Violent Galactic Clash May Solve Cosmic Mystery

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The mother of all cosmic collisions has been spotted between two galaxies containing a total of 400 billion stars, igniting the birth of 2,000 new stars per year!

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This incredible event was first spotted by the recently-retired Hershel infrared space observatory, a mission managed by the European Space Agency with significant NASA participation. Follow-up observations by NASA’s Hubble and Chandra space telescopes, plus ground-based telescopes such as the Keck Observatory, confirmed that this was one epic intergalactic smash-up.

But this isn’t just morbid fascination with a beautiful galactic train wreck some 11 billion light-years away, these observations may help us understand a cosmic mystery that has been hanging over astronomy for some time.

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By looking deep into the furthest most reaches of the universe, we look back further and further in time. As this galactic merger — called HXMM01 — is located 11 billion light-years away, we are actually witnessing an event that occurred when the universe was just 3 billion years old. It is well known that at this epoch of universal evolution that the universe contained large, red elliptical galaxies populated with old stars. Were these large galaxies slowly built via the merger of lots of small galaxies, or through rapid clashes of large galaxies?

With the help of HXMM01, it appears the latter may be true.

“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, Irvine, lead author of the study 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. “Without Herschel’s far-infrared detectors, we wouldn’t have been able to see through the dust to the action taking place behind.”

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Indeed, mergers were common in the early history of the cosmos, but what sets HXMM01 apart is the huge quantity of dust contained within the colliding galaxies, the rapid star formation and the sheer size of the two galaxies colliding. Comparing HXMM01′s star formation rate with our galaxy’s star formation rate of only 2-3 newborn stars per year, 2,000 stars per year makes this merger a veritable stellar breeding ground!

Until now, the popular “slow and small” galactic merger model has been favored, but as this example shows, it may be the “violent, fast and huge” galactic merger model that dominated large elliptical galaxy evolution 11 billion years ago.

Image: Herschel observation (right) plus composite image (right). In the composite image, red data are from the Smithsonian Astrophysical Observatory’s Submillimeter Array atop Mauna Kea, Hawaii, and show dust-enshrouded regions of star formation. The green data, taken by the National Radio Astronomy Observatory’s Very Large Array, near Socorro, N.M., show carbon monoxide gas in the galaxies. In addition, the blue shows starlight. The blue blobs outside of the circle are galaxies located much closer to us. These near-infrared light observations are from NASA’s Hubble Space Telescope and the W.M. Keck Observatory atop Mauna Kea, Hawaii. Credit: ESA/NASA/JPL-Caltech/UC Irvine/STScI/Keck/NRAO/SAO