From: Larry Klaes (
Date: Wed May 03 2000 - 14:21:52 PDT

Date: Wed, 3 May 2000 14:50:28 -0400 (EDT)
To: undisclosed-recipients:;

Donald Savage
Headquarters, Washington, DC May 3, 2000
(Phone: 202/358-1547)

Nancy Neal
Goddard Space Flight Center, Greenbelt, MD
(Phone: 301/286-0039)

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

RELEASE: 00-72


     For the past decade astronomers have looked for vast
quantities of hydrogen that were cooked-up in the Big Bang but
somehow managed to disappear into the empty blackness of space.

     Now, NASA's Hubble Space Telescope has uncovered this long-
sought missing hydrogen. It accounts for nearly half of the
"normal" matter in the universe -- the rest is locked up in myriad

     Astronomers believe at least 90 percent of the matter in the
universe is hidden in exotic "dark" form that has not yet been
seen directly. But more embarrassing is that, until now, they have
not been able to see most of the universe's ordinary, or baryonic,
matter (normal protons, electrons and neutrons).

     The confirmation of this missing hydrogen will shed new light
on the large-scale structure of the universe. The detection also
confirms fundamental models of how much hydrogen was manufactured
in the first few minutes of the universe's birth in the Big Bang.

     "This is a successful, fundamental test of cosmological
models," said Todd Tripp of Princeton University, Princeton, NJ.
"This provides strong evidence that the models are on the right
track." The results of Tripp and his collaborators, Edward Jenkins
from Princeton and Blair Savage from the University of Wisconsin-
Madison, are being published in the May 1 issue of the
Astrophysical Journal Letters.

     Previous observations show that billions of years ago this
missing matter formed vast complexes of hydrogen clouds -- but
since then has vanished. Even Hubble's keen eye didn't see the
hydrogen directly because it is too hot and rarified. Instead,
Hubble found a telltale elemental tracer -- highly ionized
(energized) oxygen -- between galaxies, which the hydrogen heats
to the temperatures observed in intergalactic space. The presence
of highly ionized oxygen between the galaxies implies there are
huge quantities of hydrogen in the universe, which is so hot it
escapes detection by normal observational techniques.

     In recent years, supercomputer models of the expanding,
evolving universe have predicted an intricate web of gas filaments
where hydrogen is concentrated along vast chain-like structures.
Clusters of galaxies form where the filaments intersect. The
models predict that vast hydrogen clouds flowing along the chains
should collide and heat up. This would squelch the formation of
more galaxies in the hottest regions, so star birth was more
abundant in the early universe when the hydrogen was cool enough
to coalesce.

     The oxygen "tracer" was probably created when exploding stars
in galaxies spewed the oxygen (created in their cores through
nuclear fusion) back into intergalactic space where it mixed with
the hydrogen and then was shocked and heated to temperatures over
360,000 degrees Fahrenheit (100,000 degrees Kelvin).

     Astronomers detected the highly ionized oxygen by using the
light of a distant quasar to probe the invisible space between the
galaxies, like shining a flashlight beam through a fog. Hubble's
Space Telescope Imaging Spectrograph found the spectral
"fingerprints" of intervening oxygen superimposed on the quasar's
light. Slicing across billions of light-years of space, the
quasar's brilliant beam penetrated at least four separate
filaments of the invisible hydrogen laced with the telltale

     Hubble's ultraviolet sensitivity and high-resolution
spectroscopic capability allowed it to probe the nearby universe,
where spectral features of hot gas can be seen at ultraviolet
wavelengths and the problems faced by X-ray astronomers are
avoided. "This result beautifully illustrates the power of
spectroscopy for revealing fundamental information about the
presence and nature of the gaseous matter in the universe,"
according to Hubble spectroscopist Blair Savage.

     Still, the hot hydrogen could not be seen directly because it
is fully ionized and so the hydrogen atoms are stripped of their
electrons. Without electrons, no spectral features were etched
into the quasar's earth-bound light. The oxygen is highly ionized
too, but still retains a few electrons which absorb specific
colors from the quasar's light.

                           - end -

NOTE TO EDITORS: A ground-based image and illustration associated
with this release are available on the Internet at:


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