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  • The cosmic commute toward star and planet formation
    Dienstag, 07.07.2020, 03:11:10 Uhr
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    The cosmic commute toward star and planet formation Heidelberg, Germany (SPX) Jul 07, 2020 -
    The molecular gas in galaxies is set into motion by physical mechanisms such as galactic rotation, supernova explosions, magnetic fields, turbulence, and gravity, shaping the structure of the gas. Understanding how these motions directly impact star and planet formation is difficult, because it requires quantifying gas motion over a huge range in spatial scale, and then linking this motion to the physical structures we observe. Modern astrophysical facilities now routinely map huge areas of the sky, with some maps containing millions of pixels, each with hundreds to thousands of independent velocity measurements. As a result, measuring these motions is both scientifically and technologically challenging. In order to address these challenges, an international team of researchers led by Jonathan Henshaw at the MPIA in Heidelberg set out to measure gas motions throughout a variety of different environments using observations of the gas in the Milky Way and a nearby galaxy. They detect these motions by measuring the apparent change in the frequency of light emitted by molecules caused by the relative motion between the source of the light and the observer; a phenomenon known as the Doppler effect. By applying novel software designed by Henshaw and Ph.D. student Manuel Riener (a co-author on the paper; also at MPIA), the team were able to analyse millions of measurements. "This method allowed us to visualise the interstellar medium in a new way," says Henshaw. The researchers found that cold molecular gas motions appear to fluctuate in velocity, reminiscent in appearance of waves on the surface of the ocean. These fluctuations represent gas motion. "The fluctuations themselves weren't particularly surprising, we know that the gas is moving," says Henshaw. Steve Longmore, co-author of the paper, based at Liverpool John Moores University, adds, "What surprised us was how similar the velocity structure of these different regions appeared. It didn't matter if we were looking at an entire galaxy or an individual cloud within our own galaxy, the structure is more or less the same." To better understand the nature of the gas flows, the team selected several regions for close examination, using advanced statistical techniques to look for differences between the fluctuations. By combining a variety of different measurements, the researchers were able to determine how the velocity fluctuations depend on the spatial scale. "A neat feature of our analysis techniques is that they are sensitive to periodicity," explains Henshaw. "If there are repeating patterns in your data, such as equally spaced giant molecular clouds along a spiral arm, we can directly identify the scale on which the pattern repeats." The team identified three filamentary gas lanes, which, despite tracing vastly different scales, all seemed to show structure that was roughly equidistantly spaced along their crests, like beads on a string, whether it was giant molecular clouds along a spiral arm or tiny "cores" forming stars along a filament. The team discovered that the velocity fluctuations associated with equidistantly spaced structure all showed a distinctive pattern. "The fluctuations look like waves oscillating along the crests of the filaments, they have a well-defined amplitude and wavelength," says Henshaw adding, "The periodic spacing of the giant molecular clouds on large-scales or individual star-forming cores on small-scales is probably the result of their parent filaments becoming gravitationally unstable. We believe that these oscillatory flows are the signature of gas streaming along spiral arms or converging towards the density peaks, supplying new fuel for star formation." In contrast, the team found that the velocity fluctuations measured throughout giant molecular clouds, on scales intermediate between entire clouds and the tiny cores within them, show no obvious characteristic scale. Diederik Kruijssen, co-author of the paper based at Heidelberg University explains: "The density and velocity structures that we see in giant molecular clouds are 'scale-free,' because the turbulent gas flows generating these structures form a chaotic cascade, revealing ever smaller fluctuations as you zoom in - much like a Romanesco broccoli, or a snowflake. This scale-free behaviour takes place between two well-defined extremes: the large scale of the entire cloud, and the small scale of the cores forming individual stars. We now find that these extremes have well-defined characteristic sizes, but in between them chaos rules." "Picture the giant molecular clouds as equally-spaced mega-cities connected by highways," says Henshaw. "From a bird's eye view, the structure of these cities, and the cars and people moving through them, appears chaotic and disordered. However, when we zoom in on individual roads, we see people who have travelled from far and wide entering their individual office buildings in an orderly fashion. The office buildings represent the dense and cold gas cores from which stars and planets are born." Research Report: "Ubiquitous Velocity Fluctuations Throughout the Molecular Interstellar Medium"
