Soup Posted at 2024-11-11 23:49:59(2Wks ago) Report Permalink URL | ||
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| Mining old data from NASA's Voyager 2 solves several Uranus mysteries by Karen Fox, Molly Wasser and Gretchen McCartney, NASA  The first panel of this artist’s concept depicts how Uranus’s magnetosphere — its protective bubble — was behaving before the flyby of NASA’s Voyager 2. The second panel shows an unusual kind of solar weather was happening during the 1986 flyby, giving scientists a skewed view of the magnetosphere. Credit: NASA/JPL-Caltech When NASA's Voyager 2 spacecraft flew by Uranus in 1986, it provided scientists' first—and, so far, only—close glimpse of this strange, sideways-rotating outer planet. Alongside the discovery of new moons and rings, baffling new mysteries confronted scientists. The energized particles around the planet defied their understanding of how magnetic fields work to trap particle radiation, and Uranus earned a reputation as an outlier in our solar system. Now, new research analyzing the data collected during that flyby 38 years ago has found that the source of that particular mystery is a cosmic coincidence. It turns out that in the days just before Voyager 2's flyby, the planet had been affected by an unusual kind of space weather that squashed the planet's magnetic field, dramatically compressing Uranus's magnetosphere. "If Voyager 2 had arrived just a few days earlier, it would have observed a completely different magnetosphere at Uranus," said Jamie Jasinski of NASA's Jet Propulsion Laboratory in Southern California and lead author of the new work published in Nature Astronomy. "The spacecraft saw Uranus in conditions that only occur about 4% of the time." Magnetospheres serve as protective bubbles around planets (including Earth) with magnetic cores and magnetic fields, shielding them from jets of ionized gas—or plasma—that stream out from the sun in the solar wind. Learning more about how magnetospheres work is important for understanding our own planet, as well as those in seldom-visited corners of our solar system and beyond. That's why scientists were eager to study Uranus's magnetosphere, and what they saw in the Voyager 2 data in 1986 flummoxed them. Inside the planet's magnetosphere were electron radiation belts with an intensity second only to Jupiter's notoriously brutal radiation belts. But there was apparently no source of energized particles to feed those active belts; in fact, the rest of Uranus's magnetosphere was almost devoid of plasma. The missing plasma also puzzled scientists because they knew that the five major Uranian moons in the magnetic bubble should have produced water ions, as icy moons around other outer planets do. They concluded that the moons must be inert with no ongoing activity  NASA’s Voyager 2 captured this image of Uranus while flying by the ice giant in 1986. New research using data from the mission shows a solar wind event took place during the flyby, leading to a mystery about the planet’s magnetosphere that now may be solved. Credit: NASA/JPL-Caltech Solving the mystery So why was no plasma observed, and what was happening to beef up the radiation belts? The new data analysis points to the solar wind. When plasma from the sun pounded and compressed the magnetosphere, it likely drove plasma out of the system. The solar wind event also would have briefly intensified the dynamics of the magnetosphere, which would have fed the belts by injecting electrons into them. The findings could be good news for those five major moons of Uranus: Some of them might be geologically active after all. With an explanation for the temporarily missing plasma, researchers say it's plausible that the moons actually may have been spewing ions into the surrounding bubble all along. Planetary scientists are focusing on bolstering their knowledge about the mysterious Uranus system, which the National Academies' 2023 Planetary Science and Astrobiology Decadal Survey prioritized as a target for a future NASA mission. JPL's Linda Spilker was among the Voyager 2 mission scientists glued to the images and other data that flowed in during the Uranus flyby in 1986. She remembers the anticipation and excitement of the event, which changed how scientists thought about the Uranian system. "The flyby was packed with surprises, and we were searching for an explanation of its unusual behavior. The magnetosphere Voyager 2 measured was only a snapshot in time," said Spilker, who has returned to the iconic mission to lead its science team as project scientist. "This new work explains some of the apparent contradictions, and it will change our view of Uranus once again." Voyager 2, now in interstellar space, is almost 13 billion miles (21 billion kilometers) from Earth. | |
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| SoupPosted at 2024-11-18 20:57:50(1Wk ago) Report Permalink URL | ||
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| Theoretical astrophysicist proposes solution to enigma of Crab Nebula's 'zebra' pattern by Brendan M. Lynch, University of Kansas  Crab Nebula. Credit: NASA A theoretical astrophysicist from the University of Kansas may have solved a nearly two-decade-old mystery over the origins of an unusual "zebra" pattern seen in high-frequency radio pulses from the Crab Nebula. His findings have just been published in Physical Review Letters. The Crab Nebula features a neutron star at its center that has formed into a 12-mile-wide pulsar pinwheeling electromagnetic radiation across the cosmos. "The emission, which resembles a lighthouse beam, repeatedly sweeps past Earth as the star rotates," said lead author Mikhail Medvedev, professor of physics & astronomy at KU. "We observe this as a pulsed emission, usually with one or