EARTH MAY HAVE CAPTURED 1960’S ROCKET BOOSTER
NASA
Earth has captured a tiny object from its orbit around the Sun and will keep it as a temporary satellite for a few months before it escapes back to a solar orbit. But the object is likely not an asteroid; it's probably the Centaur upper stage rocket booster that helped lift NASA's ill-fated Surveyor 2 spacecraft toward the Moon in 1966. This story of celestial catch-and-release begins with the detection of an object by the NASA-funded Pan-STARRS1 survey telescope on Maui in September. Astronomers at Pan-STARRS noticed that this object followed a slight but distinctly curved path in the sky, which is a sign of its proximity to Earth. The apparent curvature is caused by the rotation of the observer around Earth's axis as our planet spins. Assumed to be an asteroid orbiting the Sun, the object was given a standard designation by the Minor Planet Center in Cambridge, Massachusetts: 2020 SO. But scientists at the Center for Near-Earth Object Studies (CNEOS) at NASA's Propulsion Laboratory in Southern California saw the object's orbit and suspected it was not a normal asteroid. Most asteroids' orbits are more elongated and tilted relative to Earth's orbit. But the orbit of 2020 SO around the Sun was very similar to that of Earth: It was at about the same distance, nearly circular, and in an orbital plane that almost exactly matched that of our planet - highly unusual for a natural asteroid. As astronomers at Pan-STARRS and around the world made observations of 2020 SO, the data also started to reveal the degree to which the Sun's radiation was changing 2020 SO's trajectory - an indication that it may not be an asteroid after all. The Surveyor 2 lunar lander was launched toward the Moon on Sept. 20, 1966, on an Atlas-Centaur rocket. The mission was designed to reconnoiter the lunar surface ahead of the Apollo missions that led to the first crewed lunar landing in 1969. Shortly after lift-off, Surveyor 2 separated from its Centaur upper-stage booster as intended. But control of the spacecraft was lost a day later when one of its thrusters failed to ignite, throwing it into a spin. The spacecraft crashed into the Moon just southeast of Copernicus crater In Sept. 1966. The spent Centaur upper-stage rocket, meanwhile, sailed past the Moon and disappeared into an unknown orbit about the Sun.
BRIGHTENING COMET ERASMUS
Spaceweather.com
Every 2000 years, Comet Erasmus (C/2020 S3) visits the inner Solar System. Discovered on Sept. 17, 2020, by South African astronomer Nicolas Erasmus, the dirty snowball is plunging toward the Sun for a close encounter inside the orbit Mercury on Dec. 12th. Comet Erasmus is brightening as it approaches the Sun. Forecasters believe it will become 5th magnitude by the time it dips inside the orbit of Mercury next month. Only the glare of the nearby Sun will prevent it from being visible to the naked eye. If you can find Venus, you can find the comet. Look low and southeast before sunrise. Comet Erasmus is in the constellation Hydra just to the right of Venus in neighbouring Virgo. The bright star Spica is nearby, too, providing another useful reference point.
MARS' ANCIENT MEGAFLOOD
Cornell University
Floods of unimaginable magnitude once washed through Gale Crater on Mars' equator around 4 billion years ago -- a finding that hints at the possibility that life may have existed there, according to data collected by NASA's Curiosity rover. The raging megaflood -- likely touched off by the heat of a meteoritic impact, which unleashed ice stored on the Martian surface -- set up gigantic ripples that are tell-tale geologic structures familiar to scientists on Earth. As is the case on Earth, geological features including the work of water and wind have been frozen in time on Mars for about 4 billion years. These features convey processes that shaped the surface of both planets in the past. This case includes the occurrence of giant wave-shaped features in sedimentary layers of Gale crater, often called "megaripples" or antidunes that are about 30-feet high and spaced about 450 feet apart. The antidunes are indicative of flowing megafloods at the bottom of Mars' Gale Crater about 4 billion years ago, which are identical to the features formed by melting ice on Earth about 2 million years ago. The most likely cause of the Mars flooding was the melting of ice from heat generated by a large impact, which released carbon dioxide and methane from the planet's frozen reservoirs. The water vapour and release of gases combined to produce a short period of warm and wet conditions on the red planet. Condensation formed water vapour clouds, which in turn created torrential rain, possibly planet-wide. That water entered Gale Crater, then combined with water coming down from Mount Sharp (in Gale Crater) produce gigantic flash floods that deposited the gravel ridges in the Hummocky Plains Unit and the ridge-and-trough band formations in the Striated Unit. The Curiosity rover science team has already established that Gale Crater once had persistent lakes and streams in the ancient past. These long-lived bodies of water are good indicators that the crater, as well as Mount Sharp within it, were capable of supporting microbial life. Early Mars was an extremely active planet from a geological point of view. The planet had the conditions needed to support the presence of liquid water on the surface -- and on Earth, where there's water, there's life.