  • Dying stars breathe life into Earth
    Dienstag, 07.07.2020, 03:11:10 Uhr
    Dying stars breathe life into Earth Baltimore MD (SPX) Jul 07, 2020 -
    As dying stars take their final few breaths of life, they gently sprinkle their ashes into the cosmos through the magnificent planetary nebulae. These ashes, spread via stellar winds, are enriched with many different chemical elements, including carbon. Findings from a study published in Nature Astronomy show that the final breaths of these dying stars, called white dwarfs, shed light on carbon's origin in the Milky Way. "The findings pose new, stringent constraints on how and when carbon was produced by stars of our galaxy, ending up within the raw material from which the Sun and its planetary system were formed 4.6 billion years ago," says Jeffrey Cummings, an Associate Research Scientist in the Johns Hopkins University's Department of Physics and Astronomy and an author on the paper. The origin of carbon, an element essential to life on Earth, in the Milky Way galaxy is still debated among astrophysicists: some are in favor of low-mass stars that blew off their carbon-rich envelopes by stellar winds became white dwarfs, and others place the major site of carbon's synthesis in the winds of massive stars that eventually exploded as supernovae. Using data from the Keck Observatory near the summit of Mauna Kea volcano in Hawaii collected between August and September 2018, the researchers analyzed white dwarfs belonging to the Milky Way's open star clusters. Open star clusters are groups of up to a few thousand stars held together by mutual gravitational attraction. From this analysis, the research team measured the white dwarfs' masses, and using the theory of stellar evolution, also calculated their masses at birth. The connection between the birth masses to the final white dwarf masses is called the initial-final mass relation, a fundamental diagnostic in astrophysics that contains the entire life cycles of stars. Previous research always found an increasing linear relationship: the more massive the star at birth, the more massive the white dwarf left at its death. But when Cummings and his colleagues calculated the initial-final mass relation, they were shocked to find that the white dwarfs from this group of open clusters had larger masses than astrophysicists previously believed. This discovery, they realized, broke the linear trend other studies always found. In other words, stars born roughly 1 billion years ago in the Milky Way didn't produce white dwarfs of about 0.60-0.65 solar masses, as it was commonly thought, but they died leaving behind more massive remnants of about 0.7 - 0.75 solar masses. The researchers say that this kink in the trend explains how carbon from low-mass stars made its way into the Milky Way. In the last phases of their lives, stars twice as massive as the Milky Way's Sun produced new carbon atoms in their hot interiors, transported them to the surface and finally spread them into the surrounding interstellar environment through gentle stellar winds. The research team's stellar models indicate that the stripping of the carbon-rich outer mantle occurred slowly enough to allow the central cores of these stars, the future white dwarfs, to grow considerably in mass. The team calculated that stars had to be at least 1.5 solar masses to spread its carbon-rich ashes upon death. The findings, according to Paola Marigo, a Professor of Physics and Astronomy at the University of Padova and the study's first author, helps scientists understand the properties of galaxies in the universe. By combining the theories of cosmology and stellar evolution, the researchers expect that bright carbon-rich stars close to their death, like the progenitors of the white dwarfs analyzed in this study, are presently contributing to the light emitted by very distant galaxies. This light, which carries the signature of newly produced carbon, is routinely collected by the large telescopes from space and Earth to probe the evolution of cosmic structures. Therefore, this new understanding of how carbon is synthesized in stars also means having a more reliable interpreter of the light from the far universe.
