GEOMAGNETIC STORM BRINGS DOWN STARLINK SATELLITES
Spaceweather.com
As many as 40 Starlink satellites are currently falling out of the sky--the surprising result of a minor geomagnetic storm. Two days before launch a CME hit Earth's magnetic field. It was not a major space weather event. In fact, the weak impact did not at first spark any remarkable geomagnetic activity. However, as Earth passed through the CME's wake, some sputtering G1-class geomagnetic storms developed. It was one of these minor storms that caught the Starlink satellites on Feb. 4th. Geomagnetic storms heat Earth's upper atmosphere. Diaphanous tendrils of warming air literally reached up and grabbed the Starlink satellites. According to SpaceX, onboard GPS devices detected atmospheric drag increasing "up to 50 percent higher than during previous launches." "The Starlink team commanded the satellites into a safe-mode where they would fly edge-on (like a sheet of paper) to minimize drag," says SpaceX. "Preliminary analysis show the increased drag at the low altitudes prevented the satellites from leaving safe-mode to begin orbit raising maneuvers, and up to 40 of the satellites will reenter or already have reentered the Earth’s atmosphere." The Sociedad de Astronomia del Caribe apparently caught one of the reentries over Puerto Rico on Feb. 7th: SpaceX says that the deorbiting satellites "pose zero collision risk with other satellites and by design demise upon atmospheric reentry—meaning no orbital debris is created and no satellite parts hit the ground."
7 BILLION -YEAR-OLD STARDUST FOUND ON EARTH
Field Museum.
Scientists recently identified the oldest material on Earth: stardust that's 7 billion years old, tucked away in a massive, rocky meteorite that struck our planet half a century ago. Stars have life cycles. They're born when bits of dust and gas floating through space find each other and collapse in on each other and heat up. They burn for millions to billions of years, and then they die. When they die, they pitch the particles that formed in their winds out into space, and those bits of stardust eventually form new stars, along with new planets and moons and meteorites. And in a meteorite that fell fifty years ago in Australia, scientists have now discovered stardust that formed 5 to 7 billion years ago -- the oldest solid material ever found on Earth. The materials the team examined are called presolar grains-minerals formed before the Sun was born. These bits of stardust became trapped in meteorites where they remained unchanged for billions of years, making them time capsules of the time before the solar system. But presolar grains are hard to come by. They're rare, found only in about five percent of meteorites that have fallen to Earth, and they're tiny-a hundred of the biggest ones would fit on the period at the end of this sentence. The Field Museum has the largest portion of the Murchison meteorite, a treasure trove of presolar grains that fell in Australia in 1969 and that the people of Murchison, Victoria, made available to science. Presolar grains for this study were isolated from the Murchison meteorite for this study about 30 years ago at the University of Chicago. Once the presolar grains were isolated, the researchers figured out from what types of stars they came and how old they were. They used exposure age data, which basically measures their exposure to cosmic rays, which are high-energy particles that fly through our galaxy and penetrate solid matter. Some of these cosmic rays interact with the matter and form new elements. And the longer they get exposed, the more those elements form.
The researchers learned that some of the presolar grains in their sample were the oldest ever discovered-based on how many cosmic rays they'd soaked up, most of the grains had to be 4.6 to 4.9 billion years old, and some grains were even older than 5.5 billion years. For context, our Sun is 4.6 billion years old, and Earth is 4.5 billion. But the age of the presolar grains wasn't the end of the discovery. Since presolar grains are formed when a star dies, they can tell us about the history of stars. And 7 billion years ago, there was apparently a bumper crop of new stars forming-a sort of astral baby boom. This finding is ammo in a debate between scientists about whether or not new stars form at a steady rate, or if there are highs and lows in the number of new stars over time. As almost a side note to the main research questions, in examining the way that the minerals in the grains interacted with cosmic rays, the researchers also learned that presolar grains often float through space stuck together in large clusters.
