Herschel Space Observatory Finds Mega Merger of Galaxies

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May 22, 2013

J.D. Harrington 
Headquarters, Washington 
202-358-5241 
j.d.harrington@xxxxxxxx 

Whitney Clavin 
Jet Propulsion Laboratory, Pasadena, Calif. 
818-354-4673 
whitney.clavin@xxxxxxxxxxxx 

RELEASE: 13-151

HERSCHEL SPACE OBSERVATORY FINDS MEGA MERGER OF GALAXIES

WASHINGTON -- 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 duo is 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 
more 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 (JPL) in Pasadena, California, which contributed 
mission-enabling technology for two of Herschel's three science 
instruments. For more information, visit: 

http://www.nasa.gov/herschel 

and 

http://www.esa.int/SPECIALS/Herschel 

	
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