  • Unprecedented ground-based discovery of 2 strongly interacting exoplanets
    Dienstag, 07.07.2020, 03:11:10 Uhr
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    Unprecedented ground-based discovery of 2 strongly interacting exoplanets Paris, France (SPX) Jul 03, 2020 -
    Several interacting exoplanets have already been spotted by satellites. But a new breakthrough has been achieved with, for the first time, the detection directly from the ground of an extrasolar system of this type. An international collaboration including CNRS researchers* has discovered an unusual planetary system, dubbed WASP-148, using the French instrument SOPHIE at the Observatoire de Haute-Provence (CNRS/Aix-Marseille Universite;). The scientists analysed the star's motion and concluded that it hosted two planets, WASP-148b and WASP-148c. The observations showed that the two planets were strongly interacting, which was confirmed from other data**. Whereas the first planet, WASP-148b, orbits its star in nearly nine days, the second one, WASP-148c, takes four times longer. This ratio between the orbital periods implies that the WASP-148 system is close to resonance, meaning that there is enhanced gravitational interaction between the two planets. And it turns out that the astronomers did indeed detect variations in the orbital periods of the planets. While a single planet, uninfluenced by a second one, would move with a constant period, WASP-148b and WASP-148c undergo acceleration and deceleration that provides evidence of their interaction. Their study will shortly be published in the journal Astronomy and Astrophysics. Research paper
  • First exposed planetary core discovered allows glimpse inside other worlds
    Dienstag, 07.07.2020, 03:11:10 Uhr
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    First exposed planetary core discovered allows glimpse inside other worlds Warwick UK (SPX) Jul 02, 2020 -
    The surviving core of a gas giant has been discovered orbiting a distant star by University of Warwick astronomers, offering an unprecedented glimpse into the interior of a planet. The core, which is the same size as Neptune in our own solar system, is believed to be a gas giant that was either stripped of its gaseous atmosphere or that failed to form one in its early life. The team from the University of Warwick's Department of Physics reports the discovery in the journal Nature, and is thought to be the first time the exposed core of a planet has been observed. It offers the unique opportunity to peer inside the interior of a planet and learn about its composition. Located around a star much like our own approximately 730 light years away, the core, named TOI 849 b orbits so close to its host star that a year is a mere 18 hours and its surface temperature is around 1800K. TOI 849 b was found in a survey of stars by NASA's Transiting Exoplanet Survey Satellite (TESS), using the transit method: observing stars for the tell-tale dip in brightness that indicates that a planet has passed in front of them. It was located in the 'Neptunian desert' - a term used by astronomers for a region close to stars where we rarely see planets of Neptune's mass or larger. The object was then analysed using the HARPS instrument, on a program led by the University of Warwick, at the European Southern Observatory's La Silla Observatory in Chile. This utilises the Doppler effect to measure the mass of exoplanets by measuring their 'wobble' - small movements towards and away from us that register as tiny shifts in the star's spectrum of light. The team determined that the object's mass is 2-3 times higher than Neptune but it is also incredibly dense, with all the material that makes up that mass squashed into an object the same size. Lead author Dr David Armstrong from the University of Warwick Department of Physics said: "While this is an unusually massive planet, it's a long way from the most massive we know. But it is the most massive we know for its size, and extremely dense for something the size of Neptune, which tells us this planet has a very unusual history. The fact that it's in a strange location for its mass also helps - we don't see planets with this mass at these short orbital periods. "TOI 849 b is the most massive terrestrial planet - that has an earth like density - discovered. We would expect a planet this massive to have accreted large quantities of hydrogen and helium when it formed, growing into something similar to Jupiter. The fact that we don't see those gases lets us know this is an exposed planetary core. "This is the first time that we've discovered an intact exposed core of a gas giant around a star." There are two theories as to why we are seeing the planet's core, rather than a typical gas giant. The first is that it was once similar to Jupiter but lost nearly all of its outer gas through a variety of methods. These could include tidal disruption, where the planet is ripped apart from orbiting too close to its star, or even a collision with another planet. Large-scale photoevaporation of the atmosphere could also play a role, but can't account for all the gas that has been lost. Alternatively, it could be a 'failed' gas giant. The scientists believe that once the core of the gas giant formed then something could have gone wrong and it never formed an atmosphere. This could have occurred if there was a gap in the disc of dust that the planet formed from, or if it formed late and the disc ran out of material. Dr Armstrong