SPACECRAFT HAS ‘TOUCHED’ SUN FOR FIRST TIME
American Physical Society
NASA's Parker Solar Probe reached the Sun's extended solar atmosphere, known as the corona, and spent five hours there. The spacecraft is the first to enter the outer boundaries of our Sun. The probe made the first direct observations of what lies within the Sun's atmosphere, measuring phenomena previously only estimated. The Sun's outer edge begins at the Alfvén critical surface: the point below which the Sun and its gravitational and magnetic forces directly control the solar wind. Many scientists think that sudden reverses in the Sun's magnetic field, called switchbacks, emerge from this area. In 2018, NASA launched Parker Solar Probe with the goal of finally reaching the Sun's corona and making humanity's first visit to a star. This past April, the probe spent five hours below the Alfvén critical surface in direct contact with the Sun's plasma. Below that surface, the pressure and energy of the Sun's magnetic field was stronger than the pressure and energy of the particles. The spacecraft passed above and below the surface three separate times during its encounter. This is the first time a spacecraft has entered the solar corona and touched the atmosphere of the Sun. Surprisingly, the researchers discovered that the Alfvén critical surface is wrinkled. The data suggest that the largest and most distant wrinkle of the surface was produced by a pseudostreamer -- a large magnetic structure more than 40 degrees across, found back on the innermost visible face of the Sun. It is not currently known why a pseudostreamer would push the Alfvén critical surface away from the Sun. Researchers noticed far fewer switchbacks below the Alfvén critical surface than above it. The finding could mean that switchbacks do not form within the corona. Alternatively, low rates of magnetic reconnection on the Sun's surface could have pumped less mass into the observed wind stream, resulting in fewer switchbacks.
The probe also recorded some evidence of a potential power boost just inside the corona, which may point to unknown physics affecting heating and dissipation. The observations took place during Parker Solar Probe's eighth encounter with the Sun. All data is publicly available in the NASA PSP archive. Several previous studies predicted the probe would first pass within the Sun's boundaries in 2021. The fastest known object built by humans, Parker Solar Probe has made many new discoveries since its launch, including on explosions that create space weather and the dangers of super-speedy dust. The new findings suggest that direct observations by spacecraft have much to illuminate about the physics of coronal heating and solar wind formation. Having achieved its goal of touching the Sun, Parker Solar Probe will now descend even deeper into the Sun's atmosphere and linger for longer periods of time.
WHY COMET HEADS CAN BE GREEN BUT NEVER THEIR TAILS
University of New South Wales
Every so often, the Kuiper Belt and Oort Cloud throw galactic snowballs made up of ice, dust and rocks our way: 4.6-billion-year-old leftovers from the formation of the solar system. These snowballs -- or as we know them, comets -- go through a colourful metamorphosis as they cross the sky, with many comets' heads turning a radiant green colour that gets brighter as they approach the Sun. But strangely, this green shade disappears before it reaches the one or two tails trailing behind the comet. Astronomers, scientists and chemists have been puzzled by this mystery for almost a century. In the 1930s, physicist Gerhard Herzberg theorised the phenomenon was due to sunlight destroying diatomic carbon (also known as dicarbon or C2), a chemical created from the interaction between sunlight and organic matter on the comet's head -- but as dicarbon isn't stable, this theory has been hard to test. A new study has finally found a way to test this chemical reaction in a laboratory -- and in doing so, has proven this 90-year-old theory correct. The key player at the centre of the mystery, dicarbon, is both highly reactive and responsible for giving many comets their green colour. It's made up of two carbon atoms stuck together and can only be found in extremely energetic or low oxygen environments like stars, comets and the interstellar medium. Dicarbon doesn't exist on comets until they get close to the Sun. As the Sun starts to warm the comet up, the organic matter living on the icy nucleus evaporates and moves to the coma. Sunlight then breaks up these larger organic molecules, creating dicarbon. The team has now shown that as the comet gets even closer to the Sun, the extreme UV radiation breaks apart the dicarbon molecules it recently created in a process called 'photodissociation'. This process destroys the dicarbon before it can move far from the nucleus, causing the green coma to get brighter and shrink -- and making sure the green tinge never makes it into the tail. This is the first time this chemical interaction has been studied here on Earth. Dicarbon comes from the breakup of larger organic molecules frozen into the nucleus of the comet -- the sort of molecules that are the ingredients of life. By understanding its lifetime and destruction, we can better understand how much organic material is evaporating off comets. Discoveries like these might one day help us solve other space mysteries. To solve this puzzle, the team needed to recreate the same galactic chemical process in a controlled environment on Earth. They pulled this off with the help of a vacuum chamber, a lot of lasers, and one powerful cosmic reaction.
