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  • richardmitnick 1:46 pm on July 3, 2019 Permalink | Reply
    Tags: , , , , , Sky and Telescope   

    From Sky & Telescope: “Astronomers Identify Host Galaxy of a Third Radio Flash” 

    SKY&Telescope bloc

    From Sky & Telescope

    July 3, 2019
    Monica Young

    Astronomers have narrowed down the location of a third “fast radio burst” to a galaxy very like the Milky Way.

    Just one week after astronomers announced an incredible feat — identifying the galaxy that hosted a flash of radio waves that lasted only a fraction of a second — an independent team has done it again. The results take us one step closer to understanding the origins of the mysterious fast radio bursts.

    Vikram Ravi (Caltech) and colleagues report July 2nd in Nature that they have pinpointed the source of fast radio burst 190523 via a technique called radio interferometry. The radio waves appear to come from a massive galaxy that’s much like the Milky Way.

    10 dish array at Owens Valley Radio Observatory, near Big Pine, California USA, Altitude 1,222 m (4,009 ft used by Vikram Ravi and colleagues (Caltech)

    Where do Fast Radio Bursts Come From?

    Fast radio bursts (FRBs) are millsecond-long flashes of radio waves that sweep downward in frequency — an indication that they’ve traveled billions of light-years from their source to Earth. But here’s the rub: Astronomers have no real idea what the sources of FRBs are.

    Given the huge distances involved, it’s unlikely that astronomers will ever image the sources themselves, but a good start is to home in on the sources’ locations; that is, to understand what kind of galaxies host them.

    2
    A composite image of the field around the first repeating fast radio burst, FRB 121102 (indicated), showed that the burst came from a star-forming dwarf galaxy. Gemini Observatory / AURA / NSF / NRC

    The first FRB that astronomers ever pinned down was FRB 121102. This source was unusual because — unlike the vast majority of FRBs — it repeated. The many pulses gave astronomers the opportunity to locate the source, which lies within a large star formation region in a dwarf galaxy 3 billion light-years away. The repeating bursts and the high rate of star formation were both consistent with a scenario where the birth of a highly magnetized neutron star, known as a magnetar, sets off a flash of radio waves.

    The second localized FRB, though, countered that scenario. FRB 180924 came from an aging galaxy, where essentially zero stars are being born. Since neutron stars form when massive, fast-burning stars collapse, the magnetar scenario is basically ruled out, at least for this source.

    Now, Ravi’s team has used an array of 10 radio dishes, part of a prototype for the upcoming Deep Synoptic Array at the Owens Valley Radio Observatory, to quickly home in on a third burst, FRB 190523.

    3
    The Deep Synoptic Array ten-antenna prototype (DSA-10) searches for fast radio bursts within a sky-area the size of 150 full moons (left). Within this area, the DSA-10 can localize bursts, isolating them to regions containing just one galaxy (middle). The right panel shows the so-called “profile” of the fast radio burst FRB 190523.
    Caltech / OVRO / V. Ravi

    A deep image of the surrounding field, taken later with the Keck I telescope, shows only one galaxy, PSO 1207.0643+72.4708.

    Keck Observatory, operated by Caltech and the University of California, Maunakea, Hawaii, USA.4,207 m (13,802 ft), above sea level,

    The galaxy is massive, roughly Milky Way-sized with a Milky Way-like star formation rate of about 1 Sun per year. If this is indeed the source’s home, its radio waves traveled more than 6 billion light-years to Earth.

    If the host galaxy is like the Milky Way, that begs the question: Could our galaxy ever host one of these mysterious bursts? Eventually, Ravi says: “The lower limit on the rate in a Milky Way-like galaxy is one every 100 years. But we also think that FRBs are beamed, so that there are probably heaps that occur where we don’t see, because they’re pointed elsewhere. So the rate could be much higher.”

    Such a burst would produce radio waves at a rate a billion times that of the Sun — impressive, to be sure, but not compared to what humans make: “That’s only as bright as a typical mobile phone at a distance of 10 meters,” Ravi says.

    Fast Radio Burst Sources and the In-between

    “Interestingly, both host galaxies of FRB 180924 and FRB 190523 are more similar to each other than they are to the host of FRB121102 (the repeater),” says Keith Bannister (CSIRO), who led the team that found the host galaxy of the FRB 180924.

    The magnetar explanation also seems unlikely for FRB 190523, then, and it’s tempting to conclude that different scenarios apply for repeating and non-repeating bursts. But it’s important to note that, while no additional radio flashes have been detected from either source, it’s still possible they could repeat. The better we can pinpoint FRBs, the more conclusive the results will be.

    “We localized our FRB 180924 to an area about 1,000 times smaller than the FRB 190523,” says Bannister. But, he notes, the newer burst comes from much farther away. “It’s exciting that they have localized a burst from such a distant galaxy.”

    A distant source is useful because, in addition to wanting to understand what generates these powerful flashes of radio waves, astronomers also want to use them to study the hot, sparse gas between galaxies. This practically unseeable gas holds most of the universe’s “normal” (i.e., not dark) matter and helps form the large-scale “web” that shapes the cosmos, and studying it is vital to understanding how galaxies grow.

    As astronomers apply new radio telescopes (or rather, prototypes of still-larger telescopes to come) toward finding new fast radio bursts, the field is starting to yield some answers — and lots more 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 magazine, 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 1:49 pm on January 5, 2019 Permalink | Reply
    Tags: , , , Sky and Telescope   

    From Sky & Telescope: “NASA Renews Interest in SETI” 

    SKY&Telescope bloc

    From Sky & Telescope

    January 4, 2019
    David Grinspoon

    After a long hiatus, the space agency gets back into the SETI game.

    In July I wrote about innovative approaches for the Search for Extraterrestrial Intelligence (SETI). In that column I lamented the fact that NASA support for this field dried up in the 1990s and had not returned, even though astrobiology has since flourished. Many of us felt that the bureaucratically maintained distinction between astrobiology and SETI did not make intellectual sense, and we longed for SETI to be let in from the cold.

    Sometimes wishes come true.

    As that column went to press I received an email asking if I would help organize a workshop on “technosignatures.” The sponsor? NASA. That got my attention. The purpose was to explore how to best use NASA resources in a renewed search for extraterrestrial intelligence. Apparently, Congress’s new federal budget mandated that NASA spend $10 million “to search for technosignatures, such as radio transmissions, in order to meet the NASA objective to search for life’s origin, evolution, distribution, and future in the universe.” Wow!

    The workshop, which took place in September, was highly stimulating, and given the renewed government interest in SETI, the mood was bright and optimistic. Along with evaluation of historical and current searches, there was an openness to new ideas born of a kind of humility. We can’t really second-guess the properties or motivations of technological aliens, so we have to cast a wide net. In addition to “traditional” SETI searches for radio signals or laser pulses, we must be alert to more passive signs of technological entities that might not be trying to get in touch with anyone. These include possible artifacts beyond or within our own solar system, or planetary atmospheres altered or engineered by industrial activities.

    Attendees made an effort to stick to the prosaic questions: What observing programs can we ramp up in the next few years using NASA’s current or expected assets and instruments? How can NASA best collaborate with private partners such as the SETI Institute and Breakthrough Listen?

    SETI/Allen Telescope Array situated at the Hat Creek Radio Observatory, 290 miles (470 km) northeast of San Francisco, California, USA, Altitude 986 m (3,235 ft)

    Breakthrough Listen Project

    1

    Lick Automated Planet Finder telescope, Mount Hamilton, CA, USA



    GBO radio telescope, Green Bank, West Virginia, USA


    CSIRO/Parkes Observatory, located 20 kilometres north of the town of Parkes, New South Wales, Australia


    SKA Meerkat telescope, 90 km outside the small Northern Cape town of Carnarvon, SA

    But with SETI it’s hard to avoid deep philosophical musings. Some talks at the workshop delved into abstract but necessary puzzles about the properties and behavior of distant, advanced civilizations — even about what we mean by “advanced” and “civilization.” SETI has always combined solid engineering, daring speculation, and profound questioning.

