Subscribe free to our newsletters via your
. 24/7 Space News .




STELLAR CHEMISTRY
Caltech Astronomers Describe The Bar Scene At Beginning Of Universe
by Staff Writers
Pasadena CA (SPX) Jul 31, 2008


The Milky Way is possibly the best-known barred galaxy.

Bars abound in spiral galaxies today, but this was not always the case. A group of 16 astronomers, led by Kartik Sheth of NASA's Spitzer Science Center at the California Institute of Technology, has found that bars tripled in number over the past seven billion years, indicating that spiral galaxies evolve in shape.

The thought of spiral galaxies invokes images of star-studded arms trailing off of spinning disks. But more than two-thirds of spiral galaxies, including our own Milky Way, have a bar-shaped path through their middles.

Barred galaxies are shaped more like a tiger's eye, with two starry arms trailing off either end of a long, dark stardust lane. They take shape as stellar orbits in a disk become unstable and deviate from a circular path.

"The formation of a bar may be the final important act in the evolution of a spiral galaxy," says Sheth, a Spitzer staff scientist and lead author on a study examining the evolution of barred galaxies.

"Galaxies are thought to build themselves up through mergers with other galaxies. After settling down, the only other dramatic way for galaxies to evolve is through the action of bars."

According to new observations of over 2,000 spiral galaxies, made with NASA's Hubble Space Telescope, the bar scene was dramatically different seven billion years ago, when the universe was half as old as it is today. The study is part of the Cosmic Evolution Survey (COSMOS), Hubble's largest survey ever, in which Sheth and his team of 15 scientists is examining how galaxies form and evolve.

COSMOS covers an area of sky nine times larger than the full moon, surveying 10 times more spiral galaxies than previous studies, which Sheth says typically yielded ambiguous clues to barred galaxy evolution.

The astronomers discovered that while spiral galaxies were around in the distant past, only around 20 percent of them possessed the bars that are so common in their modern counterparts. The tripling rate does not proceed in an even-handed way, either. "They are forming mostly in the small, low-mass galaxies," says Sheth, adding that among the most massive galaxies, the proportion of bars to no bars is the same as it is today.

"We know that evolution is generally faster for more massive galaxies--they form their stars early and fast and then fade into red disks," Sheth explains. "Low-mass galaxies were also known to form more slowly, but now we see that they also made their bars slower."

Survey team member Bruce Elmegreen, an astrophysicist with IBM's Research Division, describes how a bar grows after stellar orbits in a spiral galaxy begin to deviate from a circular path. "It locks more and more of these elongated orbits into place, making the bar even stronger. Eventually a high fraction of the stars in the inner disk join the bar."

Bars are perhaps the most important catalysts for changing a galaxy, Sheth says. They force a large amount of gas towards the galactic center, fueling new star formation, building bulges--spheres in the centers of galaxies made only of stars--and feeding massive black holes.

Indeed, bars may even contribute to the growth of black holes, says Nicholas Scoville, Caltech's Moseley Professor of Astronomy and COSMOS principal investigator.

"They pull stars and gas out of their normal circular orbits into the central regions, perhaps even funneling gas to the central supermassive black hole. Without this fueling, the black holes would be starved and the central regions of galaxies devoid of young stars."

"The new observations suggest that instabilities are faster in more massive galaxies, perhaps because their inner disks are denser and their gravity is stronger," adds team member Lia Athanassoula of the Laboratoire d'Astrophysique de Marseille.

The Milky Way, possibly the best-known barred galaxy, is a massive one whose bar probably formed somewhat early, like the bars in other massive galaxies, Sheth suggests. "Understanding how this occurred in the most distant galaxies will eventually shed light on how it occurred here, in our own backyard," he adds.

.


Related Links
Stellar Chemistry, The Universe And All Within It






Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle




Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News





STELLAR CHEMISTRY
Barred Spiral Galaxies Are Latecomers To The Universe
Baltimore MD (SPX) Jul 30, 2008
A frequent sign of the maturity of a spiral galaxy is the formation of a ribbon of stars and gas that slices across the nucleus, like the slash across a "no smoking" sign. In a landmark study of more than 2,000 spiral galaxies from the largest galaxy census conducted by NASA's Hubble Space Telescope, astronomers found that so-called barred spiral galaxies were far less plentiful 7 billion ... read more


STELLAR CHEMISTRY
Robotic Moon Excavation Teams Compete For NASA Prize

Space focus shifts back toward moon

ILO Instrument On Odyssey Moon's Google Lunar X PRIZE Mission

Online Casino Reports Bets On Lunar Gambling

STELLAR CHEMISTRY
Mars Express Acquires Sharpest Images Of Martian Moon Phobos

KODAK Imaging Technology Explores Mars

Phoenix Lander Working With Sticky Soil

Phoenix Revises Method To Deliver Icy Sample

STELLAR CHEMISTRY
NASA, USDA sign space research pact

Oshkosh air show honors NASA anniversary

NASA Tests Parachute For Ares Rocket

Top US astronaut welcomes space tourism

STELLAR CHEMISTRY
China Aims For World-Class Space Industry In Seven Years

Shenzhou's Spacesuit Showdown

China's Astronauts To Wear Domestic, Russian-Made Suits

Shenzhou's Unsuitable Dilemma

STELLAR CHEMISTRY
ISS Crew Inspired By Vision And Dreams Of Jules Verne

Space chiefs ponder ISS transport problem, post-2015 future

Space Station A Test-Bed For Future Space Exploration

Two Russian cosmonauts begin new space walk

STELLAR CHEMISTRY
Rockot To Launch European GOCE Satellite September 10

IBEX Satellite Ready For Integration With Pegasus Launch Vehicle

Arianespace Ready For Fifth Ariane 5 Launch Campaign

Success Of The 1734th launch Of Soyuz

STELLAR CHEMISTRY
CoRoT Exoplanet Stands Out From The Crowd

COROT's New Find Orbits Sun-Like Star

Chemical Clues Point To Dusty Origin For Earth-Like Planets

Astronomers discover clutch of 'super-Earths'

STELLAR CHEMISTRY
Seanodes Computing Solution In The Stars For NASA Astrophysics Group

ATK MicroSat Constellation Enables NASA To Solve Scientific Mystery

LockMart Demos High Power Electric Propulsion System For TSAT Program

Big Space Junk




The content herein, unless otherwise known to be public domain, are Copyright 1995-2014 - Space Media Network. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA Portal Reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement,agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement