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  • 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.”

     
  • richardmitnick 8:49 am on May 8, 2021 Permalink | Reply
    Tags: "The Hubble Space Telescope As Cosmic-Ray Detector", , , , Sky & Telescope,   

    From Sky & Telescope : “The Hubble Space Telescope As Cosmic-Ray Detector” 

    From Sky & Telescope

    May 5, 2021
    Jure Japelj

    Astronomers, using Hubble Space Telescope as a particle detector, have traced cosmic rays flowing in Earth’s geomagnetic field.

    1
    Depiction of Earth’s geomagnetic field. Credit: National Aeronautics and Space Administration(US)

    The Hubble Space Telescope requires little or no introduction. For more than three decades, the telescope has stood at the forefront of astronomical research, while its visually stunning images have served as a paragon of awe and inspiration.

    But all this time, Hubble has also been secretly acting as a particle detector. And a good one at that, as a team of scientists demonstrated in a pilot study to appear in The Astrophysical Journal.

    Energetic charged particles, or cosmic rays, populate every corner of the solar system. A near-constant flow of galactic particles originates from supernova remnants (and the stellar cinders at their cores).

    The Sun also sheds energetic particles, mostly protons, during solar flares and coronal mass ejections.

    These cosmic rays wiggle and push their way through the solar system under the influence of the magnetized solar wind. Many end up at Earth, where they threaten astronauts, disrupt satellites, and affect atmospheric chemistry.

    Cosmic rays are every astronomer’s nightmare. Neither ground nor space telescopes are immune to the barrage of the energetic particles, and when a particle travels through a camera, it leaves a sharp and bright trace on the resulting image. Needless to say, astronomers try to remove this pollution from their data.

    But now scientists have demonstrated that one person’s garbage is another’s treasure.

    Hubble’s Treasure Trove

    “The idea for this project started five or six years ago at a conference about space weather,” says Susana Deustua (Ars Metrologia, formerly at NASA Space Telescope Science Institute (US)), who led the study. An international group of astronomers, particle physicists, and planetary scientists put their heads together and came up with a plan. “Cosmic rays interact with the geomagnetic field,” Deustua adds. “We know that Hubble collects charged particles on its detector, therefore we should be able to glean information about the field from Hubble.”

    The team dug into Hubble’s rich data archive. They looked for calibration images that were particularly well-suited for their plan and ended up with almost 100,000 images collected over the past 25 years.

    Algorithms for finding and removing cosmic-ray traces from astronomical images have been around for decades. But rather than simply getting rid of the traces, the team wanted to learn as much as possible about the cosmic rays that caused them. “For example, we wanted to know how many pixels on the camera each cosmic ray affected and how much energy the particle lost in the process,” explains graduate student Nathan Miles (University of California (US)), who is first author on the study.

    Miles developed software to extract such information, using cloud computing services to carry out the time-demanding computations. His algorithm harvested more than 1 billion cosmic rays from the images.

    2
    Map of cosmic ray traces in one of the Hubble’s images. Traces may have different shapes and affect different number of pixels on the camera. Credit: Nathan Miles.

    A Cosmic-ray Image of Earth’s Magnetic Field

    The results provide an important proof of concept with encouraging results. The cosmic ray properties from Hubble data match those detected by the Pamela experiment (IT), a defunct particle detector in low-Earth orbit. The team also saw in their data the South Atlantic Anomaly, the famous dip in the Earth’s geomagnetic field. And they observed the expected response of cosmic rays to the solar cycle.

    Claudio Corti (University of Hawai‘i at Manoa (US)), who was not involved in the study, was pleasantly surprised by the work. “There is always interest in a better understanding of the geomagnetic field and the effect it has on the particle radiation for astronauts and electronics on the satellites,” he says. The data may prove valuable to understand cosmic ray populations in the solar system.

    The analysis so far has only scratched the surface. The team is looking forward to unleashing the full power of the data to better understand the relation between galactic cosmic rays, the Sun, and Earth’s environment. “One of our interests is to look if we can find subtle secular changes in the geomagnetic field,” Deustua says. “We also want to make comparisons with geophysical observatories.”