    Laser SETI, the future of SETI Institute research

    This admixture didn’t always sit well with some. At the first international SETI conference in Byurakan, Soviet Armenia in 1971, organizers Carl Sagan and Iosif Shklovsky welcomed historians, philosophers, linguists, and social scientists along with the scientists. At the time, one young Soviet astrophysicist asked that the humanities be left out, stating he didn’t want to listen to “windbags.” A leading American physicist exclaimed, “To hell with philosophy! I came here to learn about observations and instruments . . .”

    This historical tension seemed absent from September’s workshop. Although our prime directive was to guide NASA in the use of its assets to search for technosignatures, there was respectful discussion of the more esoteric and humanistic questions that are naturally evoked, and a recognition that a mature SETI program going forward will involve more than just telescopes and computer models. Out of this will come new calls for proposals to NASA, and then a new era of federally funded SETI research. May it be long and fruitful.

    See the full article here .

    NASA might also consider aiding SETI@home, a BOINC project from the Space Science Lab at UC Berkeley processing data from The Arecibo Observatory


    SETI@home, a BOINC project originated in the Space Science Lab at UC Berkeley



    NAIC Arecibo Observatory operated by University of Central Florida, Yang Enterprises and UMET, Altitude 497 m (1,631 ft).

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

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Sky & Telescope magazine, 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 1:05 pm on November 30, 2018 Permalink | Reply
    Tags: 2018 ivc- the new supernova, A new supernova in the bright galaxy Messier 77 in Cetus is within range of amateur telescopes, , , , , DLT40 Survey-UC Davis, Sky and Telescope, Some Type II events leave a neutron star or black hole remnant,   

    From Sky & Telescope: “Supernova Discovered in the Bright Galaxy Messier 77” 

    SKY&Telescope bloc

    From Sky & Telescope

    November 29, 2018
    Bob King

    A new supernova in the bright galaxy Messier 77 in Cetus is within range of amateur telescopes. Here’s how to find it.

    1
    New supernova 2018 ivc recently appeared in the bright Messier galaxy M77 located in Cetus at R.A. 2h 42′ 41″, Dec. -00° 00′ 48″. The object is northeast of the core along the edge of the bright inner disk. Koichi Itagaki

    On November 24th, the DLT40 Survey picked up a 15th magnitude supernova in Messier 77, a bright, barred spiral galaxy in Cetus located 50′ southeast of 4th magnitude Delta Ceti. Whenever a supernova is discovered in a Messier galaxy, I get excited. Messiers are among the closer and brighter galaxies and often host supernovae visible in smaller telescopes.

    With an apparent magnitude of 9.6, Messier 77 is easy to find in telescopes as small as 3 inches though a 10-inch or larger scope will be needed to ferret out this supernova — at least at the moment.

    Designated 2018 ivc, the new supernova has brightened to about magnitude 14.5 and appears as a tiny pinprick of light 8.7″ east and 16.1″ north of the center of the galaxy along the edge of the bright inner disk. Spectroscopy reveals the “new star” as a Type II supernova in its early stages, implying that the object could brighten further. Not to throw water on the fire, but intervening dust within the galaxy has dimmed and reddened the explosion, so it’s difficult to predict how bright it might become. One outlier observation from November 25th put it at about magnitude 13.6.

    2
    Use this map to locate Delta Ceti and the supernova host galaxy, Messier 77. While you’re in the neighborhood, take a look at the variable star Mira, now rising toward maximum with a current magnitude of about 4.0. Stellarium

    This is the first recorded supernova in Messier 77 and though it looks like little more than a faint star in a telescope, the reality is we’re witnessing the collapse and explosion of a highly evolved supergiant star. As you read this, debris from the blast is expanding outward at some 13,500 kilometers per second (30.2 million mph). For perspective, that’s a little more than one Earth-diameter per second! Going along for the ride are the complex elements that were forged in the star’s core and now released into space to seed future generations of stars and their planetary systems.

    3
    “I’ve marked 2018 ivc’s location with a cross in this photograph taken by the Hubble Space Telescope. You can see the object is situated within the galaxy’s dusty inner arms.” NASA / ESA / A. van der Hoeven

    Messier 77 lies 47 million light-years from Earth in Cetus. After all those years of travel, how fortunate that the light from the supernova arrived just in time to track it down without a bright moon and the galaxy well-placed for viewing during evening hours. To find it, start with Menkar (magnitude 2.5), the second brightest star in Cetus, and slide about 2° to the southwest to Delta (δ) Ceti. Set Delta off to one side of the low-magnification field of view and you should see Messier 77 on the opposite side less than a degree to the southeast.

    4
    In a Type II supernova, an aging supergiant star runs out of nuclear fuel to burn in its core, causing a sudden collapse and rebound that rips the star apart. Some Type II events leave a neutron star or black hole remnant. NASA / CXC /M.Weiss

    To dig out the stellar cinder I recommend increasing the magnification to 200x or higher and studying the location along the bright, inner disk for a stellar point — this will be the supernova. Never fear magnification — you may need to go north of 300x depending on whether 2018 ivc brightens further or not. If seeing is poor, it can be difficult to suss out the star in a bright, galactic environment. Try again on another night.

    Coincidentally, the bright comet 46P/Wirtanen passes about 7° southeast of the galaxy on the nights of December 8th and 9th.

    For updates, head over to David Bishop’s excellent Latest Supernovae page and click on the 2018 ivc link. I’ll also update this blog with additional information including my own observation of the supernova which I hope to make tomorrow night.

    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 magazine, 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 3:20 pm on May 10, 2018 Permalink | Reply
    Tags: , , , , , Gravitational Waves Shed Light on Neutron Star Interiors, Sky and Telescope   

    From Sky & Telescope: “Gravitational Waves Shed Light on Neutron Star Interiors” 

    SKY&Telescope bloc

    From Sky & Telescope

    May 9, 2018
    Elizabeth Howell

    The gravitational-wave detection last year of a neutron star merger has revealed details on neutron star structure, ruling out exotic quark matter in the objects’ cores.

    1
    Artist’s illustration of the final stages of a neutron-star merger. NASA / Goddard Space Flight Center

    A pair of independent studies gives new constraints on the size of neutron stars, suggesting that they are no more than 14 kilometers (8.6 miles) in radius. That’s about twice the length of the Las Vegas strip. This size limit is slightly larger than previous estimates, suggesting that neutron stars might be less exotic than previously thought.

    Neutron stars are the dense stellar remnants of supernova explosions. Within a tiny radius, they contain a mass of about 1.4 times that of the sun. The extreme densities and pressures smush electrons into the atomic nuclei their orbit — protons and electrons combine into neutrons, so that neutron stars are made mostly of neutrons. But there’s a possibility that the density at their cores might become so high, it breaks matter down into even smaller particles, such as quarks.

    As astrophysicist Feryal Özel (University of Arizona) explained in the July 2017 issue of Sky & Telescope, for neutron stars size really does matter — the smaller the star, the higher its core density. Previous measurements have pointed to a maximum neutron star radius between 10 and 11 km. That may not sound very different from 14 km, but it would be enough to raise the central density by more than a factor of two. “This is enough to have a profound effect on the amount of repulsion the particles experience,” Özel wrote, which would introduce the possibility of a quark-filled core.

    The new neutron star sizes, published in two papers appearing in April 25th Physical Review Letters, are based on the August 17, 2017, LIGO/Virgo detection of gravitational waves from a pair of neutron stars merging 130 million light-years away.

    UC Santa Cruz

    UC Santa Cruz

    14

    A UC Santa Cruz special report

    Tim Stephens

    Astronomer Ryan Foley says “observing the explosion of two colliding neutron stars” [see https://sciencesprings.wordpress.com/2017/10/17/from-ucsc-first-observations-of-merging-neutron-stars-mark-a-new-era-in-astronomy ]–the first visible event ever linked to gravitational waves–is probably the biggest discovery he’ll make in his lifetime. That’s saying a lot for a young assistant professor who presumably has a long career still ahead of him.

