Rare 'Star-Making
Machine' Found In Distant Universe
(10 July 2008) Astronomers have
uncovered an extreme stellar machine -- a galaxy in the very remote universe
pumping out stars at a surprising rate of up to 4,000 per
year.
In comparison, our own Milky Way galaxy turns out an
average of just 10 stars per year.
The discovery, made possible by
several telescopes including NASA's Spitzer Space Telescope, goes against the
most common theory of galaxy formation. According to the theory, called the
Hierarchical Model, galaxies slowly bulk up their stars over time by absorbing
tiny pieces of galaxies -- and not in one big burst as observed in the
new-found "Baby Boom" galaxy.
"This galaxy is undergoing a major baby
boom, producing most of its stars all at once," said Peter Capak of NASA's
Spitzer Science Center at the California Institute of Technology, Pasadena. "If
our human population was produced in a similar boom, then almost all of the
people alive today would be the same age." Capak is lead author of a new report
detailing the discovery in the July 10th issue of Astrophysical Journal
Letters.
The Baby Boom galaxy, which belongs to a class of galaxies
called starbursts, is the new record holder for the brightest starburst galaxy
in the very distant universe, with brightness being a measure of its extreme
star-formation rate. It was discovered and characterised using a suite of
telescopes operating at different wavelengths. NASA's Hubble Space Telescope
and Japan's Subaru Telescope, atop Mauna Kea in Hawaii, first spotted the
galaxy in visible-light images, where it appeared as an inconspicuous smudge
due to is great distance.
It wasn't until Spitzer and the James Clerk
Maxwell Telescope, also on Mauna Kea in Hawaii, observed the galaxy at infrared
and submillimetre wavelengths, respectively, that the galaxy stood out as the
brightest of the bunch. This is because it has a huge number of youthful stars.
When stars are born, they shine with a lot of ultraviolet light and produce a
lot of dust. The dust absorbs the ultraviolet light but, like a car sitting in
the sun, it warms up and re-emits light at infrared and submillimetre
wavelengths, making the galaxy unusually bright to Spitzer and the James Clerk
Maxwell Telescope.
To learn more about this galaxy's unique youthful
glow, Capak and his team followed up with a number of telescopes. They used
optical measurements from Keck to determine the exact distance to the galaxy --
a whopping 12.3 billion light-years. That's looking back to a time when the
universe was 1.3 billion years old (the universe is approximately 13.7 billion
years old today).
"If the universe was a human reaching retirement age,
it would have been about 6 years old at the time we are seeing this galaxy,"
said Capak.
The astronomers made measurements at radio wavelengths with
the National Science Foundation's Very Large Array in New Mexico. Together with
Spitzer and James Clerk Maxwell data, these observations allowed the
astronomers to calculate a star-forming rate of about 1,000 to 4,000 stars per
year. At that rate, the galaxy needs only 50 million years, not very long on
cosmic timescales, to grow into a galaxy equivalent to the most massive ones we
see today.
While galaxies in our nearby universe can produce stars at
similarly high rates, the farthest one known before now was about 11.7 billion
light-years away, or a time when the universe was 1.9 billion years
old.
"Before now, we had only seen galaxies form stars like this in the
teenaged universe, but this galaxy is forming when the universe was only a
child," said Capak. "The question now is whether the majority of the very most
massive galaxies form very early in the universe like the Baby Boom galaxy, or
whether this is an exceptional case. Answering this question will help us
determine to what degree the Hierarchical Model of galaxy formation still holds
true."
"The incredible star-formation activity we have observed suggests
that we may be witnessing, for the first time, the formation of one of the most
massive elliptical galaxies in the universe," said co-author Nick Scoville of
Caltech, the principal investigator of the Cosmic Evolution Survey, also known
as Cosmos. The Cosmos program is an extensive survey of a large patch of
distant galaxies across the full spectrum of light.
"The immediate
identification of this galaxy with its extraordinary properties would not have
been possible without the full range of observations in this survey," said
Scoville.
NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages
the Spitzer Space Telescope mission for NASA's Science Mission Directorate,
Washington. Science operations are conducted at the Spitzer Science Center at
the California Institute of Technology, also in Pasadena. Caltech manages JPL
for NASA.
(source: NASA Jet Propulsion Laboratory)
