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Hubble Reveals Massive Disk Galaxies in the Early Universe (Forwarded)



 
 
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Old January 11th 08, 02:57 AM posted to sci.space.news
Andrew Yee[_1_]
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Default Hubble Reveals Massive Disk Galaxies in the Early Universe (Forwarded)

Institute for Astronomy
University of Hawaii at Manoa
Manoa, Hawaii

Contacts:

Dr. Elizabeth McGrath
University of California, Santa Cruz
1-808-255-1970

Dr. Alan Stockton
Institute for Astronomy
University of Hawaii at Manoa
Honolulu, Hawaii 96822
1-808-956-7995

Mrs. Karen Rehbock
Assistant to the Director
Institute for Astronomy
University of Hawaii at Manoa
1-808-956-6829

Embargoed until Tuesday, January 8, 2008 1:00 p.m. CST (9:00 a.m. HST)

Hubble Reveals Massive Disk Galaxies in the Early Universe

Some of the first massive galaxies in the Universe formed when huge gas
clouds rapidly collapsed, according to Elizabeth McGrath of the University
of California, Santa Cruz, Alan Stockton of the University of Hawaii, and
their collaborators. This discovery, which is based on new Hubble Space
Telescope images, challenges the commonly held idea that all of the earliest
massive galaxies formed when smaller galaxies merged. It is being presented
this week at a meeting of the American Astronomical Society in Austin, TX.

The standard theory of galaxy formation predicts that the most massive
galaxies in the Universe take a long time to grow, accumulating mass through
the coalescence of many smaller galaxies in a process that continues until
relatively recent times. To test this theory, McGrath, Stockton, and their
collaborators searched for the oldest, most massive galaxies they could find
and used clues from their shape and structure to deduce how they may have
formed. High-resolution images from the Hubble Space Telescope revealed
galaxies more massive than our own Milky Way Galaxy that existed when the
Universe was very young -- only one-fifth its current age. It is believed
that such galaxies are the distant ancestors of the most massive galaxies in
the Universe today.

"We expected these galaxies to look similar to the football-shaped
elliptical galaxies that we see at the centers of dense groups of galaxies
today, where mergers are common. We were quite surprised to find that many
of them appear instead to be flattened, rotating disks of ordered material,"
said McGrath.

Disk galaxies are pancake or saucer-shaped, and their stars orbit in circles
around the center of the galaxy, much like the planets in our solar system
orbit around the sun, or like a Frisbee spins as it moves through the air.
This type of galaxy is more likely to have formed from a single massive
cloud that collapses under its own gravity into a flattened disk rather than
through violent collisions of previously formed galaxies. Computer
simulations of the latter scenario predict that collisions would destroy
disks and send stars from each merging galaxy into more chaotic,
three-dimensional orbits, producing football-shaped, or elliptical galaxies.
The most massive galaxies in the Universe today all appear to be elliptical
in shape, and therefore can be quite naturally explained through the merger
hypothesis. The existence of massive disk galaxies in the early Universe,
however, challenges this perspective.

In total, McGrath and her collaborators observed seven of what are likely
some of the first massive galaxies to form in the Universe. Of these, four
had shapes dominated by disk-like profiles. By age-dating the galaxies from
studying properties of the stars within them, McGrath's team discovered that
these disk structures have remained in pristine condition for over one
billion years. Even so, it seems inevitable that eventually these galaxies
will merge with others and be reformed into the more elliptical-shaped
massive, old galaxies that are familiar to us in the nearby Universe.

Other researchers who participated in this study include Gabriela Canalizo
at the University of California, Riverside, Masanori Iye at the National
Astronomical Observatory of Japan, and Toshinori Maihara at Kyoto
University. The results are part of McGrath's Ph.D. dissertation, which she
recently completed at the University of Hawaii.

Founded in 1967, the Institute for Astronomy at the University of Hawaii at
Manoa conducts research into galaxies, cosmology, stars, planets, and the
sun. Its faculty and staff are also involved in astronomy education, deep
space missions, and in the development and management of the observatories
on Haleakala and Mauna Kea.

IMAGE CAPTION:
[http://www.ifa.hawaii.edu//info/pres...sk_color.5.jpg
(96KB)]
The Hubble Space Telescope captured this massive saucer-shaped galaxy more
than 9 billion light-years distant from us. Its age implies it was formed
when the Universe was very young. Meanwhile, the thin disk-like structure
has remained intact since birth, apparently unharmed by destructive galaxy
collisions for over one billion years. Previously, theories of galaxy
formation predicted such massive galaxies could only be formed by frequent
galaxy collisions that increase mass and reorganize matter into
three-dimensional football-shaped objects. This galaxy and others like it
may have formed instead from the collapse of a single massive gas cloud.
Eventually, it will merge with neighboring galaxies to form one of the most
massive galaxies in the Universe.
 




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