    2
    The first optical image of a gravitational wave source was taken by a team led by Ryan Foley of UC Santa Cruz using the Swope Telescope at the Carnegie Institution’s Las Campanas Observatory in Chile. This image of Swope Supernova Survey 2017a (SSS17a, indicated by arrow) shows the light emitted from the cataclysmic merger of two neutron stars. (Image credit: 1M2H Team/UC Santa Cruz & Carnegie Observatories/Ryan Foley)

    Carnegie Institution Swope telescope at Las Campanas, Chile, 100 kilometres (62 mi) northeast of the city of La Serena. near the north end of a 7 km (4.3 mi) long mountain ridge. Cerro Las Campanas, near the southern end and over 2,500 m (8,200 ft) high, at Las Campanas, Chile

    A neutron star forms when a massive star runs out of fuel and explodes as a supernova, throwing off its outer layers and leaving behind a collapsed core composed almost entirely of neutrons. Neutrons are the uncharged particles in the nucleus of an atom, where they are bound together with positively charged protons. In a neutron star, they are packed together just as densely as in the nucleus of an atom, resulting in an object with one to three times the mass of our sun but only about 12 miles wide.

    “Basically, a neutron star is a gigantic atom with the mass of the sun and the size of a city like San Francisco or Manhattan,” said Foley, an assistant professor of astronomy and astrophysics at UC Santa Cruz.

    These objects are so dense, a cup of neutron star material would weigh as much as Mount Everest, and a teaspoon would weigh a billion tons. It’s as dense as matter can get without collapsing into a black hole.

    THE MERGER

    Like other stars, neutron stars sometimes occur in pairs, orbiting each other and gradually spiraling inward. Eventually, they come together in a catastrophic merger that distorts space and time (creating gravitational waves) and emits a brilliant flare of electromagnetic radiation, including visible, infrared, and ultraviolet light, x-rays, gamma rays, and radio waves. Merging black holes also create gravitational waves, but there’s nothing to be seen because no light can escape from a black hole.

    Foley’s team was the first to observe the light from a neutron star merger that took place on August 17, 2017, and was detected by the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO).


    VIRGO Gravitational Wave interferometer, near Pisa, Italy

    Caltech/MIT Advanced aLigo Hanford, WA, USA installation


    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

    Gravitational waves. Credit: MPI for Gravitational Physics/W.Benger-Zib

    ESA/eLISA the future of gravitational wave research

    1
    Skymap showing how adding Virgo to LIGO helps in reducing the size of the source-likely region in the sky. (Credit: Giuseppe Greco (Virgo Urbino group)

    Now, for the first time, scientists can study both the gravitational waves (ripples in the fabric of space-time), and the radiation emitted from the violent merger of the densest objects in the universe.

    3
    The UC Santa Cruz team found SSS17a by comparing a new image of the galaxy N4993 (right) with images taken four months earlier by the Hubble Space Telescope (left). The arrows indicate where SSS17a was absent from the Hubble image and visible in the new image from the Swope Telescope. (Image credits: Left, Hubble/STScI; Right, 1M2H Team/UC Santa Cruz & Carnegie Observatories/Ryan Foley)

    It’s that combination of data, and all that can be learned from it, that has astronomers and physicists so excited. The observations of this one event are keeping hundreds of scientists busy exploring its implications for everything from fundamental physics and cosmology to the origins of gold and other heavy elements.


    A small team of UC Santa Cruz astronomers were the first team to observe light from two neutron stars merging in August. The implications are huge.

    ALL THE GOLD IN THE UNIVERSE

    It turns out that the origins of the heaviest elements, such as gold, platinum, uranium—pretty much everything heavier than iron—has been an enduring conundrum. All the lighter elements have well-explained origins in the nuclear fusion reactions that make stars shine or in the explosions of stars (supernovae). Initially, astrophysicists thought supernovae could account for the heavy elements, too, but there have always been problems with that theory, says Enrico Ramirez-Ruiz, professor and chair of astronomy and astrophysics at UC Santa Cruz.

    4
    The violent merger of two neutron stars is thought to involve three main energy-transfer processes, shown in this diagram, that give rise to the different types of radiation seen by astronomers, including a gamma-ray burst and a kilonova explosion seen in visible light. (Image credit: Murguia-Berthier et al., Science)

    A theoretical astrophysicist, Ramirez-Ruiz has been a leading proponent of the idea that neutron star mergers are the source of the heavy elements. Building a heavy atomic nucleus means adding a lot of neutrons to it. This process is called rapid neutron capture, or the r-process, and it requires some of the most extreme conditions in the universe: extreme temperatures, extreme densities, and a massive flow of neutrons. A neutron star merger fits the bill.

    Ramirez-Ruiz and other theoretical astrophysicists use supercomputers to simulate the physics of extreme events like supernovae and neutron star mergers. This work always goes hand in hand with observational astronomy. Theoretical predictions tell observers what signatures to look for to identify these events, and observations tell theorists if they got the physics right or if they need to tweak their models. The observations by Foley and others of the neutron star merger now known as SSS17a are giving theorists, for the first time, a full set of observational data to compare with their theoretical models.

    According to Ramirez-Ruiz, the observations support the theory that neutron star mergers can account for all the gold in the universe, as well as about half of all the other elements heavier than iron.

    RIPPLES IN THE FABRIC OF SPACE-TIME

    Einstein predicted the existence of gravitational waves in 1916 in his general theory of relativity, but until recently they were impossible to observe. LIGO’s extraordinarily sensitive detectors achieved the first direct detection of gravitational waves, from the collision of two black holes, in 2015. Gravitational waves are created by any massive accelerating object, but the strongest waves (and the only ones we have any chance of detecting) are produced by the most extreme phenomena.

    Two massive compact objects—such as black holes, neutron stars, or white dwarfs—orbiting around each other faster and faster as they draw closer together are just the kind of system that should radiate strong gravitational waves. Like ripples spreading in a pond, the waves get smaller as they spread outward from the source. By the time they reached Earth, the ripples detected by LIGO caused distortions of space-time thousands of times smaller than the nucleus of an atom.

    The rarefied signals recorded by LIGO’s detectors not only prove the existence of gravitational waves, they also provide crucial information about the events that produced them. Combined with the telescope observations of the neutron star merger, it’s an incredibly rich set of data.

    LIGO can tell scientists the masses of the merging objects and the mass of the new object created in the merger, which reveals whether the merger produced another neutron star or a more massive object that collapsed into a black hole. To calculate how much mass was ejected in the explosion, and how much mass was converted to energy, scientists also need the optical observations from telescopes. That’s especially important for quantifying the nucleosynthesis of heavy elements during the merger.

    LIGO can also provide a measure of the distance to the merging neutron stars, which can now be compared with the distance measurement based on the light from the merger. That’s important to cosmologists studying the expansion of the universe, because the two measurements are based on different fundamental forces (gravity and electromagnetism), giving completely independent results.

    “This is a huge step forward in astronomy,” Foley said. “Having done it once, we now know we can do it again, and it opens up a whole new world of what we call ‘multi-messenger’ astronomy, viewing the universe through different fundamental forces.”

    IN THIS REPORT

    Neutron stars
    A team from UC Santa Cruz was the first to observe the light from a neutron star merger that took place on August 17, 2017 and was detected by the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO)

    5
    Graduate students and post-doctoral scholars at UC Santa Cruz played key roles in the dramatic discovery and analysis of colliding neutron stars.Astronomer Ryan Foley leads a team of young graduate students and postdoctoral scholars who have pulled off an extraordinary coup. Following up on the detection of gravitational waves from the violent merger of two neutron stars, Foley’s team was the first to find the source with a telescope and take images of the light from this cataclysmic event. In so doing, they beat much larger and more senior teams with much more powerful telescopes at their disposal.

    “We’re sort of the scrappy young upstarts who worked hard and got the job done,” said Foley, an untenured assistant professor of astronomy and astrophysics at UC Santa Cruz.

    7
    David Coulter, graduate student

    The discovery on August 17, 2017, has been a scientific bonanza, yielding over 100 scientific papers from numerous teams investigating the new observations. Foley’s team is publishing seven papers, each of which has a graduate student or postdoc as the first author.

    “I think it speaks to Ryan’s generosity and how seriously he takes his role as a mentor that he is not putting himself front and center, but has gone out of his way to highlight the roles played by his students and postdocs,” said Enrico Ramirez-Ruiz, professor and chair of astronomy and astrophysics at UC Santa Cruz and the most senior member of Foley’s team.

    “Our team is by far the youngest and most diverse of all of the teams involved in the follow-up observations of this neutron star merger,” Ramirez-Ruiz added.

    8
    Charles Kilpatrick, postdoctoral scholar

    Charles Kilpatrick, a 29-year-old postdoctoral scholar, was the first person in the world to see an image of the light from colliding neutron stars. He was sitting in an office at UC Santa Cruz, working with first-year graduate student Cesar Rojas-Bravo to process image data as it came in from the Swope Telescope in Chile. To see if the Swope images showed anything new, he had also downloaded “template” images taken in the past of the same galaxies the team was searching.

    9
    Ariadna Murguia-Berthier, graduate student

    “In one image I saw something there that was not in the template image,” Kilpatrick said. “It took me a while to realize the ramifications of what I was seeing. This opens up so much new science, it really marks the beginning of something that will continue to be studied for years down the road.”

    At the time, Foley and most of the others in his team were at a meeting in Copenhagen. When they found out about the gravitational wave detection, they quickly got together to plan their search strategy. From Copenhagen, the team sent instructions to the telescope operators in Chile telling them where to point the telescope. Graduate student David Coulter played a key role in prioritizing the galaxies they would search to find the source, and he is the first author of the discovery paper published in Science.

    10
    Matthew Siebert, graduate student

    “It’s still a little unreal when I think about what we’ve accomplished,” Coulter said. “For me, despite the euphoria of recognizing what we were seeing at the moment, we were all incredibly focused on the task at hand. Only afterward did the significance really sink in.”

    Just as Coulter finished writing his paper about the discovery, his wife went into labor, giving birth to a baby girl on September 30. “I was doing revisions to the paper at the hospital,” he said.

    It’s been a wild ride for the whole team, first in the rush to find the source, and then under pressure to quickly analyze the data and write up their findings for publication. “It was really an all-hands-on-deck moment when we all had to pull together and work quickly to exploit this opportunity,” said Kilpatrick, who is first author of a paper comparing the observations with theoretical models.

    11
    César Rojas Bravo, graduate student

    Graduate student Matthew Siebert led a paper analyzing the unusual properties of the light emitted by the merger. Astronomers have observed thousands of supernovae (exploding stars) and other “transients” that appear suddenly in the sky and then fade away, but never before have they observed anything that looks like this neutron star merger. Siebert’s paper concluded that there is only a one in 100,000 chance that the transient they observed is not related to the gravitational waves.

    Ariadna Murguia-Berthier, a graduate student working with Ramirez-Ruiz, is first author of a paper synthesizing data from a range of sources to provide a coherent theoretical framework for understanding the observations.

    Another aspect of the discovery of great interest to astronomers is the nature of the galaxy and the galactic environment in which the merger occurred. Postdoctoral scholar Yen-Chen Pan led a paper analyzing the properties of the host galaxy. Enia Xhakaj, a new graduate student who had just joined the group in August, got the opportunity to help with the analysis and be a coauthor on the paper.

    12
    Yen-Chen Pan, postdoctoral scholar

    “There are so many interesting things to learn from this,” Foley said. “It’s a great experience for all of us to be part of such an important discovery.”

    13
    Enia Xhakaj, graduate student

    IN THIS REPORT

    Scientific Papers from the 1M2H Collaboration

    Coulter et al., Science, Swope Supernova Survey 2017a (SSS17a), the Optical Counterpart to a Gravitational Wave Source

    Drout et al., Science, Light Curves of the Neutron Star Merger GW170817/SSS17a: Implications for R-Process Nucleosynthesis

    Shappee et al., Science, Early Spectra of the Gravitational Wave Source GW170817: Evolution of a Neutron Star Merger

    Kilpatrick et al., Science, Electromagnetic Evidence that SSS17a is the Result of a Binary Neutron Star Merger

    Siebert et al., ApJL, The Unprecedented Properties of the First Electromagnetic Counterpart to a Gravitational-wave Source

    Pan et al., ApJL, The Old Host-galaxy Environment of SSS17a, the First Electromagnetic Counterpart to a Gravitational-wave Source

    Murguia-Berthier et al., ApJL, A Neutron Star Binary Merger Model for GW170817/GRB170817a/SSS17a

    Kasen et al., Nature, Origin of the heavy elements in binary neutron star mergers from a gravitational wave event

    Abbott et al., Nature, A gravitational-wave standard siren measurement of the Hubble constant (The LIGO Scientific Collaboration and The Virgo Collaboration, The 1M2H Collaboration, The Dark Energy Camera GW-EM Collaboration and the DES Collaboration, The DLT40 Collaboration, The Las Cumbres Observatory Collaboration, The VINROUGE Collaboration & The MASTER Collaboration)

    Abbott et al., ApJL, Multi-messenger Observations of a Binary Neutron Star Merger

    PRESS RELEASES AND MEDIA COVERAGE


    Watch Ryan Foley tell the story of how his team found the neutron star merger in the video below. 2.5 HOURS.

    Press releases:

    UC Santa Cruz Press Release

    UC Berkeley Press Release

    Carnegie Institution of Science Press Release

    LIGO Collaboration Press Release

    National Science Foundation Press Release

    Media coverage:

    The Atlantic – The Slack Chat That Changed Astronomy

    Washington Post – Scientists detect gravitational waves from a new kind of nova, sparking a new era in astronomy

    New York Times – LIGO Detects Fierce Collision of Neutron Stars for the First Time

    Science – Merging neutron stars generate gravitational waves and a celestial light show

    CBS News – Gravitational waves – and light – seen in neutron star collision

    CBC News – Astronomers see source of gravitational waves for 1st time

    San Jose Mercury News – A bright light seen across the universe, proving Einstein right

    Popular Science – Gravitational waves just showed us something even cooler than black holes

    Scientific American – Gravitational Wave Astronomers Hit Mother Lode

    Nature – Colliding stars spark rush to solve cosmic mysteries

    National Geographic – In a First, Gravitational Waves Linked to Neutron Star Crash

    Associated Press – Astronomers witness huge cosmic crash, find origins of gold

    Science News – Neutron star collision showers the universe with a wealth of discoveries

    UCSC press release
    First observations of merging neutron stars mark a new era in astronomy

    Credits

    Writing: Tim Stephens
    Video: Nick Gonzales
    Photos: Carolyn Lagattuta
    Header image: Illustration by Robin Dienel courtesy of the Carnegie Institution for Science
    Design and development: Rob Knight
    Project managers: Sherry Main, Scott Hernandez-Jason, Tim Stephens

    Dark Energy Survey


    Dark Energy Camera [DECam], built at FNAL


    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam at an altitude of 7200 feet

    Gemini South telescope, Cerro Tololo Inter-American Observatory (CTIO) campus near La Serena, Chile, at an altitude of 7200 feet

    Noted in the video but not in the article:

    NASA/Chandra Telescope

    NASA/SWIFT Telescope

    NRAO/Karl V Jansky VLA, on the Plains of San Agustin fifty miles west of Socorro, NM, USA

    Prompt telescope CTIO Chile

    NASA NuSTAR X-ray telescope

    See the full article here

    Massive objects, such as black holes and neutron stars, emit these ripples in spacetime as they move through space. The gravitational waves observed from the neutron star collision served as a probe of the objects’ structure. Even though the two papers used different approaches, they calculated roughly the same maximum size for neutron stars: Eemeli Annala (University of Helsinki, Finland) led a study that limited it to 13.6 km [Physical Review Letters], while Farrukh J. Fattoyev (Indiana University) and colleagues limited it to 13.76 km [Physical Review Letters]

    Neutron Stars in the Lab

    3
    Neutron star. Casey Reed / Penn State University

    Given their extremely high density, astronomers aren’t certain what neutron stars look like on the inside. Some of their ideas are based on nuclear physics, while the concept of quark matter in particular is based on the physics of high-energy particles. The various approaches can give different predictions about neutron stars’ internal structure.

