Fossil Galaxy Reveals Clues to Early Universe (Forwarded)
- From: Andrew Yee <ayee@xxxxxxxxxxxxxxxxxxxxxx>
- Date: Sat, 14 Jan 2006 12:04:08 -0500 (EST)
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CONTACT:
Lisa De Nike, (443) 287-9960
Embargoed for Release on January 12, 2006 at 9:20 A.M. EST
Fossil Galaxy Reveals Clues to Early Universe
A tiny galaxy has given astronomers a glimpse of a time when the first
bright objects in the universe formed, ending the dark ages that followed
the birth of the universe.
Astronomers from Sweden, Spain and the Johns Hopkins University used
NASA's Far Ultraviolet Spectroscopic Explorer (FUSE) satellite to make the
first direct measurement of ionizing radiation leaking from a dwarf galaxy
undergoing a burst of star formation. The result, which has ramifications
for understanding how the early universe evolved, will help astronomers
determine whether the first stars -- or some other type of object -- ended
the cosmic dark age.
The team will present its results Jan. 12 at the American Astronomical
Society's 207th meeting in Washington, D.C.
Considered by many astronomers to be relics from an early stage of the
universe, dwarf galaxies are small, very faint galaxies containing a large
fraction of gas and relatively few stars. According to one model of galaxy
formation, many of these smaller galaxies merged to build up today's
larger ones. If that is true, any dwarf galaxies observed now can be
thought of as "fossils" that managed to survive -- without significant
changes -- from an earlier period.
Led by Nils Bergvall of the Astronomical Observatory in Uppsala, Sweden,
the team observed a small galaxy, known as Haro 11, which is located about
281 million light years away in the southern constellation of Sculptor.
The team's analysis of FUSE data produced an important result: between 4
percent and 10 percent of the ionizing radiation produced by the hot stars
in Haro 11 is able to escape into intergalactic space.
Ionization is the process by which atoms and molecules are stripped of
electrons and converted to positively charged ions. The history of the
ionization level is important to understanding the evolution of structures
in the early universe, because it determines how easily stars and galaxies
can form, according to B-G Andersson, a research scientist in the Henry A.
Rowland Department of Physics and Astronomy at Johns Hopkins, and a member
of the FUSE team.
"The more ionized a gas becomes, the less efficiently it can cool. The
cooling rate in turn controls the ability of the gas to form denser
structures, such as stars and galaxies," Andersson said. The hotter the
gas, the less likely it is for structures to form, he said.
The ionization history of the universe therefore reveals when the first
luminous objects formed, and when the first stars began to shine.
The Big Bang occurred about 13.7 billion years ago. At that time, the
infant universe was too hot for light to shine. Matter was completely
ionized: atoms were broken up into electrons and atomic nuclei, which
scatter light like fog. As it expanded and then cooled, matter combined
into neutral atoms of some of the lightest elements. The imprint of this
transition today is seen as cosmic microwave background radiation.
The present universe is, however, predominantly ionized; astronomers
generally agree that this reionization occurred between 12.5 and 13
billion years ago, when the first large-scale galaxies and galaxy clusters
were forming. The details of this ionization are still unclear, but are of
intense interest to astronomers studying these so-called "dark ages" of
the universe.
Astronomers are unsure if the first stars or some other type of object
ended those dark ages, but FUSE observations of "Haro 11" provide a clue.
The observations also help increase understanding of how the universe
became reionized. According to the team, likely contributors include the
intense radiation generated as matter fell into black holes that formed
what we now see as quasars and the leakage of radiation from regions of
early star formation. But until now, direct evidence for the viability of
the latter mechanism has not been available.
"This is the latest example where the FUSE observation of a relatively
nearby object holds important ramifications for cosmological questions,"
said Dr. George Sonneborn, NASA/FUSE Project Scientist at NASA's Goddard
Space Flight Center, Greenbelt, Md.
This result has been accepted for publication by the European journal
Astronomy and Astrophysics.
Bergvall will be available to answer questions from the media about this
research at poster #175.21, during the poster-viewing sessions at the AAS
meeting on Thursday, January 12.
A high resolution image is available at
http://www.jhu.edu/news/home06/jan06/images/haro_11_a.jpg (60KB)
or by contacting Lisa De Nike at 443-287-9906.
The FUSE project is a NASA Explorer mission developed in cooperation with
the French and Canadian space agencies by the Johns Hopkins University,
Baltimore, Md., the University of Colorado, Boulder, and the University of
California, Berkeley. The mission is operated out of Johns Hopkins
University's Homewood campus in Baltimore. NASA Goddard manages the
program for NASA's Science Mission Directorate. For more information about
the FUSE mission, visit
http://fuse.pha.jhu.edu
IMAGE CAPTION:
Two views of the Haro 11 galaxy
The left hand panel shows a visible light image of Haro 11 acquired at the
European Southern Observatories in Chile. North is up and East to the
left. The image is 85 arcseconds on the side (114,000 light years at the
distance of Haro 11; 1 arcsecond equals 1/3600 degrees).
The right hand panel shows a false-color composite of the central part of
the galaxy acquired with the Hubble Space Telescope. In this composite, a
visible light image from the HST WFPC2 camera is coded in red, an
ultraviolet light image from the HST ACS camera is coded in in green, and
a spectral line emission image tracing neutral hydrogen (also from
HST-ACS), excited by the kind of radiation detected by FUSE, is coded in
blue.
The ultraviolet light traces hot, young, stars, the visible light traces
older, cooler, stars while the the line emission from hydrogen traces the
interaction of energetic radiation with the gas in the galaxy.
The size of the right hand image is 9.5 x 9.5 arcseconds, which at the
distance of Haro 11 corresponds to 12,700 x 12,700 light years.
The right hand panel is adapted from the paper by Kunth et al. 2003 in the
Astrophysical Journal, Volume 597, page 266, and is reproduced by
permission of the AAS.
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