This simulation shows the merging of two massive galaxies, sped up to
cover 1.5 billion years of time. The merging galaxies are split into two
views: a visible-light view is on the left, in which blue shows young
stars and red indicates older stars and dust. The view at right shows
emission from dust, which is what infrared telescopes like the Herschel
Space Observatory see. When the galaxies finally merge, the strong burst
of star formation can be seen best in infrared views.
Several telescopes have teamed up to discover a rare and massive merging
of two galaxies that took place when the universe was just 3 billion
years old (its current age is about 14 billion years). Image credit:
ESA/NASA/JPL-Caltech/UC Irvine/STScI/Keck/NRAO/SAO
› Full image and caption
› Full image and caption
PASADENA, Calif. - A massive and rare merging of two galaxies has been
spotted in images taken by the Herschel space observatory, a European
Space Agency mission with important NASA participation.
Follow-up studies by several telescopes on the ground and in space,
including NASA's Hubble Space Telescope and Spitzer Space Telescope,
tell a tale of two faraway galaxies intertwined and furiously making
stars. Eventually, the duo will settle down to form one super-giant
elliptical galaxy.
The findings help explain a mystery in astronomy. Back when our universe
was 3 billion to 4 billion years old, it was populated with large
reddish elliptical-shaped galaxies made up of old stars. Scientists have
wondered whether those galaxies built up slowly over time through the
acquisitions of smaller galaxies, or formed more rapidly through
powerful collisions between two large galaxies.
The new findings suggest massive mergers are responsible for the giant elliptical galaxies.
"We're looking at a younger phase in the life of these galaxies -- an
adolescent burst of activity that won't last very long," said Hai Fu of
the University of California at Irvine, who is lead author of a new
study describing the results. The study is published in the May 22
online issue of Nature.
"These merging galaxies are bursting with new stars and completely
hidden by dust," said co-author Asantha Cooray, also of the University
of California at Irvine. "Without Herschel's far-infrared detectors, we
wouldn't have been able to see through the dust to the action taking
place behind."
Herschel, which operated for almost four years, was designed to see the
longest-wavelength infrared light. As expected, it recently ran out of
the liquid coolant needed to chill its delicate infrared instruments.
While its mission in space is over, astronomers still are scrutinizing
the data, and further discoveries are expected.
In the new study, Herschel was used to spot the colliding galaxies,
called HXMM01, located about 11 billion light-years from Earth, during a
time when our universe was about 3 billion years old. At first,
astronomers thought the two galaxies were just warped, mirror images of
one galaxy. Such lensed galaxies are fairly common in astronomy and
occur when the gravity from a foreground galaxy bends the light from a
more distant object. After a thorough investigation, the team realized
they were actually looking at a massive galaxy merger.
Follow-up characterization revealed the merging galaxies are churning
out the equivalent of 2,000 stars a year. By comparison, our Milky Way
hatches about two to three stars a year. The total number of stars in
both colliding galaxies averages out to about 400 billion.
Mergers are fairly common in the cosmos, but this particular event is
unusual because of the prolific amounts of gas and star formation, and
the sheer size of the merger at such a distant epoch.
The results go against the more popular model explaining how the biggest
galaxies arise: through minor acquisitions of small galaxies. Instead,
mega smash-ups may be doing the job.
NASA's Herschel Project Office is based at the agency's Jet Propulsion
Laboratory in Pasadena, Calif., which contributed mission-enabling
technology for two of Herschel's three science instruments. JPL is a
division of the California Institute of Technology, Pasadena.
For more information about Herschel,
visit: http://www.nasa.gov/herschel
NASA
Guillermo Gonzalo Sánchez Achutegui
ayabaca@gmail.com
ayabaca@hotmail.com
ayabaca@yahoo.com
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