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  • richardmitnick 3:46 pm on October 15, 2021 Permalink | Reply
    Tags: "Two Impacts-Not Just One-May Have Formed The Moon", , , , , Sky & Telescope   

    From Sky & Telescope : “Two Impacts-Not Just One-May Have Formed The Moon” 

    From Sky & Telescope

    October 14, 2021
    Asa Stahl

    1
    In this image, the proposed hit-and-run collision is simulated in 3D, shown about an hour after impact. Theia, the impactor, barely escapes the collision. A. Emsenhuber / The University of Bern [Universität Bern](CH) / The Ludwig Maximilians University of Munich [Ludwig-Maximilians-Universität München](DE).

    Scientists have long thought that the Moon formed with a bang, when a protoplanet the size of Mars hit the newborn Earth. Evidence from Moon rocks and simulations back up this idea.

    But a new study suggests that the protoplanet most likely hit Earth twice. The first time, the impactor (dubbed “Theia”) only glanced off Earth. Then, some hundreds of thousands of years later, it came back to deliver the final blow.

    The study, which simulated the literally Earth-shattering impact thousands of times, found that such a “hit-and-run return” scenario could help answer two longstanding questions surrounding the creation of the Moon. At the same time, it might explain how Earth and Venus ended up so different.

    The One-Two Punch

    “The key issue here is planetary diversity,” says Erik Asphaug (The University of Arizona (US)), who led the study. Venus and Earth have similar sizes, masses, and distances from the Sun. If Venus is a “crushing hot-house,” he asks, “why is Earth so amazingly blue and rich?”

    The Moon might hold the secret. Its creation was the last major episode in Earth’s formation, a catastrophic event that set the stage for the rest of our planet’s evolution. “You can’t understand how Earth formed without understanding how the Moon formed,” Asphaug explains. “They are part of the same puzzle.”

    The new simulations, which were published in the October Journal of Planetary Sciences, put a few more pieces of that puzzle into place.

    The first has to do with the speed of Theia’s impact. If Theia had hit our planet too fast, it would have exploded into an interplanetary plume of debris and eroded much of Earth. Yet if it had come in too slowly, the result would be a Moon whose orbit looks nothing like what we see today. The original impact theory doesn’t explain why Theia traveled at a just-right speed between these extremes.

    “[This] new scenario fixes that,” says Matthias Meier (Natural History Museum, Switzerland), who was not involved in the study. Initially, Theia could have been going much faster, but the first impact would have slowed it down to the perfect speed for the second one.

    The other problem with the original impact theory is that our Moon ought to be mostly made of primordial Theia. But Moon rocks from the Apollo missions show that Earth and the Moon have nearly identical compositions when it comes to certain kinds of elements. How could they have formed from two different building blocks?

    “The canonical giant-impact scenario is really bad at solving [this issue],” Meier says (though others have tried).

    A hit-and-run return, on the other hand, would enable Earth’s and Theia’s materials to mix more than in a single impact, ultimately forming a Moon chemically more similar to Earth. Though Asphaug and colleagues don’t quite fix the mismatch, they argue that more advanced simulations would yield even better results.

    Earth vs. Venus

    Resolving this aspect of the giant-impact theory would be no mean feat. But Asphaug’s real surprise came when he saw how hit-and-run impacts would have affected Venus compared to Earth.

    “I first thought maybe there was a mistake,” he recalls.

    The new simulations showed that the young Earth tended to pass on half of its hit-and-runners to Venus, while Venus accreted almost everything that came its way. This dynamic could help explain the drastic differences between the two planets: If more runners ended up at Venus, they would have enriched the planet in more outer solar system material compared to Earth. And since the impactors that escaped Earth to go on to Venus would have been the faster ones, each planet would have experienced generally different collisions.

    This finding flips the original purpose of the study on its head. If Venus suffered more giant impacts than Earth, the question would no longer be “why does Earth have a moon?” but “why doesn’t Venus?”

    Perhaps there was only one hit-and-run event, the one that made our Moon. Perhaps there were many, but for the same reason that Venus collected more impacts than Earth, it also accreted more destructive debris, obliterating any moon it already had. Or perhaps the last of Venus’ impacts was just particularly violent.

    Finding out means taking a trip to Venus. That would provide “the next leap in understanding,” Meier says. If Earth and Venus both had hit-and-runs, for example, then the surface of Venus ought to be more like Earth’s than previously expected. If Venus has the same chemical similarities as the Moon and Earth, that would throw out the giant-impact theory’s last remaining problem.

    “Getting samples from Venus,” Asphaug concludes, “is the key to answering all these questions.”

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.


    Stem Education Coalition

    Sky & Telescope, founded in 1941 by Charles A. Federer Jr. and Helen Spence Federer, has the largest, most experienced staff of any astronomy magazine in the world. Its editors are virtually all amateur or professional astronomers, and every one has built a telescope, written a book, done original research, developed a new product, or otherwise distinguished him or herself.

    Sky & Telescope magazine, now in its eighth decade, came about because of some happy accidents. Its earliest known ancestor was a four-page bulletin called The Amateur Astronomer, which was begun in 1929 by the Amateur Astronomers Association in New York City. Then, in 1935, the American Museum of Natural History opened its Hayden Planetarium and began to issue a monthly bulletin that became a full-size magazine called The Sky within a year. Under the editorship of Hans Christian Adamson, The Sky featured large illustrations and articles from astronomers all over the globe. It immediately absorbed The Amateur Astronomer.

    Despite initial success, by 1939 the planetarium found itself unable to continue financial support of The Sky. Charles A. Federer, who would become the dominant force behind Sky & Telescope, was then working as a lecturer at the planetarium. He was asked to take over publishing The Sky. Federer agreed and started an independent publishing corporation in New York.

    “Our first issue came out in January 1940,” he noted. “We dropped from 32 to 24 pages, used cheaper quality paper…but editorially we further defined the departments and tried to squeeze as much information as possible between the covers.” Federer was The Sky’s editor, and his wife, Helen, served as managing editor. In that January 1940 issue, they stated their goal: “We shall try to make the magazine meet the needs of amateur astronomy, so that amateur astronomers will come to regard it as essential to their pursuit, and professionals to consider it a worthwhile medium in which to bring their work before the public.”

     
  • richardmitnick 12:59 pm on September 25, 2021 Permalink | Reply
    Tags: "Misfit Meteorite Sheds Light on Solar System History", , , , Sky & Telescope, The Nedagolla meteorite   

    From Sky & Telescope : “Misfit Meteorite Sheds Light on Solar System History” 

    From Sky & Telescope

    September 21, 2021
    Jure Japelj

    Scientists have discovered the first meteorite that doesn’t fall into one of two fundamental groups. The meteorite provides a unique glimpse into the era of asteroid formation and migration.

    1
    Artist’s impression of the asteroid belt. Credit: NASA / JPL-Caltech (US).

    The meteorite would be just another one among thousands found on Earth if it weren’t for its unusual composition. Researchers have long tried to understand its origin, and now they might have solved the mystery. In a recent study to be published in Meteoritics & Planetary Science, scientists found that the Nedagolla meteorite is a product of a collision between two asteroids of distinct origin. Its unique history opens up a new window into the research of the early stages of solar system formation.

    Two Meteorite Families

    Meteorites are time capsules that illuminate the era of planet formation. The solar system formed from a cloud of interstellar gas and dust that collapsed under its own gravity. Particles within the resulting protoplanetary disk collided and stuck, forming ever larger planetesimals, which became the parent bodies of the meteorites found on Earth.

    Meteorites come in different flavors [Space Science Reviews]. Depending on whether iron or silicates dominate, meteorites are traditionally classified as iron, stony, or stony-iron. Composition also depends on whether the meteorites originate from bodies that underwent melting, or whether the parent body was unmelted and therefore more pristine. By these classifiers, Nedagolla is an ungrouped iron meteorite.

    But one can also look at isotopes. Isotopes are elements with the same number of protons but a different number of neutrons, and they can carry a lot of information, including the time of a rock’s formation.

    “About 10 years ago, the community realized that there is an isotopic dichotomy in meteoritic material,” says graduate student Fridolin Spitzer (University of Münster [Westfälische Wilhelms-Universität Münster] (DE)), who was first author of the new study. Cosmochemists thus use isotopes to classify meteorites of all sorts, regardless of their chemical composition, as either non-carbonaceous chondrite (NC) or the carbonaceous chondrite (CC). (These groups were initially differentiated by the amount of carbon, but now the terms are used more generally.)