First the team had to make this molecule which is too reactive to store in a bottle. It did this by taking a larger molecule, known as perchloroethylene or C2Cl4, and blasting off its chlorine atoms (Cl) with a high-powered UV laser. The newly-made dicarbon molecules were sent travelling through a gas beam in a vacuum chamber, which was around two metres long. The team then pointed another two UV lasers towards the dicarbon: one to flood it with radiation, the other to make its atoms detectable. The radiation hit ripped the dicarbon apart, sending its carbon atoms flying onto a speed detector. By analysing the speed of these quickly-moving atoms, the team could measure the strength of the carbon bond to about one in 20,000 -- which is like measuring 200 metres to the nearest centimetre. There are around 3700 known comets in the solar system, although it's suspected there could be billions more. On average, a comet's nucleus is a whopping 10 kilometres wide -- but its coma is often 1000 times bigger. Bright comets can put on spectacular shows for those lucky enough to see them. But in the past, comets might have done more than that for Earth -- in fact, one of the theories about the origin of life is that comets once delivered the building blocks of life right to our doorstep. Early Earth would have experienced a jumble of different carbon-bearing molecules being delivered to its surface, allowing for even more complex reactions to occur in the leadup to life. Now that the case of the missing green tail in comets is solved, Prof. Schmidt, who specialises in space chemistry, wants to continue solving other space mysteries.
METEORITES SHOW HOW SOLAR SYSTEM FORMED
University of Chicago
Ever since scientists started looking at meteorites with microscopes, they've been puzzled -- and fascinated -- by what's inside. Most meteorites are made of tiny beads of glass that date back to the earliest days of the solar system, before the planets were even formed. Scientists have published an analysis laying out how these beads, which are found in many meteorites, came to be -- and what they can tell us about what happened in the early solar system. The beads of glass inside these meteorites are called chondrules. Scientists think they are bits of rock left over from the debris that was floating around billions of years ago, which eventually coalesced into the planets we now know and love. These are immensely useful to scientists, who can get their hands on pieces of the original stuff that comprised the solar system -- before the constant churn of volcanoes and tectonic plates of Earth changed all the rock we can find on the planet itself. But what exactly caused the formation of these chondrules remains unclear. Scientists can find clues about the early days of the solar system by looking at the types of a given element in a rock. Elements can come in several different forms, called isotopes, and the proportion in each rock varies according to what happened when that rock was born -- how hot it was, whether it cooled slowly or was flash-frozen, what other elements were around to interact with it. From there, scientists can piece together a history of likely events. To try and understand what had happened to the chondrules, scientists at the Dauphas Origins Lab tried applying a unique angle to the isotopes. First, Nie took extremely rigorous, precise measurements of the concentrations and isotopes of two elements that are depleted in meteorites, potassium and rubidium, which helped narrow down the possibilities of what could have happened in the early solar system.
From this information, the team pieced together what must have been happening as the chondrules formed. The elements would have been part of a clump of dust that got hot enough to melt, and then to vaporize. Then, as the material cooled, some of that vapour coalesced back into chondrules. Based on these constraints, scientists can theorize what kind of event would have been sudden and violent enough to cause this extreme heating and cooling. One scenario that fits would be massive shockwaves passing through the early nebula. Large planetary bodies nearby can create shocks, which would have heated and then cooled the dust as it passed through, Over the past half-century, people have proposed different scenarios to explain the formation of the chondrules -- lightning, or collisions between rocks -- but this new evidence tips the balance toward shockwaves as an explanation. This explanation may be the key to understanding a persistent finding that has bedeviled scientists for decades, involving a category of elements that are "moderately volatile," including potassium and rubidium. The Earth has less of these elements than scientists would expect, based on their general understanding of how the solar system formed. They knew the explanation could be traced to some complex chain of heating and cooling, but no one knew the exact sequence. Now, finally, the team is happy to have put a significant dent in the mystery.