16-YEAR-OLD COSMIC MYSTERY SOLVED
W. M. Keck Observatory
In 2004, scientists with NASA's space-based Galaxy Evolution Explorer (GALEX) spotted an object unlike any they'd seen before in our Milky Way galaxy: a large, faint blob of gas with a star at its centre. Though it doesn't actually emit light visible to the human eye, GALEX captured the blob in ultraviolet (UV) light and thus appeared blue in the images; subsequent observations also revealed a thick ring structure within it. So the team nicknamed it the Blue Ring Nebula. Over the next 16 years, they studied it with multiple Earth- and space-based telescopes, including W.M. Keck Observatory on Maunakea in Hawaii, but the more they learned, the more mysterious it seemed. A new study may have cracked the case. By applying cutting-edge theoretical models to the slew of data that has been collected on this object, the authors posit the nebula -- a cloud of gas in space -- is likely composed of debris from two stars that collided and merged into a single star. While merged star systems are thought to be fairly common, they are nearly impossible to study immediately after they form because they're obscured by debris kicked up by collision. Once the debris has cleared -- at least hundreds of thousands of years later -- they're challenging to identify because they resemble non-merged stars. The Blue Ring Nebula appears to be the missing link: astronomers are seeing the star system only a few thousand years after the merger, when evidence of the union is still plentiful. It appears to be the first known example of a merged star system at this stage. Operated between 2003 and 2013, GALEX was designed to help study the history of star formation by observing young star populations in UV light. Most objects seen by GALEX radiated both near-UV and far-UV, but the Blue Ring Nebula stood out because it emitted only far-UV light. The object's size was similar to that of a supernova remnant, which forms when a massive star runs out of fuel and explodes, or a planetary nebula, the puffed-up remains of a star the size of our Sun. But the Blue Ring Nebula had a living star at its centre. Furthermore, supernova remnants and planetary nebulas radiate in multiple light wavelengths outside the range, whereas the Blue Ring Nebula did not.
In 2006, the GALEX team looked at the nebula with the 5.1-meter Hale telescope at the Palomar Observatory in California, and then with the even more powerful 10-metre Keck Observatory telescopes. They found evidence of a shockwave in the nebula using Keck Observatory's Low Resolution Imaging Spectrometer suggesting the gas composing the Blue Ring Nebula had indeed been expelled by some kind of violent event around the central star. Data from Keck Observatory's High-Resolution Echelle Spectrometer (HIRES) also suggested the star was pulling a large amount of material onto its surface. But where was the material coming from? To gather more data, in 2012, the GALEX team used NASA's Wide-field Infrared Survey Explorer (WISE), a space telescope that studied the sky in infrared light, and identified a disk of dust orbiting closely around the star. Archival data from three other infrared observatories also spotted the disk. The finding didn't rule out the possibility that a planet was also orbiting the star, but eventually the team show that the disk and the material expelled into space came from something larger than even a giant planet. Then in 2017, the Hobby-Eberly Telescope in Texas confirmed there was no compact object orbiting the star.
