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  • 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.

    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 11:21 am on May 14, 2015 Permalink | Reply
    Tags: , , , , Sky and Telescope   

    From Sky and Telescope: “Mapping Dark Matter” 

    SKY&Telescope bloc

    Sky & Telescope

    May 7, 2015
    Monica Young

    Two projects are mapping the distribution of dark matter in the universe, probing scales both large and small.

    1
    A snapshot from the Bolshoi cosmology simulation shows what the universe’s current dark matter distribution should look like. This box is roughly 800 million light-years across. Anatoly Klypin (NMSU), Joel R. Primack (UCSC), and Stefan Gottloeber (AIP, Germany)

    Observations show the universe to be a cosmic spider web: galaxies and clusters of galaxies are strung along its nodes and filaments like so many caught flies. Yet the thread — dark matter, which makes up 85% of the universe’s mass — is largely invisible, fully visualized only in simulations.

    Scientists are finding ways to map this unseen backbone of the universe, plotting its effect on light coming from distant galaxies and even from the remnant glow of the Big Bang, the cosmic microwave background [CMB].

    Cosmic Microwave Background  Planck
    CMB per ESA/Planck

    ESA Planck
    ESA/Planck

    Two projects making the invisible visible are the Dark Energy Survey, led by Josh Frieman (Fermilab) and conducted at the Cerro Tololo Inter-American Observatory in the Chilean Andes, and the Atacama Cosmology Telescope [ACT] polarization survey, also in Chile and high in the Atacama Desert. These complementary surveys are taking on the universe on scales big and small.

    Dark Energy Camera
    DECam, built at FNAL
    CTIO Victor M Blanco 4m Telescope
    CTIO Victor M Blanco 4m Telescope interior
    CTIO Victor M Blanco telescope, which houses the DECam

    Princeton ACT Telescope
    ACT

    Mapping Superclusters and Supervoids

    2
    By measuring dark matter’s smearing effect on galaxy shapes, the Dark Energy Survey mapped out the mysterious stuff’s density over a 139-square-degree swath of sky. The color scale reflects dark matter density; grey circles mark galaxy clusters – bigger circles represent larger clusters.
    Dark Energy Survey

    Frieman’s team is tackling the large-scale universe using the Dark Energy Camera, a 570-megapixel CCD camera that’s in the process of surveying a huge, 5,000-square-degree swath of Southern Hemisphere sky. (Compare that to the cutting-edge yet still-measly 16-megapixel camera in a Samsung Galaxy S6 smartphone!)

    Using preliminary data that covers just 3% of the full survey, a team led by Vinu Vikram (Argonne National Laboratory) examined the shapes of more than 1 million faraway galaxies, whose light has traveled between 5.8 billion and 8.5 billion years to reach us. The team was looking for the smearing effect of intervening dark matter.

    Dark matter’s gravity acts like a lens to magnify and distort the galaxies’ light, but its effect is weak — individual galaxies vary enough in shape that the gravitational lensing isn’t noticeable. The key is quantity: measure enough galaxies and the smearing becomes plain.

    Vikram and colleagues measured the smearing to construct a two-dimensional dark matter map, plotting out how much dark matter lies along lines of sight within a 139-square-degree area.

    Since the map traces normal, luminous matter (galaxies and galaxy clusters) as well as the now-visible dark matter web, astronomers can use it to study the connection between the two. Galaxies and clusters don’t exactly trace the underlying dark matter distribution, since normal and dark matter follow different physical laws, so knowing how the two differ is essential for puzzling out longstanding mysteries.

    Mapping Galaxies’ Dark Matter Halos

    3
    This stacked image of ACT polarization data shows what a single, average dark matter halo looks like. As blobby as it is, its measurements match predictions from dark matter simulations. M. Madhavacheril & others

    After viewing the grand, 500-million-light-year scales of the Dark Energy Survey results, which still only hint at the mammoth survey to come, zooming into recent observations from the Atacama Cosmology Telescope (ACT) is like taking a sip of the shrinking potion in Alice in Wonderland.

