Tuesday, September 30, 2008

When It Comes to Galaxies, Diversity Is Everywhere

(University of Washington)

ABOUT THIS IMAGE: These images taken with NASA's Hubble Space Telescope are close-up views of four galaxies from a large survey of nearby galaxies.

The galaxies have very different masses and sizes and showcase the diversity of galaxies found in the ANGST study. Although the galaxies are separated by many light-years, they are presented as if they are all at the same distance to show their relative sizes.

The images, taken with Hubble's Advanced Camera for Surveys, reveal rich detail in the stellar populations and in the interstellar dust scattered between the stars. Hubble's sharp views reveal the colors and brightnesses of individual stars, which astronomers used to derive the history of star formation in each galaxy.

In the composite image at the top, NGC 253 is ablaze with the light from thousands of young, blue stars. The spiral galaxy is undergoing intense star formation. The image demonstrates the sharp "eye" of the Advanced Camera, which resolved individual stars. The dark filaments are clouds of dust and gas. NGC 253 is the dominant galaxy in the Sculptor Group of galaxies and it resides about 13 million light-years from Earth.

In the view of the spiral galaxy NGC 300, second from top, young, blue stars are concentrated in spiral arms that sweep diagonally through the image. The yellow blobs are glowing hot gas that has been heated by radiation from the nearest young, blue stars. NGC 300 is a member of the Sculptor Group of galaxies and it is located 7 million light-years away.

The dark clumps of material scattered around the bright nucleus of NGC 3077, the small, dense galaxy at bottom, left, are pieces of wreckage from the galaxy's interactions with its larger neighbors. NGC 3077 is a member of the M81 group of galaxies and it resides 12.5 million light-years from Earth.

The image at bottom, right, shows a swarm of young, blue stars in the diffuse dwarf irregular galaxy NGC 4163. NGC 4163 is a member of a group of dwarf galaxies near our Milky Way and is located roughly 10 million light-years away.

These galaxies are part of a detailed survey called the ACS Nearby Galaxy Survey Treasury program (ANGST). In the census, Hubble observed roughly 14 million stars in 69 galaxies. The survey explored a region called the "Local Volume," and the galaxy distances ranged from 6.5 million light-years to 13 million light-years from Earth. The Local Volume resides beyond the Local Group of galaxies, an even nearer collection of a few dozen galaxies within about 3 million light-years of our Milky Way Galaxy.



A typical galaxy contains billions of stars but looks "smooth" when viewed through a telescope, because the stars are blurred together. In contrast, the galaxies in the new survey are close enough to Earth that the sharp "eyes" of Hubble's Advanced Camera for Surveys and Wide Field Planetary Camera 2 can resolve their brightest individual stars. By measuring the brightness and colors of these stars, scientists can derive the local history of star formation within a galaxy and can tease out subtle features in a galaxy's shape.

"Past Hubble observations of the local neighborhood have provided dramatic insights into the star-formation histories of individual galaxies, but the number of galaxies studied in detail has been rather small," said Julianne Dalcanton of the University of Washington in Seattle and leader of the ANGST survey. The survey's results were submitted to The Astrophysical Journal Supplement Series. Another paper that details the star-formation history in galaxy M81 has been submitted to The Astronomical Journal.

"Instead of picking and choosing particular galaxies to study, our survey will be complete by virtue of looking at 'all' the galaxies in the region. This gives us a multi-color picture of when and where all the stars in the local universe formed."

Many stars in nearby galaxies are the fossil equivalents of the active star formation seen in galaxies in the distant universe. "When we look back in time at distant, young galaxies, we see lots of vigorous star formation. However, we can only guess as to what those galaxies might eventually turn into," Dalcanton explained. "Using the galaxies in the nearby universe as a 'fossil record,' we can compare them with young galaxies far away. This comparison gives us a history of star formation and provides a better understanding of the masses, structures, and environments of the galaxies."

