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  • 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.”

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  • 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.”

     
  • richardmitnick 9:50 am on May 1, 2016 Permalink | Reply
    Tags: , , Crater 2 dwarf galaxy, , Sky and Telescope   

    From Sky and Telescope: “Milky Way’s New Neighbor: A Giant Dwarf” 

    SKY&Telescope bloc

    Sky & Telescope

    April 27, 2016
    John Bochanski

    Astronomers have discovered a “feeble giant”: one of the largest dwarf galaxies ever seen near the Milky Way.

    Ever since astronomers discovered our universe’s accelerating expansion, tension has rippled between theory and observations, especially in studies of our galaxy’s neighborhood.

    The standard model of cosmology, which suggests that dark energy and “cold” dark matter govern the universe’s evolution, predicts many more small galaxies near the Milky Way than what we’ve observed so far. Dwarfs should be the building blocks of larger galaxies like our own, so the lack has puzzled astronomers — are they not there, or are we just not seeing them?

    Observations have closed in on theory in recent years with the advent of large surveys such as the Sloan Digital Sky Survey and the Dark Energy Survey, where observers have begun to identify hard-to-find dwarf galaxies. Dozens of dwarfs have been spotted over the last 15 years. But theory suggests perhaps even hundreds more have yet to be discovered.

    SDSS Telescope at Apache Point, NM, USA
    SDSS Telescope at Apache Point, NM, USA

    Dark Energy Icon
    Dark Energy Camera,  built at FNAL
    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, ChileCTIO Victor M Blanco 4m Telescope interior
    DECam, built at FNAL; the NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile

    Now, the list of known dwarfs has just added one of its largest members: Crater 2 [no image available]. You’d think large dwarfs would be easy to find, but this one’s stars are spread out and easily entangled with the stars of the Milky Way. It took a sensitive survey to pick out the small galaxy hidden behind the galaxy’s stars.

    A New Dwarf Galaxy

    Gabriel Torrealba (University of Cambridge, UK) led a team that discovered the Crater 2 dwarf galaxy in survey data collected at the Very Large Telescope in Chile.

    ESO/VLT at Cerro Paranal, Chile
    ESO/VLT at Cerro Paranal, Chile

    The team used specialized software to spot over-crowding among stars, searching for dim stellar clumps. But identifying a clump isn’t enough. Only Crater 2 contained red giant stars and horizontal branch stars — both old, evolved stars that mark an ancient stellar population separate from the youthful Milky Way disk.

    Torrealba and colleagues estimate that Crater 2 lies 391,000 light-years from Earth. That makes it one of the most distant dwarf galaxies known. It’s also one of the largest: at 6,500 light-years across, it comes in fourth among our galaxy’s neighbors, after the Large and Small Magellanic Clouds, and the torn-apart Sagittarius dwarf galaxy. Moreover, it’s incredibly diffuse, its stars spread out over several square degrees. So despite its size, Crater 2 is much fainter than those Milky Way companions, nearly 100 times fainter than Sagittarius and almost 10,000 times fainter than the LMC.

    Dwarf Galaxy Groups

    The discovery of Crater 2 may help unlock an ongoing puzzle in the Milky Way’s evolution. As astronomers began to discover dwarf galaxies en masse in large sky surveys, it soon became clear that some dwarfs cluster in their orbits. Crater 2 is no exception: the team estimated that the dwarf’s orbit lines up with those of the Crater globular cluster, as well as the Leo IV, Leo V and Leo II dwarf galaxies.

    Dwarf Galaxies with Messier 101  Allison Merritt  Dragonfly Telephoto Array
    Dwarf Galaxies with Messier 101 Allison Merritt Dragonfly Telephoto Array

    U Toronto Dunlap Dragonfly telescope Array
    U Toronto Dunlap Dragonfly telescope Array

    While not a definitive association, similar orbits suggest that these objects might form a group that fell together into our galaxy’s gravitational well. Astronomers have recently found similar groups near the Large Magellanic Cloud, suggesting that our galaxy’s halo might have formed through many such group captures.

    Large Magellanic Cloud. Adrian Pingstone  December 2003
    Large Magellanic Cloud. Adrian Pingstone December 2003

    As sky surveys continue to enable discoveries of dwarf galaxies such as Crater 2, the gap between theory and observations continues to narrow, clarifying our understanding of the Milky Way’s evolution. The future is bright for the study of these dim galaxies, thanks to surveys such as the Large Synoptic Sky Survey (LSST) on the horizon. LSST will push to even fainter magnitudes and may finally resolve the discrepancy between theory and observation.

    LSST/Camera, built at SLAC
    LSST Interior
    LSST telescope, currently under construction at Cerro Pachón Chile
    LSST/Camera, built at SLAC; LSST telescope, currently under construction at Cerro Pachón Chile

    Reference:
    G. Torrealba et al. The feeble giant. Discovery of a large and diffuse Milky Way dwarf galaxy in the constellation of Crater. Accepted for publication in Monthly Notices of the Royal Astronomical Society.

    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 7:53 pm on April 20, 2016 Permalink | Reply
    Tags: , , Is T CrB About to Blow its Top, Sky and Telescope   

    From Sky and Telescope: “Is T CrB About to Blow its Top?” 

    SKY&Telescope bloc

    Sky & Telescope

    April 20, 2016
    Bob King

    The recurrent nova T Coronae Borealis last made a splash just after World War II. Does its current restive state hint at an imminent outburst?

    1
    This finder chart covers about as much sky as the field of view in a typical pair of 7-power binoculars. It includes both R CrB (currently at ~14 magnitude) and T CrB. The italic numbers next to stars are their visual magnitudes to the nearest tenth (with the decimal point omitted), for comparison purposes. North is up and east is left. S&T

    We’ve been struggling lately in northern Minnesota to get past winter and get on track with spring. That’s why I was so surprised to step out my door the other night and hear the frogs in full, throaty chorus.

    Variable stars can be like that, too. You can watch a particular variable for months, even years, and its brightness might fluctuate by a few tenths of a magnitude. Then all of a sudden, it blows up like a firecracker when you least expect.

    Take T Coronae Borealis (T CrB). It’s one of only about 10 stars in the entire sky classified as a recurrent nova, with two recorded outbursts to its name. Normally, the star slumbers at 10th magnitude, but on May 12, 1866, it hit the roof, reaching magnitude +2.0 and outshining every star in Corona Borealis before quickly fading back to obscurity. Eighty years later, on February 9, 1946, it sprang back to life, topping out at magnitude +3.0.

    Many variable star observers include it in their nightly runs because it’s easy to find 1° south-southeast of Epsilon (ε) in Corona Borealis and only requires a 3-inch telescope. Not to mention the huge payoff should you happen catch the star during one of its rare explosions. Famed comet hunter and variable lover Leslie Peltier faithfully kept an eye on T CrB for over 25 years, hoping to catch it in outburst. On that fateful February morning in 1946 he’d set his alarm clock for 2:30 a.m., planning to check in on several favorite stars before dawn. But when he awoke and looked out the window, he felt a cold coming on and allowed himself instead to go back to bed. Big mistake. That very morning, T CrB came back to life.

    In his book in his book Starlight Nights, Peltier writes:

    “I alone am to blame for being remiss in my duties, nevertheless, I still have the feeling that T could have shown me more consideration. We had been friends for many years; on thousands of nights I had watched over it as it slept, and then it arose in my hour of weakness as I nodded at my post. I still am watching it but now it is with a wary eye. There is no warmth between us any more.”

    2
    Light curve depicting T CrB’s behavior between April 2011 and April 2016. Until February 2015, T CrB’s brightness was almost constant. Notice the slight increase in brightness in February 2015 and the much more dramatic rise this winter and spring. The system’s now a magnitude brighter than normal. Is a nova-like outburst in the offing? AAVSO

    T stayed under the radar for the next 69 years, holding steady around magnitude +10.2–10.3. That began to change in February 2015, when it inched up to +10.0 and remained there until early February this year. That’s when things kicked into high gear with the star steadily growing brighter from late winter through early spring to reach its current magnitude of ~9.2.