    The ACT dark matter maps focus on a scale of a mere 3 million light-years, roughly the size of a dark matter halo around an individual galaxy. Graduate student Mathew Madhavacheril and his advisor Neelima Sehgal (both Stony Brook University) led a team in measuring dark matter’s smearing effect, not on the light from faraway galaxies, but on the most well-traveled light in the universe: the cosmic microwave background (CMB).

    ACT’s polarimeter spent 3 months surveying the glow from photons freed 380,000 years after the Big Bang at a frequency of 146 GHz (corresponding to a wavelength of 2 millimeters). Even though this glow is “bumpy,” varying in brightness from one spot to the next, it’s actually pretty smooth on the arcminute scales probed by ACT. But a million-light-year-wide hunk of intervening dark matter will distort the light and create sharp changes in brightness on these small scales.

    The team looked for such brightness changes and found about 12,000 that matched up with galaxies listed in a Sloan Digital Sky Survey catalog. Each of these galaxies has a massive halo roughly 10 times that of the Milky Way. Stacking all the ACT images together, the team created an image of an average dark matter halo.

    Simply measuring the signal from galaxies’ dark matter halos is an accomplishment — little has been done on these small scales before. The average dark halo’s mass and concentration, as measured from this blobby image, so far match what’s expected from dark matter simulations. The same technique will be applied to the Advanced ACT polarization survey taking place between 2016 and 2018, which will cover ten times the sky area. Eventually, Madhavacheril hopes to trace the growth of dark matter halos over cosmic time.

    Preliminary as they are, these maps pave the way for understanding dark matter’s role in the universe, including its structure, its connection to ordinary matter, and its role in the evolution and fate of the universe.

    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 10:10 am on March 22, 2015 Permalink | Reply
    Tags: , , , Sky and Telescope   

    From S and T: “Nova in Sagittarius Now 4th Magnitude!” 

    SKY&Telescope bloc

    Sky & Telescope

    March 22, 2015
    Alan MacRobert

    The nova that erupted in the Sagittarius Teapot on March 15th continues to brighten at a steady rate. As of the morning of March 22nd it’s about magnitude 4.3, plain as can be in binoculars before dawn, looking yellowish, and naked-eye in a moderately good sky.

    Update Sunday March 22: It’s still brightening — to about magnitude 4.3 this morning! That’s almost 2 magnitudes brighter than at its discovery a week ago. It’s now the brightest star inside the main body of the Sagittarius Teapot, and it continues to gain 0.3 magnitude per day. This seems to be the brightest nova in Sagittarius since at least 1898. And, Sagittarius is getting a little higher before dawn every morning.

    1
    The nova is right on the midline of the Sagittarius Teapot. The horizon here is drawn for the beginning of astronomical twilight in mid-March for a viewer near 40° north latitude. The nova is about 15° above this horizon. Stars are plotted to magnitude 6.5. For a more detailed chart with comparison-star magnitudes, see the bottom of this page. Sky & Telescope diagram.

    You never know. On Sunday March 15th, nova hunter John Seach of Chatsworth Island, NSW, Australia, found a new 6th-magnitude star shining in three search images taken by his DSLR patrol camera. The time of the photos was March 15.634 UT. One night earlier, the camera recorded nothing there to a limiting magnitude of 10.5.

    2
    Before and after. Adriano Valvasori imaged the nova at March 16.71, using the iTelescope robotic telescope “T9” — a 0.32-m (12.5-inch) reflector in Australia. His shot is blinked here with a similarly deep earlier image. One of the tiny dots at the right spot might be the progenitor star. The frames are 1⁄3° wide.

    A spectrum taken a day after the discovery confirmed that this is a bright classical nova — a white dwarf whose thin surface layer underwent a hydrogen-fusion explosion — of the type rich in ionized iron. The spectrum showed emission lines from debris expanding at about 2,800 km per second.