    There is only one exception: “Nedagolla is the first one that does not consistently fall into one of the two categories but seems to fall in between,” says Spitzer.

    Scientists suspect that the two isotope classes formed in two different parts of the protoplanetary disk: The NCs in the disk’s inner part and the CCs in the outer solar system, beyond the Jupiter´s orbit. So where does that put the Nedagolla meteorite?

    Scientists have discovered the first meteorite that doesn’t fall into one of two fundamental groups. The meteorite provides a unique glimpse into the era of asteroid formation and migration.
    Artist’s impression of the asteroid belt
    NASA / JPL-Caltech

    A fireball embellished the night sky over India on January 23, 1870. Accompanied by a thunderous detonation, the fiery mass crashed in the village of Nedagolla with enough force to leave the bystanders stunned. The impact left behind a bit over 4 kilograms of cosmic rock — the Nedagolla meteorite.

    The meteorite would be just another one among thousands found on Earth if it weren’t for its unusual composition. Researchers have long tried to understand its origin, and now they might have solved the mystery. In a recent study to be published in Meteoritics & Planetary Science (preprint available here), scientists found that the Nedagolla meteorite is a product of a collision between two asteroids of distinct origin. Its unique history opens up a new window into the research of the early stages of solar system formation.
    Two Meteorite Families

    Meteorites are time capsules that illuminate the era of planet formation. The solar system formed from a cloud of interstellar gas and dust that collapsed under its own gravity. Particles within the resulting protoplanetary disk collided and stuck, forming ever larger planetesimals, which became the parent bodies of the meteorites found on Earth.

    Meteorites come in different flavors. Depending on whether iron or silicates dominate, meteorites are traditionally classified as iron, stony, or stony-iron. Composition also depends on whether the meteorites originate from bodies that underwent melting, or whether the parent body was unmelted and therefore more pristine. By these classifiers, Nedagolla is an ungrouped iron meteorite.

    But one can also look at isotopes. Isotopes are elements with the same number of protons but a different number of neutrons, and they can carry a lot of information, including the time of a rock’s formation.

    “About 10 years ago, the community realized that there is an isotopic dichotomy in meteoritic material,” says graduate student Fridolin Spitzer (University of Münster, Germany), who was first author of the new study. Cosmochemists thus use isotopes to classify meteorites of all sorts, regardless of their chemical composition, as either non-carbonaceous chondrite (NC) or the carbonaceous chondrite (CC). (These groups were initially differentiated by the amount of carbon, but now the terms are used more generally.)

    There is only one exception: “Nedagolla is the first one that does not consistently fall into one of the two categories but seems to fall in between,” says Spitzer.

    Scientists suspect that the two isotope classes formed in two different parts of the protoplanetary disk: The NCs in the disk’s inner part and the CCs in the outer solar system, beyond the Jupiter´s orbit. So where does that put the Nedagolla meteorite?

    Asteroid Migrations and Collisions

    After performing a new and independent analysis of the meteorite’s composition, the team proposes that its unique isotopic imprint comes from a collision of NC and CC planetesimals. “The two bodies collided, and this induced melting because of high impact velocities, and it induced mixing of materials from these two bodies,” explains Spitzer.

    Here things become interesting. Most meteorites originate from the asteroid belt, a region between the orbits of Mars and Jupiter. So, the CC-type meteorites had to migrate to the inner part of the solar system at some point, otherwise the Nedagolla meteorite wouldn´t exist.

    1
    A schematic view of the protoplanetary disk in the first few million years after its formation. The NC (red) and CC (blue) planetesimals formed in the inner and outer disk, respectively. The growing Jupiter might have separated the two classes. Credit: Bermingham et al. 2020.

    “The reason why we have any CC material to analyze on Earth, which is in itself an NC body, is because, during the disk evolution, planets like Jupiter migrated inwards and outwards, scattering material around the Solar System,” says Katherine Bermingham (Rutgers University).

    But the details are still murky. For example, did Jupiter’s movements create the isotopic divide? And why did one region of the disk have a consistently different mixture of material compared to the other?

    With the Nedagolla meteorite, scientists obtained the first isotopic evidence that the NC and CC bodies mingled. Its composition suggests that at least the CC body had a metallic core. Furthermore, the formative collision couldn’t have happened earlier than about 7 million years after the disk’s formation.

    Such information measured for a larger sample of similar meteorites would be invaluable. “I think it is important that the community does more of this kind of work to see if we can figure out better time constraints on NC-CC mixing,” says Bermingham. “There are a lot of ungrouped iron meteorites out there, and maybe this signature will be found in those that we haven’t studied yet.”

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.


    Stem Education Coalition

    Sky & Telescope, founded in 1941 by Charles A. Federer Jr. and Helen Spence Federer, has the largest, most experienced staff of any astronomy magazine in the world. Its editors are virtually all amateur or professional astronomers, and every one has built a telescope, written a book, done original research, developed a new product, or otherwise distinguished him or herself.

    Sky & Telescope magazine, now in its eighth decade, came about because of some happy accidents. Its earliest known ancestor was a four-page bulletin called The Amateur Astronomer, which was begun in 1929 by the Amateur Astronomers Association in New York City. Then, in 1935, the American Museum of Natural History opened its Hayden Planetarium and began to issue a monthly bulletin that became a full-size magazine called The Sky within a year. Under the editorship of Hans Christian Adamson, The Sky featured large illustrations and articles from astronomers all over the globe. It immediately absorbed The Amateur Astronomer.

    Despite initial success, by 1939 the planetarium found itself unable to continue financial support of The Sky. Charles A. Federer, who would become the dominant force behind Sky & Telescope, was then working as a lecturer at the planetarium. He was asked to take over publishing The Sky. Federer agreed and started an independent publishing corporation in New York.

    “Our first issue came out in January 1940,” he noted. “We dropped from 32 to 24 pages, used cheaper quality paper…but editorially we further defined the departments and tried to squeeze as much information as possible between the covers.” Federer was The Sky’s editor, and his wife, Helen, served as managing editor. In that January 1940 issue, they stated their goal: “We shall try to make the magazine meet the needs of amateur astronomy, so that amateur astronomers will come to regard it as essential to their pursuit, and professionals to consider it a worthwhile medium in which to bring their work before the public.”

     
  • richardmitnick 12:12 pm on September 25, 2021 Permalink | Reply
    Tags: "Infant 'Hot Neptune' Provides Clues to Its Birth", , , , , Sky & Telescope, The mysterious exoplanet AU Microscopii b   

    From Sky & Telescope : “Infant ‘Hot Neptune’ Provides Clues to Its Birth” 

    From Sky & Telescope

    September 20, 2021
    Arwen Rimmer

    How’d a nice young ice giant end up in such a hot orbit? Scientists investigate the mysterious exoplanet AU Microscopii b.


    Animation Depicting an Approach to AU Mic b

    AU Microscopii is a baby red dwarf star about 32 light-years away in the southern constellation Microscopium, the Microscope. It’s only 22 million years old and surrounded by a planetary debris field, first observed in 2004. Just within the last year, independent teams have discovered two exoplanets (AU Mic b and c) orbiting the star.

    A series of follow-up studies focused on AU Mic b, a young, Neptune-mass planet that whips around its star every 8½ days. This giant couldn’t have formed where it now orbits. To help determine how it got there, astronomers have sought to measure the alignment between the planet’s orbit and its host star’s spin.

    There are many things that might cause a planet’s orbit to change, such as a large body passing near the system or interactions with the planet-forming disk around the star. Over the past year, multiple measurements made with various telescopes and methods have shown that AU Mic b’s orbit is still aligned with its star’s spin. While the individual measurements are more uncertain, the evidence is mounting that a more peaceful transition occurred, like disk interactions, rather than gravitational ping-pong.

    How’d a nice young ice giant end up in such a hot orbit? Scientists investigate the mysterious exoplanet AU Microscopii b.

    AU Microscopii is a baby red dwarf star about 32 light-years away in the southern constellation Microscopium, the Microscope. It’s only 22 million years old and surrounded by a planetary debris field, first observed in 2004. Just within the last year, independent teams have discovered two exoplanets (AU Mic b and c) orbiting the star.