adds: "One way or another, TOI 849 b either used to be a gas giant or is a 'failed' gas giant. "It's a first, telling us that planets like this exist and can be found. We have the opportunity to look at the core of a planet in a way that we can't do in our own solar system. There are still big open questions about the nature of Jupiter's core, for example, so strange and unusual exoplanets like this give us a window into planet formation that we have no other way to explore. "Although we don't have any information on its chemical composition yet, we can follow it up with other telescopes. Because TOI 849 b is so close to the star, any remaining atmosphere around the planet has to be constantly replenished from the core. So if we can measure that atmosphere then we can get an insight into the composition of the core itself." Research Report: 'A remnant planetary core in the hot-Neptune desert'
  • First exposed planetary core discovered
    Dienstag, 07.07.2020, 03:11:10 Uhr
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    First exposed planetary core discovered Bern, Switzerland (SPX) Jul 02, 2020 -
    The newly discovered exoplanet TOI 849 b offers the unique opportunity to peer inside the interior of a planet and learn about its composition. It orbits around a star about 730 light years away, which is very similar to our sun. The exposed core is the same size as Neptune in our solar system. The researchers assume that it is a gas giant that was either stripped of its gaseous atmosphere or that failed to fully form one in its early life due to special circumstances. The study by the team led by Dr David Armstrong from the University of Warwick's Department of Physics is published in the journal Nature. PD Dr. Christoph Mordasini from the University of Bern Physics Institute led the theoretical interpretation of the discovery. A year that is a mere 18 hours
    TOI 849 b is an extremely unusual planet in the so-called "Neptune Desert" - a term used by astronomers for a region close to stars where we rarely see planets of Neptune's mass or larger. The lead author of the study, Dr. David Armstrong from the University of Warwick, says: "The planet is strangely close to its star, considering its mass. In other words, we don't see planets with this mass at these short orbital periods." TOI 849 b orbits so close to its host star that a year is a mere 18 hours and its surface temperature is around 1,500C. Christoph Mordasini explains: "We have determined the planet's mass and radius. TOI-849b is about 40 times heavier than the earth, but its radius is just 3.4 earth radii." So the planet has a high density and therefore has to primarily consist of iron, rock and water, but only very little hydrogen and helium. "Such a small amount of hydrogen and helium is really astonishing for such a massive planet. We would expect a planet this massive to have accreted large quantities of hydrogen and helium when it formed." David Armstrong adds: "The fact that we don't see those gases lets us know TOI 849 b is an exposed planetary core." This is the first time that an intact exposed core of a gas giant has been discovered around a star. Bern's expertise in demand worldwide
    The University of Bern has been continuously developing the "Bern Model of Planet Formation and Evolution" since 2003. Christoph Mordasini says: "In our model, we combine insights into the manifold processes involved in the formation and evolution of planets." Thanks to the world-renowned Bern model, discoveries such as those of the exoplanet TOI 849 b can be interpreted theoretically. Based on the Bern model, two theories can be formulated which explain why TOI 849 b is not a typical gas giant but an exposed planetary core. "The first is that the exoplanet was once similar to Jupiter but lost nearly all of its outer gas through a variety of processes," Christoph Mordasini says. These could include tidal disruption, where the planet is ripped apart from orbiting too close to its star, or even a collision with another planet. Large-scale photoevaporation of the atmosphere could also play a role, but can't account for all the gas that has been lost. Alternatively, TOI 849 b could be a "failed" gas giant. "Once the core of the gas giant formed then something very unusual could have happened and it never formed a massive atmosphere as normally. This could have occurred if there was a gap in the disk of dust and gas that the planet formed from due to gravitational interaction with the planet, or if the disk ran out of material right at the very moment when gas accretion normally follows," Mordasini adds. David Armstrong says: "Our discovery proves that planets like this exist and we can track them down. We have the opportunity to look at the core of a planet in a way that we can't do in our own solar system." How TOI 849 b was discovered and analyzed
    TOI 849 b was found in a survey of stars by NASA's Transiting Exoplanet Survey Satellite (TESS), using the transit method: the satellite measures the brightness of a star. A dip in brightness indicates that a planet has passed in front of them. TOI 849 b was then analyzed using the HARPS instrument built under Swiss leadership, at the European Southern Observatory's La Silla Observatory in Chile. This utilizes the Doppler effect to measure the mass of exoplanets by measuring their 'wobble' - small movements towards and away from us that register as tiny shifts in the star's spectrum of light. "Bern Model of Planet Formation and Evolution"
