This Echo is READ ONLY !   NO Un-Authorized Messages Please!
 ~~~~~~~~~~~~~~~~~~~~~~~~   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Harvard-Smithsonian Center for Astrophysics
Cambridge, Massachusetts

For more information, contact: 

David A. Aguilar
Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
617-495-7462
daguilar{at}cfa.harvard.edu 

Christine Lafon
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
Phone: 617-495-7463, Fax: 617-495-7016
clafon{at}cfa.harvard.edu

For Release: 2:00 pm EST, January 22, 2003

Release No.: 03-04 

First Milky Ways Found At Edge Of Universe

With their giant telescopes pointed toward the heavens, astronomers 
look back in time to when young galaxies were just beginning to 
coalesce and when the first generations of stars were forming -- stars 
without planets in a realm dominated by hydrogen and helium. One key 
question that has puzzled astronomers for decades is: When did the 
first stars and galaxies form after the Big Bang occurred? The answer 
-- very quickly! Astronomers Rennan Barkana (Tel Aviv University) and 
Avi Loeb (Harvard-Smithsonian Center for Astrophysics) have found the 
first direct evidence that galaxies as large as the Milky Way already 
had formed when the Universe was less than a billion years old.

"In some ways, it's surprising that such large galaxies formed so 
quickly. Most galaxies in the early Universe were only one-hundredth 
that size," said Loeb. "But our model, combined with observations by 
other researchers, provides clear evidence that massive galaxies 
existed within a relatively short time after the Big Bang."

Intriguingly, the large galaxies discovered by Barkana and Loeb are 
still around today. Over billions of years, they continued to consume 
smaller galaxies, like a cosmic software corporation absorbing many 
smaller companies.  These galactic cannibals have grown from the seeds 
that existed in a billion-year-old Universe to become monstrous giant 
elliptical galaxies, resting in the centers of galaxy clusters.

Distant Lighthouses 
-------------------
To learn about the early Universe, astronomers study the most distant 
objects -- quasars whose light has traveled for billions of years to 
reach the Earth. Quasars (short for quasi-stellar objects) are the 
brightest known astronomical objects. Their great luminosities are 
believed to be powered by supermassive black holes. A black hole acts 
as a quasar's central "engine," gulping down huge amounts of gas and 
blasting enormous quantities of radiation into space, creating a 
beacon visible for billions of light-years.

Studies of nearby galaxies have shown that a black hole's mass tends 
to be correlated with the mass of its host galaxy. That is, big 
galaxies have big black holes while little galaxies have little black 
holes. Astronomers expected that the same would be true of the more 
distant black holes in the early Universe, but they had no evidence to 
prove it. Barkana and Loeb have provided that evidence.

In studying the spectra of quasars -- the intensity of their light at 
different wavelengths, or colors -- astronomers had recorded a curious 
feature which did not attract their attention. Certain quasars showed 
a "double-horn" profile in their spectra. Barkana and Loeb created a 
computer model that explained the spectral feature as being the result 
of absorption by hydrogen gas. 

Intergalactic hydrogen falling into a quasar's host galaxy absorbs 
some of the quasar's light. This infall can be used to measure the 
host galaxy's mass. Barkana and Loeb found that the two quasars they 
examined, for which detailed spectra were available, lie in galaxies 
about as massive as the Milky Way.

"This is the first time that the mass of an early galaxy has been 
directly measured," said Barkana. 

Tip of a Cosmic Iceberg 
-----------------------
According to the widely accepted hierarchical model of galaxy
formation, the first structures to form in the early Universe were 
small protogalaxies containing the mass of only a few thousand Suns. 
Over billions of years, protogalaxies collided to form the larger 
galaxies we see today. This process takes time, so it is intriguing 
that relatively large, Milky-Way- sized galaxies could have formed in 
less than a billion years. 

"What we've found is the tip of the iceberg," said Loeb. "We studied 
the brightest quasars and found them to be in the most massive 
galaxies existing at that time. Many smaller galaxies also were 
around, containing only about one-hundredth the mass of the Milky Way. 
We don't see those baby galaxies because, even if they contain 
quasars, they would be fainter and more difficult to see."

Loeb also points out that, while the masses of the bright quasars' 
host galaxies were similar to the Milky Way, there also is an 
important difference. "The Milky Way has a small black hole at its 
center, containing only about three million solar masses. These early 
galaxies, even though they've had less time to form, contain black 
holes of up to one billion solar masses."

So far, Barkana and Loeb have applied their model to two high-redshift 
quasars for which high-resolution spectra were available. (Redshift is 
a measure of how fast an object is receding from us due to the 
expansion of the universe. Higher redshifts indicate greater 
recessional speeds and hence greater distances.) High-resolution
spectral observations of additional quasars are needed to confirm 
their model. 

This research is being reported in the January 23, 2003 issue of the 
journal Nature. 

Headquartered in Cambridge, Massachusetts, the Harvard- Smithsonian 
Center for Astrophysics (CfA) is a joint collaboration between the 
Smithsonian Astrophysical Observatory and the Harvard College 
Observatory. CfA scientists organized into six research divisions 
study the origin, evolution, and ultimate fate of the universe.

NOTE TO EDITORS: An image to accompany this release can
be found at
     http://cfa-www.harvard.edu/press/pr0304image.html

 - End of File -
================

---