    A series of follow-up studies focused on AU Mic b, a young, Neptune-mass planet that whips around its star every 8½ days. This giant couldn’t have formed where it now orbits. To help determine how it got there, astronomers have sought to measure the alignment between the planet’s orbit and its host star’s spin.

    There are many things that might cause a planet’s orbit to change, such as a large body passing near the system or interactions with the planet-forming disk around the star. Over the past year, multiple measurements made with various telescopes and methods have shown that AU Mic b’s orbit is still aligned with its star’s spin. While the individual measurements are more uncertain, the evidence is mounting that a more peaceful transition occurred, like disk interactions, rather than gravitational ping-pong.

    Pinning Down Spin

    The first of the studies was led by Teruyuki Hirano (Tokyo Institute of Technology [(東京工業大学](JP)) and published in The Astrophysical Journal Letters in August 2020. His team used the Subaru telescope to obtain the first tentative proof that AU Mic b’s orbit is aligned with its star’s spin.

    Then, one month later, Eder Martioli (Institut d’Astrophysique de Paris) published the same good spin-orbit alignment using the Canada-France-Hawaii Telescope and the NASA Infrared Telescope Facility, reporting their results in the September 2020 Astronomy and Astrophysics.

    In a third study published October 2020 in Astronomy and Astrophysics, Enric Pallé (Institute of Astrophysics of the Canaries[Instituto de Astrofísica de Canarias] (ES)) and colleagues took spectroscopy measurements with the Very Large Telescope in Chile.

    Using a couple different techniques to check Mic b’s spin-orbit angle, they again found good alignment.

    The latest of these studies appears in the October 1st The Astronomical Journal. Brett Addison (University of Southern Queensland (AU)) led the project, using radial velocity measurements from the Minerva-Australis telescope array to compare the angle of the planet’s orbit with the spin-axis of its host star.

    Minerva-Australis telescope array operated by the University of Southern Queensland (AU) located at USQ’s Mount Kent Observatory

    2
    An artist’s concept shows one interpretation of planet AU Mic b.
    Credit: NASA’s Goddard Space Flight Center / Chris Smith (Universities Space Research Association (US))

    AU Microscopii is so young, it hasn’t even begun fusing hydrogen into helium in its core, and a massive planetary debris field surrounds it. But it already has two fully formed gas giants, both of which probably made a long trek from beyond the “ice line,” where they must have formed, into very close orbits around the host star. The temperatures close to a star are too hot for gases like water and methane to condense during planet formation, and most of the hydrogen and helium gets blown away by solar winds. But on the outer edges of the star system, all this material is free to accrete on a truly massive scale.

    It’s impossible to watch planets form and migrate in real time. But if we can observe many different, comparable systems at various stages of development, then we have the next best thing: snapshots of planets’ development over time. The age and current arrangement of the AU Microscopii system thus contributes to a working knowledge of migration and timescales in the formation process. In this case, a star near the beginning of its lifespan has already had enough time to spin out two planets, both of which have apparently taken a stroll into completely different orbits.

    Scott Gaudi (Thee Ohio State University (US)), who was not involved with these studies, says that making these kinds of observations is very difficult because the spin-orbit alignment has to be observed during a transit. And in the case of Addison’s study, the telescopes used were relatively small (an array for four 0.7-meter telescopes), which affected the quality of the data.

    “The other AU Mic b studies provided a more definitive answer because they were taken with larger telescopes,” Gaudi says. “The bigger the view, the more photons you can collect, the better your data.”

    Right now, the easiest kind of planet to see is a gas giant very close to a small star. But with the next generation of dedicated exoplanet telescopes coming online in the next decade, it should be possible to detect worlds beyond the “ice line”, closer to their birth sites. Gaudi looks forward to using the Nancy Grace Roman Space Telescope, which begins operations in 2025, to find more planetary systems which look like our own.

    “It’s one of the big open questions in planetary science,” Gaudi says. “At the moment we see lots of big planets that appear to have migrated, especially those called hot Jupiters. But the solar system looks different and no one knows why. The Roman telescope should give us a better idea of how we fit into the big picture.”

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.


    Stem Education Coalition

    Sky & Telescope, founded in 1941 by Charles A. Federer Jr. and Helen Spence Federer, has the largest, most experienced staff of any astronomy magazine in the world. Its editors are virtually all amateur or professional astronomers, and every one has built a telescope, written a book, done original research, developed a new product, or otherwise distinguished him or herself.

    Sky & Telescope magazine, now in its eighth decade, came about because of some happy accidents. Its earliest known ancestor was a four-page bulletin called The Amateur Astronomer, which was begun in 1929 by the Amateur Astronomers Association in New York City. Then, in 1935, the American Museum of Natural History opened its Hayden Planetarium and began to issue a monthly bulletin that became a full-size magazine called The Sky within a year. Under the editorship of Hans Christian Adamson, The Sky featured large illustrations and articles from astronomers all over the globe. It immediately absorbed The Amateur Astronomer.

    Despite initial success, by 1939 the planetarium found itself unable to continue financial support of The Sky. Charles A. Federer, who would become the dominant force behind Sky & Telescope, was then working as a lecturer at the planetarium. He was asked to take over publishing The Sky. Federer agreed and started an independent publishing corporation in New York.

    “Our first issue came out in January 1940,” he noted. “We dropped from 32 to 24 pages, used cheaper quality paper…but editorially we further defined the departments and tried to squeeze as much information as possible between the covers.” Federer was The Sky’s editor, and his wife, Helen, served as managing editor. In that January 1940 issue, they stated their goal: “We shall try to make the magazine meet the needs of amateur astronomy, so that amateur astronomers will come to regard it as essential to their pursuit, and professionals to consider it a worthwhile medium in which to bring their work before the public.”

     
  • richardmitnick 4:29 pm on July 30, 2021 Permalink | Reply
    Tags: "A Pileup of Perpendicular Planets", , , , , , Sky & Telescope,   

    From Aarhus University [Aarhus Universitet] (DK) via Sky & Telescope : “A Pileup of Perpendicular Planets” 

    From Aarhus University [Aarhus Universitet] (DK)

    via

    Sky & Telescope

    July 27, 2021
    Susanna Kohler, AAS NOVA

    In some planetary systems, the direction that a star spins and the direction its planets orbit don’t always line up. A new study explores what we can learn from these nonconformists.

    1
    Artist’s illustration of WASP-79b, an example of an exoplanet that circles its star on a polar orbit.
    Credit: B. Addison/ European Southern Observatory [Observatoire européen austral][Europäische Südsternwarte] (EU) (CL).

    Nature Is Trending

    Much of science involves searching for patterns and trends in data. Patterns in the universe — preferences for certain shapes, locations, alignments, etc. — can often reveal hidden underlying physics that drives nature to take a non-random course. This means that patterns and trends frequently provide the key to understanding how the universe works.

    Exoplanet populations are an especially intriguing place to look for trends. In recent years, our sample of observed exoplanets has grown large enough that we can now start to do useful statistical analysis — and there’s a lot we can hope to learn from this about the formation and evolution of planetary systems.

    2
    A protostar lies embedded in a disk of gas and dust in this visualization. Since stars and their planets form from the same cloud, it would make sense for their rotations to be aligned. Credit: NASA’s Goddard Space Flight Center (US).

    One particular curiosity among exoplanets: a planet’s orbital direction is not always aligned with its host star’s spin direction. Since a star and its planets all form out of the same rotating cloud of gas and dust, conservation of angular momentum should produce planet orbits and stellar spins that are aligned. But, while we see a large population of well-aligned systems, we also see a smaller population of misaligned systems.

    What causes planets to become misaligned with their stars? A new study [The Astrophysical Journal Letters] led by Simon Albrecht (Aarhus University [Aarhus Universitet] (DK)) examines patterns in a population of observed star–planet systems to find out.

    3
    Diagram illustrating the angle between the sky-projected stellar spin and planetary orbit (λ) and the actual 3D angle between the spin and orbit (Ψ). The tilt of the star relative to the observer line of sight is marked by i. Credit: Albrecht et al. 2021.

