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Wednesday, March 12, 2014

An observational and theoretical view of the atomic gas distribution in galaxies

Fig. 1: The top and bottom rows show two galaxies with very different gas disk morphologies. From left to right: the column density contours for neutral hydrogen overlaid on optical images from the Sloan Digital Sky Survey, the neutral hydrogen itself, and the velocity maps of the neutral hydrogen.

Fig. 2: The median radial profiles of different galaxies (blue: gas rich, green: normal, red: gas poor). For all galaxies, the radius has been scaled to R1, where the gas surface density reaches 1 solar mass / square parsec. The observed profiles in the left plot are compared to results from semi- analytical models (SAM, middle) and results from smoothed particle hydrodynamical simulations (SPH, right).

Fig. 3: An extreme case of gas accretion in a ring-shape. This simulated galaxy at a redshift z~0.5 was the result of smoothed particle hydrodynamical simulations. (Image provided by Michael Aumer)

How is cold gas accreted in galaxies? Observers and theorists from MPA have joined their efforts to investigate the radial distribution of atomic gas in unusually gas-rich nearby galaxies. They found a universal shape for the radial profiles of the gas in the outer regions of the observed galaxies, and obtained remarkable agreement with simulations. In half the galaxies, the atomic gas may have been accreted in the form of "rings"

Every astronomy student learns that in galaxies stars form from huge gas clouds. However, the details of the accretion and distribution of gas in galaxies is still unclear. Therefore, an international group of scientists at MPA and ASTRON in the Netherlands joined forces and carried out the Bluedisk project to map neutral hydrogen in a sample of 25 very gas-rich galaxies as well as a similar-sized sample of “control” galaxies with similar masses, sizes and distances, but normal gas content. Their main tools were the Westerbork Synthesis Radio Telescope (WSRT) as well as elaborate computer simulations (see Research Highlight May 2013).

There have been many efforts over the past three decades to map the distribution of cold, atomic gas in galaxies using radio synthesis telescopes. The first analyses showed that the atomic gas exhibits a wide variety of detailed features. These can be attributed to irregularities in the galaxy such as spiral arms, rings, bars, warps etc. Studies of larger samples revealed basic scaling relations that provide hints of the mechanisms regulating the evolution of galaxies.

In contrast to the stellar surface density, which peaks in the centre of the galaxy and drops steeply with radius, the radial distribution of the atomic gas often flattens or even declines near the centre of the galaxy. In the outer regions, the gas disks usually extend to a larger distance from the centre than the stellar disks, and are well-fit by exponential functions.

Thanks to improvements in the WSRT instrumentation and data analysis, the observations by the Bluedisk team reached significantly lower column densities than previous surveys, i.e. they were able to map the gas in regions where the gas has low density. This sample is thus also well-suited for direct comparison with theoretical models. Observers and theorists worked together closely to improve their understanding of the radial distribution of the cold, atomic gas and to find a physical explanation for its structure.

The study revealed an interesting observational phenomenon: in the outer regions of all the galaxies, the gas exhibits a homogeneous surface density profile (if the sizes of the gas disks are properly scaled). This profile is well-fit by an exponential function with a universal scale-length. This universal profile appears to hold for all galaxies, irrespective of their stellar properties, gas masses, sizes, or morphologies (for an example see figure 1). This is remarkable, because the gas-rich galaxies contain on average 10 times more gas than the control sample.

In addition, the team found surprising agreement between their universal profile and results from simulations, both for smoothed-particle hydrodynamical simulations and for semi-analytic models of disk galaxy formation (see figure 2). It remains something of a mystery why the agreement with the smoothed-particle hydrodynamical simulations is quite so good.

In the semi-analytic models, the universal shape of the outer radial profiles is a direct consequence of the assumption that infalling gas is always distributed exponentially. However, there are observational indications that the atomic gas could be accreted in the form of "rings". Therefore, more work is underway on the theoretical side using smoothed particle hydrodynamical simulations to try and understand how gas settles onto the simulated galaxies in more detail (see figure 3).

Jing Wang & Guinevere Kauffmann

Milky Way amidst a ‘Council of Giants’

We live in a galaxy known as the Milky Way – a vast conglomeration of 300 billion stars, planets whizzing around them, and clouds of gas and dust floating in between. Though it has long been known that the Milky Way and its orbiting companion Andromeda are the dominant members of a small group of galaxies, the Local Group, which is about 3 million light years across, much less was known about our immediate neighbourhood in the universe. Now, a new paper by York University Physics & Astronomy Professor Marshall McCall, published today in the journal Monthly Notices of the Royal Astronomical Society, maps out bright galaxies within 35-million light years of the Earth, offering up an expanded picture of what lies beyond our doorstep.