Early results of the ANGST survey show the rich diversity of galaxies. Some galaxies are made up entirely of ancient stars, while others have been forming stars nearly continuously during their whole lives. There are even a few examples of galaxies that have only started forming stars in the recent past.

"With these images, we can see what makes each galaxy unique," said team member Benjamin Williams of the University of Washington. "When we look at the distribution and development of stars in each survey galaxy, we can learn how differences in the galaxies' histories have produced the diversity of galaxy shapes and colors."

The ANGST survey also includes maps of many large galaxies, including M81. "With these maps, we can track when the different parts of the galaxy formed," explained Evan Skillman of the University of Minnesota, describing work by students Dan Weisz of the University of Minnesota and Stephanie Gogarten of the University of Washington.

In a separate paper describing the star-formation history in M81, astronomers confirmed that massive spiral galaxies formed most of their stars in the early universe. Analyzing M81's outer disk, the astronomers found that most of the stars formed more than 7 billion years ago, when the universe was half its present age. M81 and other mammoth galaxies also experienced rapid enrichment of heavy elements, such as carbon, through the deaths of massive stars in supernova explosions. "We were surprised by how quickly the elements formed and how the subsequent star-formation rate for the bulk of the stars in M81 changed after that," said Williams, the paper's lead author.

"This rich survey will add to Hubble's legacy, providing a foundation for future studies," Dalcanton said. "The ANGST sample offers superb targets for future multi-wavelength surveys, which will allow us to combine the star-formation maps with the properties of gas and dust in the galaxies. With this information, we will be able to trace the complete cycle of star formation in detail."

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

Julianne Dalcanton
University of Washington, Seattle, Wash.

Evan Skillman
University of Minnesota, Minneapolis, Minn.

Friday, September 26, 2008

The Wild, Hidden Cousin of SN 1987A

ESO PR Photo 32/08
SN 1996cr in Circinus Galaxy

Powerful nearby supernova caught by web of telescopes













These results will appear in an upcoming issue of The Astrophysical Journal (F.E. Bauer et al., Supernova 1996cr: SN 1987A's Wild Cousin?, http://arxiv.org/abs/0804.3597) Other co-authors on this paper include Niel Brandt (Penn State, USA), Stefan Immler (NASA Goddard Space Flight Center), Norbert Bartel (York University, Canada), and Michael Bietenholz (York University and Hartebeesthoek Radio Observatory, South Africa). Franz Bauer was formerly at Penn State.



Franz Bauer
Columbia University, USA
Phone: +1 718-637-3071
E-mail: feb (at) astro.columbia.edu

ESO Press Officer: Dr. Henri Boffin - +49 89 3200 6222 - hboffin@eso.org

ESO Press Officer in Chile: Valentina Rodriguez - +56 2 463 3123 - vrodrigu@eso.org

The Hibernating Stellar Magnet

ESO PR Photo 31/08
The Hibernating Stellar Magnet

First Optically Active Magnetar-Candidate Discovered












Alberto J. Castro-Tirado
IAA-CSIC, Granada, Spain
Phone: +34 958 23 05 91
E-mail: ajct (at) iaa.es

Antonio de Ugarte Postigo
ESO, Chile
Phone: +56 2 463 3062
Mobile: +34 61 60 31 753
E-mail: adeugart (at) eso.org


Spacecraft discovers solar winds weakening

This artist's impression shows the Sun's heliosphere.
Credit: NASA/Goddard Space Flight Center Conceptual Image Lab

Credit: NASA, ESA

Data from the Ulysses spacecraft, a joint NASA-European Space Agency mission, show the Sun has reduced its output of solar wind to the lowest levels since accurate readings became available. The Sun's current state could reduce the natural shielding that envelops our solar system.

"The Sun's million mile-per-hour solar wind inflates a protective bubble, or heliosphere, around the solar system. It influences how things work here on Earth and even out at the boundary of our solar system where it meets the galaxy," says Dave McComas, Ulysses' solar wind instrument principal investigator and senior executive director at the Southwest Research Institute in San Antonio. "Ulysses data indicate the solar wind's global pressure is the lowest we have seen since the beginning of the space age."