    Experiments at the Large Hadron Collider (LHC) at CERN and the Relativistic Heavy Ion Collider at Brookhaven National Laboratory give a sense of what a neutron star might look like in its core. Researchers at these institutions smash lead ions together at close to the speed of light to produce the high temperatures that break down protons and neutrons into a quark-gluon plasma.

    LHC

    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

    BNL RHIC Campus

    BNL/RHIC Star Detector

    BNL RHIC PHENIX

    “These collisions create ion-sized droplets of matter so dense that the structure of the protons and neutrons melts, and we are left with a small droplet of quark matter for a very brief moment,” says theoretical physicist Aleksi Kurkela (CERN), Annala’s coauthor. “We think that this hot quark-gluon plasma is closely related to the ‘cool’ quark matter that we may find in the cores of neutron stars. By studying the properties of the quark-gluon plasma, we try to learn and infer what is happening in the cores of neutron stars.”

    If neutron stars produce quarks in their centers, they might undergo a phase change. “We could potentially observe . . . neutron stars with similar masses but with quite different radii,” Kurkela explains. “Then the interpretation would be that the one with larger radius would be made of stiffer material, supposedly neutron matter. The smaller one would be made of, or at least would have a core made of, softer material which could be quark matter.”

    “While our current theories provide a very good description of dense matter at nuclear densities, their predictions significantly deviate when extrapolated to super-nuclear densities,” adds Fattoyev (Indiana University).

    Indeed, some of LIGO’s observations aren’t matching up with what scientists previously theorized, specifically with regards to the types of matter found inside of neutron stars, Kurkela says.

    From Shape to Size

    4
    This artist’s conception portrays two neutron stars at the moment of collision.
    Dana Berry / SkyWorks Digital, Inc.

    As two neutron stars circle each other, their respective gravitational fields create tidal forces in their partner: Gravity pulls more strongly on the side of the star closer to its companion compared to its far side. As a result, both neutron stars stretch, tidally deforming into a shape resembling a rugby ball, Kurkela explains.

    The neutron stars’ shapes show what they are made of. If the matter inside of neutron stars were soft, that is, containing quarks in addition to neutrons, LIGO would see the neutron stars deform. But LIGO’s observations don’t fit those theories Instead, Kurkela explains, LIGO’s work showed that the neutron stars were like hard, unsquishable balls, even as they merged into each other, which means they contain only neutrons in their cores. The results allowed investigators to rule out the existence of quarks inside of neutron stars.

    Scientists will need more gravitational-wave observations to confirm what LIGO saw. Moreover, since neutron star collisions generate light in addition to gravitational waves, scientists hope to get more information on composition through follow-up X-ray observations, such as from the Neutron star Interior Composition Explorer (NICER) perched on the International Space Station.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Sky & Telescope magazine, 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 20, 2018 Permalink | Reply
    Tags: A small team of two astrophotographers and a professional astronomer have embarked on a project to produce a massive image of the Milky Way using only off-the-shelf photographic equipment, Amateurs Take Huge Panoramic View of the Milky Way — Without a Telescope, , , , , Sky and Telescope   

    From Sky & Telescope: “Amateurs Take Huge Panoramic View of the Milky Way — Without a Telescope” 

    SKY&Telescope bloc

    Sky & Telescope

    April 19, 2018
    Javier Barbuzano

    This is what the largest available image of the Milky Way using only off-the-shelf photographic equipment looks like.

    The Milky Way, as viewed from the Northern Hemisphere FECYT- IAC – J.C. Casado – D. Padrón -M. Serra-Ricart

    The Canary Islands, a Spanish enclave off the coast of North Africa, are famous as a favorite vacationing spot for Sun-deprived northern Europeans. But they’re also a prime location for astronomy, hosting two observatories on mountaintops that benefit from exceptionally clear and dark skies.

    Isaac Newton Group telescopes, at Roque de los Muchachos Observatory on La Palma in the Canary Islands, Spain, at an altitude of 2400m

    Instituto de Astrofísica de Canarias – IAC – Observatorios de Canarias, Altitude 2,396 m (7,861 ft)

    Gran Telescopio Canarias at the Roque de los Muchachos Observatory on the island of La Palma, in the Canaries, Spain, sited on a volcanic peak 2,267 metres (7,438 ft) above sea level

    Taking advantage of such a privileged environment, a small team of two astrophotographers and a professional astronomer have embarked on a project to produce a massive image of the Milky Way using only off-the-shelf photographic equipment.

    The team has already gathered and put together nearly 6,000 images, acquired over the course of a year and covering 70% of the Milky Way. The result is a result is a 4.37-gigapixel panoramic view of our host galaxy. To get the full picture, the team will travel to Namibia for more observations before the end of 2018.

    To capture the images, the team used two Sony A75 DSLR full-frame cameras on an equatorial mount to compensate for Earth’s rotation. Both were equipped with fast telephoto lenses: a Canon 200 mm f/1.8 was used to build the panorama, while a 400 mm f/2.8 allowed high-resolution observations of 50 objects the photographers selected for what they call the galactic fauna catalog.

    Tour the Milky Way

    Miquel Serra-Ricart (Astrophysical Institute of the Canaries) coordinated the project and also manages the Teide Observatory in Tenerife, where the cameras were installed.

    Teide Observatory in Tenerife Spain, home of two 40 cm LCO,telescopes, Altitude 2,390 m (7,840 ft)

    He says he was surprised by the sheer amount and density of objects in our galaxy. “You can imagine that this is something we already knew, but still, as we navigate the image we keep finding small objects we didn’t see at first glance,” Serra-Ricart adds.

    Navigating the image, available on the project’s website, is truly a mesmerizing experience. However, if you want to go straight to the highlights, the team has also selected and annotated some of the most interesting objects on their Flickr site. One of those highlights, a dusty view of the Pleiades and the comet Panstarr, was recently featured as NASA’s Astronomic Picture of the Day.

    Other great views include Orion’s Belt, the Witch Head Nebula, The Triangle Galaxy, or the Spaghetti Nebula, to name a few.

    However the project wasn’t without technical difficulties. Serra-Ricart acknowledges that in some areas the superposition of images wasn’t perfect, resulting in doubled stars. “We would have needed two years instead of one to go back to those areas we need to fix. In hindsight that’s the main thing we would have liked to fix: to plan for more time.”

    More to See

    If you think this is a neat idea, you might also want to check out similar projects conducted by professional and amateur astronomers alike. German astronomers used a 15-cm telescope in Chile to produce the largest-ever image of the Milky Way. They made a humongous 46-gigapixel image, which is also available and annotated online. It looks less colorful because they used a filter to reduce color variation and highlight changes in brightness over time, as their main goal was to find variable stars. NASA also produced a 20-gigapixel mosaic from infrared images captured by the Spitzer Space Telescope, and the European Southern Observatory released a 800-megapixel panoramic view of our galaxy back in 2009, although only a smaller version is still available online.

    NASA/Spitzer Infrared Telescope

    Others have tried more ambitious goals, such as astrophotographer Nick Risinger, who shot the entire sky (Sky & Telescope’s February 2012 issue, page 70.). It’s also worth noting that Sky and Telescope’s editors, Sean Walker and Dennis Di Cicco, are currently working on a survey to capture the entire night sky in hydrogen-alpha emission, thus revealing the glowing clouds of hydrogen gas that make the building blocks of our galaxy.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Sky & Telescope magazine, 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 9:23 pm on March 19, 2018 Permalink | Reply
    Tags: , , , , , , Gravastar model, , Sky and Telescope   

    From Sky & Telescope: “Physicist Proposes Alternative to Black Holes” 

    SKY&Telescope bloc

    Sky & Telescope

    March 19, 2018
    Ben Skuse

    A physicist has incorporated a quantum mechanical idea with general relativity to arrive at a new alternative to black hole singularities.