    Statements can be made about how a planet was formed and how it has evolved using the "Bern Model of Planet Formation and Evolution". The Bern model has been continuously developed at the University of Bern since 2003. Insights into the manifold processes involved in the formation and evolution of planets are integrated into the model. These are, for example, submodels of accretion (growth of a planet's core) or of how planets interact gravitationally and influence each other, and of processes in the protoplanetary disks in which planets are formed. The model is also used to create so-called population syntheses, which show which planets develop how frequently under certain conditions in a protoplanetary disk. The world-renowned Bern model is also used for the theoretical interpretation of discoveries such as that of the TOI 849 b exoplanet. Research Report: 'A remnant planetary core in the hot-Neptune desert'
  • TESS mission discovers massive ice giant
    Dienstag, 07.07.2020, 03:11:10 Uhr
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    TESS mission discovers massive ice giant Boston MA (SPX) Jul 02, 2020 -
    The "ice giant" planets Neptune and Uranus are much less dense than rocky, terrestrial planets such as Venus and Earth. Beyond our solar system, many other Neptune-sized planets, orbiting distant stars, appear to be similarly low in density. Now, a new planet discovered by NASA's Transiting Exoplanet Survey Satellite, TESS, seems to buck this trend. The planet, named TOI-849 b, is the 749th "TESS Object of Interest" identified to date. Scientists spotted the planet circling a star about 750 light years away every 18 hours, and estimate it is about 3.5 times larger than Earth, making it a Neptune-sized planet. Surprisingly, this far-flung Neptune appears to be 40 times more massive than Earth and just as dense. TOI-849 b is the most massive Neptune-sized planet discovered to date, and the first to have a density that is comparable to Earth. "This new planet is more than twice as massive as our own Neptune, which is really unusual," says Chelsea Huang, a postdoc in MIT's Kavli Institute for Astrophysics and Space Research, and a member of the TESS science team. "Imagine if you had a planet with Earth's average density, built up to 40 times the Earth's mass. It's quite crazy to think what's happening at the center of a planet with that kind of pressure." The discovery is reported in the journal Nature. The study's authors include Huang and members of the TESS science team at MIT. A blasted Jupiter?
    Since its launch on April 18, 2018, the TESS satellite has been scanning the skies for planets beyond our solar system. The project is one of NASA's Astrophysics Explorer missions and is led and operated by MIT. TESS is designed to survey almost the entire sky by pivoting its view every month to focus on a different patch of the sky as it orbits the Earth. As it scans the sky, TESS monitors the light from the brightest, nearest stars, and scientists look for periodic dips in starlight that may signal that a planet is crossing in front of a star. Data taken by TESS, in the form of a star's light curve, or measurements of brightness, is first made available to the TESS science team, an international, multi-institute group of researchers led by scientists at MIT. These researchers get a first look at the data to identify promising planet candidates, or TESS Objects of Interest. These are shared publicly with the general scientific community along with the TESS data for further analysis. For the most part, astronomers focus their search for planets on the nearest, brightest stars that TESS has observed. Huang and her team at MIT, however, recently had some extra time to look over data during September and October of 2018, and wondered if anything could be found among the fainter stars. Sure enough, they discovered a significant number of transit-like dips from a star 750 light years away, and soon after, confirmed the existence of TOI-849 b. "Stars like this usually don't get looked at carefully by our team, so this discovery was a happy coincidence," Huang says. Follow-up observations of the faint star with a number of ground-based telescopes further confirmed the planet and also helped to determine its mass and density. Huang says that TOI-849 b's curious proportions are challenging existing theories of planetary formation. "We're really puzzled about how this planet formed," Huang says. "All the current theories don't fully explain why it's so massive at its current location. We don't expect planets to grow to 40 Earth masses and then just stop there. Instead, it should just keep growing, and end up being a gas giant, like a hot Jupiter, at several hundreds of Earth masses." One hypothesis scientists have come up with to explain the new planet's mass and density is that perhaps it was once a much larger gas giant, similar to Jupiter and Saturn - planets with more massive envelopes of gas that enshroud cores thought to be as dense as the Earth. As the TESS team proposes in the new study, over time, much of the planet's gassy envelope may have been blasted away by the star's radiation - not an unlikely scenario, as TOI-849 b orbits extremely close to its host star. Its orbital period is just 0.765 days, or just over 18 hours, which exposes the planet to about 2,000 times the solar radiation that Earth receives from the sun. According to this model, the Neptune-sized planet that TESS discovered may be the remnant core of a much more massive, Jupiter-sized giant. "If this scenario is true, TOI-849 b is the only remnant planet core, and the largest gas giant core known to exist," says Huang. "This is something that gets scientists really excited, because previous theories can't explain this planet." Research Report: 'A remnant planetary core in the hot-Neptune desert'