A diagram showing the brightest galaxies within 20 million light years of the Milky Way, as seen from above. The largest galaxies, here shown in yellow at different points around the dotted line, make up the ‘Council of Giants’. Credit: Marshall McCall / York University. Click here for a full-size image

“All bright galaxies within 20 million light years, including us, are organized in a ‘Local Sheet’ 34-million light years across and only 1.5-million light years thick,” says McCall. “The Milky Way and Andromeda are encircled by twelve large galaxies arranged in a ring about 24-million light years across – this ‘Council of Giants’ stands in gravitational judgment of the Local Group by restricting its range of influence.”

A diagram showing the brightest galaxies within 20 million light years of the Milky Way, this time viewed from the side. Credit: Marshall McCall / York University. Click here for a full-size image

McCall says twelve of the fourteen giants in the Local Sheet, including the Milky Way and Andromeda, are "spiral galaxies" which have highly flattened disks in which stars are forming. The remaining two are more puffy "elliptical galaxies", whose stellar bulks were laid down long ago. Intriguingly, the two ellipticals sit on opposite sides of the Council. Winds expelled in the earliest phases of their development might have shepherded gas towards the Local Group, thereby helping to build the disks of the Milky Way and Andromeda.

McCall also examined how galaxies in the Council are spinning. He comments: “Thinking of a galaxy as a screw in a piece of wood, the direction of spin can be described as the direction the screw would move (in or out) if it were turned the same way as the galaxy rotates. Unexpectedly, the spin directions of Council giants are arranged around a small circle on the sky. This unusual alignment might have been set up by gravitational torques imposed by the Milky Way and Andromeda when the universe was smaller.”

The boundary defined by the Council has led to insights about the conditions which led to the formation of the Milky Way. Most important, only a very small enhancement in the density of matter in the universe appears to have been required to produce the Local Group. To arrive at such an orderly arrangement as the Local Sheet and its Council, it seems that nearby galaxies must have developed within a pre-existing sheet-like foundation comprised primarily of dark matter.

“Recent surveys of the more distant universe have revealed that galaxies lie in sheets and filaments with large regions of empty space called voids in between,” says McCall. “The geometry is like that of a sponge. What the new map reveals is that structure akin to that seen on large scales extends down to the smallest.”

Media Contacts

Robin Heron
Media Relations
York University
Canada
Tel: +1 416 736 2100 x22097
rheron@yorku.ca

Robert Massey
Royal Astronomical Society
Tel: +44 (0)20 7734 3307 x214
Mob: +44 (0)794 124 8035
rm@ras.org.uk

Animation

This movie illustrates the positions of the nearby galaxies, including those in the ‘Council of Giants’, in three dimensions. Credit: Marshall McCall / York University

Further information

The new work appears in “A Council of Giants”, M. L. McCall, Monthly Notices of the Royal Astronomical Society, Oxford University Press, in press.

Notes for editors

York University is helping to shape the global thinkers and thinking that will define tomorrow. York U’s unwavering commitment to excellence reflects a rich diversity of perspectives and a strong sense of social responsibility that sets us apart. A York U degree empowers graduates to thrive in the world and achieve their life goals through a rigorous academic foundation balanced by real-world experiential education. As a globally recognized research centre, York U is fully engaged in the critical discussions that lead to innovative solutions to the most pressing local and global social challenges. York U’s 11 faculties and 27 research centres are thinking bigger, broader and more globally, partnering with 288 leading universities worldwide.

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The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organizes scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 3800 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.

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Source: The Royal Astronomical Society (RAS)

Labels: Andromeda, Milky Way

Tuesday, March 11, 2014

Venus Glory

Venus glory
Copyright: ESA/MPS/DLR/IDA

A rainbow-like feature known as a ‘glory’ has been seen by ESA’s Venus Express orbiter in the atmosphere of our nearest neighbour – the first time one has been fully imaged on another planet.

Rainbows and glories occur when sunlight shines on cloud droplets – water particles in the case of Earth. While rainbows arch across wide swathes of the sky, glories are typically much smaller and comprise a series of coloured concentric rings centred on a bright core.

Glories are only seen when the observer is situated directly between the Sun and the cloud particles that are reflecting sunlight. On Earth, they are often seen from aeroplanes, surrounding the shadow of the aircraft on the clouds below, or around the shadow of climbers atop misty mountain peaks.

Venus glory details
Copyright: ESA/MPS/DLR/IDA

A glory requires two characteristics: the cloud particles are spherical, and therefore most likely liquid droplets, and they are all of a similar size.

The atmosphere of Venus is thought to contain droplets rich in sulphuric acid. By imaging the clouds with the Sun directly behind the Venus Express spacecraft, scientists hoped to spot a glory in order to determine important characteristics of the cloud droplets.

They were successful. The glory in the images here was seen at the Venus cloud tops, 70 km above the planet’s surface, on 24 July 2011. It is 1200 km wide as seen from the spacecraft, 6000 km away.