    Alongside the brightening trend, T’s become bluer as well. Astronomers describe its recent unprecedented activity as a star entering a “super active” state. This last happened in 1938, eight years before its last great outburst.

    T CrB followers can’t help but wonder if the next night we look up, Corona Borealis will twinkle with “new” second-magnitude star.

    3
    Stars like T CrB involve a red giant closely paired with a white dwarf. The giant feeds hydrogen gas into a swirling accretion disk around a massive, compact white dwarf at a rate a million times greater than the solar wind. Material funnels from the disk onto the dwarf’s surface until it ignites in a thermonuclear explosion similar to a nova. NASA.

    Recurrent novae are similar to nova and dwarf nova types but with unique characteristics that set them apart. All three types occur in close binary stars and involve mass transfer from a normal star to a small but gravitationally powerful white dwarf. Classical novae have only been seen in outburst once and typically brighten by 8-15 magnitudes before slowly fading back to their pre-outburst brightness. Dwarf novae outburst frequently — every 10-1,000 days — with moderate increases of 2-6 magnitudes. Recurrent novae fall in between and typically vary by 4-9 magnitudes over a 10-100 year period.

    4
    Use this detailed finder chart to close in on T CrB. Numbers are star magnitudes with the decimals omitted. The star marked “42 star” is Epsilon CrB. South is up. AAVSO

    T CrB has two components: a red giant star in a close, 227-day orbit with a planet-sized white dwarf. Material spills from the giant and accumulates in an accretion disk around the dwarf. Some of that gas gets funneled down to the dwarf’s surface, becomes compacted and heated, and eventually ignites in a spectacular thermonuclear explosion. We see the results as a sudden brightening of the star.

    It’s even theoretically possible for enough matter to accumulate on the dwarf to push it past the 1.4 solar mass Chandrasekhar Limit, forcing the entire star to burn explosively as a Type Ia supernova. At T CrB’s 2,500 light-year distance, it would easily cast shadows!

    Maybe we’ll have to wait until 2026 (80 years after the 1946 eruption) for T’s next upheaval. Or maybe not. Either way, let Leslie Peltier’s story serve as a cautionary tale. Keep a close eye on this star every clear night, and expect surprises.

    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 9:47 pm on January 13, 2016 Permalink | Reply
    Tags: , , , , Sky and Telescope   

    From Sky and Telescope: “About The LIGO Gravitational-Wave Rumor. . .” The Best Article on this Subject 

    SKY&Telescope bloc

    Sky & Telescope

    January 13, 2016
    Shannon Hall

    The physics and astronomy world is agossip with a rumor: has LIGO heard its first black-hole merger?

    Caltech Ligo
    MIT/Caltech Advanced aLIGO

    Rumors are swarming on social media that the newly upgraded LIGO, the Advanced Laser Interferometer Gravitational-Wave Observatory or aLIGO, has finally seen the gravitational-wave signature of two stellar-mass black holes spiraling together and merging. Maybe even two such events since September. Or not.

    Such an observation would not only confirm one of the most elusive predictions of [Albert] Einstein’s general theory of relativity, it would open a new field of cosmic observation: gravitational-wave astronomy.

    Temp 1
    Artist’s concept of gravitational waves produced by closely orbiting black holes in a 2-dimensional sheet. K. Thorne (Caltech)/ T. Carnahan (NASA GSFC)

    First, the background: According to general relativity, any accelerating mass should produce weak ripples in the fabric of spacetime itself. But it would take enormous, dense masses accelerating extremely fast to emit a significant amount of them. Neutron stars or black holes spiraling together and merging would qualify, and LIGO was built with those events particularly in mind.