    Hubble’s uninterrupted monitoring of cosmic rays over a quarter of a century nicely complements other cosmic ray detectors. “From one single-point measurement, it is hard to get information on the global space environment,” Corti says. “The more points you have, the better it is.”

    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 3:45 pm on May 5, 2021 Permalink | Reply
    Tags: "In Search of Ancient Suns", , , , , Sky & Telescope   

    From Sky & Telescope : “In Search of Ancient Suns” 

    From Sky & Telescope

    May 5, 2021
    Bob King

    1
    Sixth-magnitude HD 122563 in Boötes is the brightest, oldest star visible in the night sky. Formed nearly 13 billion years ago, it’s a member of the Milky Way’s outer halo.
    DSS2 / Aladin Sky Atlas.

    Older people never run out of stories. After all, they’ve seen a few things. Older stars likewise have tales to tell. They stood by during the Milky Way’s youth, when it eagerly gobbled up smaller galaxies until finally emerging as one of the cosmic kingpins. The first planets formed under their watch. And while galactic supernovae are few and far between today, from the long perspective of these ancient suns, they pop like flash bulbs at a press conference, their remains molded and reignited into new generations of stars. Stories to tell indeed.

    What defines old? Certainly the Sun is old. It emerged from the solar nebula 4.6 billion years ago, a respectable age by most measures. But it doesn’t compare to stars in globular clusters that have kept their wicks lit for some 12.8 billion years. While not the first generation of stars to form in the universe, globular suns are so ancient that they preceded the formation of the Milky Way galaxy as we know it. They were the first clots of stars to form in the massive cloud that would eventually collapse to form the galaxy’s bulge and ultimately its spiral disk. Through it all, the globulars watched from the periphery — our galaxy’s halo — where most of them reside to this day.

    2
    A timeline of the universe shows when the first stars emerged, around 180 million years, give or take, after the Big Bang. Their energetic radiation ionized the neutral hydrogen gas that then permeated the universe.
    N. R. Fuller / National Science Foundation (US).

    Cosmology teaches us that the universe originated in a primeval fireball ~13.8 billion years ago, so you can’t get any older than that. Some stars come close. The first generation of stars formed between 100 and 250 million years after the Big Bang from hydrogen and helium, the two most abundant elements produced in the formative universe. Fusion of these atomic lightweights within their cores produced heavier elements such as carbon, oxygen, and nitrogen, which were expelled into space when the stars exploded as supernovae. Mixed with healthy amounts of primordial hydrogen and helium, these new elements wound up in the next generation of stars.

    3
    Our Milky Way galaxy seen from a hypothetical outsider’s viewpoint. Open star clusters and emission nebulae typically reside within the spiral arms, home to young Population I stars, while globular clusters and older Population II stars pepper the spherical halo surrounding the disk. Some 26,000 light-years from our solar system, the central bulge lurks behind dust clouds in Sagittarius.
    Sky & Telescope with additions by the author.

    Astronomers call elements heavier than helium “metals,” so future generations of stars gradually became enriched in metals. Measuring a star’s metal content, then, is a handy way to determine its age. The fewer heavier elements observed, the older the star. Many of these metal-poor stars, dubbed Population II, inhabit the galactic halo and central bulge because they preceded the formation of the Milky Way’s spiral disk, home to young Population I stars like our Sun. By extension, the most ancient stars — that first generation with no metals at all — belong to the elusive Population III. I use the word elusive because we’re still searching for definitive evidence that any still exist.

    Let’s Meet These Ancient Stars

    4
    Both HD 122563 and HD 140283 are well placed for observation on May nights. They’re bright enough to easily show in this 8-second exposure at f/2.8 and ISO 2500. Credit: Bob King.

    We track down and admire five of the most ancient stars in the universe.