Simulated views of glory on Venus and Earth
Copyright: C. Wilson/P. Laven

From these observations, the cloud particles are estimated to be 1.2 micrometres across, roughly a fiftieth of the width of a human hair.

The fact that the glory is 1200 km wide means that the particles at the cloud tops are uniform on this scale at least.

The variations of brightness of the rings of the observed glory is different than that expected from clouds of only sulphuric acid mixed with water, suggesting that other chemistry may be at play.

One idea is that the cause is the “UV-absorber”, an unknown atmospheric component responsible for mysterious dark markings seen in the cloud tops of Venus at ultraviolet wavelengths. More investigation is needed to draw a firm conclusion.

“Glory on Venus Cloud Tops and the Unknown UV Absorber,” by W.J. Markiewicz et al, is accepted for publication in Icarus. http://dx.doi.org/10.1016/j.icarus.2014.01.030

For further information, please contact:

Markus Bauer   
ESA Science and Robotic Exploration Communication Officer     
Tel: +31 71 565 6799   
Mob: +31 61 594 3 954   
Email: markus.bauer@esa.int     

Wojciech Markiewicz
Max Planck Institute for Solar System Research, Germany
markiewicz@mps.mpg.de
Håkan Svedhem   
ESA Venus Express project scientist   
Email: hakan.svedhem@esa.int  

Source: ESA’s Venus Express

Labels: ESA’s Venus Express, Solar System, Venus

NASA's WISE Survey Finds Thousands of New Stars, But No 'Planet X'

A nearby star stands out in red in this image from the Second Generation Digitized Sky Survey. Image credit: DSS/NASA/JPL-Caltech. Full image and caption

Data from NASA's Wide-field Infrared Survey Explorer, or WISE, has found no evidence for a hypothesized body sometimes referred to as "Planet X." Image credit: Penn State University. Full image and caption - enlarge image

The third closest star system to the sun, called WISE J104915.57-531906, is at the center of the larger image, which was taken by NASA's Wide-field Infrared Survey Explorer (WISE). Image credit: NASA/JPL/Gemini Observatory/AURA/NSF. Full image and caption - enlarge image

After searching hundreds of millions of objects across our sky, NASA's Wide-Field Infrared Survey Explorer (WISE) has turned up no evidence of the hypothesized celestial body in our solar system commonly dubbed "Planet X."

Researchers previously had theorized about the existence of this large, but unseen celestial body, suspected to lie somewhere beyond the orbit of Pluto. In addition to "Planet X," the body had garnered other nicknames, including "Nemesis" and "Tyche."

This recent study, which involved an examination of WISE data covering the entire sky in infrared light, found no object the size of Saturn or larger exists out to a distance of 10,000 astronomical units (au), and no object larger than Jupiter exists out to 26,000 au. One astronomical unit equals 93 million miles. Earth is 1 au, and Pluto about 40 au, from the sun.

"The outer solar system probably does not contain a large gas giant planet, or a small, companion star," said Kevin Luhman of the Center for Exoplanets and Habitable Worlds at Penn State University, University Park, Pa., author of a paper in the Astrophysical Journal describing the results.

But searches of the WISE catalog are not coming up empty. A second study reveals several thousand new residents in our sun's "backyard," consisting of stars and cool bodies called brown dwarfs.

"Neighboring star systems that have been hiding in plain sight just jump out in the WISE data," said Ned Wright of the University of California, Los Angeles, the principal investigator of the mission.

The second WISE study, which concentrated on objects beyond our solar system, found 3,525 stars and brown dwarfs within 500 light-years of our sun.

"We're finding objects that were totally overlooked before," said Davy Kirkpatrick of NASA's Infrared and Processing Analysis Center at the California Institute of Technology, Pasadena, Calif. Kirkpatrick is lead author of the second paper, also in the Astrophysical Journal. Some of these 3,525 objects also were found in the Luhman study, which catalogued 762 objects.

The WISE mission operated from 2010 through early 2011, during which time it performed two full scans of the sky -- with essentially a six-month gap between scans. The survey captured images of nearly 750 million asteroids, stars and galaxies. In November 2013, NASA released data from the AllWISE program, which now enables astronomers to compare the two full-sky surveys to look for moving objects.

In general, the more an object in the WISE images appears to move over time, the closer it is. This visual clue is the same effect at work when one observes a plane flying low to the ground versus the same plane flying at higher altitude. Though traveling at the same speed, the plane at higher altitude will appear to be moving more slowly.

Searches of the WISE data catalog for these moving objects are uncovering some of the closest stars. The discoveries include a star located about 20 light-years away in the constellation Norma, and as reported last March, a pair of brown dwarfs only 6.5 light-years away -- making it the closest star system to be discovered in nearly a century.

Despite the large number of new solar neighbors found by WISE, "Planet X" did not show up. Previous speculations about this hypothesized body stemmed in part from geological studies that suggested a regular timing associated with mass extinctions on Earth. The idea was that a large planet or small star hidden in the farthest reaches of our solar system might periodically sweep through bands of outer comets, sending them flying toward our planet. The Planet X-based mass extinction theories were largely ruled out even prior to the new WISE study.