More than a decade after discovering the Blue Ring Nebula, the team had gathered data on the system from four space telescopes, four ground-based historical observations of the star going back to 1895 (in order to look for changes in its brightness over time), and the help of citizen scientists through the American Association of Variable Star Observers (AAVSO). But an explanation for what had created the nebula still eluded them. The team concluded the nebula was the product of a relatively fresh stellar merger that likely occurred between a star to our Sun and another only about one tenth that size (or about 100 times the mass of Jupiter). Nearing the end of its life, the Sun-like star began to swell, creeping closer to its companion. Eventually, the smaller star fell into a downward spiral toward its larger companion. Along the way, the larger star tore the smaller star apart, wrapping itself in a ring of debris before swallowing the smaller star This was the violent event that led to the formation of the Blue Ring Nebula. The merger launched a cloud of hot debris into space that was sliced in two by the gas disk. This created two cone-shaped debris clouds, their bases moving away from the star in opposite directions and getting wider as they travel outward. The base of one cone is coming almost directly toward Earth and the other almost directly away. They are too faint to see alone, but the area where the cones overlap (as seen from Earth) forms the central blue ring GALEX observed. Millennia passed, and the expanding debris cloud cooled and formed molecules and dust, including hydrogen molecules that collided with the interstellar medium, the sparse collection of atoms and energetic particles that fill the space between stars. The collisions excited the hydrogen molecules, causing them to radiate in a specific wavelength of far-UV light. Over time, the glow became just bright enough for GALEX to see. Stellar mergers may occur as often as once every 10 years in our Milky Way galaxy, meaning it's possible that a sizeable population of the stars we see in the sky were once two.
BIRTH OF MAGNETSTAR POSSIBLY OBSERVED
Northwestern University
Long ago and far across the Universe, an enormous burst of gamma rays unleashed more energy in a half-second than the Sun will produce over its entire 10-billion-year lifetime. After examining the incredibly bright burst with optical, X-ray, near-infrared and radio wavelengths, an astrophysics team believes it potentially spotted the birth of a magnetar. Researchers believe the magnetar was formed by two neutron stars merging, which has never before been observed. The merger resulted in a brilliant kilonova -- the brightest ever seen -- whose light finally reached Earth on May 22, 2020. The light first came as a blast of gamma-rays, called a short gamma-ray burst. When two neutron stars merge, the most predicted outcome is that they form a heavy neutron star that collapses into a black hole within milliseconds or less. The study shows that it's possible that, for this particular short gamma-ray burst, the heavy object survived. Instead of collapsing into a black hole, it became a magnetar: A rapidly spinning neutron star that has large magnetic fields, dumping energy into its surrounding environment and creating the very bright that we see. After the light was first detected by NASA's Neil Gehrels Swift Observatory, scientists quickly enlisted other telescopes -- including NASA's Hubble Space Telescope, the Very Large Array, the W.M. Keck Observatory and the Las Cumbres Observatory Global Telescope network -- to study the explosion's aftermath and its host galaxy. Compared to X-ray and radio observations, the near-infrared emission detected with Hubble was much too bright. In fact, it was 10 times brighter than predicted. As the data were coming in, researchers were forming a picture of the mechanism that was producing the light they were seeing.
The information that Hubble added made the team realize it had to discard conventional thinking and that there was a new phenomenon going on. The team has discussed several possibilities to explain the unusual brightness -- known as a short gamma-ray burst -- that Hubble saw. Researchers think short bursts are caused by the merger of two neutron stars, extremely dense objects about the mass of the Sun compressed into the volume of a large city like Chicago. While most short gamma-ray bursts probably result in a black hole, the two neutron stars that merged in this case may have combined to form a magnetar, a supermassive neutron star with a very powerful magnetic field. Basically there are magnetic field lines that are anchored to the star that are whipping around at about 1,000 times a second, and this produces a magnetized wind. These spinning field lines extract the rotational energy of the neutron star formed in the merger, and deposit that energy into the ejecta from the blast, causing the material to glow even brighter. We know that magnetars exist because we see them in our galaxy. Researchers think most of them are formed in the explosive deaths of massive stars, leaving these highly magnetized neutron stars behind. However, it is possible that a small fraction form in neutron star mergers. We have never seen evidence of that before, let alone in infrared light, making this discovery special. Kilonovae, which are typically 1,000 times brighter than a classic nova, are expected to accompany short gamma-ray bursts. Unique to the merger of two compact objects, kilonovae glow from the radioactive decay of heavy elements ejected during the merger, producing coveted elements like gold and uranium. Only one confirmed kilonova has been identified to date so it is especially exciting to find a new potential kilonova that looks so different. If the unexpected brightness seen by Hubble came from a magnetar that deposited energy into the kilonova material, then, within a few years, the ejected
material from the burst will produce light that shows up at radio wavelengths. Follow-up radio observations may ultimately prove that this was a magnetar, leading to an explanation of the origin of such objects.