    Sixth-magnitude HD 122563 in Boötes is the brightest, oldest star visible in the night sky. Formed nearly 13 billion years ago, it’s a member of the Milky Way’s outer halo.
    DSS2 / Aladin Sky Atlas.

    Older people never run out of stories. After all, they’ve seen a few things. Older stars likewise have tales to tell. They stood by during the Milky Way’s youth, when it eagerly gobbled up smaller galaxies until finally emerging as one of the cosmic kingpins. The first planets formed under their watch. And while galactic supernovae are few and far between today, from the long perspective of these ancient suns, they pop like flash bulbs at a press conference, their remains molded and reignited into new generations of stars. Stories to tell indeed.

    What defines old? Certainly the Sun is old. It emerged from the solar nebula 4.6 billion years ago, a respectable age by most measures. But it doesn’t compare to stars in globular clusters that have kept their wicks lit for some 12.8 billion years. While not the first generation of stars to form in the universe, globular suns are so ancient that they preceded the formation of the Milky Way galaxy as we know it. They were the first clots of stars to form in the massive cloud that would eventually collapse to form the galaxy’s bulge and ultimately its spiral disk. Through it all, the globulars watched from the periphery — our galaxy’s halo — where most of them reside to this day.

    Timeline of the universe

    A timeline of the universe shows when the first stars emerged, around 180 million years, give or take, after the Big Bang. Their energetic radiation ionized the neutral hydrogen gas that then permeated the universe.
    N. R. Fuller / National Science Foundation (US).

    Cosmology teaches us that the universe originated in a primeval fireball ~13.8 billion years ago, so you can’t get any older than that. Some stars come close. The first generation of stars formed between 100 and 250 million years after the Big Bang from hydrogen and helium, the two most abundant elements produced in the formative universe. Fusion of these atomic lightweights within their cores produced heavier elements such as carbon, oxygen, and nitrogen, which were expelled into space when the stars exploded as supernovae. Mixed with healthy amounts of primordial hydrogen and helium, these new elements wound up in the next generation of stars.

    Astronomers call elements heavier than helium “metals,” so future generations of stars gradually became enriched in metals. Measuring a star’s metal content, then, is a handy way to determine its age. The fewer heavier elements observed, the older the star. Many of these metal-poor stars, dubbed Population II, inhabit the galactic halo and central bulge because they preceded the formation of the Milky Way’s spiral disk, home to young Population I stars like our Sun. By extension, the most ancient stars — that first generation with no metals at all — belong to the elusive Population III. I use the word elusive because we’re still searching for definitive evidence that any still exist.

    Let’s Meet These Ancient Stars

    Boötes and Libra
    Both HD 122563 and HD 140283 are well placed for observation on May nights. They’re bright enough to easily show in this 8-second exposure at f/2.8 and ISO 2500.
    Bob King.

    We’re going to pay a visit to five extremely metal-poor stars that have more in common with their primeval cohorts than most of the stars that spangle the sky on a dark night. We’ll begin our pilgrimage to the ancient ones with the brightest, HD 122563, a magnitude-6.2 red giant in Boötes. Located 950 light-years away in the galactic halo it’s about 12.6 billion years old. If the Sun’s a middle-aged 45 years old, say, then HD 122563 would be its great grandparent, aged 123 years. Through the telescope the star glowed pale orange and serene.

    6
    HD 140283, nicknamed the Methuselah Star, is visible in binoculars.
    DSS2 / Aladin Sky Atlas.

    Next, we meet another halo member that might just be the oldest star visible in an amateur telescope. Never mind a telescope, binoculars will do. Dubbed the Methuselah Star, HD 140283 is a magnitude-7.2 object 202 light-years away in Libra. It belongs to the subgiant class with a mass 0.8 times solar but twice as big around and almost five times as luminous. After a precise determination of its distance using the Hubble Space Telescope (HST), a 2014 study concluded that Methuselah was one of the oldest stars yet discovered, with an age of 14.27 ± 0.38 billion years.

