• Galaxy's giant black hole may be cooking up meals

    ESA–C. Carreau

    The gas near the central part of the Milky Way's center is warmer than the rest of the mass of gas and dust circling the galaxy's black hole, as shown in this image released Tuesday.

    By Miriam Kramer
    Space.com

    The huge, hot mess of cosmic gas that feeds the colossal black hole at the center of our Milky Way galaxy may be getting "cooked" before being devoured, scientists say.

    Before its retirement earlier this year, the European Space Agency's (ESA) Herschel Space Observatory found that clouds of molecular gas near the galaxy's center are much hotter than expected, possibly due to the gigantic black hole at the Milky Way's heart.

    Called Sagittarius A* (pronounced "Sagittarius A-star"), the humongous black hole holds about 4 million times the mass of the sun and sits about 26,000 light-years from the solar system. Emissions from collisions between gas clouds sparked by the galaxy's turbulent core could help account for the high temperatures of the gas and dust closest to the black hole, ESA scientists have found. [See amazing photos by the Herschel Observatory]

    "The observations are also consistent with streamers of hot gas speeding towards Sgr A*, falling towards the very center of the galaxy," astronomer Javier Goicoechea of Spain's national Astrobiology Center and lead author of the study, said in a statement. "Our galaxy's black hole may be cooking its dinner right in front of Herschel's eyes."

    Herschel found that some of the molecular gas collected in an area around one light-year from the black hole was about 1,832 degrees Fahrenheit (1,000 degrees Celsius) — much hotter than an average interstellar cloud, ESA officials said.

    Most of these kinds of molecular clouds are usually pretty cold, with temperatures only a few tens of degrees above absolute zero, ESA officials added.

    "The black hole appears to be devouring the gas," Paul Goldsmith, the project scientist for Herschel at NASA's Jet Propulsion Laboratory in Pasadena, Calif., said in a statement. "This will teach us about how supermassive black holes grow."

    The research was detailed in Tuesday's issue of Astrophysical Journal Letters.

    In September, scientists may get the chance to see Sagittarius A*'s feeding in action. Astronomers have their eyes on a different blob of gas (not studied by Herschel) that is expected to fall into the galaxy's center later this year. The cosmic cloud is about three times the mass of Earth and even closer to the galactic center than the gas studied by the ESA spacecraft.

    The gas blob's destruction will give researchers an unprecedented chance to see what Sagittarius A* looks like when gobbling up matter, scientists have said.

    Last month, the $1.4 billion Herschel Space Telescope completed a planned shutdown after running out of the vital coolant needed to chill its sensitive instruments. The Herschel observatory launched in 2009 and collected a massive amount of data that is still being processed by scientists around the world.

    Follow Miriam Kramer on Twitter and Google+. Follow us on Twitter, Facebook and Google+. Original article on Space.com.

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  • Distance to Milky Way's neighbor galaxy refined

    ASA, ESA. Acknowledgement: Josh Lake

    Nearly 200 000 light-years from Earth, the Large Magellanic Cloud, a satellite galaxy of the Milky Way, floats in space around our galaxy. As the Milky Way's gravity gently tugs on its neighbor's gas clouds, they collapse to form new stars. In turn, these light up the gas clouds in a kaleidoscope of colors, visible in this image from the Hubble Space Telescope.

    By Clara Moskowitz
    Space.com

    The distance to one of the Milky Way's next-door neighbors, a satellite galaxy that orbits its outskirts, has been determined more accurately than ever before, astronomers announced Wednesday.

    The achievement could help scientists calibrate other cosmic distances, which are essential for understanding how quickly the universe is expanding and solving the mystery of dark energy. Dark energy is the name given to whatever is tugging the universe apart and causing its expansion to accelerate.

    According to the new measurement, the nearby dwarf galaxy called the Large Magellanic Cloud lies 163,000 light-years away.

    "I am very excited because astronomers have been trying for a hundred years to accurately measure the distance to the Large Magellanic Cloud, and it has proved to be extremely difficult," Wolfgang Gieren, an astronomer at Chile's Universidad de Concepción, Chile, said in a statement. "Now we have solved this problem by demonstrably having a result accurate to 2 percent."

    The finding was nearly a decade in the making, and required repeated precise measurements of rare pairs of binary stars that are oriented so that they eclipse each other as they orbit, from the perspective of Earth. [How Scientists Measured the Large Magellanic Cloud Distance (Video)]

    ESO / L. Calcada

    This illustration shows an eclipsing binary star system. As the two stars orbit each other, they pass in front of one another and their combined brightness, seen from a distance, decreases. By studying how the light changes, and other system properties, astronomers can measure the distances to eclipsing binaries accurately.