The Sun's solar wind plasma is a stream of charged particles ejected from the Sun's upper atmosphere. The solar wind interacts with every planet in our solar system. It also defines the border between our solar system and interstellar space.

This border, called the heliopause, is a bubble-shaped boundary surrounding our solar system where the solar wind's strength is no longer great enough to push back the wind of other stars. The region around the heliopause also acts as a shield for our solar system, warding off a significant portion of the cosmic rays outside the galaxy.

"Galactic cosmic rays carry with them radiation from other parts of our galaxy," says Ed Smith, NASA's Ulysses project scientist at the Jet Propulsion Laboratory in Pasadena, California. "With the solar wind at an all-time low, there is an excellent chance the heliosphere will diminish in size and strength. If that occurs, more galactic cosmic rays will make it into the inner part of our solar system."

Galactic cosmic rays are of great interest to NASA. Cosmic rays are linked to engineering decisions for unmanned interplanetary spacecraft and exposure limits for astronauts traveling beyond low-Earth orbit.

In 2007, Ulysses made its third rapid scan of the solar wind and magnetic field from the Sun's south pole to the north pole. When the results were compared with observations from the previous solar cycle, the strength of the solar wind pressure and the magnetic field embedded in the solar wind was found to have decreased by 20 percent. The field strength near the spacecraft has decreased by 36 percent.

"The Sun cycles between periods of great activity and lesser activity," Smith says. "Right now, we are in a period of minimal activity that has stretched on longer than anyone anticipated."

Ulysses was the first mission to survey the space environment over the Sun's poles. Data from Ulysses have forever changed the way scientists view our star and its effects. The venerable spacecraft has lasted more than 17 years, or almost four times its expected mission lifetime.

The Ulysses solar wind findings were published in a recent edition of Geophysical Research Letters.

The Ulysses spacecraft was carried into Earth orbit aboard space shuttle Discovery on October 6, 1990. From Earth orbit it was propelled toward Jupiter, passing the planet on February 8, 1992. Jupiter's immense gravity bent the spacecraft's flight path downward and away from the plane of the planets' orbits. This placed Ulysses into a final orbit around the Sun that would take it over the north and south poles.

Wednesday, September 24, 2008

Dusty Disk Evidence of Planetary Collision

Credit: Artwork by Lynette Cook

What astronomers had expected to be a run-of-the-mill protoplanetary disk turned out to be evidence of a much more intriguing story. While observing the sun-like star BD 20 307, a team of astronomers noticed a large disk of dust surrounding the star. Usually, this is evidence of planetary formation around younger stars. The 8 planets (and plutoids…) in our own solar system formed out of just such a disk. Disks like this aren't generally found around older stars, though, and when the age of the star was calculated to be several billion years old, the source of the dust appears to come from a rare event: it is the resulting debris of two planets slamming into each other.

Using data from the Chandra X-ray Observatory, and taking the brightness using one of Tennessee State University's automated telescopes in Arizona, the team first discovered BD 20 307 to in fact be part of a close binary pair. Not only that, but the system was much older than previously thought: several billions of years old, rather than a few hundred million. The system is 300 light-years away from Earth in the constellation Ares.

The curiously large amount of dust orbiting BD 20 307 is 1 million times the amount of dust than is found in our own solar system, and orbits at a distance from the star that is similar to the orbits of Earth and Venus around our own Sun. The abundance of dust particles in this orbit – and around such a mature star – led scientists to the conclusion that it was created by the violent collision of two exoplanets.

Benjamin Zuckerman, UCLA professor of physics and astronomy and co-author of a paper on the discovery said, "It's as if Earth and Venus collided with each other. Astronomers have never seen anything like this before. Apparently, major catastrophic collisions can take place in a fully mature planetary system." Zuckerman and his team will report their findings in the December issue of the Astrophysical Journal.

