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CONTACT: Don Savage FOR RELEASE: JULY 24, 1995
NASA Headquarters, Washington, DC
(Phone: 202-358-1547)

Tammy Jones
Goddard Space Flight Center, Greenbelt, MD
(Phone: 301-286-5566)

Ray Villard
Space Telescope Science Institute, Baltimore, MD
(Phone: 410-338-4514)


PRESS RELEASE NO.: STScI-PR95-08

HUBBLE SHEDS LIGHT ON THE "FAINT BLUE GALAXY" MYSTERY

Astronomers using NASA's Hubble Space Telescope have solved a 20-year-old
mystery by showing that a class of galaxy once thought to be rare is actually
the most common type of galaxy in the universe.

Analyzing some of the deepest images ever taken of the heavens, the
astronomers conclude that small irregular objects called "blue dwarfs" were
more numerous several billion years ago, outnumbering the spiral galaxies like
our Milky Way, and giant elliptical galaxies as well. This means the blue
dwarfs are a more important constituent of the universe and figure more
prominently in the evolution of galaxies than previously thought, researchers
say.

The discovery was made by the international Medium Deep Survey team, led by
Richard Griffiths of the Johns Hopkins University, Baltimore, MD, and extended
by a deeper survey with Hubble Space Telescope by a team led by Rogier
Windhorst of Arizona State University, Tempe, AZ.

"The new results have overturned the conventional picture of a universe
dominated by giant grand-design spiral systems and elliptical galaxies," said
Griffiths. "Instead, we're going to have to come up with a new way of
understanding the distorted galaxies we see in huge numbers, which seemed to
have formed later than the giant galaxies."

However, they say it is not clear whether these small irregular systems are
indeed the building blocks of galaxies like the Milky Way, or have simply
faded into obscurity. "Most of these faint objects are extremely blue in
color, a strong indication that they are undergoing a brief, rapid burst of
star formation," said Windhorst, who along with William Keel of the University
of Alabama, Birmingham, AL, conducted a separate survey of remote galaxies.

These faint galaxies were randomly imaged as part of a key Hubble Space
Telescope project, called the "Medium Deep Survey." The survey uses Hubble's
Wide Field and Planetary Camera 2 (WFPC2) to search for unexpected objects in
uncharted areas of sky. This highly efficient and cost-effective survey is
conducted in "parallel mode" where the WFPC2 takes detailed pictures while
a "primary" instrument, such as a spectrograph, collects data from a
predetermined celestial target.

For the past 17 months, Griffiths and co-investigators from the United States
(Richard Green, John Huchra, Garth Illingworth, David Koo, Kavan Ratnatunga,
Tony Tyson, Rogier Windhorst) and the United Kingdom (Richard Ellis, Gerry
Gilmore), have studied more than 50 random snapshots containing high
resolution information for a total of tens of thousands of galaxies.

"We were immediately struck by the large numbers of irregular and peculiar
galaxies in these HST random images," said Griffiths.

Another deeper Hubble image has further extended these exciting results. The
image was obtained by Windhorst and Keel, and analyzed by Simon Driver of
Arizona State University, Windhorst, and associates.

"At last, Hubble has allowed crystal clear images of these extremely faint
objects, and we find that our universe is dominated by distorted systems of
stars," said Driver. "At the faintest limits more than half the galaxies seen
are such systems."

"We all know that the (clear) sky during the day is blue -- due to scattered
sunlight -- but if your eyes had much more sensitivity, they would also see a
very dim blue glow in the sky at night caused by myriads of faint blue
galaxies, the mysterious nature of which was unknown until we imaged them
in detail with Hubble," said Windhorst.

The researchers are now measuring the distances to these galaxies using the
new generation giant telescopes on Earth.


* * * * * *


The Space Telescope Science Institute is operated by the Association of
Universities for Research in Astronomy, Inc. (AURA) for NASA, under contract
with the Goddard Space Flight Center, Greenbelt, MD. The Hubble Space
Telescope is a project of international cooperation between NASA and the
European Space Agency (ESA).


Image files in GIF and JPEG format may be accessed on Internet via anonymous
ftp from oposite.stsci.edu in /pubinfo:

GIF JPEG
STScI-PRC95-08b Faint Blue Galaxies gif/fbgalax.gif jpeg/fbgalax.jpg
STScI-PRC94-39b MDS Peculiar Galaxies gif/MDSgalax.gif jpeg/MDSgalax.jpg

The same images are available via World Wide Web from URL
http://www.stsci.edu/Latest.html
or via links in http://www.stsci.edu/Pictures.html.