Other theories based on irregular comet orbits had also postulated a Planet X-type body. The new WISE study now argues against these theories as well.

Both of the WISE searches were able to find objects the other missed, suggesting many other celestial bodies likely await discovery in the WISE data.

"We think there are even more stars out there left to find with WISE. We don't know our own sun's backyard as well as you might think," said Wright.

WISE was put into hibernation upon completing its primary mission in 2011. In September 2013, it was reactivated, renamed NEOWISE and assigned a new mission to assist NASA's efforts to identify the population of potentially hazardous near-Earth objects. NEOWISE will also characterize previously known asteroids and comets to better understand their sizes and compositions.

JPL managed and operated WISE for NASA's Science Mission Directorate. The mission was selected competitively under NASA's Explorers Program managed by the agency's Goddard Space Flight Center in Greenbelt, Md. The science instrument was built by the Space Dynamics Laboratory in Logan, Utah. The spacecraft was built by Ball Aerospace & Technologies Corp. in Boulder, Colo. Science operations and data processing take place at the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA. More information is online at: http://www.nasa.gov/wise and http://wise.astro.ucla.edu and http://jpl.nasa.gov/wise.

Contact:

Whitney Clavin
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-4673
Email: whitney.clavin@jpl.nasa.gov

J.D. Harrington
Headquarters, Washington
202-358-5241
Email: j.d.harrington@nasa.gov

Labels: JPL-Caltech, NEOWISE, WISE, WISE J104915.57-531906

Monday, March 10, 2014

Loops of Gas and Dust Rise from Planetary Disks

Magnetic loops carry gas and dust above disks of planet-forming material circling stars, as shown in this artist's conception. These loops give off extra heat, which NASA's Spitzer Space Telescope detects as infrared light. The colors in this illustration show what an alien observer with eyes sensitive to both visible light and infrared wavelengths might see. Credit: NASA/JPL-Caltech/R. Hurt (IPAC).

Astronomers say that magnetic storms in the gas orbiting young stars may explain a mystery that has persisted since before 2006.

Researchers using NASA's Spitzer Space Telescope to study developing stars have had a hard time figuring out why the stars give off more infrared light than expected. The planet-forming disks that circle the young stars are heated by starlight and glow with infrared light, but Spitzer detected additional infrared light coming from an unknown source.

A new theory, based on three-dimensional models of planet-forming disks, suggests the answer: Gas and dust suspended above the disks on gigantic magnetic loops like those seen on the sun absorb the starlight and glow with infrared light.

"If you could somehow stand on one of these planet-forming disks and look at the star in the center through the disk atmosphere, you would see what looks like a sunset," said Neal Turner of NASA's Jet Propulsion Laboratory, Pasadena, Calif.

The new models better describe how planet-forming material around stars is stirred up, making its way into future planets, asteroids and comets.

While the idea of magnetic atmospheres on planet-forming disks is not new, this is the first time they have been linked to the mystery of the observed excess infrared light. According to Turner and colleagues, the magnetic atmospheres are similar to what takes place on the surface of our sun, where moving magnetic field lines spur tremendous solar prominences to flare up in big loops.

Stars are born out of collapsing pockets in enormous clouds of gas and dust, rotating as they shrink down under the pull of gravity. As a star grows in size, more material rains down toward it from the cloud, and the rotation flattens this material out into a turbulent disk. Ultimately, planets clump together out of the disk material.

In the 1980s, the Infrared Astronomical Satellite mission, a joint project that included NASA, began finding more infrared light than expected around young stars. Using data from other telescopes, astronomers pieced together the presence of dusty disks of planet-forming material. But eventually it became clear the disks alone weren't enough to account for the extra infrared light -- especially in the case of stars a few times the mass of the sun.

One theory introduced the idea that instead of a disk, the stars were surrounded by a giant dusty halo, which intercepted the star's visible light and re-radiated it at infrared wavelengths. Then, recent observations from ground-based telescopes suggested that both a disk and a halo were needed. Finally, three-dimensional computer modeling of the turbulence in the disks showed the disks ought to have fuzzy surfaces, with layers of low-density gas supported by magnetic fields, similar to the way solar prominences are supported by the sun's magnetic field.

The new work brings these pieces together by calculating how the starlight falls across the disk and its fuzzy atmosphere. The result is that the atmosphere absorbs and re-radiates enough to account for all the extra infrared light.

"The starlight-intercepting material lies not in a halo, and not in a traditional disk either, but in a disk atmosphere supported by magnetic fields," said Turner. "Such magnetized atmospheres were predicted to form as the disk drives gas inward to crash onto the growing star."