  • NASA's TESS delivers new insights into an ultrahot world
    Dienstag, 07.07.2020, 03:11:10 Uhr
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    NASA's TESS delivers new insights into an ultrahot world Greenbelt MD (SPX) Jul 01, 2020 -
    Measurements from NASA's Transiting Exoplanet Survey Satellite (TESS) have enabled astronomers to greatly improve their understanding of the bizarre environment of KELT-9 b, one of the hottest planets known. "The weirdness factor is high with KELT-9 b," said John Ahlers, an astronomer at Universities Space Research Association in Columbia, Maryland, and NASA's Goddard Space Flight Center in Greenbelt, Maryland. "It's a giant planet in a very close, nearly polar orbit around a rapidly rotating star, and these features complicate our ability to understand the star and its effects on the planet." The new findings appear in a paper led by Ahlers published on June 5 in The Astronomical Journal. Located about 670 light-years away in the constellation Cygnus, KELT-9 b was discovered in 2017 because the planet passed in front of its star for a part of each orbit, an event called a transit. Transits regularly dim the star's light by a small but detectable amount. The transits of KELT-9 b were first observed by the KELT transit survey, a project that collected observations from two robotic telescopes located in Arizona and South Africa. Between July 18 and Sept. 11, 2019, as part of the mission's yearlong campaign to observe the northern sky, TESS observed 27 transits of KELT-9 b, taking measurements every two minutes. These observations allowed the team to model the system's unusual star and its impact on the planet. KELT-9 b is a gas giant world about 1.8 times bigger than Jupiter, with 2.9 times its mass. Tidal forces have locked its rotation so the same side always faces its star. The planet swings around its star in just 36 hours on an orbit that carries it almost directly above both of the star's poles. KELT-9 b receives 44,000 times more energy from its star than Earth does from the Sun. This makes the planet's dayside temperature around 7,800 degrees Fahrenheit (4,300 C), hotter than the surfaces of some stars. This intense heating also causes the planet's atmosphere to stream away into space. Its host star is an oddity, too. It's about twice the size of the Sun and averages about 56 percent hotter. But it spins 38 times faster than the Sun, completing a full rotation in just 16 hours. Its rapid spin distorts the star's shape, flattening it at the poles and widening its midsection. This causes the star's poles to heat up and brighten while its equatorial region cools and dims - a phenomenon called gravity darkening. The result is a temperature difference across the star's surface of almost 1,500 F (800 C). With each orbit, KELT-9 b twice experiences the full range of stellar temperatures, producing what amounts to a peculiar seasonal sequence. The planet experiences "summer" when it swings over each hot pole and "winter" when it passes over the star's cooler midsection. So KELT-9 b experiences two summers and two winters every year, with each season about nine hours. "It's really intriguing to think about how the star's temperature gradient impacts the planet," said Goddard's Knicole Colon, a co-author of the paper. "The varying levels of energy received from its star likely produce an extremely dynamic atmosphere." KELT-9 b's polar orbit around its flattened star produces distinctly lopsided transits. The planet begins its transit near the star's bright poles and then blocks less and less light as it travels over the star's dimmer equator. This asymmetry provides clues to the temperature and brightness changes across the star's surface, and they permitted the team to reconstruct the star's out-of-round shape, how it's oriented in space, its range of surface temperatures, and other factors impacting the planet. "Of the planetary systems that we've studied via gravity darkening, the effects on KELT-9 b are by far the most spectacular," said Jason Barnes, a professor of physics at the University of Idaho and a co-author of the paper. "This work goes a long way toward unifying gravity darkening with other techniques that measure planetary alignment, which in the end we hope will tease out secrets about the formation and evolutionary history of planets around high-mass stars." Research paper
  • First measurement of spin-orbit alignment on planet Beta Pictoris b
    Dienstag, 07.07.2020, 03:11:10 Uhr
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    First measurement of spin-orbit alignment on planet Beta Pictoris b Exeter UK (SPX) Jun 30, 2020 -