    So wait. Is it older than the universe? Of course that can’t be. Slight uncertainties in distance and stellar modeling leave enough room for it to have been born post-Big Bang. But make no mistake. It’s really, really old, likely to have formed from enriched material after the metal-free generation exploded as supernovae. Despite its age, HD 140283 races across the galaxy at 800,000 miles per hour (1.3 million km/h) like a gold-medalist sprinter. For the moment it’s near our solar system, but the galactic halo is home sweet home.

    7
    These maps plot the locations of HD 122563 in Boötes (left) and HD 140283 in Libra (right). Stars are shown to magnitude 7 (left) and magnitude 8 (right). North is up in all maps.
    Stellarium.

    Libra hosts another of the “old ones” in He 1523-0901, a red giant embering away 2.2° due east of Beta (β) Librae and 4.5° northwest of HD 140283. It’s about 7,500 light-years from Earth and shines more faintly at magnitude 11.5, so you’ll need a 4.5-inch telescope to spot it. Aged 13.2 billion years, the star was likely present at the Milky Way’s first birthday party, long before party hats would come into fashion.

    8
    On the left, stars are plotted to magnitude 10 for BD+17°3248 and magnitude 11.5 for He 1523-0901 (right).
    Stellarium.

    From here, tilt your telescope northward to Hercules for a look at BD+17°3248, a magnitude-9.3 orange subgiant 13.8 ± 4 billion years old and approximately 2,600 light-years away.

    In 2002, a team of astronomers using the HST literally discovered gold here, the first time the element had ever been observed in a star other than the Sun. Its outer atmosphere also is tainted with radioactive thorium and other heavy elements. These could only have originated through a process called rapid neutron capture that occurs when massive stars explode as supernovae. Given BD+17°3248’s advanced age, it may well have been forged from the dregs of the sought-after Population III clan.

    We end with Sneden’s Star, a faint red giant slightly more massive than the Sun situated 17,000 light-years from Earth in the Milky Way’s halo. Located in Aquarius, this old Population II star is just now emerging into the morning sky. Look for it about 5.5° south of Jupiter in early May. At magnitude 13.2 you’ll need an 8-inch telescope for a good look.

    8
    The wide map provides context for Sneden’s Star, while the inset (left) is a detailed chart with stars to magnitude 13.5. The star is located south of a small, umbrella-like asterism.
    Stellarium.

    Sneden’s Star is named for Chris Sneden of the University of Texas (Austin)(US) who, along with his team, measured the abundance of 53 elements in the star. It hails from ~13 billion years ago and like BD+17°3248 possesses heavy elements formed by neutron capture.

    The other day, while hiking a ridge trail not far from my home, I encountered a small stand of old growth trees — behemoth white pines more than 200 years old. I felt respect for the trees. They had survived thunderstorms, changing climate, and disease to stand proudly in the present. In the same way, these ancient suns continue to shine when so many others have gone dark. They are our eyes. Through them we see nothing less than the birth and evolution of the galaxy we call home.

    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 5:11 pm on May 4, 2021 Permalink | Reply
    Tags: "What’s Inside Neutron Stars?", , , , , Neutron star J0030+0451, Neutron star J0470+6620, , Sky & Telescope   

    From Sky & Telescope : “What’s Inside Neutron Stars?” 

    From Sky & Telescope

    May 4, 2021
    Monica Young

    Size measurements of two neutron stars are narrowing down what kinds of exotic matter might exist in their extremely dense cores.

    Neutron stars are the tricksters of the celestial sphere. Their age, their temperature, even their size is not always what it first appears to be.

    But with the Neutron star Interior Composition Explorer (NICER) aboard the International Space Station, astronomers are finally beginning to make some headway measuring these stars’ actual size — and with that, some insight into their strange interiors.

    Members of the NICER team presented two independent size measurements of the most massive neutron star known at the recent virtual meeting of the American Physical Society.

    These studies, now undergoing scientific review, suggest that nuclear physicists might need to rethink what happens in the stars’ ultra-dense cores.


