing can escape, not even light. In January 1965, ten years after Einstein's death, Roger Penrose proved that black holes really can form and described them in detail; at their heart, black holes hide a singularity in which all the known laws of nature cease. His groundbreaking article is still regarded as the most important contribution to the general theory of relativity since Einstein. Reinhard Genzel and Andrea Ghez each lead a group of astronomers that, since the early 1990s, has focused on a region called Sagittarius A* at the centre of our galaxy. The orbits of the brightest stars closest to the middle of the Milky Way have been mapped with increasing precision. The measurements of these two groups agree, with both finding an extremely heavy, invisible object that pulls on the jumble of stars, causing them to rush around at dizzying speeds. Around four million solar masses are packed together in a region no larger than our solar system. Using the world's largest telescopes, Genzel and Ghez developed methods to see through the huge clouds of interstellar gas and dust to the centre of the Milky Way. Stretching the limits of technology, they refined new techniques to compensate for distortions caused by the Earth's atmosphere, building unique instruments and committing themselves to long-term research. Their pioneering work has given us the most convincing evidence yet of a supermassive black hole at the centre of the Milky Way.

Winner BBC Quiz of the Year 2015, 2016 and yet again in 2017.


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