Over the next few years, astronomers will further test these ideas about the structure of the disk atmospheres by using giant ground-based telescopes linked together as interferometers. An interferometer combines and processes data from multiple telescopes to show details finer than each telescope can see alone. Spectra of the turbulent gas in the disks will also come from NASA's SOFIA telescope, the Atacama Large Millimeter/submillimeter Array (ALMA) telescope in Chile, and from NASA's James Webb Space Telescope after its launch in 2018.

JPL manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. Spacecraft operations are based at Lockheed Martin Space Systems Company, Littleton, Colo. Data are archived at the Infrared Science Archive housed at the Infrared Processing and Analysis Center at Caltech. Caltech manages JPL for NASA.

Source: JPL/Spitzer Space Telescope

Labels: JPL-Caltech, planet-forming, planetary disks, Spitzer Space Telescope

Saturday, March 08, 2014

X-rays From Other Galaxies Could Emanate From Particles of Dark Matter

A tiny fraction of the x-rays in this image of the central area of the Andromeda galaxy—obtained with NASA's spaceborne Chandra X-ray Observatory—could originate from dark matter.

X-rays of a specific wavelength emanating from the hearts of nearby galaxies and galaxy clusters could be signs of particles of dark matter decaying in space, two independent teams of astronomers report. If that interpretation is correct, then dark matter could consist of strange particles called sterile neutrinos that weigh about 1/100 as much as an electron. However, some other researches are skeptical.

For decades, astronomers and astrophysicists have thought that some sort of mysterious dark matter must provide the gravity that keeps individual galaxies from falling apart. In fact, the current standard model of cosmology indicates that a typical galaxy forms within a vast clump, or halo, of dark matter whose gravity keeps the stars from flying out into space. However, scientists do not know what dark matter is, as they have never detected it by any means other than sensing its gravity.

Now, two teams report possible signs of dark matter particles revealing themselves in another way—by very, very slowly decaying into normal photons. Both groups relied on data from one of the most successful space observatories, the European Space Agency's X-ray Multi-Mirror Mission (XMM-Newton), which launched in December 1999 and is still taking data. Esra Bulbul, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, and colleagues discovered x-rays of a specific energy—3.5 kiloelectron volts (keV)—shining from 73 galaxy clusters, including the Perseus cluster. The Harvard group also used data from NASA's orbiting Chandra X-ray Observatory launched by NASA in July 1999, as it reports in a paper submitted to The Astrophysical Journal.

Source: Harvard Smithsonian Institute for Astrophysics

Labels: Dark Matter

Friday, March 07, 2014

Hubble Witnesses an Asteroid Mysteriously Disintegrating

Asteroid P/2013 R3

Credit: NASA, ESA, and D. Jewitt (University of California, Los Angeles)

Release Images / Release Videos

NASA's Hubble Space Telescope has photographed the never-before-seen breakup of an asteroid into as many as 10 smaller pieces.

Though fragile comet nuclei have been seen falling apart as they near the Sun, nothing like this breakup has ever before been observed in the asteroid belt.

"This is a rock. Seeing it fall apart before our eyes is pretty amazing," said David Jewitt of UCLA, who led the astronomical forensics investigation.

The crumbling asteroid, designated P/2013 R3, was first noticed as an anomalous, fuzzy-looking object on Sept. 15, 2013, by the Catalina and Pan-STARRS sky surveys. A follow-up observation on October 1 with the W. M. Keck Observatory on the summit of Mauna Kea, Hawaii revealed three co-moving bodies embedded in a dusty envelope that is nearly the diameter of Earth.

"Keck showed us that this thing was worth looking at with Hubble," Jewitt said. With its superior resolution, Hubble observations soon showed that there were really 10 embedded objects, each with comet-like dust tails. The four largest rocky fragments are up to 200 yards in radius, about twice the length of a football field.

The Hubble data showed that the fragments are drifting away from each other at a leisurely one mile per hour — slower than the speed of a strolling human. The asteroid began coming apart early last year, but new pieces continue to emerge in the most recent images.

This makes it unlikely that the asteroid is disintegrating because of a collision with another asteroid, which would be instantaneous and violent by comparison to what has been observed. Some of the debris from such a high-velocity smashup would also be expected to travel much faster than observed.

Nor is the asteroid coming unglued due to the pressure of interior ices warming and vaporizing. The asteroid is too cold for ices to significantly sublimate, and it has presumably maintained its nearly 300-million-mile distance from the Sun for much of the age of the solar system.

This leaves a scenario in which the asteroid is disintegrating due to a subtle effect of sunlight, which causes the rotation rate to slowly increase. Eventually, its component pieces, like grapes on a stem, gently pull apart due to centrifugal force. The possibility of disruption by this so-called YORP torque has been discussed by scientists for several years but, so far, never reliably observed.

For this to happen, P/2013 R3 must have a weak, fractured interior, probably as the result of numerous, ancient, non-destructive collisions with other asteroids. Most small asteroids, in fact, are thought to have been severely damaged in this way, giving them a "rubble pile" internal structure. P/2013 R3 itself is probably the product of collisional shattering of a bigger body some time in the last billion years.