DID COMET LEAD TO DEMISE OF ANCIENT CULTURE? :
University of Cincinnati
The rapid decline of the Hopewell culture about 1,500 years ago might be explained by falling debris from a near-Earth comet that created a devastating explosion over North America, laying waste to forests and Native American villages alike. Researchers found evidence of a cosmic airburst at 11 Hopewell archaeological sites in three states stretching across the Ohio River Valley. This was home to the Ohio Hopewell, part of a notable Native American culture found across much of the American East. The comet's glancing pass rained debris down into the Earth's atmosphere, creating a fiery explosion. UC archaeologists used radiocarbon and typological dating to determine the age of the event. The airburst affected an area bigger than New Jersey, setting fires across 9,200 square miles between the years A.D. 252 and 383. This coincides with a period when 69 near-Earth comets were observed and documented by Chinese astronomers and witnessed by Native Americans as told through their oral histories. Archaeologists found an unusually high concentration and diversity of meteorites at Hopewell sites compared to other time periods. The meteorite fragments were identified from the telltale concentrations of iridium and platinum they contained. They also found a charcoal layer that suggests the area was exposed to fire and extreme heat.
Stony meteorites called pallasites, were found at Hopewell sites. These micrometeorites have a chemical fingerprint. Cosmic events like asteroids and comet airbursts leave behind high quantities of platinum. The problem is platinum also occurs in volcanic eruptions. So scientists also look for another element found in nonterrestrial events such as meteorite impact craters -- iridium. And they found a spike in both, iridium and platinum. The Hopewell people collected the meteorites and forged malleable metal from them into flat sheets used in jewellry and musical instruments called pan flutes. Beyond the physical evidence are cultural clues left behind in the masterworks and oral histories of the Hopewell. A comet-shaped mound was constructed near the epicenter of the airburst at a Hopewell site called the Milford Earthworks. Various Algonquin and Iroquoian tribes, descendants of the Hopewell, spoke of a calamity that befell the Earth. The Miami tell of a horned serpent that flew across the sky and dropped rocks onto the land before plummeting into the river. When you see a comet going through the air, it would look like a large snake, The Shawnee refer to a 'sky panther' that had the power to tear down forest. The Ottawa talk of a day when the Sun fell from the sky. And when a comet hits the thermosphere, it would have exploded like a nuclear bomb. That's a lot like the description the Russians gave for Tunguska when a comet airburst documented over Siberia in 1908 that levelled 830 square miles of forest and shattered windows hundreds of miles away. Witnesses reported seeing a fireball, a bluish light nearly as bright as the Sun, moving across the sky. A flash and sound similar to artillery fire was said to follow it. A powerful shockwave broke windows hundreds of miles away and knocked people off their feet. It looks like this event was very injurious to agriculture. People didn't have good ways to store corn for a long period of time. Losing a crop or two would have caused widespread suffering. And if the airburst levelled forests like the one in Russia, native people would have lost nut trees such as walnut and hickory that provided a good winter source of food.
NEW EARTH TROJAN ASTEROID
University of Barcelona
A team of astronomers has confirmed the existence of the second Earth Trojan asteroid known to date, the 2020 XL5, after a decade of search. All celestial objects that roam around our solar system feel the gravitational influence of all the other massive bodies that build it, including the Sun and the planets. If we consider only the Earth-Sun system, Newton's laws of gravity state that there are five points where all the forces that act upon an object located at that point cancel each other out. These regions are called Lagrangian points, and they are areas of great stability. Earth Trojan asteroids are small bodies that orbit around the L4 or L5 Lagrangian points of the Sun-Earth system. These results confirm that 2020 XL5 is the second transient Earth Trojan asteroid known to date, and everything indicates it will remain Trojan -- that is, it will be located at the Lagrangian point -- for four thousand years, thus it is qualified as transient. The researchers have provided an estimation of the object bulk size around one kilometre in diameter, larger than the Earth Trojan asteroid known to date, the 2010 TK7, which was 0.3 kilometres in diameter), and have made a study of the impulse a rocket needs to reach the asteroid from Earth. Although Trojan asteroids have been known to exist for decades in other planets such as Venus, Mars, Jupiter, Uranus and Neptune, it was not until 2011 that the first Earth Trojan asteroid was found. The astronomers have described many observational strategies for the detection of new Earth Trojans.