    NASA’s NICER Tests Matter’s Limits

    Matter at Its Most Extreme

    Neutron stars are the cinders left when massive stars implode, shedding their outer layers in supernova explosions. The stars are poised on the edge, just this side of collapsing into a black hole, and the immense gravitational pressure squeezes their electrons and protons into neutrons. Lifting a teaspoon of this matter would be a feat similar to drinking empty a horn attached to the ocean — even Thor could not lift 4 billion tons.

    However, there’s more to neutron stars than what’s in their name — they’re at most 95% neutrons and possibly even less. Their crystalline crusts contain relatively ordinary electrons and ions (the latter of which are made of neutrons and protons). As gravitational pressure increases with depth, the neutrons squeeze out of the nuclei, which eventually dissolve completely. Most protons merge with electrons; only a smattering remain for stability.

    2
    Neutron stars are not all neutrons — they likely have layers of different material. The state of matter in their inner cores remains unknown. NASA’s Goddard Space Flight Center (US) / Conceptual Image Lab

    Deeper still, in the core, the density reaches something like twice that of an atomic nucleus. Here, the matter may transform again, releasing even the quarks that make up neutrons.

    Or that’s what some theories say. But in fact nuclear physicists offer many answers to the riddle of neutron star interiors. “We have a theory for how quarks and gluons behave; this is quantum chromodynamics,” Miller says. “But the problem is you can’t really calculate this once you go past a couple of particles.” So nuclear physicists use approximations and assumptions to predict the behavior of lots of particles — and they come up with a variety of answers.

    To tell which idea is right, astronomers must do something deceptively simple: measure these objects’ mass and radius. From there they can use well-understood physics to calculate how pressure changes with density, a relation known as the equation of state, and then compare that equation to the nuclear physicists’ offerings.

    Neutrons, Quarks, or Hyperons?

    Obtaining the mass of a neutron star is easy, at least if the neutron star has a stellar companion whirling around it. But measuring size is trickier. Neutron stars’ gravity is so extreme, it bends the path of light leaving the surface. Like a funhouse mirror, this gravitational distortion makes the neutron star appear bigger than it really is.

    3
    A neutron star’s gravity warps nearby spacetime like a bowling ball resting on a trampoline. The distortion is strong enough that it redirects light from the star’s far side toward us, which makes the star look bigger than it really is.
    NASA’s Goddard Space Flight Center / Chris Smith (Universities Space Research Association (US) / NASA GESTAR [Goddard Earth Science Technology and Research] (US))

    Anna Watts (University of Amsterdam [Universiteit van Amsterdam] (NL)) and Cole Miller (University of Maryland (US)) lead two independent teams that analyze NICER data to see through this light-bending effect and put a ruler to neutron stars.

    NICER is designed to measure the rapidly changing brightness of neutron stars as they whirl around. Some of these city-size objects spin faster than the blades in a kitchen blender, but NICER can catch changes over time periods as short as 100 nanoseconds. Additional observations by the European Space Agency’s XMM-Newton telescope helped the teams understand the X-ray background and obtain more accurate results.

    The X-ray emission NICER picks up comes primarily from hotspots at the base of the neutron star’s magnetic poles, where spiraling particles crash into the surface. Right away, it became clear that the magnetic field is complex. The hotspots are on the same hemisphere for both J0030 and J0740, which means that these neutron stars do not have perfect “bar magnet” dipole fields.

    Watts’ and Miller’s teams have now analyzed hotspots on two neutron stars, mapping their locations and shapes as they whirl around. The first one, designated J0030+0451, is a lightweight at 1.4 times the mass of the Sun, with barely the heft to collapse into a neutron star rather than a white dwarf. Results for this object were published in 2019. The second, J0470+6620, is in the heavyweight class with 2.1 solar masses.

    There are some slight differences between the teams’ analyses, but the end result is the same: Neutron stars are generally larger than scientists thought they might be.