    6
    Simulation of gravitational lensing by a black hole, which distorts the image of a galaxy in the background.

    7
    Radiation from the pulsar PSR B1509-58, a rapidly spinning neutron star, makes nearby gas glow in X-rays (gold, from [NASA]Chandra) and illuminates the rest of the nebula, here seen in infrared (blue and red, from [NASA] WISE)

    NASA Chandra Telescope
    Chandra

    NASA Wise Telescope
    WISE

    As gravitational waves pass by, they stress and compress time and distance. But after travelling millions of light-years across the universe, they would be extremely weak. The typical expected signal strength would stretch and squeeze the distance from the Earth to the Sun, for instance, by the width of a hydrogen atom. Yet even that weak an effect could be detected by the laser beams bouncing back and forth along LIGO’s 4-kilometer vacuum pipes. It would be the first direct detection of gravitational radiation. (We already know it exists by its indirect effect of draining orbital energy away from close neutron-star binaries.) A Nobel Prize probably awaits the first direct observation. If it ever happens.

    3
    The tunnel for one of the LIGO arms in Livingston, Louisiana. Having two units nearly 2,000 miles apart provides essential error checking and would help triangulate to find the incoming direction of any gravitational waves. A third detector in Italy, named VIRGO, is scheduled to join the network.

    Advanced Virgo
    VIRGO

    Such a feat “will open up a new window into the way we see the universe,” says astronomer Tanaka Takamitsu (Stonybrook University). Take gamma-ray bursts, for instance. These are quick, incredibly powerful explosions that are presumed to come, in some cases, from a pair of neutron stars spiraling together and merging, and in other cases from the fraction-of-a-second disruption of a dying star’s neutron-star-like core. Both kinds of cataclysm should be violent enough to send detectable gravitational waves far across the universe. “If we could see such events from gravitational-wave and conventional telescopes [both], then we can learn a lot more about the physics and what’s really going on with those events,” says Takamitsu.

    Still, the rumors remain just rumors. And they’re really bothering the LIGO people.

    Gravitational Whispers

    The gossip started spreading in physics circles just a week after the upgraded aLIGO began running in September. The rumors escaped from physics circles when cosmologist Lawrence Krauss (Arizona State University) tweeted about them on September 25th: “Rumor of a gravitational wave detection at LIGO detector. Amazing if true. Will post details if it survives.” More recently he commented that he’s 60% sure the story will pan out. Yesterday he noted the caveat that he is not one of the 900-plus members of the LIGO scientific collaboration, nor does he represent anyone there.

    Steinn Sigurdsson (Pennsylvania State University), who has also speculated on the rumors via social media, says “I have absolutely no inside information on what is going on. I hear stories, I can make inferences, I can see patterns in activity. And there has been a consistent whisper for several months now that [aLIGO] saw something as soon as they turned it on.”

    4
    Researchers work on a LIGO detector in Livingston in 2014. Michael Fyffe/LIGO

    Those whispers grew to a lively babble after further tantalizing clues. First, Sigurdsson points to a flurry of papers that have appeared this week on the arXiv preprint server that were curiously specific. Astronomers, says Sigurdsson, “posted somewhat different scenarios for ways in which you could have black hole binaries form, all of which coincidentally predicted almost the exact same final configuration, and said ‘Gosh our model predicted that this very specific sort of thing will be the most likely thing that LIGO sees.’ ” And Sigurdsson isn’t the only one who has noticed. Derek Fox (Pennsylvania State University) pointed to one paper, for example, tweeting “this seems a rather specific GW [gravitational wave] scenario to pull out of thin air?”

    Temp 1
    The meeting of the arms. The light pipes and the equipment in their ends (seen here) are kept in an ultrahigh vacuum.

    But again, Lawrence, Sigurdsson, and Takamitsu claim to have no privileged information. “It’s the equivalent of watching for pizza deliveries at the Pentagon,” says Sigurdsson. He’s referring to the open-source intelligence technique that Washington reporters reportedly used to spot when big events were about to emerge based on the number of late-night pizzas delivered to the White House. “You can play the same game with physicists,” he says. (Unfortunately there have been no reports of LIGO ordering an overabundance of Dominos.)

    Second, it’s a small community. So when a few collaborators — who all happen to be members of LIGO — duck out of a future conference due to new overlapping commitments, it doesn’t go unnoticed. A similar pattern played out right before physicists announced the discovery of the Higgs boson.

    Higgs Boson Event
    Possible Higgs event.

    Based on dates cancelled, Sigurdsson speculates that an announcement will come from the team on February 11th. Takamitsu, however, speculates that it will take months.

    Details of the supposed detection, however, were not publicly bandied about until Monday, when theoretical physicist Luboš Motl posted on his blog the latest version of the rumor: that aLIGO has picked up waves produced by two colliding black holes each with 10 or more solar masses. He also said he’s been told that two events have been detected.

    Reason for Silence

    There’s a good reason why LIGO’s people refuse to confirm or deny that something is going on. Scientists really want to get things right before they announce a major finding to the world, whether positive or negative. LIGO’s data-analysis task alone is vast and full of potential gotchas, and the most likely gravitational-wave detections would be buried deep in the noise. The experiment is looking for changes in the distance between mirrored blocks of metal 4 km apart as slight as 10–22 meter, about a millionth the diameter of a proton. In other words, changes in measurement of 1 part in 1025. What could possibly go wrong?

    Fresh on the minds of everyone in astronomy and physics is an announcement fiasco that blew up spectacularly in 2014. The astronomers of the Harvard-based BICEP2 collaboration announced to the world’s media, at a packed press conference, that they had very likely discovered primordial gravitational waves from the earliest instant of the Big Bang.

    12
    BICEP images

    BICEP 2
    BICEP 2 interior
    BICEP at the South Pole, exterior and interior

    The signal was unexpectedly strong. It would have been the much-sought, crowning evidence for the inflationary-universe theory of how the Big Bang happened. Not until later did their work go through full peer review. The discovery literally turned to dust — leaving a very public mess and a lot of criticism. Many dread a repeat.

    The current excitement could easily be a false alarm. Even if LIGO has a promising signal, it may be a false test signal planted as a drill. It’s been done before, in 2010 near the end of LIGO’s last pre-upgrade run. Three members of the LIGO team are empowered to move the mirrored blocks by just the right traces in just the right way. Only they know the truth, and the test protocol is that they not reveal a planted signal until the collaboration has finished analyzing it and is ready to publish a paper and hold a press conference. “Blind tests” like this are the gold standard in all branches of science.

    So we’ll just have to cool our heels. But maybe not for long. If the detection is real, it’s likely to be announced in February or March according to various reports. If it was just a test, this will presumably be announced in a similar time frame.

    “Essential to the Process”

    A premature “discovery” getting loose, and then being denied or retracted, could diminish the public’s trust in scientists — and the scientific process — in general. “We live in a crazy time when it comes to science and the public, as the ongoing ‘debate’ about climate change shows us again and again,” wrote astronomer Adam Frank (University of Rochester) in his NPR blog on the BICEP2 fiasco in 2014. “I wish they’d have let the usual scientific process run its course before they made such a grand announcement. If they had, odds are, it would have been clear that no such announcement was warranted — at least not yet — and we’d all be better off.”

    Sigurdsson, however, disagrees. When the BICEP2 team announced their results, he used it as an example in his cosmology 101 class, encouraging students to view it as an uncertain result in mid-discovery phase. “I think most of the public appreciates the fact that you can make mistakes for the right reasons and that’s part of the process,” says Sigurdsson. “We proceed by falsification. We make conjectures, we test them, and some of the time we find that things were wrong and we throw them out. But that’s still essential to the process. We need to get that across.”