    1
    An artist’s rendering of Cygnus X-1, an X-ray-emitting black hole that formed when a large star caved in. (We see its X-rays now as it feeds from its stellar companion.) But are black holes the inevitable next step after neutron stars? NASA / CXC / M.Weiss.

    What do you get when you cross two hypothetical alternatives to black holes? A self-consistent semiclassical relativistic star, according to Raúl Carballo-Rubio (International School for Advanced Studies, Trieste, Italy) whose recently published results in the February 6th Physical Review Letters describe a new mathematical model for the fate of massive stars.

    When a massive star comes to the end of its life, it goes supernova, leaving behind a dense core that — according to conventional thought — continues to collapse to form either a neutron star or black hole. To which fate a particular star is destined comes down to its mass. Neutron stars find a balance between the repulsive force of quantum mechanical degeneracy pressure and the attractive force of gravity, while more massive cores collapse into black holes, unable to fight the overwhelming pull of their own gravity.

    Repulsive Gravity

    Now, Carballo-Rubio adds an extra force into the mix: quantum fluctuations. Quantum mechanics has shown that virtual particles spontaneously pop into and out of existence — the effects can be measured best in a vacuum, but these fluctuations can happen anywhere in spacetime. These particles can be thought of as fluctuations of positive and negative energy that under normal conditions would cancel out. But the extreme gravity of compact objects breaks this balance, effectively generating negative energy. This negative energy creates a repulsive gravitational force.

    “The existence of quantum [fluctuations] due to gravitational fields has been known since the late 1970s,” explains Carballo-Rubio. But physicists didn’t know how to take this effect into account in collapsing stars.

    Carballo-Rubio derived equations that combine general relativity and quantum mechanics in a way that accounts for quantum fluctuations. Moreover, he found solutions that balance attractive and negative gravity for stellar masses that would otherwise have produced black holes. Dubbing them “semiclassical relativistic stars,” these compact objects do not fully collapse under their own weight to form an event horizon, and are therefore not black holes.

    Hybrid Star

    Interestingly, Carballo-Rubio’s semiclassical relativistic stars bear hallmarks of previously proposed black hole alternatives: gravastars and black stars.

    Gravastars and black stars also consist of ordinary matter and quantum fluctuations. But when these ideas were first conceived, equations incorporating quantum flluctuations were not yet known, so theorists Carballo-Rubio’s stars, on the other hand, emerge naturally from a consistent set of equations based on known physics.

    Gravastars and black stars are structured differently: In gravastar cores, large quantum fluctuations push ordinary matter outward to form an ultra-thin shell at the surface. Black stars, on the other hand, balance matter and the quantum fluctuations throughout their structure.

    Carballo-Rubio’s stars are like a hybrid of the two previous ideas. “On the one hand, both matter and the quantum [fluctuations] are present throughout the structure, as in the black star model,” he says. “On the other, the star displays two distinct elements, namely a core and an ultra-thin shell, as in the gravastar model.”

    2
    Artist’s drawing of a neutron star. Casey Reed / Penn State University.

    The Question of Stability

    Whether these hybrid stars exist in the real world is a matter of debate. Carballo-Rubio’s solutions do not incorporate time, so it isn’t clear if a such a star would remain stable or rapidly morph into something else . . . like a black hole.

    “Equilibrium solutions can be found for a pen standing on its tip,” remarks relativistic astrophysicist Luciano Rezzolla (Institute of Theoretical Physics, Germany). “Such a solution is obviously unstable to small perturbations.”

    However, if Carballo-Rubio can show that his semiclassical relativistic stars are indeed dynamically stable — which he will start work on next — the next generation of gravitational wave observatories should offer the level of precision necessary in the coming decades to distinguish unconventional compact bodies from black holes, potentially providing evidence to support the existence of this new type of star.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Sky & Telescope magazine, 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 1:12 pm on January 20, 2018 Permalink | Reply
    Tags: , , , , , Galaxies Show Order in Chaotic Young Universe, , , Sky and Telescope   

    From Sky & Telescope: “Galaxies Show Order in Chaotic Young Universe” 

    SKY&Telescope bloc

    Sky & Telescope

    January 15, 2018
    Monica Young

    New observations of galaxies in a universe just 800 million years old show that they’ve already settled into rotating disks. They must have evolved quickly to display such surprising maturity.

    1
    Data visualization of the the velocity gradient across the two surprisingly evolved young galaxies.
    Hubble (NASA/ESA), ALMA (ESO/NAOJ/NRAO), P. Oesch (University of Geneva) and R. Smit (University of Cambridge).

    NASA/ESA Hubble Telescope

    ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres

    Our cosmos was a messy youngster. Hotter and denser than the universe we live in now, it was home to turbulent gas flinging about under the influence of gravity. Theorists think the earliest galaxies built up gradually, first clump by clump, then by mergers with other galaxies.

    Astronomers expected that most galaxies living among this early chaos would be turbulent masses themselves. But new observations have revealed two surprisingly mature galaxies when the universe was only 800 million years old. Renske Smit (University of Cambridge, UK) and colleagues report in the January 11th Nature that these two galaxies have already settled into rotating disks, suggesting they evolved rapidly right after they were born.

    Smit and colleagues first found the two galaxies in deep Spitzer Space Telescope images,

    NASA/Spitzer Infrared Telescope

    then followed up using the Atacama Large Millimeter/submillimeter Array (ALMA), a network of radio dishes high in the Atacama Desert in Chile. ALMA’s incredible resolution enabled the astronomers to measure radiation from ionized carbon — an element associated with forming stars — across the face of these diminutive galaxies.

    Consider for a moment: These galaxies are a fifth the size of the Milky Way, and they’re incredibly far away — their light has traveled 13 billion years to Earth. Even in images taken by the eagle-eyed Hubble Space Telescope, such galaxies appear as small red dots.

    3
    Distant Galaxies in the Hubble Ultra Deep Field
    This Hubble Space Telescope image shows 28 of the more than 500 young galaxies that existed when the universe was less than 1 billion years old. The galaxies were uncovered in a study of two of the most distant surveys of the cosmos, the Hubble Ultra Deep Field (HUDF), completed in 2004, and the Great Observatories Origins Deep Survey (GOODS), made in 2003.

    Just a few years ago, astronomers had not spotted any galaxies that existed significantly less than 1 billion years after the Big Bang. The galaxies spied in the HUDF and GOODS surveys are blue galaxies brimming with star birth.

    The large image at left shows the Hubble Ultra Deep Field, taken by the Hubble telescope. The numbers next to the small boxes correspond to close-up views of 28 of the newly found galaxies at right. The galaxies in the postage-stamp size images appear red because of their tremendous distance from Earth. The blue light from their young stars took nearly 13 billion years to arrive at Earth. During the journey, the blue light was shifted to red light due to the expansion of space.

    Yet astronomers are now able to point an array of radio dishes to not only spot the galaxies themselves but also capture features within them down to a couple thousand light-years across.

    They Grow Up So Fast

    The ALMA observations revealed that these two galaxies aren’t the turbulent free-for-all that astronomers expect for most galaxies in this early time period. Their rotating disks aren’t quite like the Milky Way’s, as spiral arms take time to form. Instead, they look more like the fluffy disk galaxies typically seen at so-called cosmic noon, the universe’s adolescent period of star formation and galaxy growth. That implies rapid evolution, as cosmic noon occurred more than 2 billion years after these two galaxies existed.

    Simulations had predicted that it’s possible for some galaxies to evolve more quickly than their peers, notes Nicolas LaPorte (University College London), but it had never been observed before. “This paper represents a great leap forward in the study of the first galaxies,” he says.