Normally, warm disks of dust surround younger star systems, out of which larger and larger structures can form, eventually yielding planets. To find a disk of dust in around a star that is several billions of years old is odd, because the pressure of stellar radiation pushes out the lighter dust over time, and the larger chunks either form planets and asteroids, or break down in collisions and get blown away.

The collision between the planets took place within the past few hundred thousand years, though it is possible that it happened even more recently. Such a colossal collision raises the question of how the orbits of the two planets became destabilized, and whether such a collision could happen in our own solar system.

"The stability of planetary orbits in our own solar system has been considered for nearly two decades by astronomer Jacques Laskar in France and, more recently, by Konstantin Batygin and Greg Laughlin in the U.S.A. Their computer models predict planetary motions into the distant future and they find a small probability for collisions of Mercury with Earth or Venus sometime in the next billion years or more. The small probability of this happening may be related to the rarity of very dusty planetary systems like BD+20 307," said paper co-author Gregory Henry, astronomer at Tennessee State University (TSU).

Scientists Detect "Dark Flow:" Matter From Beyond the Visible Universe

Galaxy clusters like 1E 0657-56 (inset) seem to be drifting toward a 20-degree-wide patch of sky (ellipse) between the constellations of Centaurus and Vela.
Credit: NASA/WMAP/A. Kashlinsky et al.

Just as unseen dark energy is increasing the rate of expansion of the universe, there's something else out there causing an unexpected motion in distant galaxy clusters. Scientists believe the cause is the gravitational attraction of matter that lies beyond the observable universe, and they are calling it "Dark Flow," in the vein of two other cosmological mysteries, dark matter and dark energy. "The clusters show a small but measurable velocity that is independent of the universe's expansion and does not change as distances increase," said lead researcher Alexander Kashlinsky at NASA's Goddard Space Flight Center in Greenbelt, Md. "The distribution of matter in the observed universe cannot account for this motion."

"We never expected to find anything like this," he said.

Using NASA's Wilkinson Microwave Anisotropy Probe's (WMAP) three-year view of the microwave background and a catalog of clusters, the astronomers detected hundreds of galaxy clusters that appear to be carried along by a mysterious cosmic flow. The bulk cluster motions are traveling at nearly 2 million miles per hour. The clusters are heading toward a 20-degree patch of sky between the constellations of Centaurus and Vela.

Several astronomers teamed up to identify some 700 X-ray clusters that exhibited a subtle spectral shift. This sample includes objects up to 6 billion light-years — or nearly half of the observable universe — away.

They found this motion is constant out to at least a billion light-years. "Because the dark flow already extends so far, it likely extends across the visible universe," Kashlinsky says.

The finding flies in the face of predictions from standard cosmological models, which describe such motions as decreasing at ever greater distances.

Cosmologists view the microwave background - a flash of light emitted 380,000 years after the big bang - as the universe's ultimate reference frame. Relative to it, all large-scale motion should show no preferred direction.

Big-bang models that include a feature called inflation offer a possible explanation for the flow. Inflation is a brief hyper-expansion early in the universe's history. If inflation did occur, then the universe we can see is only a small portion of the whole cosmos.

WMAP data released in 2006 support the idea that our universe experienced inflation. Kashlinsky and his team suggest that their clusters are responding to the gravitational attraction of matter that was pushed far beyond the observable universe by inflation. "This measurement may give us a way to explore the state of the cosmos before inflation occurred," he says.

The next step is to narrow down uncertainties in the measurements. "We need a more accurate accounting of how the million-degree gas in these galaxy clusters is distributed," says Atrio-Barandela.

"We’re assembling an even larger and deeper catalog of X-ray clusters to better measure the flow," Ebeling adds. The researchers also plan to extend their analysis by using the latest WMAP results, released in March.

The result will appear in the October 20 edition of Astrophysical Journal Letters, which is available electronically this week.

Monday, September 22, 2008

Pinning down the Milky Way's spin

ESO PR Photo 30/08
Cepheids in the Solar Neighbourhood










Nardetto, N., Stoekl, A., Bersier, D. & Barnes, T. G., High resolution spectroscopy for Cepheids distance determination. III. A relation between γ-velocities and γ-asymmetries", to appear in Astronomy & Astrophysics.