    Using telescopes at the European Southern Observatory's La Silla Observatory and the Las Campanas Observatory, both in Chile, Gieren and his colleagues identified eight pairs of eclipsing binaries in the Large Magellanic Cloud.

    By tracking the changes in the star pairs' brightness when one star passed in front of the other, and vice versa, as well as measuring the stars' orbital speeds, the scientists could deduce the stars' sizes and masses, as well as details regarding their orbits. With this information, combined with measurements of the stars' total brightness and colors, their precise distances could be determined.

    These measurements improve on previous estimates of the Large Magellanic Cloud's distance, which were all based on methods that had inherent uncertainties.

    "Because the LMC is close and contains a significant number of different stellar distance indicators, hundreds of distance measurements using it have been recorded over the years," said team member Ian Thompson of the Carnegie Institution for Science in Washington, D.C. "Unfortunately, nearly all the determinations have systemic errors, with each method carrying its own uncertainties."

    Pinning down the distance of the LMC, in turn, allows scientists to refine their estimates of other, farther cosmic distances. That's because the measurements of close distances are used to calibrate measurements of far-off objects. The new findings should help astronomers narrow down the Hubble Constant, which denotes the rate of the universe's expansion, and is integral for the study of dark energy.

    "We are working to improve our method still further and hope to have a 1 percent LMC distance in a very few years from now," said researcher Dariusz Graczyk. "This has far-reaching consequences not only for cosmology, but for many fields of astrophysics."

    The findings are to be detailed in Friday's issue of the journal Nature.

    Follow Clara Moskowitz @ClaraMoskowitz and Google+. Follow us @Spacedotcom, Facebook and Google+. Original article on Space.com.

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  • Black hole's mystery 'wave' surprises scientists

    Gabriel Perez Diaz, Instituto de Astrofisica de Canarias (Servicio MultiMedia)

    This image is a simulation of the X-ray binary system Swift J1357.2-0933, a black hole and star system, in which the effect of a strange, vertical mystery structure are at their maximum.

    By Nola Taylor Redd, SPACE.com

    Astronomers studying an unusual black hole system have spotted a never-before-seen structure in the disk of matter encircling the system.

    Swift J1357.2, an X-ray binary system that regularly emits outbursts of high energy, consists of a black hole slowly consuming its companion star. Matter from the doomed star falls into the accretion disk, which surrounds the black hole, feeding it dust and gas.

    While observing the system, a team of scientists noticed an unusual vertical feature traveling through the material.

    "It's the first time we can resolve such [a] structure in an accretion disk, and it might be ubiquitous in X-ray binaries during the outburst state," Jesus Corral-Santana, of the Astrophysical Institute of the Canary Islands in Spain, told SPACE.com by email. [The Strangest Black Holes in the Universe]

    A hidden structure
    The black hole contained in Swift J1357.2 is one of the millions of stellar black holes that dot the Milky Way galaxy.

    About three times as massive as the sun, the behemoth likely formed when a single star collapsed inward on itself. The resulting, city-sized body packed a great deal of mass into a tiny package, creating a strong gravitational pull on nearby dust and gas.

    Located in the Virgo constellation, approximately 4,900 light-years from Earth, Swift J1357.2 also contains a small companion star, which has only a quarter the mass of the sun. This companion star orbits the pair's center of mass every 2.8 hours, one of the shortest known orbital periods for such systems.

    The black hole pulls material from the companion star into its accretion disk, occasionally emitting the X-ray bursts that enabled scientists to find this otherwise hard-to-spot system, researchers said.

    Corral-Santana and his team took hundreds of optical images of the system using the Isaac Newton and the William Herschel Telescopes, both of which are in the Canary Islands. Studying the light produced by the accretion disk, the researchers noticed a periodic dimming in the system, sometimes occurring over the course of only a few seconds.

    "Since the orbital period of the system is 2.8 hours, those dips cannot be produced by eclipses of the companion star. They are much faster," Corral-Santana said. "Therefore, they must be produced by a hidden structure placed very close to the black hole, in the inner accretion disk."

    The new find can only been seen in the outer, optical portion of the accretion disk, not on the inside, where X-ray bursts originate. The X-ray emission, which shows no periodic variation, unlike its optical counterpart, indicated a vertical structure was hiding the black hole, Corral-Santana said.