    Albrecht and collaborators explored a valuable sample of 57 star–planet systems. For the majority of planetary systems with observed spin/orbital directions, we can only measure the angle between the sky-projected orbital and spin axes. But for the sample that Albrecht and collaborators used, we have independent measurements of the inclination angle of the star relative to our line of sight. Thus, for these 57 systems, the authors were able to identify the actual angle in 3D space between the planets’ orbital axes and the stars’ spin axes.

    The result? Albrecht and collaborators find that the majority of the systems are aligned, as expected. But the 19 misaligned systems do not have misalignments that are distributed randomly through all angles. Instead, almost all of the misalignments cluster around 90° (ranging from 80°–125°) — meaning that the planet orbits the poles of the star, perpendicular to the direction that the star spins.

    3
    Left: The angle between the sky-projected orbital and spin axes (λ) for the authors’ sample. Right: The actual angle between the axes (Ψ). The actual angles show two clusterings: one near zero (aligned), and one around 90° (perpendicular). Adapted from Albrecht et al. 2021

    What could cause this polar pileup? The authors propose several theoretical possibilities that include dynamical interactions between the planet and the star, or between the planet and an additional unseen, distant companion body. But, as we’ve seen, nature has a mind of its own — and there may be multiple mechanisms at work! We don’t yet have enough information to solve this puzzle with certainty, but a continued search for patterns is sure to point us in the right direction eventually.

    This work was accomplished with National Aeronautics Space Agency (US)/Massachusetts Institute of Technology (US) TESS

    _____________________________________________________________________________________

    National Aeronautics Space Agency (US)/Massachusetts Institute of Technology (US) TESS

    Additional partners include Northrop Grumman, based in Falls Church, Virginia; NASA’s Ames Research Center in California’s Silicon Valley; the Center for Astrophysics – Harvard and Smithsonian; MIT Lincoln Laboratory; and the NASA Space Telescope Science Institute (US) in Baltimore.


    _____________________________________________________________________________________

    See the full article here.

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Aarhus Universitet DK campus.

    Aarhus University [Aarhus Universitet] (DK), abbreviated AU) is the largest and second oldest research university in Denmark. The university belongs to the Coimbra Group, the Guild, and Utrecht Network of European universities and is a member of the European University Association.

    The university was founded in Aarhus, Denmark, in 1928 and comprises five faculties in Arts, Natural Sciences, Technical Sciences, Health, and Business and Social Sciences and has a total of twenty-seven departments. It is home to over thirty internationally recognised research centres, including fifteen Centres of Excellence funded by the Danish National Research Foundation. The university is ranked among the top 100 world’s best universities. The business school within Aarhus University, called Aarhus BSS, holds the EFMD (European Foundation for Management Development) Equis accreditation, the Association to Advance Collegiate Schools of Business (AACSB) and the Association of MBAs (AMBA). This makes the business school of Aarhus University one of the few in the world to hold the so-called Triple Crown accreditation. Times Higher Education ranks Aarhus University in the top 10 of the most beautiful universities in Europe (2018).

    The university’s alumni include Bjarne Stroustrup, the inventor of programming language C++, Queen Margrethe II of Denmark, Crown Prince Frederik of Denmark, and Anders Fogh Rasmussen, former Prime Minister of Denmark and a Secretary General of NATO.

    Nobel Laureate Jens Christian Skou (Chemistry, 1997), conducted his groundbreaking work on the Na/K-ATPase in Aarhus and remained employed at the university until his retirement. Two other nobel laureates: Trygve Haavelmo (Economics, 1989) and Dale T. Mortensen (Economics, 2010). were affiliated with the university.

     
  • richardmitnick 11:16 am on July 17, 2021 Permalink | Reply
    Tags: "Gravitationally Unstable Disk May Collapse to Form Planets", , , , , , , Sky & Telescope   

    From Sky & Telescope : “Gravitationally Unstable Disk May Collapse to Form Planets” 

    From Sky & Telescope

    July 16, 2021
    Lauren Sgro

    Astronomers investigate the spiral arms of a young star’s disk and find evidence of a disk so massive that it could collapse to form planets.

    1
    The protoplanetary disk of Elias 2-27, shown with the dust continuum data in blue, along with different forms of carbon monoxide shown in yellow and red. The top panel shows the dust in blue along with gas probed at different velocities. Each image shows all the gas that travels at the specific velocity measured. The bottom panel is a composite of all dust and gas observed. Credit: ALMA (European Southern Observatory [Observatoire européen austral][Europäische Südsternwarte] (EU) (CL)/National Astronomy Observatory of Japan (JP)/B. Saxton National Radio Astronomy Observatory (US))/T. Paneque-Carreño (University of Chile [Universidad de Chile] (CL)).

    Astronomers have found the first signposts of a gravitationally unstable disk around the young star Elias 2-27 — the first evidence to support this method of giant planet formation.

    Protoplanetary disks of gas and dust leftover from stellar formation are known as the birthplace of planets. Astronomers understand that these disks give way to planets, but they’re still working to determine the exact evolution from dust to new worlds.

    There’s more than one way to form a planet, and one path might be gravitational instability – when disks become so massive that they begin to fragment and cave in on themselves, directly collapsing into planets or forming spiral arms that trap material for future planet formation. An already-formed giant planet or interactions with a nearby star can also create spirals, but spiral structure born out of gravitational instability carries special characteristics.

    A team led by Cassandra Hall (University of Georgia (US)) was the first to predict what the markers of gravitational instability might look like. Hall and collaborators used simulations to determine the telltale sign of gravitational instability in a disk, affectionately dubbed the “wiggle.” This wiggle disturbs the disk’s rotation on scales coinciding with the spirals, instead of in one specific location like the swirling kinks caused by planets.

    In 2016, scientists at the Atacama Large Millimeter/submillimeter Array (ALMA) first saw spiral arms in the disk of Elias 2-27.

    Now, research led by Teresa Paneque-Carreño (now at Leiden University [Universiteit Leiden] (NL)), has spotted the hallmark wiggle. The finding makes these spiral arms the first convincing evidence for a gravitationally unstable disk. This study will appear in The Astrophysical Journal.

    Evidence for Instability

    With Hall’s predictions in mind, Paneque-Carreño’s collaboration used ALMA to observe the dust and gas in Elias 2-27’s disk. The results show that the expansive spiral arms are symmetric, with similar shapes and sizes, as predicted if gravitational instability were at work.

    The key piece of evidence for instability, however, is the wiggle. The team used ALMA to observe the motions of carbon monoxide – which traces the harder-to-observe, but more abundant, hydrogen gas – and discovered the sought-after signature. As predicted, this disturbance coincides with the spiral arms in most observations. “It is really amazing to see this confirmation of velocity perturbations that so closely resembles what was predicted,” Hall says, who also worked on the Elias 2-27 studies.

    2
    Components of Elias 2-27’s disk, with images of the dust (blue) and carbon monoxide gas (C18O in yellow, 13CO in red) cycled through.
    ALMA (ESO/NAOJ/NRAO)/T. Paneque-Carreño (Universidad de Chile), B. Saxton (NRAO).

    These signals of gravitational instability also led to the first direct measurement of the mass in a planet-forming disk. Using the ALMA data, collaborator Benedetta Veronesi (University of Milan [Università degli Studi di Milano Statale] (IT)) reported the mass in a companion study that will appear in Astrophysical Journal Letters. Veronesi’s team concluded that Elias 2-27’s disk has 17% the mass of its star, creating conditions ripe for gravitational instabilities. In thinner disks, the star calls the shots with its powerful gravity governing the motions of the disk. But for a massive disk like the one around Elias 2-27, the disk’s own gravity starts to influence its dynamics, which enabled Veronesi’s team to determine its mass budget for future planet formation.

    Oddities of Elias 2-27

    While the spiral, wiggle, and mass all indicate the disk is experiencing gravitational instability, gaps in that same disk are throwing astronomers for a loop. For instance, there is a gap in the middle of the disk that is devoid of dust – a trait typically attributed to the commotion of a forming planet. However, a planet forming a gap of this size wouldn’t be large enough to form the spiral structure. Even if there were a planet at this location, it would get sucked into the star. On the other hand, gravitational instability cannot explain the gap, even though it explains the spirals.

    While neither phenomenon can explain both features, the evidence for gravitational instability is still valid, says Ken Rice (University of Edinburgh (SCT)), who was not involved in the study. “I don’t think the presence of a gap necessarily suggests that spirals aren’t being driven by the gravitational instability.”