    The nova has been named Nova Sagittarii 2015 No. 2, after receiving the preliminary designation PNV J18365700-2855420. Here’s its up-to-date preliminary light curve from the American Association of Variable Star Observers (AAVSO). Here is the AAVSO’s list of recent observations.

    Although the nova is fairly far south (at declination –28° 55′ 40″, right ascension 18h 36m 56.8s), and although Sagittarius only recently emerged from the glow of sunrise, it’s still a good 15° above the horizon just before the beginning of dawn for observers near 40° north latitude. If you’re south of there it’ll be higher; if you’re north it’ll be lower. Binoculars are all you’ll need.

    It looks yellowish. Here’s a color image of its spectrum taken March 17th, by Jerome Jooste in South Africa using a Star Analyser spectrograph on an 8-inch reflector. Note the wide, bright emission lines. They’re flanked on their short-wavelength ends by blueshifted dark absorption lines: the classic P Cygni profile of a star with a thick, fast-expanding cooler shell or wind.

    To find when morning astronomical twilight begins at your location, you can use our online almanac. (If you’re on daylight time like most of North America, be sure to check the Daylight-Saving Time box.)

    Below is a comparison-star chart from the AAVSO. Stars’ visual magnitudes are given to the nearest tenth with the decimal points omitted.

    3
    The cross at center is Nova Sagittarii 2015 No. 2. Magnitudes of comparison stars are given to the nearest tenth with the decimal points omitted. The frame is 15° wide, two or three times the width of a typical binocular’s field of view. Courtesy AAVSO.

    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 4:06 pm on March 10, 2015 Permalink | Reply
    Tags: , , , Sky and Telescope   

    From S&T: “New Stars On Strange Orbits in Milky Way” 

    SKY&Telescope bloc

    Sky & Telescope

    March 5, 2015
    Monica Young

    1
    The view from newborn stars found far above the Milky Way’s plane would have a (heavily obscured) view of the galactic disk.
    NASA / JPL-Caltech

    Astronomers have found two just-born star clusters, part of our galaxy’s stellar disk, that float an incredible 16,000 light-years above the plane of the Milky Way.

    Two clusters of stars, still embedded in their natal clouds of dust and gas, are floating 16,000 light-years above the pancake-shaped disk of the Milky Way.

    Denilso Camargo (Colegio Militar de Porto Alegre, Brazil) and colleagues reported the surprising find, part of a larger study of embedded star clusters in Wide-field Infrared Survey Explorer (WISE) data, in the February 26th Monthly Notices of the Royal Astronomical Society.

    NASA Wise Telescope
    WISE

    The Milky Way is a paper-thin spiral galaxy, with 85% of its stars in a disk about 100,000 light-years across and only 3,000 light-years tall. A thicker and sparser disk of older stars extends up to 16,000 light-years above the galactic plane. The two disks appear to contain distinct stellar populations — the thick disk likely forged stars at an earlier stage of the Milky Way’s formation.

    So the discovery of new stars so far above the galactic plane, firmly in thick disk territory, is unexpected to say the least. No other such high-altitude star clusters have ever been found, even though violent supernova explosions have ejected plenty of molecular hydrogen clouds high above the galaxy’s plane, any of which could potentially form stars given the right trigger.

    The star clusters themselves are only about 2 million years old. Their age, distance, and mass come from models that Camargo’s team fit to the color and brightness measurements of their stellar populations.

    At an altitude of 16,000 light-years, the 33 and 42 stars belonging to clusters Camargo 438 and Camargo 439, respectively, have an exceptional (if heavily obscured) outsider’s view of the Milky Way’s spiral design. But they won’t for long, astronomically speaking. The authors calculated the velocity of the cloud containing the young and still-forming stars, and they find that the cloud has crossed paths with the disk before, sometime between 45 and 50 million years ago, an event that likely caused the clouds to condense and form stars. The clusters will cross paths with the disk again in another 50 million years or so.

    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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