There have been many previous attempts to find Earth Trojans, including in situ surveys such as the search within the L4 region, carried out by the NASA OSIRIS-Rex spacecraft, or the search within the L5 region, conducted by the JAXA Hayabusa-2 mission. all the dedicated efforts had so far failed to discover any new member of this population but the low success in these searches can be explained by the geometry of an object orbiting the Earth-Sun L4 or L5 as seen from our planet. These objects are usually observable close to the Sun. The observation time window between the asteroid rising above the horizon and sunrise is, therefore, very small. Therefore, astronomers point their telescopes very low on the sky where the visibility conditions are at their worst and with the handicap of the imminent sunlight saturating the background light of the images just a few minutes in the observation. To solve this problem, the team carried out a search of 4-meter telescopes that would be able to observe under such conditions, and they finally obtained the data from the 4.3m Lowel Discovery telescope (Arizona, United States), and the 4.1m SOAR telescope, operated by the National Science Foundation NOIRLab (Cerro Pachón, Chile). The discovery of the Earth Trojan asteroids is very significant because these can hold a pristine record on the early conditions in the formation of the Solar System, since the primitive trojans might have been co-orbiting the planets during their formation, and they add restrictions to the dynamic evolution of the Solar System. In addition, Earth Trojans are the ideal candidates for potential space missions in the future. Since the L4 Lagrangian point shares the same orbit as the Earth, it takes a low change in velocity to be reached. This implies that a spacecraft would need a low energy budget to remain in its shared orbit with the Earth, keeping a fixed distance to it. Earth Trojans could become ideal bases for an advanced exploration of the Solar System; they could even become a source of resources.
MOONS MAY MAKE PLANETS HABITABLE
University of Rochester
Earth's Moon is vitally important in making Earth the planet we know today: the Moon controls the length of the day and ocean tides, which affect the biological cycles of lifeforms on our planet. The Moon also contributes to Earth's climate by stabilizing Earth's spin axis, offering an ideal environment for life to develop and evolve. Because the Moon is so important to life on Earth, scientists conjecture that a moon may be a potentially beneficial feature in harbouring life on other planets. Most planets have moons, but Earth's Moon is distinct in that it is large compared to the size of Earth; the Moon's radius is larger than a quarter of Earth's radius, a much larger ratio than most moons to their planets. Many scientists have historically believed Earth's large moon was generated by a collision between proto-Earth -- Earth at its early stages of development -- and a large, Mars-sized impactor, approximately 4.5 billion years ago. The collision resulted in the formation of a partially vaporized disk around Earth, which eventually formed into the Moon. In order to find out whether other planets can form similarly large moons, astronomers conducted impact simulations on the computer, with a number of hypothetical Earth-like rocky planets and icy planets of varying masses. They hoped to identify whether the simulated impacts would result in partially vaporized disks, like the disk that formed Earth's Moon.
The researchers found that rocky planets larger than six times the mass of Earth (6M) and icy planets larger than one Earth mass (1M) produce fully -- rather than partially -- vaporized disks, and these fully-vaporized disks are not capable of forming fractionally large moons. After an impact that results in a vaporized disk, over time, the disk cools and liquid moonlets -- a moon's building blocks -- emerge. In a fully-vaporized disk, the growing moonlets in the disk experience strong gas drag from vapor, falling onto the planet very quickly. In contrast, if the disk is only partially vaporized, moonlets do not feel such strong gas drag. The constraints outlined by the team are important for astronomers investigating our Universe; researchers have detected thousands of exoplanets and possible exomoons, but have yet to definitively spot a moon orbiting a planet outside our solar system. The exoplanet search has typically been focused on planets larger than six earth masses. We are proposing that instead we should look at smaller planets because they are probably better candidates to host fractionally large moons.