FAMILY TREE OF MILKY WAY DECIPHERED
RAS
Scientists have known for some time that galaxies can grow by the merging of smaller galaxies, but the ancestry of our own Milky Way galaxy has been a long-standing mystery. Now, an international team of astrophysicists has succeeded in reconstructing the first complete family tree of our home galaxy by analysing the properties of globular clusters orbiting the Milky Way with artificial intelligence. Globular clusters are dense groups of up to a million stars that are almost as old as the Universe itself. The Milky Way hosts over 150 such clusters, many of which formed in the smaller galaxies that merged to form the galaxy that we live in today. Astronomers have suspected for decades that the old ages of globular clusters would mean that they could be used as “fossils” to reconstruct the early assembly histories of galaxies. However it is only with the latest models and observations that it has become possible to realise this promise. An international team of researchers has now managed to infer the Milky Way’s merger history and reconstruct its family tree, using only its globular clusters. To achieve this, they developed a suite of advanced computer simulations of the formation of Milky Way-like galaxies. Their simulations, called E-MOSAICS, are unique because they include a complete model for the formation, evolution, and destruction of globular clusters. In the simulations, the researchers were able to relate the ages, chemical compositions, and orbital motions of globular clusters to the properties of the progenitor galaxies in which they formed, more than 10 billion years ago. By applying these insights to groups of globular clusters in the Milky Way, they could not only determine how many stars these progenitor galaxies contained, but also when they merged into the Milky Way. The main challenge of connecting the properties of globular clusters to the merger history of their host galaxy has always been that galaxy assembly is an messy process, during which the orbits of the globular clusters are completely reshuffled. To make sense of the complex system that is left today, scientists trained an artificial neural network on the E-MOSAICS simulations to relate the globular cluster properties to the host galaxy merger history. They tested the algorithm tens of thousands of times on the simulations and were amazed at how accurately it was able to reconstruct the merger histories of the simulated galaxies, using only their globular cluster populations.
Inspired by this success, the researchers set out to decipher the merger history of the Milky Way. To achieve this, they used groups of globular clusters that are each thought to have formed in the same progenitor galaxy based on their orbital motion. By applying the neural network to these groups of globular clusters, the researchers could not only predict the stellar masses and merger times of the progenitor to high precision, but it also revealed a previously unknown collision between the Milky Way
and an enigmatic galaxy, which the researchers named “Kraken”.The collision with Kraken must have been the most significant merger the Milky Way ever experienced. Before, it was thought that a collision with the Gaia-Enceladus-Sausage galaxy, which took place some 9 billion years ago, was the biggest collision event. However, the merger with Kraken took place 11 billion years ago, when the Milky Way was four times less massive. As a result, the collision with Kraken must have truly transformed what the Milky Way looked like at the time. Taken together, these findings allowed the team of researchers to reconstruct the first complete merger tree of our Galaxy. Over the course of its history, the Milky Way cannibalised about five galaxies with more than 100 million stars, and about fifteen with at least 10 million stars. The most massive progenitor galaxies collided with the Milky Way
between 6 and 11 billion years ago. The researchers expect their predictions to stimulate future studies to search for the remains of these progenitor galaxies. The debris of more than five progenitor galaxies has now been identified. With current and upcoming telescopes, it should be possible to find them all.
DARK MATTER FROM DEPTHS OF UNIVERSE
Johannes Gutenberg Universitaet Mainz
Cataclysmic astrophysical events such as black hole mergers could release energy in unexpected forms. Exotic low-mass fields (ELFs), for example, could propagate through space and cause feeble signals detectable with quantum sensor networks such as the atomic clocks of the GPS network or the magnetometers of GNOME network. These are the results of theoretical calculations undertaken by a research group. They are particularly interesting in the context of the search for dark matter, as low-mass fields are regarded as promising candidates for this exotic form of matter. Multi-messenger astronomy involves the coordinated observation of disparate signals that stem from the same astrophysical event. Since the first detection of gravitational waves with the LIGO interferometer several years ago, the interest in this field has expanded enormously and it has yielded a tremendous amount of new information originating from the depths of the Universe. When gravitational waves are generated somewhere in space and detected on Earth, numerous telescopes now focus on the event to record various signals, such as those in the form of electromagnetic radiation, for instance. The group wanted to know what would happen if part of the observed energy released by such events
was also radiated in the form of exotic low-mass fields or ELFs. Would they be detectable with existing networks of quantum sensors?