    Rather than appearing at a set, predictable time, the structure shows up over a steadily increasing period, indicating a wave-like movement through the accretion disk.

    "It is a wave produced in the accretion disk, moving outward," Corral-Santana said, "like the wave produced when a stone is dropped in calm water."

    The missing population
    The wave-like feature also provides information about the orientation of the black hole.

    Objects in space face Earth at a variety of angles, or inclinations. They can be seen edge-on, face-on or somewhere in between. Swift J1357.2 is the only one of 50 suspected similar black-hole systems found with an edge-on accretion disk — what scientists call a high inclination. However, astronomers think approximately 20 percent of these systems should provide such a perspective.

    In order to see the wave-like structure in the accretion disk, scientists must have such an edge-on view of the disk, or one close to it. A view from a lower inclination, closer to face-on, would not reveal the sudden rises and falls in the total light coming from the system.

    "Swift J1357.2 is the prototype of the hitherto missing population of high-inclination black holes in transient X-ray binaries," Corral-Santana said.

    Because Swift J1357.2 is the first such system to allow such an edge-on view, the presence of the vertical structure takes on an added significance. No signs of such structures appear in other similar systems, but that could result simply from their unfortunate angles. Such structures could in fact exist in other, previously discovered transient X-ray binary systems, hidden only by their observational angles.

    The findings were published online Feb. 28 in the journal Science.

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  • Hubble telescope reveals Milky Way's cannibal past

    NASA, ESA and A. Field (STScI)

    This illustration shows the disk of our Milky Way galaxy, surrounded by a faint halo of old stars. Hubble Space Telescope measurements of 13 halo stars' motion indicate the possible presence of a shell in the halo, which may have formed from the accretion of a dwarf galaxy.

    By Mike Wall
    Space.com

    The Milky Way's far outer reaches may harbor a shell of stars left over from a long-ago act of galactic cannibalism, a new study suggests.

    The finding supports the idea that our Milky Way has continued to grow over the eons by gobbling up smaller satellite galaxies, researchers said. And the results may help astronomers better understand how mass is distributed throughout the galaxy, which could shed light on the mysterious dark matter that's thought to make up more than 80 percent of all matter in the universe.

    In the new study, scientists used NASA's Hubble Space Telescope to precisely measure the motion of 13 stars in the Milky Way's ancient outer halo, about 80,000 light-years from the galactic center. They picked the stars out of seven years' worth of archival Hubble observations, which were acquired when the telescope was staring at the neighboring Andromeda galaxy.

    Identifying the handful of far-flung Milky Way residents was no picnic, as each Hubble image contained more than 100,000 stars. [Stunning Photos of Our Milky Way Galaxy]

    "It was like finding needles in a haystack," co-author Roeland van der Marel of the Space Telescope Science Institute in Baltimore said in a statement.

    The team found that the outer halo stars had a surprisingly high level of sideways, or tangential, motion relative to their radial motion (which describes movement toward or away from the Milky Way's core).

    The existence of a shell structure — which can be created by the accretion of a satellite galaxy — could explain the halo stars' unexpected motion, researchers said, noting that shell-like features have been observed around other galaxies.

    "What may be happening is that the stars are moving quite slowly because they are at the apocenter, the farthest point in their orbit about the hub of our Milky Way," lead author Alis Deason of the University of California, Santa Cruz, said in a statement. "The slowdown creates a pileup of stars as they loop around in their path and travel back towards the galaxy. So their in and out or radial motion decreases compared with their sideways or tangential motion."

    Deason and her colleagues plan to study more outer halo stars to determine if the shell at 80,000 light-years really does exist. Their overall goals are to gain a better understanding of the Milky Way's formation and evolution, and to calculate an accurate mass for the galaxy.

    This latter aim has proven elusive to date.

    "Until now, what we have been missing is the stars’ tangential motion, which is a key component," Deason said. "The tangential motion will allow us to better measure the total mass distribution of the galaxy, which is dominated by dark matter. By studying the mass distribution, we can see whether it follows the same distribution as predicted in theories of structure formation."

    The new study has been accepted for publication in The Astrophysical Journal.

    Follow Space.com senior writer Mike Wall on Twitter @michaeldwall or Space.com @Spacedotcom. We're also on Facebook and Google+.

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  • Ultrafast stars zip along at 2 million miles an hour

    ESO / MPE

    Hypervelocity stars zoom around the center of the Milky Way, where a supermassive black hole lurks.

