January 8, 2008
Baby Versions of Milky Way Spotted
have spotted small galaxies near the beginning of time that resemble ancestors
of our own galactic home.
galaxies are about one-tenth to one-twentieth the size of the Milky Way and
have 40 times fewer stars. Light from the ancient clusters was emitted about 2
billion years after the Big Bang, the theoretical beginning to the universe
that occurred about 13.7 billion years ago. So the galaxies are seen as
they existed in a very young universe.
galaxies are not the most distant seen by the Hubble Space Telescope, but
astronomers consider them to be the best evidence of precursors to larger,
spiral structures such as the Milky Way.
these objects and discovering that they are a step in the evolution of our
galaxy is akin to finding a key fossil in the path of human evolution," said
Eric Gawiser, an astronomer at the Rutgers School of Arts and Sciences.
Caryl Gronwall, an astrophysicist at Pennsylvania State University, detailed
their findings today at the American Astronomical Society (AAS) annual meeting
in Austin, Texas.
in a variety of shapes — round, oblong and even somewhat linear — and we are
starting to make precise measurements of their sizes," Gronwall said of
the spiral galaxies, which are made mostly of hot, bright stars that emit a
unique "Lyman alpha" signature of ultraviolet light.
analyses and computer simulations of how galaxies bump into one another led
Gronwall and Gawiser to conclude that galaxies with strong Lyman alpha signatures
are the ancestors
of spiral galaxies.
"We knew by
our understanding of cosmological theory that spiral galaxies had to evolve
from low-mass galaxies such as these," Gawiser said. "The challenge was to
actually find them. We'd seen other early universe galaxies, but they were
bigger and destined to evolve into elliptical galaxies, not spirals."
Sharp, a program officer at the National Science Foundation's Division of
Astronomical Sciences who was not involved in the work, said Gronwall and
Gawiser used Hubble
and other observatories to extract an important finding.
team has come the closest yet to finding young galaxies that resemble our own
Milky Way in its infancy," Sharp said.