    3
    This illustration shows how the spiral arms caused by gravitational instability can help dust grains accumulate, which may move on to form planetary systems.
    ALMA (ESO/NAOJ/NRAO)/T. Paneque-Carreño (Universidad de Chile), B. Saxton (NRAO).

    Paneque-Carreño’s team also finds that the gas in Elias 2-27’s disk is unexpectedly asymmetric, such that the gas is thicker on one side of the disk than the other. The varying layers of gas indicate that material could still be falling onto the disk from the cloud that formed the Elias 2-27 system. This inbound gas might have ignited the gravitational instability and even caused a disk warp that morphed into the currently observed dust gap.

    Although more observations are needed to solve the conundrums of Elias 2-27’s disk, the evidence for a massive, gravitationally unstable disk is quite compelling, says Rice.

    Astronomers still need to work out how gravitational instability leads to planets — via direct collapse or indirectly, inciting spiral structures that help funnel material. Elias 2-27 and others like it will help astronomers piece together the planet formation puzzle.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.


    Stem Education Coalition

    Sky & Telescope, founded in 1941 by Charles A. Federer Jr. and Helen Spence Federer, has the largest, most experienced staff of any astronomy magazine in the world. Its editors are virtually all amateur or professional astronomers, and every one has built a telescope, written a book, done original research, developed a new product, or otherwise distinguished him or herself.

    Sky & Telescope magazine, now in its eighth decade, came about because of some happy accidents. Its earliest known ancestor was a four-page bulletin called The Amateur Astronomer, which was begun in 1929 by the Amateur Astronomers Association in New York City. Then, in 1935, the American Museum of Natural History opened its Hayden Planetarium and began to issue a monthly bulletin that became a full-size magazine called The Sky within a year. Under the editorship of Hans Christian Adamson, The Sky featured large illustrations and articles from astronomers all over the globe. It immediately absorbed The Amateur Astronomer.

    Despite initial success, by 1939 the planetarium found itself unable to continue financial support of The Sky. Charles A. Federer, who would become the dominant force behind Sky & Telescope, was then working as a lecturer at the planetarium. He was asked to take over publishing The Sky. Federer agreed and started an independent publishing corporation in New York.

    “Our first issue came out in January 1940,” he noted. “We dropped from 32 to 24 pages, used cheaper quality paper…but editorially we further defined the departments and tried to squeeze as much information as possible between the covers.” Federer was The Sky’s editor, and his wife, Helen, served as managing editor. In that January 1940 issue, they stated their goal: “We shall try to make the magazine meet the needs of amateur astronomy, so that amateur astronomers will come to regard it as essential to their pursuit, and professionals to consider it a worthwhile medium in which to bring their work before the public.”

     
  • richardmitnick 10:29 am on July 17, 2021 Permalink | Reply
    Tags: "NASA’s Kepler Finds Outcast Earths", , , , , Sky & Telescope,   

    From NASA/Kepler via Sky & Telescope : “NASA’s Kepler Finds Outcast Earths” 

    NASA Kepler Logo


    From NASA/Kepler

    via

    Sky & Telescope

    July 13, 2021
    Lauren Sgro

    Astronomers uncovered four new Earth-mass rogue planet candidates by searching for microlensing events observed with Kepler.

    1
    An artist’s impression of a free-floating planet, drifting by its lonesome through the cosmos. Although this depiction shows a Jupiter-like planet, astronomers found four new Earth-mass rogue planet candidates using the Kepler space telescope. Credit: NASA/JPL (US).

    No longer part of any stellar system, rogue planets drift aimlessly through space after the tumultuous early stages of planet formation eject them. Now, using NASA’s Kepler telescope, astronomers have announced four new Earth-mass outcast planet candidates.

    When a star or planet passes in front of a distant star, it acts like a magnifying lens to temporarily brighten the background star, an effect known as microlensing. Since rogue planets don’t have the luxury of a host star to reveal their presence, they are best detected via microlensing. The smaller the “lens,” the shorter the microlensing event; Earth-mass planets magnify background stars for a couple hours at most, which makes these microlensing episodes hard to find.

    In the first search for rogue planets using a space-based observatory, a team lead by Iain McDonald (now at Open University (UK)) used data from a two-month span of the rejuvenated Kepler mission, dubbed K2, to scavenge for microlensing events. K2 was not meant to look at the dense galactic bulge, so the team had to develop new methods to sift through the data. They found 27 microlensing events, five of them brand new. Four of these new events have the shortest duration of all their findings, lasting a little over an hour at most and hinting at the presence of Earth-mass rogue planets. The team presents the results in the July MNRAS.

    The Hunt for Rogue Planets

    Even though planets cause many microlensing events, most of these worlds are bound to a star – in fact, one of the newly discovered events shows the signature of a bound planet. Previously, astronomers knew of only five super short-lived microlensing episodes (including one we’ve reported previously) thought to be caused by low-mass rogue planets. McDonald’s team has almost doubled that number.

    2
    How a gravitational lens temporarily brightens a background star. To search for instances of microlensing, astronomers use light curves, which show how stars change in brightness over time. When they see a burst in the brightness of a star, they know microlensing may be to blame. In this example, a bound planet gives itself away by causing an extra peak in the light curve, in addition to the primary peak caused by the parent star. In the case of free-floating planets, astronomers only see one single peak that lasts for a very short amount of time. Credit: National Aeronautics Space Agency (US), European Space Agency [Agence spatiale européenne][Europäische Weltraumorganisation](EU), and K. Sahu (Space Telescope Science Institute (US))

    Przemek Mro̒z (California Institute of Technology (US)), a fellow rogue planet hunter, isn’t convinced that all of these planets are actually drifters. “Figuring out whether these objects are indeed free-floating or not is more tricky,” he says. It’s possible, he adds, that some of these planets might be orbiting far from their host star while remaining gravitationally bound. “Their microlensing signature would look like nearly identical to the signal expected from free-floating planets.”

    While there’s always a chance that the four new microlensing events could indicate something less interesting, such as bound planets or stellar flares, the fact that they lasted such a short time suggests that free-floating planets are a serious contender. Ground-based observations are needed to confirm these events, but these findings present exciting evidence that an Earth-mass population of rogue planets might wander our galaxy.

    “The new results from Kepler confirm our earlier studies [Nature] based on ground-based OGLE observations that such low-mass (Earth-mass) free-floating or widely-orbiting planets are quite common in the Milky Way,” says Mro̒z. If these outcast earths are truly typical in our galactic neighborhood, future telescopes like Euclid and Nancy Grace Roman will be able to detect their signals easily.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    NASA’s Ames Research Center (US) manages the Kepler and K2 missions for NASA’s Science Mission Directorate. NASA’s Jet Propulsion Laboratory in Pasadena, California, managed Kepler mission development. Ball Aerospace & Technologies Corporation operates the flight system with support from the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder.

    In October 2009, oversight of the Kepler project was transferred from the Discovery Program at NASA’s Marshall Space Flight Center, Huntsville, AL, to the Exoplanet Exploration Program at JPL

    The loss of a second of the four reaction wheels on board the Kepler spacecraft in May 2013 brought an end to Kepler’s four plus year science mission to continuously monitor more than 150,000 stars to search for transiting exoplanets. Developed over the months following this failure, the K2 mission represents a new concept for spacecraft operations that enables continued scientific observations with the Kepler space telescope. K2 became fully operational in June 2014 and is expected to continue operating until 2017 or 2018.

    NASA JPL Icon

     
  • richardmitnick 4:06 pm on July 9, 2021 Permalink | Reply
    Tags: "Amateur Astronomer Discovers New Moon of Jupiter", , , , , It would bring the tally of Jovian satellites to 80., , Sky & Telescope   

    From Sky & Telescope : “Amateur Astronomer Discovers New Moon of Jupiter” 

    From Sky & Telescope

    July 8, 2021
    Jeff Hecht

    An amateur astronomer has discovered a new moon of Jupiter. While it hasn’t received official designation yet, it would bring the tally of Jovian satellites to 80.

    The amateur astronomer who last year recovered four lost Jovian moons has become the first amateur to discover a previously unknown moon. Kai Ly reported the discovery to the Minor Planet Mailing List on June 30th and has submitted it for publication as a Minor Planet Electronic Circular.

