A Space & astronomy forum. SpaceBanter.com

Go Back   Home » SpaceBanter.com forum » Astronomy and Astrophysics » Astronomy Misc
Site Map Home Authors List Search Today's Posts Mark Forums Read Web Partners

U.Texas Astronomer's Studies of Galactic Bulges May Alter LeadingTheory of Galaxy Evolution (Forwarded)



 
 
Thread Tools Display Modes
  #1  
Old January 9th 07, 06:13 AM posted to sci.astro
Andrew Yee
external usenet poster
 
Posts: 667
Default U.Texas Astronomer's Studies of Galactic Bulges May Alter LeadingTheory of Galaxy Evolution (Forwarded)

McDonald Observatory
University of Texas
Fort Davis, Texas

Contact: Rebecca Johnson
ph: 512-475-6763
fax: 512-471-5060

08 January 2007

University of Texas Astronomer's Studies of Galactic Bulges May Alter
Leading Theory of Galaxy Evolution

SEATTLE, Wash. -- David Fisher, an astronomy graduate student at The
University of Texas at Austin, is making important contributions to the
future understanding of galaxy evolution by studying the different types
of bulges at the hearts of nearby spiral galaxies. This work is being
presented this week at the 207th meeting of the American Astronomical
Society in Seattle, Washington.

A bulge is a concentration of stars in the center of a spiral galaxy. In
recent years, evidence has shown that there are two types of bulges -- the
so-called "classical bulges" and "pseudobulges."

Studying these bulges and finding out how many nearby galaxies have the
different types is important, Fisher says, because "we believe that the
formation of these two types of bulges is dramatically different." Such
findings could be important to theories of galaxy formation.

A classical bulge is a mostly featureless, round ball of stars, he says. A
pseudobulge, on the other hand, "looks very much like the [galaxy's] outer
disk, with a spiral structure. It can have a bar, and can be very flat,
instead of round."

Fisher and his colleague Niv Drory (Max-Planck-Institut für
extraterrestrische Physik) studied archival images of 40 galaxies within
about 150 million light-years from both Hubble Space Telescope and the
Sloan Digital Sky Survey. The archival Hubble images were of the very
heart -- the bulge -- of these galaxies. The Sloan images provided a look
at the same galaxies in their entirety -- providing information on the
context for the bulge.

Fisher and Drory find that the global properties of galaxies are tightly
coupled to the type of bulge a galaxy contains, even when the bulge
accounts for only a few percent of the galaxy's mass.

This work is the basis for Fisher's doctoral dissertation. His goal is to
find a much more quantitative way to distinguish between the two bulge
types. His work presented at this conference shows that he is well on his
way. Once achieved, this would enable astronomers "to count how many of
each bulge type there are in the local universe," he says.

He explains that current theories of galaxy evolution focus on mergers,
and typically argue that the vast majority of nearby galaxies were built
up through mergers with other galaxies over time. Further, most galaxies
are predicted to have experienced a major merger in the past billion
years.

Classical bulges are the result of mergers, Fisher says. "We feel
comfortable that they form through some kind of merger. You take two sets
of stars, you mix them up, and you're left with a ball that's essentially
featureless."

But pseudobulges form differently, through so-called "secular evolution."
Essentially, this means that the galaxy evolves on its own, without any
mergers. "In secular evolution," Fisher says, "the galaxy will start to
re-arrange itself, do it in an ordered way, rotating very fast. This
causes the spiral structure and nuclear bars in the center" that are seen
in pseudobulges. Pseudobulges are signposts of a history (since the
formation of the disk) that is free of mergers. Current theories of galaxy
formation do not predict this to be a common process. "We are trying to
find out how right or wrong these theories are," Fisher says.

An efficient method for counting the number of classical bulges and
pseudobulges in local galaxies will reveal which type is more prominent.
If there are a lot of pseudobulges, then there were not as many galactic
mergers in the past as astronomers think.

"The hints are there" that this is the case, Fisher says. If this turns
out to be correct, then "our galaxy formation models need more work."

-- END --

Note to Editors:

David Fisher can be reached this week in Seattle, and thereafter in Austin
at 512-471-1495.


 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
U.Texas Astronomer's Studies of Galactic Bulges May Alter Leading Theory of Galaxy Evolution (Forwarded) Andrew Yee News 0 January 9th 07 06:15 AM
Giant filament structures give rare insight into galaxy cluster evolution(Forwarded) Andrew Yee Astronomy Misc 0 April 6th 06 05:22 PM
A New Insight into Galaxy Formation and Evolution (Forwarded) Andrew Yee Astronomy Misc 0 February 3rd 06 05:07 PM
A New Insight into Galaxy Formation and Evolution (Forwarded) Andrew Yee News 0 February 3rd 06 04:37 PM
Viewing the Andromeda Galaxy in Houston,Texas? Phil Misc 17 March 20th 04 10:04 PM


All times are GMT +1. The time now is 09:41 PM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 SpaceBanter.com.
The comments are property of their posters.