    Astronomers have made the first measurement of spin-orbit alignment for a distant 'super-Jupiter' planet, demonstrating a technique that could enable breakthroughs in the quest to understand how exoplanetary systems form and evolved. An international team of scientists, led by Professor Stefan Kraus from the University of Exeter, has carried out the measurements for the exoplanet Beta Pictoris b - located 63 light years from Earth. The planet, found in the Pictor constellation, has a mass of around 11 times that of Jupiter and orbits a young star on a similar orbit as Saturn in our solar system. The study, published today (June 29th 2020) in the Astrophysical Journal Letters, marks the first time that scientists have measured the spin-orbit alignment for a directly-imaged planetary system. Crucially, the results give a fresh insight into enhancing our understanding of the formation history and evolution of the planetary system. Professor Kraus said: "The degree to that a star and a planetary orbit are aligned with each other tells us a lot about how a planet formed and whether multiple planets in the system interacted dynamically after their formation." Some of the earliest theories of the planet formation process were proposed by prominent 18th century astronomers Kant and Laplace. They noted that the orbits of the solar system planets are aligned with each other, and with the Sun's spin axis, and concluded that the solar system formed from a rotating and flattened protoplanetary disc. "It was a major surprise when it was found that more than a third of all close-in exoplanets orbit their host star on orbits that are misaligned with respect to the stellar equator.", said Prof. Kraus. "A few exoplanets were even found to orbit in the opposite direction than the rotation direction of the star. These observations challenge the perception of planet formation as a neat and well-ordered process taking place in a geometrically thin and co-planar disc." For the study, the researchers devised an innovative method that measures the tiny spatial displacement of less than a billionth of a degree that is caused by Beta Pictoris' rotation. The team used the GRAVITY instrument at the VLTI, which combines the light from telescopes separated 140 metres apart, to carry out the measurements. They found that the stellar rotation axis is aligned with the orbital axes of the planet Beta Pictoris b and its extended debris disc. "Gas absorption in the stellar atmosphere causes a tiny spatial displacement in spectral lines that can be used to determine the orientation of the stellar rotation axis.", said Dr. Jean-Baptiste LeBouquin, an astronomer at the University of Grenoble in France and a member of the team. "The challenge is that this spatial displacement is extremely small: about 1/100th of the apparent diameter of the star, or the equivalent to the size of a human footstep on the moon as seen from Earth." The results show that the Beta Pictoris system is as well-aligned as our own solar system. This finding favors planet-planet scattering as the cause for the orbit obliquities that are observed in more exotic systems with Hot Jupiters. However, observations on a large sample of planetary systems will be required to answer this question conclusively. The team proposes a new interferometric instrument that will allow them to obtain these measurements on many more planetary systems that are about to be discovered. "A dedicated high-spectral resolution instrument at VLTI could measure the spin-orbit alignment for hundreds of planets, including those on long-period orbits.", said Prof. Kraus, "This will help us to answer the question what dynamical processes shape the architecture of planetary systems." Research paper
  • Astronomers measure spin-orbit alignment of a distant super-Jupiter
    Dienstag, 07.07.2020, 03:11:10 Uhr
    Astronomers measure spin-orbit alignment of a distant super-Jupiter Washington DC (UPI) Jun 29, 2020 -

    For the first time, astronomers have measured the spin-orbit alignment of a faraway super-Jupiter exoplanet, located 63 light-years from the Earth in the Pictor constellation.

    The super-Jupiter exoplanet, Beta Pictoris b, has a mass 11 times that of Jupiter and enjoys an orbit around its host star similar to the trajectory Jupiter takes around our own sun.

    The detailed observations of Beta Pictoris b -- shared Monday in the Astrophysical Journal Letters -- could help scientists better understand the formation and evolution of planetary systems.

    "The degree to that a star and a planetary orbit are aligned with each other tells us a lot about how a planet formed and whether multiple planets in the system interacted dynamically after their formation," lead study author Stefan Kraus said in a news release.

    During the 18th century, scientists Immanuel Kant and Pierre-Simon Laplace noticed that the orbital planes of the solar system's planets were largely aligned. They estimated that Earth and its planetary neighbors formed from a rotating and flattened protoplanetary disc.

    "It was a major surprise when it was found that more than a third of all close-in exoplanets orbit their host star on orbits that are misaligned with respect to the stellar equator," said Kraus, professor of astronomy and physics at the University of Exeter in Britain.

    "A few exoplanets were even found to orbit in the opposite direction than the rotation direction of the star," Kraus said. "These observations challenge the perception of planet formation as a neat and well-ordered process taking place in a geometrically thin and co-planar disc."

    Using the GRAVITY instrument on the Very Large Telescope in Chile, scientists measured the minuscule spatial displacement caused by the stellar rotation of Beta Pictoris. The data revealed an alignment between the star's rotational axis and the orbital axis of the planet Beta Pictoris b and its surrounding debris disk.