    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 4:21 pm on November 25, 2015 Permalink | Reply
    Tags: , , , Sky and Telescope   

    From Sky and Telescope: “Star-Counting in the Galactic Bulge” 

    SKY&Telescope bloc

    Sky & Telescope

    November 24, 2015
    John Bochanski

    1
    An artist’s impression of what Milky Way, and especially its peanut-shaped bulge, would look like from the outside.
    ESO / NASA / JPL-Caltech / M. Kornmesser / R. Hurt

    Astronomers root their response in a mathematical function that describes how many stars exist at any given mass, known as the initial mass function. In general, we know there are many more low-mass stars than high-mass ones, just as you’ll find far more fine grains of sand than large pebbles on a beach.

    And just as knowing exactly how many more fine grains there are than pebbles will tell you something about how that beach came to be, stars’ initial mass function helps astronomers investigate everything from the details of star formation to the mass of the Milky Way and other galaxies.

    Until now, astronomers’ best measurements of the initial mass function have been limited to relatively nearby stars, which lie within the Milky Way’s pancake-shaped disk. But other galaxies have shown tantalizing hints that the mass distribution of stars might differ from place to place within a galaxy.

    Now, a recent study has applied the power of the Hubble Space Telescope to go beyond the disk and count stars within the Milky Way’s bulge, the sardine-packed collection of stars far away in the center of our galaxy.

    NASA Hubble Telescope
    NASA/ESA Hubble

    A team led by Annalisa Calamida (Space Telescope Science Institute) reported the initial mass function for low-mass bulge stars in the September 1st Astrophysical Journal, focusing stars less massive than the Sun. The astronomers tracked stars’ proper motions across the sky using the exquisitely sharp Hubble images, then picked out the background bulge stars by their odd, boxy orbits. The result is a sample of low-mass stars with near-zero “contamination” from nearby stars.

    Overall, the team’s results aren’t surprising: they estimate an initial mass function that roughly agrees with previous measurements, including one made by this author. But there are hints of something interesting afoot: the new results suggest that the bulge might contain relatively fewer very low-mass stars. More work is needed to test whether this result pans out, but if it’s real, the difference would suggest a difference in how stars form in the galactic bulge compared to the disk.

    This study is an important first step in going beyond the nearby disk stars that are often observed. And there’s more to come: with the Gaia mission already at work surveying more than 1 billion stars and the Large Synoptic Survey Telescope on the way, astronomers will soon be counting stars throughout our galaxy. And the initial mass functions they measure will tell us not only how many stars are out there, but how star formation varies from place to place in our galaxy.

    ESA Gaia satellite
    ESA/Gaia

    LSST Exterior
    LSST Interior
    LSST Camera
    Future home of the LSST telescope and Camera (camera being built by SLAC)

    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 1:43 pm on November 24, 2015 Permalink | Reply
    Tags: , , , Sky and Telescope   

    From Sky and Telescope: “Mystery Signal from a Black Hole-Powered Jet” 

    SKY&Telescope bloc

    Sky & Telescope

    November 23, 2015
    Monica Young

    1
    This artist’s concept shows a supermassive black hole shooting out a jet of plasma headed almost straight for Earth. In the telescope, though, this object would appear as a (usually) randomly flickering point of light. NASA / JPL-Caltech

    Observing a blazar is a little like standing beneath a relativistic waterfall. Look up: that flickering point of light is a head-on view of the powerful plasma jet shooting out from a supermassive black hole.

    The free-flying electrons within that mess of plasma twirl at almost light speed around magnetic fields, and they radiate across the electromagnetic spectrum, often drowning out any other forms of emission. We might even see a sudden outburst when turbulence, a sudden influx of plasma, or some other force roils the jet.

    But when Markus Ackermann (DESY, Germany) and colleagues pored through almost seven years of data collected with the Fermi Gamma-Ray Space Telescope, they saw something completely unexpected: a regular signal coming from a blazar. Gamma rays from PG 1553+113 seem to brighten roughly every 2.2 years, with three complete cycles captured so far.