    “Our new measurements of J0740 show that even though it’s almost 50% more massive than J0030, it’s essentially the same size,” Watts says. “That challenges some of the more squeezable models of neutron star cores, including versions where the interior is just a sea of quarks.”

    4
    This simplified mass-radius plot shows two extreme possibilities for neutron star cores: Either matter in the cores is “squishy,” disintegrating into quarks, or “stiff,” remaining bound in neutrons, hyperons, or other exotic material. While gravitational-wave data (GW 170817) spans both scenarios, NICER measurements (J0030 and J0740) show that neutron star cores are made of stiffer stuff that stands up to high pressure.
    Sanjay Redding / APS meeting.

    Yet even as quark soup cores are ruled out, the larger size also suggests that the pressure in the core is more intense than previously realized. Whatever is in the core has to stand up to that pressure, and that also appears to rule out simpler neutron cores. Some hybrid scenarios incorporating neutrons and quarks might work.

    There’s another option too: Neutron star cores might contain something more massive than neutrons: a type of particle known as a hyperon. There are several particles classified as hyperons, and each one incorporates strange quarks. (Neutrons and protons have only up and down quarks.) Hyperons thus have some “strange” properties compared to neutrons and protons. Though they’ve been detected in particle accelerators, they’re unstable and decay quickly — but in neutron star cores, they might be stable enough to stick around for awhile.

    “Our fervent hope is that at least we’re able to make a lot of nuclear physicists sweat, because [the NICER result] is not easy to get into their models,” Miller says.

    5
    The NICER measurements of the two neutron stars, the less massive J0030 and the more massive J0740, rule out the “squishiest” scenarios for matter in the core, including pure quark models. However, the measurements also appear to preclude simpler models, labeled “nucleonic,” in which the core consists of just neutrons (with some protons for stability). Possible remaining scenarios include exotic hyperons or a combination of particles (hybrid). Anna Watts / APS meeting.

    Zaven Arzoumanian (NASA Goddard Space Flight Center), the deputy principal investigator and science lead of the NICER mission, says there’s more to come.

    “We have a handful of additional pulsars that NICER is targeting,” he says. “We have collected a significant amount of data already for all of them, and we are analyzing them mostly in turn as we go.” Each additional mass and radius measurement will continue to narrow down the possibilities for what’s really inside neutron star cores.

    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 3:15 pm on April 12, 2021 Permalink | Reply
    Tags: , , , , , Flares from the Milky Way’s Supermassive Black Hole, Sky & Telescope   

    From AAS NOVA via From Sky & Telescope : “Flares from the Milky Way’s Supermassive Black Hole” 

    AASNOVA

    From AAS NOVA

    via

    Sky & Telescope

    April 12, 2021

    The supermassive black hole at the center of the Milky Way released an unusual number of strong flares in 2019. Now, astronomers are trying to figure out why.

    1
    Artist’s impression of the disruption of a gas cloud as it passes close to Sgr A*, the supermassive black hole at the center of our galaxy.
    European Southern Observatory(EU) / MPG Institute for extraterrestrial Physics [MPG Institut für extraterrestrische Physik] ( DE)/ Marc Schartmann

    In 2019, the supermassive black hole at the center of our galaxy woke up and emitted a series of burps. A new study now examines what meal may have led to this indigestion.

    Waking Up for a Snack

    3
    Artist’s impression of the dramatic outflows from an active galaxy’s nucleus. The Milky Way’s supermassive black hole, in contrast, is very quiet.

    Lynette Cook

    Sgr A*, the 4.6-million-solar-mass black hole that lies at the center of the Milky Way, is normally a fairly quiet beast. The black hole slowly feeds on accreting material in the galactic center — but this food source is sparse, and Sgr A*’s accretion doesn’t produce anything like the fireworks we associate with supermassive black holes in active galaxies.

    In May 2019, however, Sgr A* suddenly became substantially more active than usual, producing an unprecedented bright, near-infrared flare that lasted roughly 2.5 hours. This flare was more than 100 times brighter than the typical emission from Sgr A*’s casual accretion, and more than twice as bright as the brightest flare we’ve ever measured from our neighborhood monster.