two pulses per rotation. The specific pulsar I'm discussing is known as the Crab Pulsar, located in the center of the Crab Nebula 6,000 light years away from us." The Crab Nebula is the remnant of a supernova that appeared in 1054. "Historical records, including Chinese accounts, describe an unusually bright star appearing in the sky," said the KU researcher. But unlike any other known pulsar, Medvedev said the Crab Pulsar features a zebra pattern—unusual band spacing in the electromagnetic spectrum proportional to band frequencies, and other weird features like high polarization and stability. "It's very bright, across practically all wave bands," he said. "This is the only object we know of that produces the zebra pattern, and it only appears in a single emission component from the Crab Pulsar. "The main pulse is a broadband pulse, typical of most pulsars, with other broadband components common to neutron stars. However, the high-frequency interpulse is unique, ranging between 5 and 30 gigahertz—frequencies similar to those in a microwave oven." Since this pattern was discovered in a 2007 paper, the KU researcher said the pattern had proved "baffling" for investigators.  Medvedev modeled wave diffraction off a circular reflecting region with radially varying index of refraction outside of it to better understand the Crab Nebula's zebra pattern. Credit: Mikhail Medvedev "Researchers proposed various emission mechanisms, but none have convincingly explained the observed patterns," he said. Using data from the Crab Pulsar, Medvedev established a method using wave optics to gauge the density of the pulsar's plasma—the "gas" of charged particles (electrons and positrons)—using a fringe pattern found in the electromagnetic pulses. "If you have a screen and an electromagnetic wave passes by, the wave doesn't propagate straight through," Medvedev said. "In geometrical optics, shadows cast by obstacles would extend indefinitely—if you're in the shadow, there's no light; outside of it, you see light. But wave optics introduces a different behavior—waves bend around obstacles and interfere with each other, creating a sequence of bright and dim fringes due to constructive and destructive interference." This well-known fringe pattern phenomenon is caused by consistent constructive interference but has different characteristics when radio waves propagate around a neutron star. "A typical diffraction pattern would produce evenly spaced fringes if we just had a neutron star as a shield," the KU researcher said. "But here, the neutron star's magnetic field generates charged particles constituting a dense plasma, which varies with distance from the star. | |
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| SoupPosted at 2024-11-19 00:46:17(1Wk ago) Report Permalink URL | ||
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| Hubble sees aftermath of galaxy's scrape with Milky Way by NASA  This artist's concept shows the Large Magellanic Cloud, or LMC, in the foreground as it passes through the gaseous halo of the much more massive Milky Way galaxy. The encounter has blown away most of the spherical halo of gas that surrounds the LMC, as illustrated by the trailing gas stream reminiscent of a comet's tail. Still, a compact halo remains, and scientists do not expect this residual halo to be lost. The team surveyed the halo by using the background light of 28 quasars, an exceptionally bright type of active galactic nucleus that shines across the universe like a lighthouse beacon. Their light allows scientists to "see" the intervening halo gas indirectly through the absorption of the background light. The lines represent the Hubble Space Telescope's view from its orbit around Earth to the distant quasars through the LMC's gas. Credit: NASA, ESA, Ralf Crawford (STScI) A story of survival is unfolding at the outer reaches of our galaxy, and NASA's Hubble Space Telescope is witnessing the saga. The Large Magellanic Cloud, also called the LMC, is one of the Milky Way galaxy's nearest neighbors. This dwarf galaxy looms large on the southern nighttime sky at 20 times the apparent diameter of the full moon. Many researchers theorize that the LMC is not in orbit around our galaxy, but is just passing by. These scientists think that the LMC has just completed its closest approach to the much more massive Milky Way. This passage has blown away most of the spherical halo of gas that surrounds the LMC. Now, for the first time, astronomers have been able to measure the size of the LMC's halo—something they could do only with Hubble. In a new study, available on the preprint server arXiv and to be published in The Astrophysical Journal Letters, researchers were surprised to find that it is so extremely small, about 50,000 light-years across. That's around 10 times smaller than halos of other galaxies that are the LMC's mass. Its compactness tells the story of its encounter with the Milky Way. "The LMC is a survivor," said Andrew Fox of AURA/STScI for the European Space Agency in Baltimore, who was principal investigator on the observations. "Even though it's lost a lot of its gas, it's got enough left to keep forming new stars. So new star-forming regions can still be created. A smaller galaxy wouldn't have lasted—there would be no gas left, just a collection of aging red stars." Though quite a bit worse for wear, the LMC still retains a compact, stubby halo of gas—something that it wouldn't have been able to hold onto gravitationally had it been less massive. The LMC is 10 percent the mass of the Milky Way, making it heftier than most dwarf galaxies. "Because of the Milky Way's own giant halo, the LMC's gas is getting truncated, or quenched," explained STScI's Sapna Mishra, the lead author on the paper chronicling this discovery. "But even with this catastrophic interaction with the Milky Way, the LMC is able to retain 10 percent of its halo because of its high mass." A gigantic hair dryer Most of the LMC's halo was blown away due to a phenomenon called ram-pressure stripping. The dense environment of the Milky Way pushes back against the incoming LMC and creates a wake of gas trailing the dwarf galaxy—like the tail of a comet. "I like to think of the Milky Way as this giant hairdryer, and it's blowing gas off the LMC as it comes into us," said Fox. "The Milky Way is pushing back so forcefully that the ram pressure has stripped off most of the original mass of the LMC's halo. There's only a little bit left, and it's this small, compact leftover that we're seeing now."  