    By Tia Ghose
    Space.com

    Six speedy stars rocketing through space at up to 2 million miles per hour were likely ejected from the giant black hole at the Milky Way's heart, astronomers say. They represent the first known "hypervelocity stars" with masses similar to that of our sun.

    The discovery, unveiled last month, could shed light on how stars form in the dust-shrouded core of our home galaxy.

    Black hole suns
    The galactic center is cloaked in a halo of dust that obscures all but the brightest stars from astronomers' telescopes. But hypervelocity stars could provide a window into the star formation going on at the Milky Way's dark heart. [Video: Milky Way's Supermassive Black Hole Caught Eating]

    That's because hypervelocity stars are thought to form when the supermassive black hole at the center of a galaxy devours one star in a binary system and ejects its twin, flinging it through space at superfast speeds, said study author Keith Hawkins, an astronomy student at Ohio University.

    "These are incredibly fast-moving objects that are actually gravitationally unbound to the Milky Way," he said during the 221st annual meeting of the American Astronomical Society in Long Beach, Calif., last month.

    Though these speed demons may be close to the black hole, they are not shrouded by dust and can be detected with telescopes.

    Because speedy rogue stars have been ejected from the galactic center, identifying them can reveal the types of star formation occurring there.

    But until now, astronomers searching for these hypervelocity stars looked for bright, blue stars in locations where they weren't supposed to form. Those stars, while easier to find, are typically three to four times as massive as our own sun, while most stars forming in other regions of the galaxy are the size of our sun or smaller, Hawkins said.

    Needle in a haystack
    Because of the abundance of sunlike stars in the galaxy, finding hypervelocity stars of that mass is tricky, said Brad Hansen, an astronomer at UCLA who was not involved in the research.

    "It really becomes a 'needle in a haystack'-type problem," Hansen told Space.com. "How do you search through a billion stars to find a couple that are moving in a strange way?"

    To accomplish that task, Hawkins and Adam Kraus, an astronomer at the University of Hawaii, used data from the Palomar 5-meter telescope in California.

    They found 130 stars on the edges of the Milky Way's central black hole that had traveled a remarkable distance. They then narrowed that group to stars traveling at extreme speeds consistent with ejection from the Milky Way's center. Six stars met those criteria.

    While the new results are intriguing, they need to be confirmed, Hawkins said.

    But if verified, they could shed light on the types of stars that form in the galaxy's heart, and help astronomers estimate the size of the black hole lurking there, Hansen said.

    Follow Space.com on Twitter @Spacedotcom. We're also on Facebook and Google+.

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  • Baffling star birth mystery finally solved

    NASA/Spitzer/Benjamin et al., Churchwell et al.

    In this image, taken by NASA's Spitzer Space Telescope, the mysterious gas cloud G0.253+0.016 is the black object on the left. The Milky Way's center is the bright spot at right.

    By SPACE.com

    Astronomers have finally solved a longstanding cosmic mystery — why a super-dense gas cloud near our Milky Way galaxy's core isn't churning out many new stars.

    The gas cloud, known as G0.253+0.016, is simply swirling too fast, researchers said. And it lacks the requisite pockets of even denser material, which eventually collapse under their own gravity to form stars.

    The results suggest that star formation is more complex than astronomers had thought and may help them better understand the process, researchers said.

    An oddly barren cloud
    G0.253+0.016, which is about 30 light-years long, defies the conventional wisdom that dense gas glouds should produce lots of stars. [ 8 Baffling Astronomy Mysteries ]

    The cloud is 25 times more dense than the famous Orion Nebula, which is birthing stars at a furious rate. But only a few stars are being born in G0.253+0.016, and they're pretty much all runts.

    "It's a very dense cloud and it doesn't form any massive stars, which is very weird," study lead author Jens Kauffmann, of Caltech in Pasadena, said in a statement.

    Kauffmann and his colleagues determined to find out why. Using the Submillimeter Array, a set of eight radiotelescopes atop Mauna Kea in Hawaii, they found that G0.253+0.016 possesses very few ultra-dense nuggets that could collapse to form stars.

    "That was very surprising," said co-author Thushara Pillai, also of Caltech. "We expected to see a lot more dense gas."

    Spinning out of control
    The researchers then probed the cloud with another network of telescopes, the Combined Array for Research in Millimeter-wave Astronomy in California.