    Ly began planning the quest in May, but their real work began in June, when they began examining data taken in 2003 with the 3.6-meter Canada-France-Hawaii Telescope (CFHT).

    David Jewitt and Scott Sheppard (University of Hawai‘i (US)) had led a group that used these images to discover 23 new moons. The images remain available online, and Sheppard and others later used them to discover other Jovian moons, including Valetudo, Ersa, and Pandia.

    2
    Jupiter has 79 moons acknowledged by the International Astronomical Union’s Minor Planet Center, but an amateur astronomer has just discovered another one (not shown here). Most of the planet’s prograde moons (purple, blue) orbit relatively close to Jupiter, while its retrograde moons (red) orbit farther out. One exceptions is Valetudo (green), a prograde-moving body discovered in 2018 that’s far out.
    Carnegie Inst. for Science (US) / Roberto Molar Candanosa.

    Pre-discovery images of those moons suggested that more undiscovered moons might be hiding in the 2003 data set. Ly started with images taken in February, when Jupiter was at opposition and the moons were brightest. They examined 19 of 36 image panels recorded on February 24th, and found three potential moons moving at 13 to 21 arcseconds per hour during the night.

    Ly could not recover two of the potential moons on other nights, but did find the third, temporarily designated EJc0061, on survey observations on February 25 to 27, and on images taken with the Subaru Telescope on February 5 and 6.


    That established a 22-day arc that suggested the object was bound to Jupiter.

    Ly thus had enough information to trace the moon’s orbit on survey images from March 12 to April 30. “From there on, the orbit and ephemeris quality was decent enough for me to begin searching observations beyond 2003,” Ly says. They found the moon near its predicted position in later images from the Subaru, CFHT, and Cerro Tololo Inter-American Observatory taken through early 2018.

    The faint moon ranges from magnitude 23.2 to 23.5.

    The end result was an arc of 76 observations over 15.26 years (5,574 days), enough for Ly to consider its orbit well-secured for decades. The data track the moon — provisionally designated S/2003 J 24 pending publication — through nearly eight 1.9-year orbits of Jupiter, says David Tholen (University of Hawai‘i), more than enough to show it’s a moon. Tholen has not checked the images, but says the evidence seems solid: “It would be nearly impossible for artifacts to fit a Jovicentric orbit over so many different nights using different cameras.”

    “I’m proud to say that this is the first planetary moon discovered by an amateur astronomer!” says Ly. But otherwise, they admit, “it’s just a typical member of the retrograde Carme group.” This group includes 22 other small moons orbiting Jupiter in the opposite direction of its spin with periods of around two years. Their orbits are similar enough to suggest they were all fragments from a single impact. They’re probably chips off Carme, the first of the group to be discovered and at 45 kilometers across, by far the largest.

    Such small retrograde Jovian moons may have plenty of company awaiting discovery. Last year, Edward Ashton, Matthew Beaudoin, and Brett J. Gladman (University of British Columbia (CA)) spotted some four dozen objects as small as 800 meters across that appeared to be orbiting Jupiter. They did not follow them long enough to prove the objects were Jovian moons, but from their preliminary observations, they suggested that Jupiter could have some 600 satellites at least 800 meters in diameter. The development of bigger and more sensitive telescopes will create room for new discoveries, Tholen says.

    Ly describes their moon-hunting as “a summer hobby before I return to school.” They hope to find more, but with more data than they can process by themselves from the February 2003 observations alone, they decided to publicize their results to raise interest.

    Amateur Sam Deen is “quite impressed” with Ly’s accomplishment. He adds that when observatories post survey data openly, it creates more opportunities for amateurs to make discoveries. “The main obstacle is just getting to know what you’re doing and having the tolerance to go looking through the data for hours before turning up anything worthwhile,” he says.

    Software and services can aid in interpreting the results, including the Find_Orb orbit determination software, the interactive Aladin Sky Atlas, the Minor Planet Center’s many services, and the Canadian Astronomical Data Center’s Solar System Object Image Search. The field is open for amateur astronomers to make their own discoveries.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Sky & Telescope, founded in 1941 by Charles A. Federer Jr. and Helen Spence Federer, has the largest, most experienced staff of any astronomy magazine in the world. Its editors are virtually all amateur or professional astronomers, and every one has built a telescope, written a book, done original research, developed a new product, or otherwise distinguished him or herself.

    Sky & Telescope magazine, now in its eighth decade, came about because of some happy accidents. Its earliest known ancestor was a four-page bulletin called The Amateur Astronomer, which was begun in 1929 by the Amateur Astronomers Association in New York City. Then, in 1935, the American Museum of Natural History opened its Hayden Planetarium and began to issue a monthly bulletin that became a full-size magazine called The Sky within a year. Under the editorship of Hans Christian Adamson, The Sky featured large illustrations and articles from astronomers all over the globe. It immediately absorbed The Amateur Astronomer.

    Despite initial success, by 1939 the planetarium found itself unable to continue financial support of The Sky. Charles A. Federer, who would become the dominant force behind Sky & Telescope, was then working as a lecturer at the planetarium. He was asked to take over publishing The Sky. Federer agreed and started an independent publishing corporation in New York.

    “Our first issue came out in January 1940,” he noted. “We dropped from 32 to 24 pages, used cheaper quality paper…but editorially we further defined the departments and tried to squeeze as much information as possible between the covers.” Federer was The Sky’s editor, and his wife, Helen, served as managing editor. In that January 1940 issue, they stated their goal: “We shall try to make the magazine meet the needs of amateur astronomy, so that amateur astronomers will come to regard it as essential to their pursuit, and professionals to consider it a worthwhile medium in which to bring their work before the public.”

     
  • richardmitnick 4:48 pm on June 18, 2021 Permalink | Reply
    Tags: "Astronomers Look into the Past of Local Dwarf Galaxies", , , , , Effects of gravity, Sky & Telescope   

    From Sky & Telescope : “Astronomers Look into the Past of Local Dwarf Galaxies” 

    From Sky & Telescope

    June 14, 2021
    Camille M. Carlisle

    A combination of simulations and observations indicates that galaxies like the Large Magellanic Cloud control when punier dwarfs plunge into large galaxies [is this really news?].

    When midsize galaxies merge with large ones, they drag a lot of little galaxies with them, Eric Bell (University of Michigan (US), Ann Arbor) reported June 9th at the virtual summer meeting of the American Astronomical Society (US).

    2
    This visible-light mosaic shows the Large and Small Magellanic Clouds below the Milky Way plane.
    Axel Mellinger, Central Michigan University (US).

    To investigate the dwarf galaxy population of the Local Group in which the Milky Way and Andromeda galaxies live, Bell and Richard D’Souza (Vatican Observatory (VCS), Italy) simulated the clouds of dark matter in which Milky Way–mass galaxies reside. By following the interactions of 48 of these simulated haloes with smaller surrounding ones (stand-ins for dwarf galaxies), the astronomers discovered something interesting: Satellites tended to merge in groups with the big galaxy, with smaller galaxies tagging along [by gravity] when a midsize one merged with the central leviathan. The effect didn’t increase the number of infalling galaxies; it only changed when they fell in.

    To test these predictions, the team looked at when star formation shut off in real-life, smaller galaxies surrounding the Milky Way and Andromeda. Starbirth, the astronomers reasoned, is a good proxy for merger time, because the little galaxies would likely be stripped of their star-forming gas when they fell into the big, hot halo of the central galaxy. And indeed, observations show that star formation shut off in the Milky Way satellites around two periods of time when a sizable galaxy was falling in — about 2 billion years ago for the Large Magellanic Cloud and 10 billion years ago for Gaia-Enceladus.

    2
    A visualization of the moment of impact between the MW’s progenitor and the Gaia-Enceladus dwarf galaxy. Credit: Instituto de Astrofísica de Canarias (ES).

    Andromeda Galaxy Messier 31 with Messier 32 -a satellite galaxy. Credit:Terry Hancock-DownUnderObservatory.

    Conversely, there’s only one turn-off time for Andromeda satellites: about 6 billion years ago. That suggests that Andromeda’s largest companion, Messier 33, might have started its nosedive into Andromeda’s halo around then. The timeline would problematize others’ suggestion that Messier 33 is on its first flyby past Andromeda and, like the LMC, had only arrived in the last couple billion years. A closer look at Andromeda’s satellite family could elucidate just when Messier 33 showed up for its visit.