DYING STARS CAN GIVE BIRTH TO PLANETS
KU Leuven
Planets such as Earth, and all other planets in our solar system, were formed not long after the Sun. Our Sun started to burn 4.6 billion years ago, and in the next million years, the matter around it clumped into protoplanets. The birth of the planets in that protoplanetary disc, a gigantic pancake made of dust and gas, so to speak, with the Sun in the middle, explains why they all orbit in the same plane. But such discs of dust and gas needn't necessarily only surround newborn stars. They can also develop independently from star formation, for example around binary stars of which one is dying (binary stars are two stars that orbit each other, also called a binary system). When the end approaches for a medium-sized star (like the Sun), it catapults the outer part of its atmosphere into space, after which it slowly dies out as a so-called white dwarf. However, in the case of binary stars, the gravitational pull of the second star causes the matter ejected by the dying star to form a flat, rotating disc. Moreover, this disc strongly resembles the protoplanetary discs that astronomers observe around young stars elsewhere in the Milky Way. This we already knew. However, what is new is that the discs surrounding so-called evolved binary stars not uncommonly show signs that could point to planet formation. What's more, observations show that this is the case for one in ten of these binary stars. The clean-up of the matter could be the work of a planet. That planet might not have formed at the very beginning of one of the binary stars' life, but at the very end. The astronomers moreover found further strong indications for the presence of such planets.
In the evolved binary stars with a large cavity in the disc, astronomers saw that heavy elements such as iron were very scarce on the surface of the dying star. This observation leads one to suspect that dust particles rich in these elements were trapped by a planet.The discovery was made when the astronomers were drawing up an inventory of evolved binary stars in our Milky Way. They did that based on existing, publicly available observations. The team counted 85 of such binary star pairs. In ten pairs, the researchers came across a disc with a large cavity on the infrared images. If new observations confirm the existence of planets around evolved binary stars, and if it turns out the planets were only formed after one of the stars had reached the end of its life, the theories on planet formation will need to be adjusted. The KU Leuven astronomers soon want to verify their hypothesis themselves. To this end, they will use the big telescopes of the European Southern Observatory in Chile to take a closer look at the ten pairs of binary stars whose discs show a large cavity.
IMMINENT COLLISION OF GIANT BLACK HOLES PREDICTED
Goddard Space Center
In the centre of a galaxy 1.2 billion light-years from Earth, astronomers say they have seen signs that two giant black holes, with a combined mass of hundreds of millions of Suns, are gearing up for a cataclysmic merger as soon as 100 days from now. The event, if it happens, would be momentous for astronomy, offering a glimpse of a long-predicted, but never witnessed mechanism for black hole growth. It might also unleash an explosion of light across the electromagnetic spectrum, as well as a surge of gravitational waves and ghostly particles called neutrinos that could reveal intimate details of the collision. Astronomers, eager to confirm the tantalizing signals, rushed to secure telescope observing time. , says team member Huan Yang of the Perimeter Institute in Waterloo, Canada. But the prediction may be a mirage. It’s not clear that the observed galaxy holds a pair of black holes, let alone a pair that’s about to merge. Supermassive black holes are thought to lurk at the heart of most, if not all, galaxies, but theorists don’t know how they grow so big. Some sporadically suck in surrounding material, fiercely heating it and causing the galaxy to shine brightly as a so-called active galactic nucleus (AGN). But the trickle of material may not be enough to account for the black holes’ bulk. They could gain weight more quickly through mergers: After galaxies collide, their central black holes become gravitationally bound and they gradually spiral together.