With the previous discovery of an active asteroid spouting six tails (P/2013 P5), astronomers are seeing more circumstantial evidence that the pressure of sunlight may be the primary force that disintegrates small asteroids (less than a mile across) in the solar system.

The asteroid's remnant debris, weighing in at 200,000 tons, will in the future provide a rich source of meteoroids. Most will eventually plunge into the Sun but a small fraction of the debris may one day hit the Earth to blaze across the sky as meteors.

CONTACT

Donna Weaver / Ray Villard
Space Telescope Science Institute, Baltimore, Md.
410-338-4493 / 410-338-4514
dweaver@stsci.edu / villard@stsci.edu

Source: HubbleSite

Labels: Asteroid P/2013 R3, Hubble Space Telescope

Crashing Comets Explain Surprise Gas Clump Around Young Star

PR Image eso1408a

Artist's impression of Beta Pictoris

PR Image eso1408b
Map of the sky around Beta Pictoris

PR Image eso1408c

Around Beta Pictoris

PR Image eso1408d

ALMA image of carbon monoxide around Beta Pictoris (infographic)

ALMA reveals an enigmatic gas clump in debris disc around Beta Pictoris

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) telescope in northern Chile have today announced the discovery of an unexpected clump of carbon monoxide gas in the dusty disc around the star Beta Pictoris. This is a surprise, as such gas is expected to be rapidly destroyed by starlight. Something — probably frequent collisions between small, icy objects such as comets — must be causing the gas to be continuously replenished. The new results are published today in the journal Science.

Beta Pictoris, a nearby star easily visible to the naked eye in the southern sky, is already hailed as the archetypal young planetary system. It is known to harbour a planet that orbits some 1.2 billion kilometres from the star, and it was one of the first stars found to be surrounded by a large disc of dusty debris [1].

New observations from ALMA now show that the disc is permeated by carbon monoxide gas. Paradoxically the presence of carbon monoxide, which is so harmful to humans on Earth, could indicate that the Beta Pictoris planetary system may eventually become a good habitat for life. The cometary bombardment that its planets are currently undergoing is likely providing them with life-enabling water [2].

But carbon monoxide is easily and rapidly broken up by starlight — it can only last about 100 years where it is observed in the Beta Pictoris disc. Seeing it in the 20-million year old Beta Pictoris disc is a complete surprise. So where did it come from, and why is it still there?

“Unless we are observing Beta Pictoris at a very unusual time, the carbon monoxide must be continuously replenished,” said Bill Dent, an ESO astronomer at the Joint ALMA Office in Santiago, Chile, and lead author on a paper published today in the journal Science. “The most abundant source of carbon monoxide in a young solar system is collisions between icy bodies, from comets up to larger planet-sized objects.”

But the rate of destruction must be very high: “To get the amount of carbon monoxide we observe, the rate of collisions would be truly startling — one large comet collision every five minutes,” noted Aki Roberge, an astronomer at NASA’s Goddard Research Center in Greenbelt, USA, and coauthor of the paper. “To get this number of collisions, this would have to be a very tight, massive comet swarm.”

But there was another surprise in the ALMA observations, which did not just discover the carbon monoxide, but also mapped its location in the disc, through ALMA’s unique ability to simultaneously measure both position and velocity: the gas is concentrated in a single compact clump. This concentration lies 13 billion kilometres from the star, which is about three times the distance of Neptune from the Sun. Why the gas is in this small clump so far from the star is a mystery.

“This clump is an important clue to what is going on in the outer reaches of this young planetary system,” says Mark Wyatt, an astronomer at the University of Cambridge, UK, and a co-author on the paper. He goes on to explain that there are two ways such a clump can form: “Either the gravitational pull of an as yet unseen planet similar in mass to Saturn is concentrating the cometary collisions into a small area, or what we are seeing are the remnants of a single catastrophic collision between two icy Mars-mass planets”.

Both of these possibilities give astronomers reason to be optimistic that there are several more planets waiting to be found around Beta Pictoris. “Carbon monoxide is just the beginning — there may be other more complex pre-organic molecules released from these icy bodies,” adds Roberge.

Further observations are planned with ALMA, which is still ramping up to its full capabilities, to shed more light on this intriguing planetary system, and so help us to understand what conditions were like during the formation of the Solar System.

Notes

[1] Many stars are surrounded by swirling clouds of dust, known as debris discs.They are the remains of a collisional cascade of the rocks in orbit around the star, much like the collisional breakup of the space station depicted in the movie Gravity (but on a much larger scale). Earlier observations of Beta Pictoris were reported in eso1024 and eso0842.

[2] Comets contain ices of carbon monoxide, carbon dioxide, ammonia and methane, but the majority component is a mixture of dust and water ice.