    Astronomers are now able to explore the satellites of large galaxies out to several tens of millions of light-years from us, and if borne out, these results may enable them to discern such galaxies’ histories more clearly. The team’s work appears in the July MNRAS.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Sky & Telescope, founded in 1941 by Charles A. Federer Jr. and Helen Spence Federer, has the largest, most experienced staff of any astronomy magazine in the world. Its editors are virtually all amateur or professional astronomers, and every one has built a telescope, written a book, done original research, developed a new product, or otherwise distinguished him or herself.

    Sky & Telescope magazine, now in its eighth decade, came about because of some happy accidents. Its earliest known ancestor was a four-page bulletin called The Amateur Astronomer, which was begun in 1929 by the Amateur Astronomers Association in New York City. Then, in 1935, the American Museum of Natural History opened its Hayden Planetarium and began to issue a monthly bulletin that became a full-size magazine called The Sky within a year. Under the editorship of Hans Christian Adamson, The Sky featured large illustrations and articles from astronomers all over the globe. It immediately absorbed The Amateur Astronomer.

    Despite initial success, by 1939 the planetarium found itself unable to continue financial support of The Sky. Charles A. Federer, who would become the dominant force behind Sky & Telescope, was then working as a lecturer at the planetarium. He was asked to take over publishing The Sky. Federer agreed and started an independent publishing corporation in New York.

    “Our first issue came out in January 1940,” he noted. “We dropped from 32 to 24 pages, used cheaper quality paper…but editorially we further defined the departments and tried to squeeze as much information as possible between the covers.” Federer was The Sky’s editor, and his wife, Helen, served as managing editor. In that January 1940 issue, they stated their goal: “We shall try to make the magazine meet the needs of amateur astronomy, so that amateur astronomers will come to regard it as essential to their pursuit, and professionals to consider it a worthwhile medium in which to bring their work before the public.”

     
  • richardmitnick 4:57 pm on June 2, 2021 Permalink | Reply
    Tags: "Metal-poor Stars Shed Light on the Origin of Gold", , , , , Explosions of massive stars might have produced gold and other rare heavy elements observed in metal-poor stars in our galaxy’s halo., , Sky & Telescope, Women in STEM-Kaley Brauer   

    From Sky & Telescope : Women in STEM-Kaley Brauer “Metal-poor Stars Shed Light on the Origin of Gold” 

    From Sky & Telescope

    June 2, 2021
    Jure Japelj

    Explosions of massive stars might have produced gold and other rare heavy elements observed in metal-poor stars in our galaxy’s halo.

    1
    Neutron star mergers produce rare heavy elements like gold. It is not yet clear whether collapsing stars also produce such elements. Credit: L. Calçada / M. Kornmesser/ ESO [Observatoire européen austral][Europäische Südsternwarte] (EU) (CL)

    “We finally know where gold comes from!” announced the headlines in 2017 following the detection of gravitational waves from the neutron star collision known as GW170817.

    But do we really?

    The recipe to make elements heavier than iron sounds simple enough: Bombard a lighter nucleus with neutrons and watch it grow. But there’s a catch — to produce heavy elements like gold, platinum, and uranium, a nucleus has to grow really fast, otherwise it decays into lighter elements before it reaches a stable form. This rapid process produces about half of all elements heavier than iron.

    The cosmic origin of these rapid-process, or r-process elements has long been subject to debate. The fortuitous case of GW170817 precipitated a great leap forward. Short-lived visible and infrared light accompanying the neutron star merger carried clear signatures of r-process elements. While only one element, namely strontium, has been identified in the data, scientists nonetheless estimated that this event alone likely produced between 3 and 13 Earth masses’ worth of gold.

    But while there’s no doubt that neutron star mergers produce r-process elements, the jury is still out on how important these events are in the grand scheme of things.

    After all, other cosmic events might produce these elements, too. For example, the violent deaths of massive stars could also play a role. In a recent study to appear in The Astrophysical Journal, a team of scientists shows that we shouldn’t discount supernovae just yet.

    History, as Told by Metal-poor Stars

    “There are a lot of problems with neutron star mergers as a source of heavy elements in the early universe,” explains Kaley Brauer (Massachusetts Institute of Technology (US), who led the new study.

    One long-standing issue concerns metal-poor stars found in the galactic halo. These sparse stars surround the galaxy’s spiral disk and formed a long time ago from nearly pristine gas that was barely touched by earlier generations of stars.

    Yet these metal-poor stars have a relatively high amount of r-process elements in their atmospheres. How did these elements get into the gas from which the stars were born?

    It usually takes billions of years for two stars in a binary system to become neutron stars, spiral toward each other, and merge. By the time the merger seeds the surrounding gas with r-process elements, the metal-poor star had already been born.

    The collapse of a massive star nearing the end of its brief life could also create conditions conducive to the formation of r-process elements, but on shorter time scales than that of a binary merger. The idea works in theory but hasn’t been proven directly.

    Brauer and her colleagues decided to test whether the collapsing star scenario could account for the abundances of r-process elements, in particular the europium observed in metal-poor stars. “We started with a simple assumption,” says Brauer. “What if you said all heavy elements were formed in this way in the early universe?”

    Europium, Barium & Nanodiamonds

    The team constructed a simple yet self-consistent model of a galaxy, represented by a giant ball of gas in which a number of stars collapse. Each stellar explosion enriches the gas with metals like iron, and some of these supernovae also produce r-process elements. The model successfully reproduces the relative abundances of europium and iron in metal-poor stars.

    One key question is, how many supernovae have to explode to account for the observed abundances of r-process elements? “[The researchers] come to some interesting conclusions,” says Darach Watson (University of Copenhagen [Københavns Universitet](DK)). “They find frequencies which are similar to those of long gamma-ray bursts.”

    Such gamma-ray bursts are associated with the most extreme explosions of giant stars. The result implies that not every supernova would be producing r-process elements, only the most extreme ones.

    Despite the promising results, it’s too early to draw strong conclusions. “The team looks only at one element, europium, but it could also be possible to use barium, for example,” says Watson. Barium is relatively easy to detect in the metal-poor stars and could help constrain the model. Furthermore, Brauer is already studying how the complex mixing of elements in the gas from which the stars are born affects the results.

    Watson also draws attention to another often-overlooked line of evidence: nanodiamonds. Some of these tiny, sub-micron diamonds found in meteorites contain traces of r-process elements. “The question is, where is that coming from?” asks Watson. “Probably from a core-collapse supernova, but who knows?”

    Ultimately, scientists will have to tackle the complex question of the origin of r-process elements from different angles. The way things stand now, it seems that more than one type of cosmic source contributes to the overall abundance of gold and related elements in the universe.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Sky & Telescope, founded in 1941 by Charles A. Federer Jr. and Helen Spence Federer, has the largest, most experienced staff of any astronomy magazine in the world. Its editors are virtually all amateur or professional astronomers, and every one has built a telescope, written a book, done original research, developed a new product, or otherwise distinguished him or herself.

    Sky & Telescope magazine, now in its eighth decade, came about because of some happy accidents. Its earliest known ancestor was a four-page bulletin called The Amateur Astronomer, which was begun in 1929 by the Amateur Astronomers Association in New York City. Then, in 1935, the American Museum of Natural History opened its Hayden Planetarium and began to issue a monthly bulletin that became a full-size magazine called The Sky within a year. Under the editorship of Hans Christian Adamson, The Sky featured large illustrations and articles from astronomers all over the globe. It immediately absorbed The Amateur Astronomer.

    Despite initial success, by 1939 the planetarium found itself unable to continue financial support of The Sky. Charles A. Federer, who would become the dominant force behind Sky & Telescope, was then working as a lecturer at the planetarium. He was asked to take over publishing The Sky. Federer agreed and started an independent publishing corporation in New York.

    “Our first issue came out in January 1940,” he noted. “We dropped from 32 to 24 pages, used cheaper quality paper…but editorially we further defined the departments and tried to squeeze as much information as possible between the covers.” Federer was The Sky’s editor, and his wife, Helen, served as managing editor. In that January 1940 issue, they stated their goal: “We shall try to make the magazine meet the needs of amateur astronomy, so that amateur astronomers will come to regard it as essential to their pursuit, and professionals to consider it a worthwhile medium in which to bring their work before the public.”