    The May 2019 flare marked the start of prolonged increased activity — an unusual number of strong flares that continued at least throughout 2019 (currently analyzed data extends only to the end of that year). What caused Sgr A* to wake up? And do we expect more flaring ahead? A new study by Lena Murchikova (Institute for Advanced Study (US)) explores the options.

    Star S0-2 Andrea Ghez Keck/UCLA Galactic Center Group (US) at SGR A*, the supermassive black hole at the center of the Milky Way.

    Sgr A*’s flares likely came from an abrupt increase in the amount of material available to accrete onto this black hole. Murchikova identifies two likely sources of this excess material.

    Shedding S stars
    The dense nucleus of our galaxy hosts a population of stars on tight orbits around Sgr A*. These stars shed mass via stellar winds, and when the stars swing close around Sgr A* at the pericenter of their orbit, this shed mass could accrete onto Sgr A*.
    Disintegrating G objects
    Also known to orbit close to Sgr A* are so-called G objects. These extended sources may be gas clouds, stars, or a combination of the two — we’re not sure yet! Tenuous G objects lose mass as a result of friction as they orbit, exhibiting higher rates of mass loss as they get closer to Sgr A* and are stretched out into shapes with large surfaces areas passing through dense background material. The mass they lose through this disintegration at pericenter could then accrete onto Sgr A*.

    3
    The objects G2 (colored red) and G1 (colored blue) and the star S2 are visible in these high-resolution images of the galactic center, taken in 2006 (left) and in 2008 (right). The position of Sgr A* is marked with an X.
    SOFIA / Lynette Cook [above]

    Through a series of calculations, Murchikova estimates how much material is shed by these two types of objects and how long it would take that material to accrete onto Sgr A*. Based on the available observations, the author finds that the most likely explanation for our black hole’s unexpected rumblings in 2019 is currently accreting material from the combined past pericenter passages of the objects G1 and G2.

    If this interpretation is correct, we would expect to see flaring continue for a limited time, but Sgr A* should then return to its quiescent state. If the flaring was instead a part of normal variability in the flow of accreting material onto Sgr A*, we would expect the activity to continue for years to come. Continued observations of this rumbling giant will tell!

    Citation

    “S0-2 Star, G1- and G2-objects, and Flaring Activity of the Milky Way’s Galactic Center Black Hole in 2019,” Lena Murchikova 2021 ApJL 910 L1. https://iopscience.iop.org/article/10.3847/2041-8213/abeb70

    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.”

    From AAS NOVA

    1

    AAS Mission and Vision Statement

    The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

    The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
    The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
    The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
    The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
    The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

    Adopted June 7, 2009

    The society was founded in 1899 through the efforts of George Ellery Hale. The constitution of the group was written by Hale, George Comstock, Edward Morley, Simon Newcomb and Edward Charles Pickering. These men, plus four others, were the first Executive Council of the society; Newcomb was the first president. The initial membership was 114. The AAS name of the society was not finally decided until 1915, previously it was the “Astronomical and Astrophysical Society of America”. One proposed name that preceded this interim name was “American Astrophysical Society”.

    The AAS today has over 7,000 members and six divisions – the Division for Planetary Sciences (1968); the Division on Dynamical Astronomy (1969); the High Energy Astrophysics Division (1969); the Solar Physics Division (1969); the Historical Astronomy Division (1980); and the Laboratory Astrophysics Division (2012). The membership includes physicists, mathematicians, geologists, engineers and others whose research interests lie within the broad spectrum of subjects now comprising contemporary astronomy.

    In 2019 three AAS members were selected into the tenth anniversary class of TED Fellows.

    The AAS established the AAS Fellows program in 2019 to “confer recognition upon AAS members for achievement and extraordinary service to the field of astronomy and the American Astronomical Society.” The inaugural class was designated by the AAS Board of Trustees and includes an initial group of 232 Legacy Fellows.

     
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