More information

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ALMA is funded in Europe by the European Southern Observatory (ESO), in North America by the U.S. National Science Foundation (NSF) in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and in East Asia by the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Academia Sinica (AS) in Taiwan. ALMA construction and operations are led on behalf of Europe by ESO, on behalf of North America by the National Radio Astronomy Observatory (NRAO), which is managed by Associated Universities, Inc. (AUI) and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

This research was presented in a paper entitled “Molecular Gas Clumps from the Destruction of Icy Bodies in the β Pictoris Debris Disk” to appear in the journal Science on 6 March 2014.

The team is composed of W.R.F. Dent (Joint ALMA Office, Santiago, Chile [JAO]), M.C. Wyatt (Institute of Astronomy, Cambridge, UK [IoA]), A. Roberge (NASA Goddard Space Flight Center, Greenbank, USA), J.-C. Augereau (Institut de Planétologie et d'Astrophysique de Grenoble, France [IPAG]), S. Casassus (Universidad de Chile, Santiago, Chile), S. Corder (JAO), J.S. Greaves (University of St. Andrews, UK), I. de Gregorio-Monsalvo (JAO), A. Hales (JAO), A.P.Jackson (IoA), A. Meredith Hughes (Wesleyan University, Middletown, USA), A.-M. Lagrange (IPAG), B. Matthews (National Research Council of Canada, Victoria, Canada) and D. Wilner (Smithsonian Astrophysical Observatory, Cambridge, USA).

ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning the 39-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Contacts

Bill Dent
Joint ALMA Office
Santiago, Chile
Email: wdent@alma.cl

Richard Hook
ESO, Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org

Source: ESO

Labels: ALMA, Beta Pictoris, ESO

Thursday, March 06, 2014

RX J1131-1231: Chandra & XMM-Newton Provide Direct Measurement of Distant Black Hole's Spin

Quasar - RX J1131-1231 (Labeled)

Credit: X-ray: NASA/CXC/Univ of Michigan/R.C.Reis et al; Optical: NASA/STScI

JPEG (654.1 kb) - Large JPEG (4.5 MB)
Tiff (13.1 MB) - More Images
View on the Sky (WWT)

Multiple images of a distant quasar are visible in this combined view from NASA's Chandra X-ray Observatory and the Hubble Space Telescope. The Chandra data, along with data from ESA's XMM-Newton, were used to directly measure the spin of the supermassive black hole powering this quasar. This is the most distant black hole where such a measurement has been made, as reported in our press release.

Gravitational lensing by an intervening elliptical galaxy has created four different images of the quasar, shown by the Chandra data in pink. Such lensing, first predicted by Einstein, offers a rare opportunity to study regions close to the black hole in distant quasars, by acting as a natural telescope and magnifying the light from these sources. The Hubble data in red, green and blue shows the elliptical galaxy in the middle of the image, along with other galaxies in the field.

The quasar is known as RX J1131-1231 (RX J1131 for short), located about 6 billion light years from Earth. Using the gravitational lens, a high quality X-ray spectrum - that is, the amount of X-rays seen at different energies - of RX J1131 was obtained.

The X-rays are produced when a swirling accretion disk of gas and dust that surrounds the black hole creates a multimillion-degree cloud, or corona near the black hole. X-rays from this corona reflect off the inner edge of the accretion disk. The reflected X-ray spectrum is altered by the strong gravitational forces near the black hole. The larger the change in the spectrum, the closer the inner edge of the disk must be to the black hole.

The authors of the new study found that the X-rays are coming from a region in the disk located only about three times the radius of the event horizon, the point of no return for infalling matter. This implies that the black hole must be spinning extremely rapidly to allow a disk to survive at such a small radius.

This result is important because black holes are defined by just two simple characteristics: mass and spin. While astronomers have long been able to measure black hole masses very effectively, determining their spins have been much more difficult.

These spin measurements can give researchers important clues about how black holes grow over time. If black holes grow mainly from collisions and mergers between galaxies they should accumulate material in a stable disk, and the steady supply of new material from the disk should lead to rapidly spinning black holes. In contrast if black holes grow through many small accretion episodes, they will accumulate material from random directions. Like a merry go round that is pushed both backwards and forwards, this would make the black hole spin more slowly.

The discovery that the black hole in RX J1131 is spinning at over half the speed of light suggests that this black hole has grown via mergers, rather than pulling material in from different directions.

These results were published online in the journal Nature. The lead author is Rubens Reis of the University of Michigan. His co-authors are Mark Reynolds and Jon M. Miller, also of Michigan, as well as Dominic Walton of the California Institute of Technology.