     
  • richardmitnick 11:48 am on May 29, 2021 Permalink | Reply
    Tags: "Dark Frames and Bias Frames Demystified", A “bias frame” is an image taken with no light falling on the image sensor using the shortest exposure time you can manage with your camera., A “dark frame” is like a bias frame in that it's an image taken with no light falling on the image sensor but dark frames need to be the same length as your light frames., , If you use a master dark frame you don’t need a master bias frame — you really don’t want to subtract the dark fixed-pattern twice!, Image calibration is the first step of post processing., Many imagers skip calibration completely and some do it improperly., One of the keys to facilitating image post processing is to record better data in the first place., Sky & Telescope, Technological developments may eventually make dark frames obsolete., We use three different kinds of master calibration frames. You’ve probably heard of them: bias; darks; and flats.   

    From Sky & Telescope : “Dark Frames and Bias Frames Demystified” 

    From Sky & Telescope

    May 24, 2021
    Richard S. Wright Jr.

    “One of the keys to facilitating image post processing is to record better data in the first place. I’ve already talked a lot about fundamental techniques to help you capture the best data possible and understand the limits of your equipment or the weather. Once you’ve collected your images though, you need to calibrate them to obtain the best results.

    1
    There is nothing wrong with your camera. Proper calibration is always needed for low light images.
    Credit: Richard S. Wright Jr.

    Image calibration is the first step of post processing, and when it’s done right it makes subsequent adjustments easier. Calibration helps remove artifacts that come with the image-acquisition process, so that your post processing deals with the actual good data you have worked so hard to acquire. Image calibration is also called data reduction, because it reduces all that you have collected to just the “data” part.

    Many imagers skip calibration completely and some do it improperly. Skipping a step can cost you time and effort later, and doing it improperly can make your initial starting point even worse than not doing it at all. Once images are clean, they require only minimal processing and produce stunning, informative, and honest images.

    2
    This is simulated, but I’ve seen worse. Faint signal stretched hard will bring out your sensor’s dark fixed-pattern noise. Proper calibration can help a great deal with this. Credit: Richard S. Wright Jr.

    To remove the artifacts of the camera and optical system from our data, we use three different kinds of master calibration frames. You’ve probably heard of them: bias, darks, and flats. Flats are important enough to get a blog all their own, so this month I’m going to focus on biases and darks.

    Bias Frames

    A bias frame is an image taken with no light falling on the image sensor, using the shortest exposure time you can manage with your camera. Either close the shutter or cap your telescope. Bias frames should be recorded at the same temperature as your light frames (the actual exposure of your target), and using all the same camera gain or ISO settings.

    If you take your biases during the day, be careful that there are no light leaks getting to your sensor. Filter wheels and focusers often leak ambient light into your camera, which will ruin your bias frames. When I need to record bias frames during the day, I wrap much of the imaging train up with aluminum foil to keep this from happening.

    3
    Bias frames capture dark fixed-pattern noise, shown here, from variations in manufacturing that affects all image sensors to some degree. Credit: Richard S. Wright Jr.

    Every image sensor, be it a CCD or CMOS, has what is known as dark fixed-pattern noise, a pattern that is the result of the manufacturing process. Every image you take records this faint pattern, no matter how long the exposure was or how much signal falls on your image sensor. The pattern then shows up in your images when you start to stretch (or brighten) the areas of your picture that collected little light.

    To remove dark fixed-pattern noise, subtract a bias calibration image from your light image. In order for this step to work well, a master bias frame is created by stacking many individual bias frames, which removes the read noise. You can subtract the master bias frame from any image you take with that camera, with whatever length exposure, as long as the other camera settings (temperature, gain, offset, etc.) are the same.

    Dark Frames

    A dark frame is like a bias frame in that it’s an image taken with no light falling on the image sensor, but dark frames need to be the same length as your light frames. In other words, if you take several 3-minute exposures on your target, you’ll want to calibrate them using a 3-minute master dark frame, which you’ll subtract from the image. This calibration step removes two things: First, your master dark contains the same dark fixed-pattern noise that your master bias frame does. It also collects dark current, and more pattern noise called DSNU (Dark Signal Non Uniformity). Individual dark frames also contain their associated shot noise with that comes along the dark current.

    If you use a master dark frame you don’t need a master bias frame — you really don’t want to subtract the dark fixed-pattern twice!

    4
    The left image was recorded without cooling and suffers from excessive noise from the resulting dark current. Credit: Richard S. Wright Jr.

    The dark current comes from thermal activity (that is, heat) in the image sensor, and it creates a growing offset to all our pixel values that increases with both time and higher temperatures. If the effect were uniform we might not mind so much, but the offset is spread randomly among the pixels (the DSNU). The dark current also feeds “hot pixels” — pixels that appear much brighter than their neighbors. A good master dark can do a lot to remove that salty appearance from your raw frames. Cooling the sensor also greatly reduces the thermal current that pollutes images.

    We can’t simply subtract the shot noise associated with dark current from the dark frame; instead, we have to stack dark frames to minimize the noise. That way, this random noise doesn’t pollute all the light frames that we’re calibrating. The dark current’s shot noise is also in our light frames, but we can only remove this noise by stacking lot of light frames. When we subtract a dark frame, we remove hot pixel offsets and the dark current offset, but we can’t subtract the dark current’s shot noise — stacking is the only way to remove shot noise of any kind.

    5
    Hot pixels can detract from a monochrome or color image. There are many techniques for removing them, but dark frames are a good first defense. Credit: Richard S. Wright Jr.

    The Future

    So why talk about bias frames if all you really need is a dark frame? Because technological developments may eventually make dark frames obsolete. There are many newer image sensors with extremely low dark current when cooled sufficiently. I really hope this trend continues. Once cooled they may gain a single electron or less per pixel over long periods of time — even 20 minutes in one sensor I’ve tested.

    If the camera sensor has no appreciative dark current when cooled, you can apply bias frames to your data and skip doing darks all together. You may still get some hot pixels here and there with these cameras, but those are easily removed with a pixel map in post processing or by dithering your exposures and stacking with a rejection algorithm.

    Some CMOS sensors also actively drain off dark current as it accumulates. You can watch this happen by taking longer and longer dark frames and observing that no additional background signal accumulates, even at warm temperatures! Again, in these cases, a good clean bias frame is all you’ll really need, plus stacking plenty of individual exposures.

    Stay tuned: Next time I’m going to talk about the alchemy of flat-frame calibration and why often people have such a hard time getting them to work properly for them.”

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Sky & Telescope, founded in 1941 by Charles A. Federer Jr. and Helen Spence Federer, has the largest, most experienced staff of any astronomy magazine in the world. Its editors are virtually all amateur or professional astronomers, and every one has built a telescope, written a book, done original research, developed a new product, or otherwise distinguished him or herself.

    Sky & Telescope magazine, now in its eighth decade, came about because of some happy accidents. Its earliest known ancestor was a four-page bulletin called The Amateur Astronomer, which was begun in 1929 by the Amateur Astronomers Association in New York City. Then, in 1935, the American Museum of Natural History opened its Hayden Planetarium and began to issue a monthly bulletin that became a full-size magazine called The Sky within a year. Under the editorship of Hans Christian Adamson, The Sky featured large illustrations and articles from astronomers all over the globe. It immediately absorbed The Amateur Astronomer.

    Despite initial success, by 1939 the planetarium found itself unable to continue financial support of The Sky. Charles A. Federer, who would become the dominant force behind Sky & Telescope, was then working as a lecturer at the planetarium. He was asked to take over publishing The Sky. Federer agreed and started an independent publishing corporation in New York.

    “Our first issue came out in January 1940,” he noted. “We dropped from 32 to 24 pages, used cheaper quality paper…but editorially we further defined the departments and tried to squeeze as much information as possible between the covers.” Federer was The Sky’s editor, and his wife, Helen, served as managing editor. In that January 1940 issue, they stated their goal: “We shall try to make the magazine meet the needs of amateur astronomy, so that amateur astronomers will come to regard it as essential to their pursuit, and professionals to consider it a worthwhile medium in which to bring their work before the public.”

     
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