    NASA Fermi Telescope
    NASA/Fermi

    Moreover, other wavelengths seem to echo this cycle. Inspired by the gamma-ray find, Ackermann’s team sought out radio and optical measurements from blazar-monitoring campaigns — and both wavelengths show hints of the same periodic signal. The team also looked at X-ray data collected over the years by the Swift and Rossi X-ray Timing Explorer spacecraft, but there weren’t enough data points for a proper analysis.

    NASA SWIFT Telescope
    NASA/Swift

    NASA ROSSI
    NASA/ROSSI

    The results are published in the November 10th Astrophysical Journal Letters. (Click here for full text).

    2
    This light curve shows how the brightness of blazar PG 1553+113 varies for gamma rays with more than 100 million electron volts of energy. The plot, which includes data from August 4, 2008, to July 19, 2015, displays three complete cycles of an apparently regular, 2-year cycle. M. Ackermann & others / Astrophysics Journal Letters

    If this signal is real, it has to come from the black hole-powered jet, and the authors explore a number of explanations.

    For example, the jet might be precessing or rotating, sweeping its beam past Earth every 2 years or so. Or perhaps a strong magnetic field chokes the flow of gas toward the black hole, creating instabilities that then regularly flood the jet with material. The most intriguing prospect is another supermassive black hole in the system, its presence affecting gas flow and jet alignment.

    At this point, though, the authors admit they don’t have enough data to distinguish between these possibilities. Further monitoring might remedy that.
    Keep Watching

    “I am always skeptical about claims of periodicity based on only 2 to 3 cycles,” says Alan Marscher (Boston University), a blazar expert not involved in the study. Even completely random processes, he adds, can create apparently regular signals over short periods of time.

    3
    These light curves compare how the blazar varies in X-rays (top panel), optical (middle), and radio waves (bottom). Though there aren’t enough X-rays to track the regular variation seen in gamma rays, the optical and radio data seem to echo the gamma-ray cycle, which is shown as a dotted line in the middle panel. M. Ackermann & others / Astrophysics Journal Letters

    And Ackermann’s team is frank about the data’s limits. After all, blazars are known to flare randomly and, due to the length of the suspected cycle, only three complete periods have been captured so far. The authors estimate a few percent probability that this signal is indeed a chance alignment of random flares.

    Still, the fact that the signal is observed across radio, optical, and gamma rays strengthens the case. “Seeing such well-correlated oscillations across the different wavebands isn’t as common as simple models would expect,” Marscher notes.

    “It’s worth keeping an eye on this object.”

    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 2:23 pm on September 1, 2015 Permalink | Reply
    Tags: , , Sky and Telescope   

    From Sky and Telescope: “Amateurs Help Discover Rare Eclipsing Binary” 

    SKY&Telescope bloc

    Sky & Telescope

    September 1, 2015
    David Dickinson

    1
    An artist’s conception of the Gaia14aae star system. Marisa Grove / Institute of Astronomy

    A collaboration of amateur and professional astronomers has uncovered a rare variety of eclipsing binaries. The European Space Agency’s Gaia satellite first imaged the eclipsing pair, named Gaia14aae, in August 2014. Researchers took notice of Gaia14aae when it suddenly flared five-fold within a single day.

    The Gaia14aae system is composed of a white dwarf in a tight orbital embrace with a larger (by volume) companion. The tilt of orbit is along our line of sight, so observers on and near Earth — such as the Gaia mission in space — see an eclipse of the pair once every 50 minutes.

    ESA Gaia satellite
    ESA Gaia Camera
    ESA/GAIA satellite and its camera

    A worldwide pro-am collaboration carried out follow-up observations of Gaia14aae, cinching its nature as an eclipsing binary star. This effort included the Centre for Backyard Astrophysics (CBA), a group of amateurs who monitor cataclysmic variables using small telescopes in backyards around the world. CBA members kept eyes on the system after Gaia’s initial sighting of its outburst, as did a collaboration of 86 professionals based at facilities including the Catalina Real-time Transient Survey, PanSTARRS-1, and ASAS-SN based in Chile and Hawaii.