Fast Facts for RX J1131-1231:

Scale: Image is 1.2 arcmin on a side (About 1.6 million light years)
Category: Quasars & Active Galaxies, Black Holes
Coordinates (J2000): RA 11h 31m 51.60s | Dec -12° 31' 57.00"
Constellation: Crater
Observation Date: 28 Nov 2009
Observation Time: 7 hours 39 min
Obs. ID: 11540
Instrument: ACIS
References: Reis, R.C., et al, 2014 Nature, in press.
Color Code: X-ray (Pink); Optical (Red, Green, Blue) Optical:
Distance Estimate: 6.05 billion light years (z=0.658)

Source: NASA’s Chandra X-ray Observatory

Labels: NASA’s Chandra X-ray Observatory, Quasars, RX J1131-1231, supermassive black holes, XMM-Newton

First Light for MUSE

PR Image eso1407a

MUSE views the strange galaxy NGC 4650A

PR Image eso1407b

MUSE views of the Orion Nebula

PR Image eso1407c

MUSE colour-coded image of NGC 4650A

PR Image eso1407d

MUSE image of the Orion Nebula

PR Image eso1407e

The MUSE instrument attached to the Very Large Telescope

PR Image eso1407f

The MUSE instrument at night

PR Image eso1407g

The MUSE instrument during installation at ESO’s Paranal Observatory

PR Image eso1407h

The MUSE instrument during installation at ESO’s Paranal Observatory

PR Image eso1407i

The MUSE instrument makes the final ascent to the Very Large Telescope at ESO’s Paranal Observatory

PR Image eso1407j

MUSE image of the strange galaxy NGC 4650A

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Videos

PR Video eso1407a

MUSE views the unusual galaxy NGC 4650A

PR Video eso1407b

MUSE video of the transit of Europa across the disc of Jupiter

PR Video eso1407c

MUSE views the Orion Nebula

PR Video eso1407d

MUSE — Running through the 3D data of NGC 4650A

PR Video eso1407e

MUSE — Close up of the H-alpha line in the strange galaxy NGC 4650A

PR Video eso1407f

MUSE views the unusual galaxy NGC 4650A

Powerful 3D spectrograph successfully installed on VLT

A new innovative instrument called MUSE (Multi Unit Spectroscopic Explorer) has been successfully installed on ESO’s Very Large Telescope (VLT) at the Paranal Observatory in northern Chile. MUSE has observed distant galaxies, bright stars and other test targets during the first period of very successful observations.

Following testing and preliminary acceptance in Europe in September 2013, MUSE was shipped to ESO’s Paranal Observatory in Chile. It was reassembled at the base camp before being carefully transported to its new home at the VLT, where it is now installed on Unit Telescope 4. MUSE is the latest of the second generation instruments for the VLT (the first two were X-shooter and KMOS and the next, SPHERE, will follow shortly).

The leader of the team and principal investigator for the instrument, Roland Bacon (Centre de Recherche Astrophysique de Lyon, France), expressed his feelings: “It has taken a lot of work by many people over many years, but we have done it! It seems strange that this seven-tonne collection of optics, mechanics and electronics is now a fantastic time machine for probing the early Universe. We are very proud of the achievement — MUSE will remain a unique instrument for years to come.”

MUSE’s science goals include delving into the early epochs of the Universe to probe the mechanisms of galaxy formation and studying both the motions of material in nearby galaxies and their chemical properties. It will have many other applications, ranging all the way from studies of the planets and satellites in the Solar System, through the properties of star-forming regions in the Milky Way and out to the distant Universe.

As a unique and powerful tool for discovery MUSE uses 24 spectrographs to separate light into its component colours to create both images and spectra of selected regions of the sky. It creates 3D views of the Universe with a spectrum for each pixel as the third dimension [1]. During the subsequent analysis the astronomer can move through the data and study different views of the object at different wavelengths, just like tuning a television to different channels at different frequencies.

MUSE couples the discovery potential of an imaging device with the measuring capabilities of a spectrograph, while taking advantage of the much better image sharpness provided by adaptive optics. The instrument is mounted on Unit Telescope 4 of the VLT, which is currently being converted into a fully adaptive telescope.

MUSE is the result of ten years of design and development by the MUSE consortium — headed by the Centre de Recherche Astrophysique de Lyon, France and the partner institutes Leibniz-Institut für Astrophysik Potsdam (AIP, Germany), Institut für Astrophysik Göttingen (IAG, Germany), Institute for Astronomy ETH Zurich (Switzerland), L'Institut de Recherche en Astrophysique et Planétologie (IRAP, France), Nederlandse Onderzoekschool voor de Astronomie (NOVA, the Netherlands) and ESO.

Since the start of 2014, Bacon and the rest of the MUSE integration and commissioning team at Paranal have recorded the MUSE story in a series of blog posts which can be followed here. The team will present the first results from MUSE at the forthcoming 3D2014 workshop at ESO in Garching bei München, Germany.

“A muse is there to inspire. Indeed, MUSE has inspired us for many years and will continue to do so,” says Bacon in a blog post on the first light. “No doubt many astronomers from all over the world will also be charmed by our MUSE.“