Hubble Gallery of Ultra-Bright Galaxies
Boosted
by natural magnifying lenses in space, NASA's Hubble Space Telescope
has captured unique close-up views of the universe's brightest infrared
galaxies, which are as much as 10,000 times more luminous than our Milky
Way.
The galaxy images, magnified through a phenomenon called
gravitational lensing, reveal a tangled web of misshapen objects
punctuated by exotic patterns such as rings and arcs. The odd shapes are
due largely to the foreground lensing galaxies' powerful gravity
distorting the images of the background galaxies. The unusual forms also
may have been produced by spectacular collisions between distant,
massive galaxies in a sort of cosmic demolition derby.
"We have hit the jackpot of gravitational lenses," said lead
researcher James Lowenthal of Smith College in Northampton,
Massachusetts. "These ultra-luminous, massive, starburst galaxies are
very rare. Gravitational lensing magnifies them so that you can see
small details that otherwise are unimaginable. We can see features as
small as about 100 light-years or less across. We want to understand
what's powering these monsters, and gravitational lensing allows us to
study them in greater detail."
The galaxies are ablaze with runaway star formation, pumping out more
than 10,000 new stars a year. This unusually rapid star birth is
occurring at the peak of the universe's star-making boom more than 8
billion years ago. The star-birth frenzy creates lots of dust, which
enshrouds the galaxies, making them too faint to detect in visible
light. But they glow fiercely in infrared light, shining with the
brilliance of 10 trillion to 100 trillion suns.
Gravitational lenses occur when the intense gravity of a massive
galaxy or cluster of galaxies magnifies the light of fainter, more
distant background sources. Previous observations of the galaxies,
discovered in far-infrared light by ground- and space-based
observatories, had hinted of gravitational lensing. But Hubble's keen
vision confirmed the researchers' suspicion.
Lowenthal is presenting his results at 3:15 p.m. (EDT), June 6, at the American Astronomical Society meeting in Austin, Texas.
According to the research team, only a few dozen of these bright
infrared galaxies exist in the universe, scattered across the sky. They
reside in unusually dense regions of space that somehow triggered rapid
star formation in the early universe.
The galaxies may hold clues to how galaxies formed billions of years
ago. "There are so many unknowns about star and galaxy formation,"
Lowenthal explained. "We need to understand the extreme cases, such as
these galaxies, as well as the average cases, like our Milky Way, in
order to have a complete story about how galaxy and star formation
happen."
In studying these strange galaxies, astronomers first must detangle
the foreground lensing galaxies from the background ultra-bright
galaxies. Seeing this effect is like looking at objects at the bottom of
a swimming pool. The water distorts your view, just as the lensing
galaxies' gravity stretches the shapes of the distant galaxies. "We need
to understand the nature and scale of those lensing effects to
interpret properly what we're seeing in the distant, early universe,"
Lowenthal said. "This applies not only to these brightest infrared
galaxies, but probably to most or maybe even all distant galaxies."
Lowenthal's team is halfway through its Hubble survey of 22 galaxies.
An international team of astronomers first discovered the galaxies in
far-infrared light using survey data from the European Space Agency's
(ESA) Planck space observatory, and some clever sleuthing. The team then
compared those sources to galaxies found in ESA's Herschel Space
Observatory's catalog of far-infrared objects and to ground-based radio
data taken by the Very Large Array in New Mexico. The researchers next
used the Large Millimeter Telescope (LMT) in Mexico to measure their
exact distances from Earth. The LMT's far-infrared images also revealed
multiple objects, hinting that the galaxies were being gravitationally
lensed.
These bright objects existed between 8 billion and 11.5 billion years
ago, when the universe was making stars more vigorously than it is
today. The galaxies' star-birth production is 5,000 to 10,000 times
higher than that of our Milky Way. However, the ultra-bright galaxies
are pumping out stars using only the same amount of gas contained in the
Milky Way.
So, the nagging question is, what is powering the prodigious star
birth? "We've known for two decades that some of the most luminous
galaxies in the universe are very dusty and massive, and they're
undergoing bursts of star formation," Lowenthal said. "But they've been
very hard to study because the dust makes them practically impossible to
observe in visible light. They're also very rare: they don't appear in
any of Hubble's deep-field surveys. They are in random parts of the sky
that nobody's looked at before in detail. That's why finding that they
are gravitationally lensed is so important."
These galaxies may be the brighter, more distant cousins of the
ultra-luminous infrared galaxies (ULIRGS), hefty, dust-cocooned,
starburst galaxies, seen in the nearby universe. The ULIRGS' star-making
output is stoked by the merger of two spiral galaxies, which is one
possibility for the stellar baby boom in their more-distant relatives.
However, Lowenthal said that computer simulations of the birth and
growth of galaxies show that major mergers occur at a later epoch than
the one in which these galaxies are seen.
Another idea for the star-making surge is that lots of gas, the
material that makes stars, is flooding into the faraway galaxies. "The
early universe was denser, so maybe gas is raining down on the galaxies,
or they are fed by some sort of channel or conduit, which we have not
figured out yet," Lowenthal said. "This is what theoreticians struggle
with: How do you get all the gas into a galaxy fast enough to make it
happen?"
The research team plans to use Hubble and the Gemini Observatory in
Hawaii to try to distinguish between the foreground and background
galaxies so they can begin to analyze the details of the brilliant
monster galaxies.
Future telescopes, such as NASA's James Webb Space Telescope, an
infrared observatory scheduled to launch in 2018, will measure the speed
of the galaxies' stars so that astronomers can calculate the mass of
these ultra-luminous objects.
"The sky is covered with all kinds of galaxies, including those that
shine in far-infrared light," Lowenthal said. "What we're seeing here is
the tip of the iceberg: the very brightest of all."
The Hubble Space Telescope is a project of international cooperation
between NASA and ESA (European Space Agency). NASA's Goddard Space
Flight Center in Greenbelt, Maryland, manages the telescope. The Space
Telescope Science Institute (STScI) in Baltimore conducts Hubble science
operations. STScI is operated for NASA by the Association of
Universities for Research in Astronomy, Inc., in Washington, D.C.
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Contacts
Donna Weaver / Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
410-338-4493 / 410-338-4514
dweaver@stsci.edu / villard@stsci.edu
James Lowenthal
Smith College, Northampton, Massachusetts
413-585-6995
jlowenth@smith.edu
Source: HubbleSite/News