This artist's concept illustrates the Large Magellanic Cloud's (LMC's) encounter with the Milky Way galaxy's gaseous halo. In the top panel, at the middle of the right side, the LMC begins crashing through our galaxy's much more massive halo. The bright purple bow shock represents the leading edge of the LMC's halo, which is being compressed as the Milky Way's halo pushes back against the incoming LMC. In the middle panel, part of the halo is being stripped and blown back into a streaming tail of gas that eventually will rain into the Milky Way. The bottom panel shows the progression of this interaction, as the LMC's comet-like tail becomes more defined. A compact LMC halo remains. Because the LMC is just past its closest approach to the Milky Way and is moving outward into deep space again, scientists do not expect the residual halo will be lost. Credit: NASA, ESA, Ralf Crawford (STScI) As the ram pressure pushes away much of the LMC's halo, the gas slows down and eventually will rain into the Milky Way. But because the LMC has just gotten past its closest approach to the Milky Way and is moving outward into deep space again, scientists do not expect the whole halo will be lost. Only with Hubble To conduct this study, the research team analyzed ultraviolet observations from the Mikulski Archive for Space Telescopes at STScI. Most ultraviolet light is blocked by the Earth's atmosphere, so it cannot be observed with ground-based telescopes. Hubble is the only current space telescope tuned to detect these wavelengths of light, so this study was only possible with Hubble. The team surveyed the halo by using the background light of 28 bright quasars. The brightest type of active galactic nucleus, quasars are believed to be powered by supermassive black holes. Shining like lighthouse beacons, they allow scientists to "see" the intervening halo gas indirectly through the absorption of the background light. Quasars reside throughout the universe at extreme distances from our galaxy. The scientists used data from Hubble's Cosmic Origins Spectrograph (COS) to detect the presence of the halo's gas by the way it absorbs certain colors of light from background quasars. A spectrograph breaks light into its component wavelengths to reveal clues to the object's state, temperature, speed, quantity, distance, and composition. With COS, they measured the velocity of the gas around the LMC, which allowed them to determine the size of the halo. Because of its mass and proximity to the Milky Way, the LMC is a unique astrophysics laboratory. Seeing the LMC's interplay with our galaxy helps scientists understand what happened in the early universe, when galaxies were closer together. It also shows just how messy and complicated the process of galaxy interaction is. Looking to the future The team will next study the front side of the LMC's halo, an area that has not yet been explored. "In this new program, we are going to probe five sightlines in the region where the LMC's halo and the Milky Way's halo are colliding," said co-author Scott Lucchini of the Center for Astrophysics | Harvard & Smithsonian. "This is the location where the halos are compressed, like two balloons pushing against each other." | |
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| SoupPosted at 2024-11-28 00:14:43(18Hrs ago) Report Permalink URL | ||
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| Investigating how the biggest galaxies in the cosmos grew so quickly before dying by Jonathan O'Callaghan, Horizon: The EU Research & Innovation Magazine  The formation of galaxies in the universe should follow a fairly simple path. It starts with small galaxies, which then grow bigger and bigger until they become the giant galaxies we see in the modern universe, like our Milky Way. Easy, right? But that is not strictly true for a particular class of elliptical galaxies—huge spherical collections of stars without a clear structure. With the help of EU funding, researchers have set out to discover the origin of these galaxies and unlock more mysteries of the universe. To do that, they have traveled back in time, using powerful telescopes that can follow light to remote corners of the universe. This has allowed scientists to look at galaxies as they appeared in the past, even billions of years ago. "Galaxies are the flag posts of the universe. They are the origins of everything," said Sune Toft, a cosmologist at the Niels Bohr Institute in Denmark. "Understanding the detailed formation scenarios is the only way to understand the beginning of the universe and where we come from." Toft led the EU-funded ConTExt project from 2015 to 2021. The goal was to observe some of the oldest elliptical galaxies possible, stretching back into the first 2 billion years of the 13.8-billion-year history of the universe. Time travel to remote dark corners: no answers yet Although researchers have gained some insight into elliptical galaxies, they remain a mystery. "These have been known for many years, but it's kind of a conundrum how they form because they are