Such black hole pairs are not easy to detect. X-ray telescopes have discovered a handful of AGNs with two bright, separated central sources, but the putative black holes are hundreds of light-years apart and wouldn’t collide for billions of years. Once they get closer, it’s almost impossible to separate their light with a telescope. But some AGNs regularly dim and brighten, which astronomers have recently argued is a sign they harbour pairs of black holes orbiting each other that regularly churn and heat the surrounding material. Some of these periodic oscillations have faded, however, calling into question the binary interpretation. In data from a survey telescope in California called the Zwicky Transient Facility (ZTF), scientists stumbled on a periodic AGN called SDSSJ1430+2303. Then, the researchers found: a trend they interpret as a binary pair closing in on a merger. The cycles were getting shorter, going from 1 year to 1 month in the space of 3 years. It is “the first official report of decaying periods which reduced over time. The researchers confirmed the monthlong oscillation in x-ray observations from NASA’s orbiting Neil Gehrels Swift Observatory. If this decreasing trend continues, the black holes, which Jiang says come as close to each other as the Sun is to Pluto, will merge in the next 100 to 300 days. If the merger comes to pass, observers could have a field day. There should be a huge burst across the electromagnetic spectrum, from gamma rays to radio. Some also expect a flood of neutrinos, which the IceCube detector at the South Pole—1 cubic kilometer of polar ice outfitted with light sensors to detect neutrino impacts—could pick up. Neither, however, is certain. Some predict a whimper rather than a bang. The only certain signal is gravitational waves, but the ponderous colliding masses would emit them at too low a frequency to be picked up by detectors such as the Laser Interferometer Gravitational-Wave Observatory, which is tuned to smaller mergers. They should, however, leave an imprint on spacetime itself, a sort of relaxation of distance and time dubbed gravitational wave memory, which could be detected over many years by monitoring the metronomic pulses of spinning stellar remnants known as pulsars. Observations in the coming months should show whether the oscillation continues to shorten. Andrew Fabian of the University of Cambridge is among the astronomers who will be chasing the will o’ the wisp, having applied for time on NASA’s Neutron star Interior Composition Explorer, an x-ray telescope attached to the International Space Station. “If this is true, then it’s important to get as many observations as possible now to see what it’s doing,” he says. Fabian says the chance of such a merger taking place so close to Earth in any given year is one in 10,000. He’s skeptical that one is imminent, but says it’s worth monitoring for a few months to see whether the claim holds up. “Rare events do happen,” he says.
1,000 MYSTERIOUS STRANDS IN MILKY WAY CENTRE
Northwestern University
An unprecedented new telescope image of the Milky Way galaxy's turbulent centre has revealed nearly 1,000 mysterious strands, inexplicably dangling in space. Stretching up to 150 light years long, the one-dimensional strands (or filaments) are found in pairs and clusters, often stacked equally spaced, side by side like strings on a harp. Using observations at radio wavelengths, scientists discovered the highly organized, magnetic filaments in the early 1980s. The mystifying filaments, he found, comprise cosmic ray electrons gyrating the magnetic field at close to the speed of light. But their origin has remained an unsolved mystery ever since. Now, the new image has exposed 10 times more filaments than previously discovered, enabling the team to conduct statistical studies across a broad population of filaments for the first time. This information potentially could help them finally unravel the long-standing mystery. To construct the image with unprecedented clarity and detail, astronomers spent three years surveying the sky and analyzing data at the South African Radio Astronomy Observatory (SARAO). Using 200 hours of time on SARAO's MeerKAT telescope, researchers pieced together a mosaic of 20 separate observations of different sections of the sky toward the centre of the Milky Way galaxy, 25,000 light years from Earth. To view the filaments at a finer scale, the team used a technique to remove the background from the main image in order to isolate the filaments from the surrounding structures. The resulting picture astounded him.
