When scientists peer at distant galaxies, it's like looking
back in time because their light has taken so long to reach us. Recently, two
groups of astronomers were able to see two classes of unique galaxies from the
early universe.
One group glimpsed galaxies that looked old even when the
universe was young, suggesting they must have been some of the first galaxies
to form after the birth of the universe. The other group found galaxies
dating from the strongest burst of star formation in the universe.
The former set of galaxies seem to have reached an advanced
stage of life even as the universe was in its
infancy.
"They're already kind of dying," said Will Hartley, a Ph.D. student at the University
of Nottingham in the U.K. who led the team that discovered them. "They've
mostly finished forming stars."
Hartley will discuss
his findings at the Royal Astronomical Society's National Astronomy Meeting in
Belfast on today.
Quick work
The galaxies give away
their elderly and inactive status by their reddish color, indicative of old
stars. The astronomers saw them as they were 4 billion years after the Big
Bang.
"It is a puzzle and a challenge for us to explain how
these galaxies formed their stars so quickly that they are already dead
galaxies when we observe them," Hartley told SPACE.com.
The scientists think
the objects must have been among the very first galaxies born in our universe.
They would have formed from the few clumps of higher density stuff in the
mostly smooth spread of matter at the time. Therefore, they were more massive
than the average galaxies that formed later, so they probably remain as some of
the largest galaxies around today.
Another group of
scientists, led by Scott Chapman of the Institute of Astronomy in Cambridge,
U.K., discovered galaxies likely undergoing tremendous bouts of star
formation.
"Here we've maybe
discovered a population of galaxies that is very, very vigorously forming
stars, but maybe for a short period of time," said Frank Bertoldi, an
astronomer at the University of Bonn in Germany who worked on the study.
The scientists think these galaxies form stars at more
moderate rates most of the time, but happen to be in a rare period of extreme
star creation.
"Maybe only
ten percent of their lives are they in such a state of high star
formation," Bertoldi said.
Collisions to blame
These bouts of extreme
star production are likely triggered by collisions
with other galaxies that stir up the galaxies' gas. Galaxies collided more
often at this early stage because the universe was smaller, so they were more
crowded together. More recently, the universe has been expanding, space is
getting emptier and collisions happen less frequently.
The astronomers saw
these prolific galaxies as they were 3 billion years after the Big Bang,
offering a view of the early epochs of star formation in the universe.
These galaxies had been
missed by previous searches for similar galaxies that favored the discovery of
slightly colder galaxies.
"This is one class of objects, a particular phase in
evolution, that has been missed so far," Bertoldi said. "We hadn't
discovered them because we had a bias in our selection."
The scientists hope to find more galaxies like these to better
understand the dynamics of rapid star formation in the early universe.
Chapman will also present the group's findings today at the National Astronomy Meeting.
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