    Smit says that these two galaxies seem to stand out from their cohort, which makes sense given their quick growth: Among other things, they’re forming tens of Suns’ worth of stars every year, more than is typical for their time period. Smit is already planning additional observations to see just how different these galaxies are from their peers.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Sky & Telescope magazine, 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 9:11 am on January 13, 2018 Permalink | Reply
    Tags: , , , , Iron-rich stars host planets on closer orbits than their iron-poor siblings, Metal-rich Stars Host Closer Planets, , Sky and Telescope,   

    From U VA via Sky and Telescope: “Metal-rich Stars Host Closer Planets” 

    UVA bloc

    University of Virginia

    Sky and Telescope

    January 10, 2018
    Monica Young

    1
    Artist’s impression of the view just above the surface of one of the middle planets in the TRAPPIST-1 system. Impression based on the known physical parameters for the planets and stars seen, and using a vast database of objects in the Universe. ESO/N. Bartmann/spaceengine.org

    2
    An artist’s rendering of how the iron content of a star can impact its planets. A normal star (green label) is more likely to host a longer-period planet (green orbit), while an iron-rich star (yellow label) is more likely to host a shorter-period planet (yellow orbit). Credit: Dana Berry/SkyWorks Digital Inc.; SDSS collaboration

    Iron-rich stars host planets on closer orbits than their iron-poor siblings, astronomers find. The results could help reveal how planets form.

    The more iron a star contains, the closer its planet’s orbit. And astronomers aren’t quite sure why.

    Robert Wilson, a graduate student at the University of Virginia, announced the puzzling result at a meeting of the American Astronomical Society in Washington, D.C.

    Stars are mostly hydrogen and helium, with just a smattering of heavier elements. Since stars forge heavy elements in their core, the ones we see on the surface come from previous generations of stars. The longer a star’s lineage, the more such elements enrich it (or pollute it, depending on your point of view). The heaviest element a star can make is iron, so its abundance serves as a proxy for the presence of all the other elements in the star, or in astro-speak, the star’s metallicity.

    Planets form out of the same natal gas as their parent star. So a star’s high metallicity is a sign that its planets came together within metal-enriched gas. Previous studies [Nature] have found that metallicity plays a role in planet formation — but astronomers don’t yet understand how the connection works.

    Wilson studied metallicity’s effect on planet formation using data from the exoplanet-hunting Kepler mission, a space telescope that imaged a field of stars, looking for the momentary dips in brightness that signal an exoplanet’s crossing.

    NASA/Kepler Telescope

    Kepler has found more than 2,500 confirmed planets to date. For roughly half of these, the Sloan 2.5-meter telescope in New Mexico took additional spectroscopic data, revealing each star’s iron abundance.

    SDSS Telescope at Apache Point Observatory, near Sunspot NM, USA, Altitude 2,788 meters (9,147 ft)

    Apache Point Observatory, Apache Point Observatory, NM, USA. n the Sacramento Mountains in Sunspot, New Mexico, Altitude 2,788 meters (9,147 ft)

    2
    This artist’s conception shows the silhouette of a rocky planet, dubbed HD 219134b, as it passes in front of its star. NASA/JPL-Caltech.

    To Wilson’s surprise, the stars richest in iron host planets on scorchingly close orbits, while stars with lower iron abundances have planets on farther-out orbits. The results point to different formation histories for the two types of planets.

    A clear line divides the two groups of planets: iron-rich stars host planets with orbits of 8 days or less, while the farther-out planets circle their iron-poor stars on periods longer than 8 days. Yet the two sets of stars aren’t all that different from each other — the ones labeled iron-rich have only 25% more iron than those labeled iron-poor.

    “That’s like adding five-eighths of a teaspoon of salt into a cupcake recipe that calls for half a teaspoon, among all its other ingredients,” Wilson says. When baking a planet, it turns out, even a small difference in the metallicity of a planet’s natal cloud can have surprisingly strong effects on its formation.

    But how? Wilson suspects that higher-metallicity gas makes for flatter planet-forming disks. The presence of heavy elements helps gas in the planetary disk cool and collapse to the centerline — like someone forgot the baking powder when making pancakes. Thinner disks make it easier for forming planets to migrate inward, closer to the star.

    The next step will be an astronomer’s version of America’s Test Kitchen: Wilson is working with theorists to cook up stars and their planet-forming disks within different metallicity environments to see if they can reproduce the same iron-rich/iron-poor divide.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    UVA campus

    The University of Virginia (U.Va. or UVA), frequently referred to simply as Virginia, is a public-private flagship and research university.[1][2][3] Founded in 1819 by Declaration of Independence author Thomas Jefferson, UVA is known for its historic foundations, student-run honor code, and secret societies.

    UNESCO designated UVA as America’s first and only collegiate World Heritage Site in 1987, an honor shared with nearby Monticello.[7] The university was established in 1819, and its original governing Board of Visitors included Thomas Jefferson, James Madison, and James Monroe. Monroe was the sitting President of the United States at the time of its foundation. Former Presidents Jefferson and Madison were UVA’s first two rectors and the Academical Village and original courses of study were conceived and designed by Jefferson.

    The university’s research endeavors are highly recognized. In 2015, Science honored UVA faculty for discovering two of its top 10 annual scientific breakthroughs; from the fields of Medicine and Psychology.[8] UVA is one of 62 institutions in the Association of American Universities (AAU), an organization of preeminent North American research universities. It is the only AAU member university located in Virginia. UVA is classified as a Research University with Very High Research by the Carnegie Foundation, and is considered Virginia’s flagship university by the College Board.[9][10][11] The university was the first non-founding member, and the first university of the American South, to attain AAU membership in 1904. UVA has been referred to as a “Public Ivy” by various sources.[12][13] Companies founded by UVA students and alumni, such as Reddit, generate more than $1.6 trillion in annual revenue – equivalent to an economy the size of Canada, 10th-largest in the world.[14][15]

    UVA’s academic strength is broad, with 121 majors across the eight undergraduate and three professional schools.[16] Students compete in 26 collegiate sports and UVA leads the Atlantic Coast Conference in men’s NCAA team national championships with 17. UVA is second in women’s NCAA titles with 7. UVA was awarded the Capital One Cup in 2015 after fielding the top overall men’s athletics programs in the nation.[17]

    Students come to attend the university in Charlottesville from all 50 states and 147 countries.[18][19][20] The historical campus occupies 1,682-acre (2.6 sq mi; 680.7 ha), many of which are internationally protected by UNESCO and widely recognized as some of the most beautiful collegiate grounds in the country.[21] UVA additionally maintains 2,913-acre (4.6 sq mi; 1,178.8 ha) southeast of the city, at Morven Farm.[22] The university also manages the College at Wise in Southwest Virginia, and until 1972 operated George Mason University and the University of Mary Washington in Northern Virginia.

     
  • richardmitnick 1:40 pm on December 9, 2017 Permalink | Reply
    Tags: , , , , Sky and Telescope, Thanks to churning convection in its liquid outer core Earth has a substantial magnetic field, The generation of a global magnetic field requires core convection which in turn requires extraction of heat from the core into the overlying mantle" explains Francis Nimmo (University of California L, The team concludes "Earth was struck violently [by planet Theia] at the end of its growth simultaneously creating its Moon and homogenizing its core, Venus lacks any of the plate tectonism that's a hallmark of Earth — there's no rising and sinking of plates to carry heat from the deep interior in conveyor-belt fashion, Why is Earth Magnetized and Venus Not?   

    From Sky & Telescope: “Why is Earth Magnetized and Venus Not?” 

    SKY&Telescope bloc

    Sky & Telescope

    1
    Based on their bulk density, Venus and Earth have cores that take up about half of their radius and roughly 15% of their volumes. Researchers don’t know if Venus has a solid inner core, as Earth does.
    Don Davis / The New Solar System (4th ed.)

    December 5, 2017
    Kelly Beatty

    A new analysis reveals that the gigantic impact that led to the Moon’s formation might have also switched on Earth’s magnetic field.

    Planetary scientists don’t really know what to make of Venus. Although it’s a near twin of Earth in size, mass, and overall rocky composition, the two are worlds apart (so to speak) in many ways. One obvious difference is our sister planet’s dense, cloud-choked atmosphere. This enormous blanket of carbon dioxide has triggered a runaway greenhouse effect, trapping solar energy so well that the planet’s surface temperature has rocketed to roughly 460°C (860°F).

    Dig deeper, and the differences become even starker. Based on its density alone, Venus must have an iron-rich core that’s at least partly molten — so why does it lack the kind of global magnetic field that Earth has? To generate a field, the liquid core needs to be in motion, and for a long time theorists suspected that the planet’s glacially slow 243-day spin was inhibiting the necessary internal churning.

    But that’s not the cause, researchers say. “The generation of a global magnetic field requires core convection, which in turn requires extraction of heat from the core into the overlying mantle,” explains Francis Nimmo (University of California, Los Angeles). Venus lacks any of the plate tectonism that’s a hallmark of Earth — there’s no rising and sinking of plates to carry heat from the deep interior in conveyor-belt fashion. So for the past two decades Nimmo and others have concluded that the mantle of Venus must be overly hot, and heat can’t escape from the core fast enough to drive convection [semanticscholar.org].

    Now a new idea has emerged that attacks the problem from a wholly new angle. As Seth Jacobson (now at Northwestern University) and four colleagues detail in September’s Earth and Planetary Science Letters, Earth and Venus might both have ended up without magnetic fields, save for one critical difference: The nearly assembled Earth endured a catastrophic collision with a Mars-size impactor — the one that led to the Moon’s creation — and Venus did not.

    Jacobson and his team [Earth and Planetary Science Letters] simulated the gradual build-up of rocky planets like Venus and Earth from countless smaller planetesimals early in solar system history. As bigger and bigger chunks came together, whatever iron they delivered sank into the completely molten planets to form cores. At first the cores consisted almost completely of iron and nickel. But more core-forming metals arrived by way of impacts, and this dense matter sank through each planet’s molten mantle — picking up lighter elements (oxygen, silicon, and sulfur) along the way.

    Over time these hot, molten cores developed several stable layers (maybe as many as 10) of differing compositions. “In effect,” the team explains, “they create an onion-like shell structure within the core, where convective mixing eventually homogenizes the fluids within each shell but prevents homogenization between shells.” Heat would still bleed out into the mantle but only slowly, via conduction from one layer to the next. Such a stratified core would lack the wholesale circulation necessary for a dynamo, so there’d be no magnetic field. This might have been the fate of Venus.

    3
    Thanks to churning convection in its liquid outer core, Earth has a substantial magnetic field. Blue arrow indicates pole direction; yellow arrow points toward the Sun.
    NASA-GSFC Scientific Visualization Studio / JPL / NAIF

    On Earth, meanwhile, the Moon-forming impact affected our planet literally to its core, creating turbulent mixing that disrupted any compositional layering and creating the same mix of elements throughout. With this kind of homogeneity, the core started convecting as a whole and drove heat readily into the mantle. From there, plate tectonism took over and delivered that heat to the surface. The churning core became the dynamo that created our planet’s strong, global magnetic field.

    What’s not yet clear is how stable these compositional layers would really be. The next step, Jacobson says, is to grind through more rigorous numerical modeling of the fluid dynamics involved.

    The researchers note that Venus certainly endured its share of big impacts as it grew in size and mass. But apparently none of them hit planet hard enough — or late enough — to disrupt the compositional layering that had already settled out in its core. By contrast, the team concludes, “Earth was struck violently at the end of its growth, simultaneously creating its Moon and homogenizing its core.” If they’re right, then the divergence of Earth and Venus becomes a classic story of planetary “haves” and “have nots.”

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Sky & Telescope magazine, 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 4:20 pm on September 2, 2016 Permalink | Reply
    Tags: , , Density waves, Sky and Telescope,   

    From Sky and Telescope: “Why [Some] Galaxies Have Spiral Arms” 

    SKY&Telescope bloc

    Sky & Telescope

    August 29, 2016
    Camille M. Carlisle

    1
    The galaxy M101 is a “grand design” spiral (meaning it’s dominated by prominent, well-organized arms) of type Sc. Of its estimated trillion stars, many thousands of its brightest supergiants are resolved by Hubble. NASA / ESA / K. Kuntz (JHU) / F. Bresolin (Univ. of Hawaii) / J. Trauger (JPL) / J. Mould (NOAO) / Y.-H. Chu (Univ. of Illinois, Urbana) / STScI

    Arguably the prettiest objects in space are spiral galaxies. Young, bright stars trace the arms of these graceful whorls, and dark dust lanes act like galactic eyeliner to dramatically shade them.

    In principle it’s easy to make a spiral arm. For various reasons, stuff in the disk sometimes clumps together, but the clump won’t stay a clump for long: stars and clouds near the galactic center circle the galaxy faster than the material farther out does, so over time the clump gets stretched into a spiral.

    However, by this reasoning, the arm should quickly wrap itself around the galaxy’s center, destroying the spiral. That generally doesn’t happen. Thus for at least half a century, astronomers have debated why these patterns persist. Maybe, many have suggested, stars don’t actually create the pattern — instead, they’re just passing through it. The arms instead would arise thanks to what are called density waves. Now, observations published in the August 10th Astrophysical Journal Letters provide long-looked-for evidence that these waves do exist.

    Yield to Oncoming Stars

    If you’ve ever been in a slowdown on the highway, you’ve experienced a density wave. Cars whizzing down the road encounter a region where, for whatever reason, they have to decelerate. Once they’ve passed it, they speed up again. Yet even though cars are successfully passing through the jam, the slow stretch persists and keeps propagating along the highway.

    The same thing happens (we think) in spiral galaxies. Even as a clump in the disk stretches into a spiral, all the stars and clouds keep moving through that arm, just as cars continue to pass through a highway choke point. Essentially, clouds and stars slow down and speed up again in a chain reaction — a density wave — that moves through the galaxy.

    2
    This diagram shows the authors’ scenario for how density waves create spiral arms. The green dashed line is the co-rotation radius, where the density wave (brownish curve, labeled “stellar arm”) and the stars and gas in the galactic disk travel at the same speed. Within that radius, the stars travel faster than the wave; outside the radius, the stars travel slower. In the scenario above, the density wave compresses the gaseous arm (black), which then forms new stars (blue arm) that age as they travel farther from the density wave. Those newborn stars combine with other, old-and-red stars that were already in the disk and were squeezed closer together by the wave (red). Because arms wind up with time, a galaxy’s arms will look tighter or looser depending on which population of stars astronomers observe. Hamed Pour-Imani et al. / Astrophysical Journal Letters 827:L2, 2016 August 10. © AAS

    The reason we can see this spiral pattern is because as it passes through the galaxy the density wave compresses gas clouds, triggering star formation. The youngest, brightest stars will thus be nearest the wave and trace out an arm. As stars move out of the wave and spread out across the disk they will age and these biggest, brightest stars will die off, preventing the arm from totally winding up.

    But that doesn’t mean there’s no winding. An important prediction comes out of this scenario: how tightly wound a spiral’s arms appear depends on which population of stars you observe. As time goes on the stars get farther from the wave, and — because the inner stars move faster and the outer stars move slower — their orbital motions do wind the arm they’re tracing, tightening the spiral over time.

    But because the hot, bluish, live-fast-die-young ones kick the bucket soon after they encounter the density wave, they’ll only trace loosely wound arms. Conversely the older, redder stars will trace more tightly wound arms. So if astronomers look at a galaxy in wavelengths that pick up young stars, they’ll see a more relaxed spiral than if they look in wavelengths that pick up old stars.

    Density Waves Detected

    Until now, astronomers hadn’t conclusively seen this effect. But the new study by Hamed Pour-Imani (University of Arkansas) and colleagues is convincing proof in its favor. The team compiled archival images of 28 spiral galaxies in far-infrared, near-infrared, optical, and ultraviolet wavelengths. The far-infrared and ultraviolet wavelengths pick up star-forming regions, while optical and near-infrared probe older stars.

    The team checked its results three ways and sure enough, it found exactly what’s predicted: arms traced by older stars hug the galactic centers more tightly than those traced by star-forming regions. The result is a neat confirmation that density waves exist.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Sky & Telescope magazine, 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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