Nicolas Nardetto
Departamento de Astronomia
Universidad de Concepcion, Chile
Phone: + 56 41 220 33 66
E-mail: nnardetto (at) astro-udec.cl

ESO Press Officer:

ESO Press Officer in Chile:
Valentina Rodriguez - +56 2 463 3123 - vrodrigu@eso.org

NASA Satellite Sees Oldest-Ever Gamma-Ray Burst, Long Before Milky Way Existed

GRB 080913 exploded Sept. 13 at a whopping distance of 12.8 billion light-years away in the constellation Eridanus. The box indicates the sky area shown in the Swift image.

This image merges the view through Swift's UltraViolet and Optical Telescope, which shows bright stars, and its X-ray Telescope, which captures the burst (orange and yellow).
Credit: NASA/Swift/Stefan Immler

Whenever satellites like NASA's Swift sees a gamma-ray burst, it's really a look back in time. Now, scientists have seen one that happened farther back in time than any other seen before.

Gamma-ray bursts or "GRBs" are the most powerful and brightest explosions of energy in our universe. They last only a few milliseconds to several minutes and they outshine all other sources of gamma rays combined. Astronomers now think that most GRBs, those lasting 2 seconds or longer, are associated with the explosive deaths of massive stars. These stars collapse and explode when they run out of nuclear fuel.

Now, NASA's Swift satellite has found the most distant gamma-ray burst ever detected! The blast was named "GRB 080913." The GRB number is actually the date YYMMDD of the burst, with letters used for the first, second, etc. burst of the day. This burst came from an exploding star 12.8 billion light-years away. A light-year is the distance light travels, at a speed 186,000 miles per second, in one year.

"This is the most amazing burst Swift has seen," says the mission’s lead scientist Neil Gehrels at Goddard Space Flight Center in Greenbelt, Md. "It's coming to us from near the edge of the visible universe."

Because light moves at a set speed, looking farther into the universe means looking back in time. GRB 080913's "lookback time" reveals that the burst occurred less than 825 million years after the universe began. Scientists think that the universe is 13.7 billion years old. That means this gamma-ray burst happened 12.8 billion years ago! That's long before our galaxy, called the Milky Way, even existed. Scientists believe the galaxy formed about 10 billion years ago.

The star that created this gamma-ray burst died when the universe was less than one-seventh its present age. "This burst accompanies the death of a star from one of the universe’s early generations," says Patricia Schady of the Mullard Space Science Laboratory at University College London, who is organizing Swift observations of the event.

The star's gamma-rays were registered on NASA's Swift satellite at 1:47 a.m. EDT on Sept. 13. The spacecraft established the burst's location in the constellation Eridanus. The previous record holder was a burst from about 12.1 billion years ago.

Friday, September 19, 2008

Water Hit with Young Star's Best Shot

A jet of gas firing out of a very young star can be seen ramming into a wall of material in this infrared image from NASA's Spitzer Space Telescope.
Credit: NASA/JPL-Caltech/A. Tappe (Harvard-Smithsonian CfA)










Tappe is the lead author of a paper on this topic, which was published in a recent issue of the Astrophysical Journal. Co-authors on the paper include Charlie Lada, and August Muench, also of the Harvard-Smithsonian Center for Astrophysics; and J. H. Black, of the Chalmers University of Technology, in Onsala, Sweden.

Tuesday, September 16, 2008

Galaxy Silhouettes

Overlapping Galaxies 2MASX J00482185-2507365






The results have been submitted for publication in The Astronomical Journal.

