Barred spiral galaxies came quite late in the UniverseJuly 30th, 2008 - 3:03 pm ICT by ANI
Washington, July 30 (ANI): In a landmark study of more than 2,000 spiral galaxies from the largest galaxy census conducted by NASAs Hubble Space Telescope, astronomers found that so-called barred spiral galaxies were far less plentiful 7 billion years ago than they are today, in the local universe.
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.
The studys results confirm the idea that bars are a sign of galaxies reaching full maturity as the formative years end.
The observations are part of the Cosmic Evolution Survey (COSMOS).
This new detailed look at the history of bar formation, made with Hubbles Advanced Camera for Surveys, provides clues to understanding when and how spiral galaxies formed and evolved over time.
A team led by Kartik Sheth of the Spitzer Science Center at the California Institute of Technology in Pasadena discovered that only 20 percent of the spiral galaxies in the distant past possessed bars, compared with nearly 70 percent of their modern counterparts.
Bars have been forming steadily over the last 7 billion years, more than tripling in number.
The recently forming bars are not uniformly distributed across galaxy masses, however, and this is a key finding from our investigation, explained Sheth. They are forming mostly in the small, low-mass galaxies, whereas among the most massive galaxies, the fraction of bars was the same in the past as it is today, he added.
The findings, according to Sheth, have important ramifications for galaxy evolution.
We know that evolution is generally faster for more massive galaxies: They form their stars early and fast and then fade into red disks. Low-mass galaxies are known to form stars at a slower pace, but now we see that they also made their bars slowly over time, he said.
Bars form when stellar orbits in a spiral galaxy become unstable and deviate from a circular path.
The tiny elongations in the stars orbits grow and they get locked into place, making a bar, explained team member Bruce Elmegreen of IBMs research Division in Yorktown Heights, N.Y. The bar becomes even stronger as it locks more and more of these elongated orbits into place. Eventually a high fraction of the stars in the galaxys inner region join the bar, he added.
According to team member Lia Athanassoula of the Laboratoire dAstrophysique de Marseille in France, The new observations suggest that the instability is faster in more massive galaxies, perhaps because their inner disks are denser and their gravity is stronger. (ANI)
- Galaxy merger dilemma solved - Apr 21, 2010
- Thick disc of older stars discovered in nearby Andromeda galaxy - Feb 16, 2011
- NASA finds giant ring of black holes - Feb 10, 2011
- Galaxies 'formed much earlier than thought' - Apr 13, 2011
- Why massive stellar explosions occur in the tiniest of galaxies? - Apr 22, 2011
- Magnetic fields play important role in birth of massive stars - Feb 22, 2010
- How cosmic dust shape the twinkling stars - Nov 23, 2010
- How galaxy disks are stirred vigorously - Jan 08, 2010
- Parent star's long 'napping' could trigger the formation of baby stars - Mar 10, 2011
- Majestic spiral galaxy discovered within the Coma Cluster - Aug 11, 2010
- Scientists ferret out planet-hunting targets with NASA telescope - Apr 08, 2011
- How Earth survived its birth - Jan 08, 2010
- The hidden side of star formation revealed - May 07, 2010
- M81's 'halo' offers insight into formation of galaxies - Apr 23, 2010
- What makes black holes at galaxy centre become active - Jun 16, 2010
Tags: advanced camera, california institute of technology, circular path, cosmic evolution, formative years, galaxy evolution, galaxy masses, hubble space telescope, institute of technology, landmark study, low mass, massive galaxies, maturity, nucleus, ramifications, science center, sheth, spiral galaxies, spiral galaxy, stellar orbits