JUPITER-LIKE OBJECT MISSED BY EXOPLANET SEARCHES
American Museum of Natural History
Citizen scientists have discovered a new object orbiting a Sun-like star that had been missed by previous searches. The object is very distant from its host star -- more than 1,600 times farther than the Earth is from the Sun -- and is thought to be a large planet or a small brown dwarf, a type of object that is not massive enough to burn hydrogen like true stars. The Backyard Worlds project lets volunteers search through nearly five years of digital images taken from NASA's Wide-field Infrared Survey Explorer (WISE) mission to try to identify new worlds inside and outside of our solar system. If an object close to Earth is moving, it will appear to "jump" in the same part of the sky over the years, similar to an object "moving" in a flipbook. Users can then flag these objects for further study by scientists. In 2018, Backyard Worlds participant Jörg Schümann, who lives in Germany, alerted scientists to a new co-moving system: an object that appeared to be moving with a star. After confirming the system's motion, scientists used telescopes in California and Hawai'i to observe the star and object separately and were immediately excited by what they saw. The new object is young and has a low mass, between 10 and 20 times the mass of Jupiter. This range overlaps with an important cutoff point -- 13 times the mass of Jupiter -- which is sometimes used to distinguish planets from brown dwarfs. But scientists still aren't sure how heavy planets can be, which can make relying on this cutoff challenging. Another defining feature is how they form: planets form from material gathering in disks around stars, while brown dwarfs are born from the collapse of giant clouds of gas, similar to how stars form. But the physical properties of this new object do not provide any clues to its formation. There are hints that maybe it's more like an exoplanet, but there's nothing conclusive yet. However, it is an outlier
What surprised the team the most is the new object's relationship to its host star. The object is farther away from the star than expected based on its comparatively low mass -- over 1,600 times farther than the Earth is from the Sun. Few objects with such different masses from their host star have been found this far apart. Ultimately, this discovery may help scientists get a better sense of how solar systems form,
INFANT STARS FOUND AT CENTRE OF OUR GALAXY :
University of Cologne
What was previously identified as a gas and dust cloud at the centre of our galaxy actually consists of three very young stars. scientists from the University of Cologne's Institute of Astrophysics. The European Southern Observatory's Very Large Telescope (VLT) - a telescope with mirror diameters of 8.20 metres on the summit of Cerro Paranal in Chile - provided the data for the study . The stars began to form less than 1 million years ago, which is very young in astrophysical terms. By comparison, our Sun is just under 5 billion years old. In 2011, an object was found by means of the infrared data measured by the Very Large Telescope, promising to reveal an unprecedented process at the centre of our galaxy. Based on a multi-wavelength analysis, scientists determined that it must be a cloud of gas and dust, which was named G2. The interaction with the black hole at the centre of our galaxy, SgrA*, should have torn G2 apart and caused proverbial fireworks. The researchers assumed that when G2 collided with SgrA*, various processes would cause the gas and dust to make the black hole flare up. But that did not happen. In addition, there were other factors that gave astronomers around the world a headache and fuelled controversial discussions. Studies showed that the temperature of G2 is almost twice as high as that of surrounding dust sources. One possible explanation for G2's temperature is the extreme number of stars at the centre of our galaxy. So these stars could have heated up G2. The only question is why all other known dust sources at the centre of the galaxy show a much lower temperature. The black hole, SgrA*, was also ruled out as a heat source. The temperature of G2 should have increased the closer the supposed dust cloud came to the black hole - like we would feel if we approached a radiator. However, the temperature remained constant over a long period of time, although the distance to the black hole varied. The more closely G2 was observed around the world, the more it became apparent that the cosmic object had to be more than just a cloud of gas and dust.
The new results show that G2 actually consists of three individual stars. 'We had the opportunity to observe the centre of our galaxy ourselves several times with the Very Large Telescope. Together with the data from the Southern Observatory archive, we were able to cover a period from 2005 to 2019The unusual structure of the data was also helpful in locating G2. Each pixel of the captured image has an associated spectrum that covers a very specific and detailed waveband. For the scientists, this offers an enormous level of detail. 'That G2 actually consists of three evolving young stars is sensational. Never before have stars younger than the ones found been observed around SgrA*, The results open the door to many more fascinating research questions - for example where these young stars come from. The radiation-intensive environment of a supermassive black hole is not necessarily the best place to produce young stars.
LARGEST GROUP OF ROGUE PLANETS YET
ESO
Rogue planets are elusive cosmic objects that have masses comparable to those of the planets in our Solar System but do not orbit a star, instead roaming freely on their own. Not many were known until now, but a team of astronomers, using data from several European Southern Observatory (ESO) telescopes and other facilities, have just discovered at least 70 new rogue planets in our galaxy. This is the largest group of rogue planets ever discovered, an important step towards understanding the origins and features of these mysterious galactic nomads. Rogue planets, lurking far away from any star illuminating them, would normally be impossible to image. However, astronomers took advantage of the fact that, in the few million years after their formation, these planets are still hot enough to glow, making them directly detectable by sensitive cameras on large telescopes. They found at least 70 new rogue planets with masses comparable to Jupiter’s in a star-forming region close to our Sun, located within the Scorpius and Ophiuchus constellations. The team used observations from ESO’s Very Large Telescope (VLT), the Visible and Infrared Survey Telescope for Astronomy (VISTA), the VLT Survey Telescope (VST) and the MPG/ESO 2.2-metre telescope located in Chile, along with other facilities. The team also used data from the European Space Agency’s Gaia satellite, marking a huge success for the collaboration of ground- and space-based telescopes in the exploration and understanding of our Universe. The study suggests there could be many more of these elusive, starless planets that we have yet to discover. By studying the newly found rogue planets, astronomers may find clues to how these mysterious objects form. Some scientists believe rogue planets can form from the collapse of a gas cloud that is too small to lead to the formation of a star, or that they could have been kicked out from their parent system. But which mechanism is more likely remains unknown.
SUPER-BRIGHT STELLAR EXPLOSION
Massachusetts Institute of Technology
In June of 2018, telescopes around the world picked up a brilliant blue flash from the spiral arm of a galaxy 200 million light years away. The powerful burst appeared at first to be a supernova, though it was much faster and far brighter than any stellar explosion scientists had yet seen. The signal, procedurally labelled AT2018cow, has since been dubbed simply "the Cow," and astronomers have catalogued it as a fast blue optical transient, or FBOT -- a bright, short-lived event of unknown origin. Now astronomers have found strong evidence for the signal's source. In addition to a bright optical flash, the scientists detected a strobe-like pulse of high-energy X-rays. They traced hundreds of millions of such X-ray pulses back to the Cow, and found the pulses occurred like clockwork, every 4.4 milliseconds, over a span of 60 days. Based on the frequency of the pulses , the team calculated that the X-rays must have come from an object measuring no more than 1,000 kilometres wide, with a mass smaller than 800 suns. By astrophysical standards, such an object would be considered compact, much like a small black hole or a neutron star. Their findings strongly suggest that AT2018cow was likely a product of a dying star that, in collapsing, gave birth to a compact object in the form of a black hole or neutron star. The newborn object continued to devour surrounding material, eating the star from the inside -- a process that released an enormous burst of energy. AT2018cow is one of many "astronomical transients" discovered in 2018. The "cow" in its name is a random coincidence of the astronomical naming process (for instance, "aaa" refers to the very first astronomical transient discovered in 2018). The signal is among a few dozen known FBOTs, and it is one of only a few such signals that have been observed in real-time. Its powerful flash -- up to 100 times brighter than a typical supernova -- was detected by a survey in Hawaii, which immediately sent out alerts to observatories around the world.