    Pann-STARSR1 Telescope
    PanSTARRS1

    ASAS-SN Brutus
    ASAS-SN Brutus

    “Enrique de Miguel from CBA noticed that the system appeared to be eclipsing, based on a period of dips in the brightness of the system,” says Morgan Fraser (Cambridge Institute for Astronomy, UK). “From this, we realized that this could be quite an exciting system, and this led us to take further observations.”

    This movie shows 30-second exposures from the Loiano Observatory over a span of 88 minutes (sped up by a factor of 250), revealing two eclipses of the Gaia14aae system.

    Gaia14aae is located 730 light-years from Earth in the constellation Draco. The ‘Gaia14aae’ designation denotes the discovery year (2014) followed by the sequence, with ‘aaa’ being the first object of interest discovered in that particular year. Astronomers conducted spectroscopic analysis of the system using the William Herschel Telescope in the Canary Islands.

    ING William Herschel Telescope
    ING William Herschel Telescope Interior
    ING William Herschel telescope

    They found that Gaia14aae is in fact a rare type of binary system that varies dramatically in brightness over short periods of time, known as an AM Canum Venaticorum (AM CVn) cataclysmic variable. This type is characterized by the absence of hydrogen and the abundance of helium in its spectrum.

    Forty other such binary systems are known, but this one’s an eclipsing binary, each star passing in front of and blocking the light of its partner in turn. Eclipsing binaries are valuable because they reveal a key ingredient, the tilt of the system’s orbit — it has to be edge-on for the stars to eclipse each other. Knowing that one fact makes calculating other properties, like the mass of the two stars and the distance between them, easy.

    A Supernova in the Making

    The discovery is important to researchers studying Type 1a supernovae, the apocalyptic explosions of white dwarfs that eat too much and whose detonations shine with a characteristic brightness. These “standard candles” are crucial for measuring extragalactic distances and serve as a cornerstone for the discovery of the acceleration of the expansion of the universe due to dark energy.

    Here, we’re seeing the anatomy of a probable Type 1a supernova in the making: a star 125 times the volume of our Sun locked in a death spiral with a white dwarf 100 times more massive than it. Researchers are unsure whether the two stars will collide in a dramatic supernova explosion, or if the white dwarf will devour its tenuous companion first.

    The eclipsing nature of the system gives researchers the unprecedented opportunity to measure the physical parameters of a Type 1a supernova before it occurs. A galactic supernova courtesy of Gaia14aae would be easily visible from Earth, though such a spectacle is probably still thousands of years in the future.

    “The eclipse means we can measure exactly the mass of both stars and their separation and work out their evolution,” says Heather Campbell (Cambridge Institute of Astronomy, UK). “The system could also be an important laboratory for studying ultra-bright supernova explosions, which are a vital tool for measuring the expansion of the universe.”

    Fraser adds that the masses are essential to testing theory. “This means we can start to understand how systems like Gaia14aae come about — and what it would have looked like billions of years ago when it formed,” he adds.

    More Discoveries to Come

    And this could be the first of many exciting new discoveries. “This year, [the Gaia team has] been searching for new transients in a very manual way, but we are switching to doing things in a much more automated way,” says Campbell. “This means we will start finding lots more transients every day. Many of these will be supernova explosions, but it also opens up the potential for finding many more exciting objects.“

    Launched in 2013, the Gaia observatory’s primary mission is astrometry, or the ultra-precise measurement of stars’ positions. As a spinoff, researchers expect Gaia to make serendipitous discoveries both near and far during its five-year mission, including new asteroids, comets, Kuiper Belt objects, variable stars, quasars, and much more. Gaia may spy transiting exoplanets
    as well.

    3
    Objects of the Kuiper belt (blue). Plot displays the known positions of objects in the outer Solar System within 60 astronomical units (AU) from the Sun. Epoch as of January 1, 2015.

    The discovery of Gaia14aae is a great example of amateur and professional astronomers working together, and a sign of more exciting discoveries to come down the road.

    See the full article here.

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    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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