uniformly old and dead in the local universe," Toft said. The thinking behind his research was this: as we look further back in time, by observing galaxies that are billions of light years away, at some point we should start to see the progenitors of these galaxies and be able to explain how they were able to grow so massive. "But the further away we looked, they kept looking old and dead. They have virtually no star formation," said Toft, referring to the process at the core of galaxies' evolution. That meant the galaxies must have grown very quickly in the early universe. Still, it remains unknown exactly how and when. And there is another riddle: if the galaxies grew quickly, why did they stop growing? And what did that mean for our understanding of hierarchical galaxy structure in the universe, which comprises stars, planetary systems, star clusters and galaxies? "The small galaxies are supposed to form first. So why are these massive galaxies the first ones to form?" Toft said. Star formation His hypothesis was that these galaxies might have undergone intense star formation early on in their history, becoming what are known as starburst galaxies. Starburst galaxies have extremely dense amounts of dust and gas and can form stars thousands of times the mass of our sun every year. Our Milky Way, by comparison, forms one new solar mass per year on average. Using a telescope in Chile called the Atacama Large Millimeter Array, as well as the Hubble Space Telescope and Spitzer Space Telescope, both of which orbited the Earth at the time, Toft set to work. He found that, in the first 1 to 2 billion years after the Big Bang, "there were enough of these star-forming galaxies to turn into the dead galaxies." These galaxies were dense and compact and looked similar to the cores of elliptical galaxies we see today. Toft worked on the premise that these progenitor elliptical galaxies formed quickly in the universe before something shut off their star formation. Then, over the next 10 billion or so years, they gradually accumulated more stars by gobbling up smaller galaxies, adding their stars to the galaxy's outer regions. Thus, the elliptical galaxies remained old and dead, but could still grow to immense sizes. The early growth of the ellipticals was likely caused by galaxy mergers that ignited star formation. "You have two major galaxies going head-on into each other, and the gas gets compressed into the center of this collision," said Toft. "This is what you need to have very high star formation rates." But what was still not clear was how these galaxies switched off. How did they stop forming stars so quickly and eventually become the dead galaxies we see today? Quenching Sirio Belli, an astronomer at the University of Bologna in Italy, is investigating this problem with his Red Cardinal project, an EU-funded initiative running from 2023 to 2028. It is using the powerful James Webb Space Telescope (JWST), which orbits the sun, to probe these early galaxies like never before. The emerging idea is that black holes found at the centers of these galaxies are responsible for their evolution. Almost all galaxies today, including our own, contain a supermassive black hole at their center, a huge object millions to billions of times the mass of our sun. These black holes drive the formation and evolution of a galaxy, churning and expelling gas and dust throughout a galaxy's history. Belli has found that these black holes might also be responsible for stopping star formation in early galaxies, in a process referred to as quenching. In April 2024, his team used JWST to report the discovery of a massive galaxy undergoing quenching about 2.6 billion years after the Big Bang. "It's a lucky coincidence because we observed this galaxy exactly when quenching was happening," he said. The galaxy appeared to have been growing until recently. "It just stopped forming stars," said Belli. "At the same time, we found this giant wind coming out of the galaxy. We think this is due to the supermassive black hole at the center of the galaxy." The idea is that the black hole became extremely active, which "pushed the gas away from the galaxy," said Belli. "So you don't have any gas to form new stars. It's like a car that runs out of fuel." What is unclear is exactly why the black hole became active. One possibility is that once the black hole eats enough material and gains enough mass, it suddenly starts releasing a lot of energy, causing quenching. "We think that once a galaxy reaches a certain mass, 100 billion solar masses, they are then eventually all quenched," said Belli. "We don't see any massive galaxy in today's universe that is still forming stars." An extremely large telescope to probe further More answers might come from new telescopes like the European Extremely Large Telescope (ELT), which is being built in Chile and due to begin its observations in 2028. "With the ELT, we can look in detail inside these galaxies" in the early universe, said Belli, something JWST is not able to do. That will tell researchers the overall star formation rate, but also "where the stars are being formed," he said. "If the ELT works as promised, it should be pretty cool." Determining the mechanism of the quenching process will be crucial in unraveling the enigma of why galaxies die, an issue that continues to perplex scientists. "It shouldn't be possible because when a galaxy is in the early universe, it's filled with gas," said Toft. "How do you go from forming thousands of solar masses per year to nothing? If we want to prove black holes are responsible, we have to find galaxies right in the process of shutting down." With that understanding, we will learn how the cosmos as we see it today came to be. | |
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