For additional information, contact:

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

Benne Holwerda
Space Telescope Science Institute, Baltimore, Md.
/University of Cape Town, South Africa

Object Name: 2MASX J00482185-2507365

Acknowledgment: B. Holwerda (Space Telescope Science Institute)
and J. Dalcanton (University of Washington)

Monday, September 15, 2008

First Picture of Likely Planet around Sun-like Star

Photo Credit: Gemini Observatory













The preprint of the paper is available at http://arxiv.org/abs/0809.1424

Wednesday, September 10, 2008

The Double Firing Burst

ESO PR Photo 28/08
A Gamma-Ray Burst with Two Jets

Brightest Gamma-Ray
Burst Provides Wealth of Information on How Stars Explode

Astronomers from around the world combined data from ground- and space-based telescopes to paint a detailed portrait of the brightest explosion ever see. The observations reveal that the jets of the gamma-ray burst called GRB 080319B were aimed almost directly at the Earth.

GRB 080319B was so intense that, despite happening halfway across the Universe, it could have been seen briefly with the unaided eye (ESO 08/08). In a paper to appear in the 11 September issue of Nature, Judith Racusin of Penn State University, Pennsylvania (USA), and a team of 92 co-authors report observations across the electromagnetic spectrum that began 30 minutes before the explosion and followed it for months afterwards.











Guido Chincarini, Stefano Covino, Cristiano Guidorzi
University of Miliano Bicocca and INAF-Brera, Italy
Phone: +39 039 597 10 74
Cell phone: +39 340 280 36 12
E-mail: guido.chincarini (at) brera.inaf.it

European Organisation for Astronomical Research
in the Southern Hemisphere

Mind the Gap

ESO PR Photo 27a/08
Planet-forming Disc

VLT instrument hints at the presence of planets in young gas discs












Notes for editors





[4] Alain Smette is the CRIRES Instrument Scientist.


Klaus Pontoppidan
California Institute of Technology, Pasadena, USA
Phone: +1 626 395 4900
Mobile: +1 626 679 5793
E-mail: pontoppi (at) gps.caltech.edu

Ewine van Dishoeck
Leiden University, The Netherlands
Phone: +31 71 527 58 14
E-mail: ewine (at) strw.leidenuniv.nl

European Organisation for Astronomical Research
in the Southern Hemisphere

Tuesday, September 09, 2008

M110 - Satellite of the Andromeda Galaxy

Explanation: Our Milky Way Galaxy is not alone. It is part of a gathering of about 25 galaxies known as the Local Group. Members include the Great Andromeda Galaxy (M31), M32, M33, the Large Magellanic Cloud, the Small Magellanic Cloud, Dwingeloo 1, several small irregular galaxies, and many dwarf elliptical and dwarf spheroidal galaxies. Pictured on the lower right is one of the dwarf ellipticals: NGC 205. Like M32, NGC 205 is a companion to the large M31, and can sometimes be seen to the south of M31's center in photographs. The image shows NGC 205 to be unusual for an elliptical galaxy in that it contains at least two dust clouds (at 9 and 2 o'clock - they are visible but hard to spot) and signs of recent star formation. This galaxy is sometimes known as M110, although it was actually not part of Messier's original catalog.

Astronomy Picture of the Day

Friday, September 05, 2008

Perseus A - A Monster Galaxy at the Heart of Perseus Cluster




Cassini Images Ring Arcs Among Saturn's Moons

Credit: NASA/JPL/Space Science Institute)

In this image, most of the visible material in the arc lies ahead of Anthe in its orbit. However, over time the moon drifts slowly back and forth with respect to the arc. PASADENA, Calif. -- NASA's Cassini spacecraft has detected a faint, partial ring orbiting with one small moon of Saturn, and has confirmed the presence of another partial ring orbiting with a second moon. This is further evidence that most of the planet's small, inner moons orbit within partial or complete rings.




Credit: NASA/JPL/Space Science Institute)






Images of Anthe and Methone with their ring arcs are available at: http://www.nasa.gov/cassini, http://saturn.jpl.nasa.gov and http://ciclops.org.


Carolina Martinez 818-354-9382
Jet Propulsion Laboratory, Pasadena, Calif.

Preston Dyches 720-974-5859
Space Science Institute, Boulder, Colo.

Julia Maddock +44 (0)1793 442 094
Science and Technology Facilities Council