The scientists' calculations have confirmed that this could be the case for certain parameters. They also reasoned that such fields, when radiated, would cause a characteristic frequency signature in the networks. The signal would be similar to the sound of a passing siren, sweeping from high to low frequencies. researchers have two particular networks in mind: the worldwide GPS network atomic clocks and the GNOME network, which is comprised of a multitude of magnetometers distributed around the globe. On the basis of the expected strength of the signal, the GPS system should currently be sensitive enough to detect ELFs. Scientists are currently upgrading the GNOME network, and on completion this should also be sensitive enough to observe such events. Potential ELFs are of particular significance in the search for dark matter. Although we know this strange form of matter must exist, nobody yet knows what it is made of. Specialists considering and researching a whole range of possible particles that might theoretically qualify as candidates. Among the most promising current candidates are extremely light bosonic particles, which can also be seen in terms of a classic field oscillating at a particular frequency. Thus, in the depths of the Universe, dark matter in the form of ELFs may be created during the merger of two black holes. Precision quantum sensor networks, in turn, could function as ELF telescopes, adding another important element to the toolbox of multi-messenger astronomy.
BUILDING BLOCKS OF LIFE CAN FORM BEFORE STARS
Queen Mary University of London
An international team of scientists have shown that glycine, the simplest amino acid and an important building block of life, can form under the harsh conditions that govern chemistry in space. The results suggest that glycine, and very likely other amino acids, form in dense interstellar clouds well before they transform into new stars and planets. Comets are the most pristine material in our Solar System and reflect the molecular composition present at the time our Sun and planets were just about to form. The detection of glycine in the coma of comet 67P/Churyumov-Gerasimenko and in samples returned to Earth from the Stardust mission suggests that amino acids, such as glycine, form long before stars. However until recently, it was thought that glycine formation required energy, setting clear constraints to the environment in which it can be formed. In the new study the international team of astrophysicists and astrochemical modellers, has shown that it is possible for glycine to form on the surface of icy dust grains, in the absence of energy, through 'dark chemistry'. The findings contradict previous studies that have suggested UV radiation was required to produce this molecule. Dark chemistry refers to chemistry without the need of energetic radiation. In the laboratory scientists were able to simulate the conditions in dark interstellar clouds where cold dust particles are covered by thin layers of ice and subsequently processed by impacting atoms causing precursor species to fragment and reactive intermediates to recombine. The scientists first showed methylamine, the precursor species of glycine that was detected in the coma of the comet 67P, could form. Then, using a unique ultra-high vacuum setup, equipped with a series of atomic beam lines and accurate diagnostic tools, they were able to confirm glycine could also be formed, and that the presence of water ice was essential in this process.
investigation using astrochemical models confirmed the experimental results and allowed the researchers to extrapolate data obtained on a typical timescale of just one day to interstellar conditions, bridging millions of years. From this they found that low but substantial amounts of glycine can be formed in space with time. The important conclusion from this work is that molecules that are considered building blocks of life already form at a stage that is well before the start of star and planet
formation. Such an early formation of glycine in the evolution of star-forming regions implies that this amino acid can be formed more ubiquitously in space and is preserved in the bulk of ice before inclusion in comets and planetesimals that make up the material from which ultimately planets are made. Once formed, glycine can also become a precursor to other complex organic molecules. Following the same mechanism, in principle, other functional groups can be added to the glycine backbone, resulting in the formation of other amino acids, such as alanine and serine in dark clouds in space. In the end, this enriched organic molecular inventory is included in celestial bodies, like comets, and delivered to young planets, as happened to our Earth and many other planets.
Topic: Late November Astronomy Bulletin (Read 1412 times)