    CARMA data showed that gas within G0.253+0.016 is zipping around 10 times faster than gas in similar clouds. G0.253+0.016 is on the verge of flying apart, with its gas churning too violently to coalesce into stars.

    Further, the team found that the cloud is full of silicon monoxide, a compound typically produced when fast-moving gas smashes into dust particles. The abnormally large amounts of silicon monoxide suggest that G0.253+0.016 may actually consist of two colliding clouds, whose impact is generating powerful shockwaves.

    "To see such shocks on such large scales is very surprising," Pillai said.

    G0.253+0.016 may eventually be able to churn out stars. But its position near the center of the Milky Way could make it tough for the cloud to settle down, as it may smash into other clouds or be ripped apart by the immense gravitational pull near the galaxy's central black hole, researchers said.

    The study has been accepted for publication in the Astrophysical Journal Letters. The team also presented the results last week at the 221st meeting of the American Astronomical Society in Long Beach, Calif.

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  • 'Exocomets' common across Milky Way galaxy

    NASA/JPL-Caltech

    An artist's illustration of a comet storm around a nearby star.

    By SPACE.com staff

    Comets may be as common as alien planets in star systems throughout the Milky Way galaxy, scientists say.

    Astronomers have spotted likely comets around six faraway stars, bringing the total number of systems now thought to host the so-called "exocomets" to 10. It's likely that all 10 of these systems also harbor alien planets, suggesting that comets and exoplanets are often found together, as they are in our own solar system, the new study found.

    The number of exocomet-hosting systems could thus number in the billions across the Milky Way, as astronomers think our galaxy harbors at least 100 billion alien planets.

    "This is sort of the missing link in current planetary formation studies," lead author Barry Welsh, of the University of California, Berkeley, said in a statement. [A Sky Full of Alien Planets: Infographic]

    "We see dust disks — presumably the primordial planet-forming material — around a whole load of stars, and we see planets, but we don't see much of the stuff in between: the asteroid-like planetesimals and the comets," Welsh added. "Now, I think we have nailed it. These exocomets are more common and easier to detect than people previously thought."

    Welsh presented the findings Jan. 7 dufing a meeting of the American Astronomical Society in Long Beach, Calif.

    The researchers discovered the six new exocomet systems using the 2.1-meter telescope of the McDonald Observatory in Texas.

    The telescope picked up faint absorption lines that varied from night to night. The astronomers determined these features were caused by large clouds of gas emanating from comets as they drew close to their host stars and heated up.

    In our own solar system, comets usually stay far from the sun, only venturing close after a gravitational disturbance sends them veering off on a new course. It's likely that alien planets caused the newly discovered exocomets to plunge toward their stars, Welsh said.

    The newfound exocomets all orbit very young and bright stars that are about 5 million years old, because the team's detection technique works best with such stars. But higher-resolution instruments may reveal comets around older, more sun-like stars — the type around which most exoplanets have been found to date, researchers said.

    The first exocomet system was discovered in 1987, and three more were spotted over the years.

    "But then, people just lost interest. They decided that exocomets were a done deal, and everybody switched to the more exciting thing, exoplanets," Welsh said. "But I came back to it last year and thought, 'Four exocomets is not all that many compared to the couple of thousand exoplanets known — perhaps I can improve on that.'"

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  • Watch the Milky Way spin

    Time-lapse video from the International Space Station shows off the Milky Way.

    By Alan Boyle, Science Editor, NBC News

    The International Space Station's crew has been sending down tons of stunning imagery of the planet below, but the main appeal of this video goes in a different direction — toward the gorgeous galaxy right above our heads.

    The time-lapse video is based on pictures taken on Dec. 29 while the space station sailed high above Africa, crossing over to the South Indian Ocean. You can make out the flashes of lightning storms, and if you look very closely you can see the long streak of Comet Lovejoy against the backdrop of the Milky Way. The best frame for seeing the comet comes around the 12-second mark in the 23-second clip displayed above. If you need help spotting it, play this YouTube alternative. Here's the HD version from NASA.

    To see the latest and greatest time-lapse and still imagery from the International Space Station's vantage point, check out NASA's Gateway to Astronaut Photography of Earth (and particularly the video page). For still more, you'll want to keep tabs on the Fragile Oasis Facebook page as well as NASA astronaut Ron Garan's Google+ page.

    More views of Earth from space:

    Tip o' the Log to Jason Major, who watches over Lights in the Dark.

    Alan Boyle is msnbc.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter or adding Cosmic Log's Google+ page to your circle. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for other worlds.