While many mysteries surrounding the filaments remain, the team has been able to piece together more of the puzzle. In their latest paper, collaborators specifically explored the filaments' magnetic fields and the role of cosmic rays in illuminating the magnetic fields. The variation in radiation emitting from the filaments is very different from that of the newly uncovered supernova remnant, suggesting that the phenomena have different origins. It is more likely, the researchers found, that the filaments are related to past activity of the Milky Way's central supermassive black hole rather than coordinated bursts of supernovae. The filaments also could be related to enormous, radio-emitting bubbles, which were discovered in 2019. And, while it was already known the filaments are magnetized, now we can say magnetic fields are amplified along the filaments, a primary characteristic all the filaments share. Astronomers are particularly puzzled by how structured the filaments appear. Filaments within clusters are separated from one another at perfectly equal distances -- about the distance from Earth to the Sun. They almost resemble the regular spacing in solar loops. We still don't know why they come in clusters or understand how they separate, and we don't know how these regular spacings happen. Every time we answer one question, multiple other questions arise. The team also still don't know whether the filaments move or change over time or what is causing the electrons to accelerate at such incredible speeds. Researchers are currently identifying and cataloguing each filament. The angle, curve, magnetic field, spectrum and intensity of each filament will be published in a future study. Understanding these properties will give the astrophysics community more clues into the filaments' elusive nature. The MeerKAT telescope, which launched in July 2018, will continue to unveil new secrets.
TEMPERATURE OF YOUNG UNIVERSE REVEALED
University of Cologne
A group of astrophysicists has discovered a new method to estimate the cosmic microwave background temperature of the young Universe only 880 million years after the Big Bang. It is the first time that the temperature of the cosmic microwave background radiation -- a relic of the energy released by the Big Bang -- has been measured at such an early epoch of the Universe. The prevailing cosmological model assumes that the Universe has cooled off since the Big Bang -- and still continues to do so. The model also describes how the cooling process should proceed, but so far it has only been directly confirmed for relatively recent cosmic times. The discovery not only sets a very early milestone in the development of the cosmic background temperature, but could also have implications for the enigmatic dark energy. The scientists used the NOEMA (Northern Extended Millimeter Array) observatory in the French Alps, the most powerful radio telescope in the Northern Hemisphere, to observe HFLS3, a massive starburst galaxy at a distance corresponding to an age of only 880 million years after the Big Bang. They discovered a screen of cold water gas that casts a shadow on the cosmic microwave background radiation. The shadow appears because the colder water absorbs the warmer microwave radiation on its path towards Earth, and its darkness reveals the temperature difference. As the temperature of the water can be determined from other observed properties of the starburst, the difference indicates the temperature of the Big Bang's relic radiation, which at that time was about seven times higher than in the Universe today.
Besides proof of cooling, this discovery also shows us that the Universe in its infancy had some quite specific physical characteristics that no longer exist today. Quite early, about 1.5 billion years after the Big Bang, the cosmic microwave background was already too cold for this effect to be observable. We have therefore a unique observing window that opens up to a very young Universe only. In other words, if a galaxy with otherwise identical properties as HFLS3 were to exist today, the water shadow would not be observable because the required contrast in temperatures would no longer exist. This important milestone not only confirms the expected cooling trend for a much earlier epoch than has previously been possible to measure, but could also have direct implications for the nature of the elusive dark energy. Dark energy is thought to be responsible for the accelerated expansion of the Universe over the past few billion years, but its properties remain poorly understood because it cannot be directly observed with the currently available facilities and instruments. However, its properties influence the evolution of cosmic expansion, and hence the cooling rate of the Universe over cosmic time. Based on this experiment, the properties of dark energy remain -- for now -- consistent with those of Einstein's 'cosmological constant'. 'That is to say, an expanding Universe in which the density of dark energy does not change. Having discovered one such cold water cloud in a starburst galaxy in the early Universe, the team is now setting out to find many more across the sky. Their aim is to map out the cooling of the Big Bang echo within the first 1.5 billion years of cosmic history. 'This new technique provides important new insights into the evolution of the Universe, which are very difficult to constrain otherwise at such early epochs.
Topic: Mid February Astronomy Bulletin (Read 939 times)