Johns Hopkins Gazette: August 7, 1995

On Research: Astronomers Peer Deep In Space, Far Back In Time
Hubble Sheds Light On Small, Odd-Shaped Galaxies

Emil Venere
Homewood News and Information

     A team of astronomers has used the Hubble Space Telescope to
solve a 20-year mystery:  what is the nature of an enormous
number of faint galaxies seen by the world's largest telescopes
in the deepest regions of the universe?

     After a year and a half of using the repaired space
telescope, scientists have learned that the blue-colored objects
are actually small, odd-shaped galaxies that become more numerous
as astronomers look deeper into space, and therefore farther back
in time.

    But in the process of learning more, astronomers have raised
new questions.

     The faint galaxies are seen everywhere in the sky;
astronomers using ultra-powerful telescopes see tens of thousands
of them in an area the size of the full moon. Some of the
galaxies are as distant as six billion light-years away. They
emit blue light because they are in the process of hatching many
new stars at once, stars that are massive and very hot, said
Richard Griffiths, who heads an international project called the
Medium Deep Survey, which uses the Hubble Space Telescope.

     Astronomers aren't sure where all the faint galaxies are
today. They may still be just as numerous as they were billions
of years ago but are not as bright as they used to be, making
them more difficult to see, said Griffiths, an associate research
professor in the Department of Physics and Astronomy.

     The survey's main goal was to learn the nature of the
distant objects.

     "We've come a long way in terms of solving that particular
problem," Griffiths said.

     Scientists on the survey team are using the space
telescope's Wide Field Planetary Camera-2, which was part of a
package of corrective optics installed in December 1993, during a
mission to repair an image-blurring mirror flaw. Griffiths was a
member of the team of scientists responsible for building the new

     Shortly after the orbiting observatory was launched, in
April 1990, it was discovered that the telescope's primary mirror
was not ground to the proper shape.

     Much of the original wide field planetary camera's function
was negated by the mirror's flaw, since it prevented the
telescope from focusing light into a tight point, resulting in
fuzzy halos around images. That made it very difficult, if not
impossible, to pick out faint objects in a field of brighter

     Although astronomers can see faint galaxies with the largest
telescopes on Earth, even the most powerful ground-based
telescopes cannot resolve details. Astronomers had to wait until
the space telescope's blurry vision was corrected before they
could get a good look at the galaxies.

     "We've known about them for nearly two decades, but we
didn't know what they were," Griffiths said. "We couldn't say
anything about their actual structure."

     Scientists have learned that the galaxies are about
one-tenth the size of the typical elliptical and spiral galaxies,
like our Milky Way, previously thought to dominate the universe.
Whereas galaxies common in today's cosmos might contain about a
hundred thousand million stars, the very faint, distant galaxies
contain roughly a thousand million stars, Griffiths said.

     Not only are they much smaller, they also have irregular
shapes, unlike the nearly symmetric spiral and elliptical

     Astronomers are puzzled about whether the small galaxies
were the building blocks of large galaxies like the Milky Way, or
whether they have simply faded into obscurity.

     While some of the odd-shaped galaxies might have merged to
form large galaxies, it now appears more likely that many of them
did not.

     "They are apparently not merging into big spirals because we
don't see them around big spirals," Griffiths said. "We see them
everywhere and they're mainly isolated objects, not in pairs or

     That adds a new chapter to the mystery: where are the small
galaxies today? Scientists think many of them may still exist but
cannot be seen because they have grown much fainter over the
years. If that's true, perhaps large telescopes on the ground
might be used to find the galaxies, Griffiths said.

     "If you want to look at nearby galaxies of this kind you
have to do very large area surveys," he said. The space telescope
can take in only small areas of the sky at a time, an area about
one-tenth the diameter of the moon.

     The latest findings made by a team of astronomers led by
Griffiths will be published this month and in November in the
Astrophysical Journal. One of their papers was published July 15
in Britain, in the Monthly Notices of the Royal Astronomical
Society. Scientists based their findings directly on an extensive
Medium Deep Survey database put together by astronomer Kavan
Ratnatunga, an associate research scientist in the Hopkins
Department of Physics and Astronomy, and his colleagues at

     However, the data are yielding many additional cosmic
fruits, besides the faint galaxy findings. 

     Although astronomers could not use the original wide field
camera to study faint galaxies, the instrument could be used for
other research. For example, the survey, which began in 1990, has
enabled scientists to learn details about the frequency of
exceptionally bright galactic cores, called active galactic

     It also has provided insights into "gravitational lenses,"
the bending and shaping of light by massive objects. Astronomers
have studied two such lenses; light from a faint blue galaxy or
quasar located exactly behind the center of an elliptical galaxy
is distorted as it passes through the center of the elliptical
galaxy. As seen by viewers on Earth, the light is forced into the
shape of a cross.

     Astronomers on the survey team have published about 30
scientific papers so far. 

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