    "Gas absorption in the stellar atmosphere causes a tiny spatial displacement in spectral lines that can be used to determine the orientation of the stellar rotation axis," said study co-author Jean-Baptiste LeBouquin, an astronomer at the University of Grenoble in France. "The challenge is that this spatial displacement is extremely small: about 1/100th of the apparent diameter of the star, or the equivalent to the size of a human footstep on the moon as seen from Earth."

    The latest findings showed the Beta Pictoris system is just as aligned as our own solar system, but authors of the new study suggest a wider sample size is needed to confirm how common spin orbit alignment is throughout the cosmos.

    "A dedicated high-spectral resolution instrument at VLTI could measure the spin-orbit alignment for hundreds of planets, including those on long-period orbits," said Kraus. "This will help us to answer the question what dynamical processes shape the architecture of planetary systems."
  • Neptune-sized planet discovered orbiting young, nearby star
    Dienstag, 07.07.2020, 03:11:10 Uhr
    Weitere Links:
    Neptune-sized planet discovered orbiting young, nearby star Baltimore MD (SPX) Jun 25, 2020 -
    New research published in Nature reports the discovery of a planet about the size of Neptune orbiting an especially young, nearby star. The planet, named AU Mic b, is orbiting AU Microscopii, which is relatively close to the Milky Way at 31.9 light years away. AU Microscopii is also "only" 20 or 30 million years old--at least 150 times younger than our Sun. There are only two or three known stars that are both nearby and young, and scientists have been searching for planets orbiting them for at least a decade. This means the new finding creates a major opportunity for breakthrough research into solar system formation dynamics. "One of the things we want to understand is, 'When do planets form, and what do they do in their early days?'" says Tom Barclay. He's an associate research scientist with UMBC's Center for Space Sciences and Technology, a partnership with the NASA Goddard Space Flight Center in Greenbelt, Maryland. Because AU Mic b is so young, Barclay adds, "studying this planet, and hopefully others like it, can give us insight into how our own solar system formed." Shining light on a new planet
    Barclay primarily works on NASA's Transiting Exoplanet Survey Satellite (TESS) mission. TESS observes the same section of sky for weeks at a time, collecting data about the brightness of stars in its field of view every two minutes. Thanks to this constant watchfulness, TESS can help detect planets by recording when a star's brightness temporarily dims. That can sometimes signal a planet crossing in front of the star, or "transiting." "My role is to take the brightness data for the star and use that to understand what the size and other properties of the planet are," says Barclay, who is second author on the new paper. Peter Plavchan of George Mason University leads the project. "Dips in brightness tell you about the size of the planet, and measuring how regularly spaced the transits are tells us how long it takes the planet to go around the star," Barclay explains. TESS detected two transits of AU Mic b, but the research team needed a third to "be confident that what we'd seen wasn't something else in the data trying to fool us," Barclay says. So they called on additional data collected by NASA's Spitzer satellite and ground-based instruments in Hawaii and Chile. Barclay analyzed the combined information and was able to confirm that AU Mic b has a mass of no more than 58 Earths and completes an orbit of AU Microscopii every 8.5 days. An orbit that short indicates that the planet is extremely close to the star. Discovery dominoes
    Next, Barclay and his colleagues want to learn more about the atmosphere of the new planet. Because it only recently formed, "it may well be losing its atmosphere at a rate that we can see," Barclay says. "It might even appear somewhat teardrop-shaped, as the planet is moving and leaving some of its atmosphere behind. So we're going to go and look for that." In addition to the rate of atmosphere loss, careful observations can also help determine what the planet's atmosphere is made of. Determining the atmosphere's components could help the team figure out where the planet formed, because certain substances can only exist at a known distance from the star. Knowing where the planet formed would provide clues about how it had moved since it first came into being. And knowing that would get scientists closer to understanding more generally how planets form and migrate in a new solar system. Planet migration puzzle
    AU Mic b is likely primarily comprised of gases. "This star probably hasn't had time to form small, rocky planets yet," Barclay says. "It gives us a chance to get a picture of what might have happened before our own terrestrial planets like Earth and Venus formed." But the work is not easy. "Understanding the migration of planets is a really difficult problem. One of the fun things and one of the most frustrating things about studying stars is that we can never go to them," Barclay says. "So this discovery is just one more puzzle piece in trying to understand what's going on." Research Report: "A planet within the debris disk around the pre-main-sequence star AU Microscopii"
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