Astronomers have proposed various scenarios to explain the super-bright signal. For instance, it could have been a product of a black hole born in a supernova. Or it could have resulted from a middle-weight black hole stripping away material from a passing star. However, the data collected by optical telescopes haven't resolved the source of the signal in any definitive way. The team looked to X-ray data collected by NASA's Neutron Star Interior Composition Explorer (NICER), an X-ray-monitoring telescope aboard the International Space Station. NICER started observing the Cow about five days after its initial detection by optical telescopes, monitoring the signal over the next 60 days. This data was recorded in a publicly available archive, which the team downloaded and analyzed. The team looked through the data to identify X-ray signals emanating near AT2018cow, and confirmed that the emissions were not from other sources such as instrument noise or cosmic background phenomena. They focused on the X-rays and found that the Cow appeared to be giving off bursts at a frequency of 225 hertz, or once every 4.4 milliseconds. Astronomers seized on this pulse, recognizing that its frequency could be used to directly calculate the size of whatever was pulsing. In this case, the size of the pulsing object cannot be larger than the distance that the speed of light can cover in 4.4 milliseconds. By this reasoning, he calculated that the size of the object must be no larger than 1.3x108 centimetres, or roughly 1,000 kilometres wide. The only thing that can be that small is a compact object -- either a neutron star or black hole . The team further calculated that, based on the energy emitted by AT2018cow, it must amount to no more than 800 solar masses. This rules out the idea that the signal is from an intermediate black hole. Apart from pinning down the source for this particular signal, the study demonstrates that X-ray analyses of FBOTs and other ultrabright phenomena could be a new tool for studying infant black holes.
ARE BLACK HOLES AND DARK MATTER THE SAME?
University of Miami
Proposing an alternative model for how the Universe came to be, a team of astrophysicists suggests that all black holes -- from those as tiny as a pin head to those covering billions of miles -- were created instantly after the Big Bang and account for all dark matter. That's the implication of a study by astrophysicists at the University of Miami, Yale University, and the European Space Agency that suggests that black holes have existed since the beginning of the Universe and that these primordial black holes could be as-of-yet unexplained dark matter. If proven true with data collected from this month's launch of the James Webb Space Telescope, the discovery may transform scientific understanding of the origins and nature of two cosmic mysteries: dark matter and black holes. The study predicts how the early Universe would look if, instead of unknown particles, dark matter was made by black holes formed during the Big Bang -- as Stephen Hawking suggested in the 1970s. This would have several important implications - first, we would not need 'new physics' to explain dark matter. Moreover, this would help us to answer one of the most compelling questions of modern astrophysics: How could supermassive black holes in the early Universe have grown so big so fast? Given the mechanisms we observe today in the modern Universe, they would not have had enough time to form. This would also solve the long-standing mystery of why the mass of a galaxy is always proportional to the mass of the super massive black hole in its centre,
Dark matter, which has never been directly observed, is thought to be most of the matter in the Universe and act as the scaffolding upon which galaxies form and develop. On the other hand, black holes, which can be found at the centres of most galaxies, have been observed. A point in space where matter is so tightly compacted, they create intense gravity. The new study suggests that so-called primordial black holes of all sizes account for all black matter in the Universe. Their model tweaks the theory first proposed by Hawking and fellow physicist Bernard Carr, who argued that in the first fraction of a second after the Big Bang, tiny fluctuations in the density of the Universe may have created an undulating landscape with "lumpy" regions that had extra mass. These lumpy areas would collapse into black holes. That theory did not gain scientific traction, but it could be valid with some slight modifications. Their model shows that the first stars and galaxies would have formed around black holes in the early Universe. They also propose that primordial black holes would have had the ability to grow into supermassive black holes by feasting on gas and stars in their vicinity, or by merging with other black holes. Primordial black holes, if they do exist, could well be the seeds from which all the supermassive black holes form, including the one at the centre of the Milky Way, Primordial black holes also may resolve another cosmological puzzle: the excess of infrared radiation, synced with X-ray radiation, that has been detected from distant, dim sources scattered around the Universe. The study authors said growing primordial black holes would present "exactly" the same radiation signature. machine will be able to see.
Topic: Late December Astronomy Bulletin (Read 1434 times)