Astronomers detect the merging of two massive galaxies

23 May 2013

Astronomers spot the merging of two galaxies. The image on the rights depicts a close-up view, with the merging galaxies circled. Image via ESA/NASA/JPL-Caltech/UC Irvine/STScI/Keck/NRAO/SAO

Scientists have pinpointed the merging of two galaxies when the universe was just 3bn years old using images taken from the European Space Agency’s Herschel space observatory.

The universe’s current age is about 14bn years old. According to NASA, these two colliding galaxies will eventually form one super-giant elliptical galaxy.

Dubbed HXMM01 and located around 11bn light years from Earth, the two galaxies are collectively producing stars at a rate of about 2,000 suns a year. Our own Milky Way, in contrast, churns out about two or three suns a year.

The total number of stars in both galaxies equals about 400bn suns. The galaxies are linked by bridge of gas, indicating that they are merging, the European Space Agency (ESA) said.

To detect the two galaxies, scientists used images from the Herschel space observatory, which recently finished three years of universe observations.

Follow-up observations were performed using several telescopes on the ground and in space, including the Keck Observatory and the Submillimeter Array at Mauna Kea in Hawaii and the Hubble space telescope.

A study describing the findings from these observations has been published in Nature this week.

“This monster system of interacting galaxies is the most efficient star-forming factory ever found in the universe at a time when it was only 3bn years old,” said Hai Fu from University of California, Irvine, who led the Nature study.

Fu’s team predict it will take about 200m years to convert all the gas into stars, with the merging of the two galaxies set to be completed within a billion years.

“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 Fu.

Seb Oliver, an astrophysics professor at University of Sussex who was involved in the research, said the scientists were very lucky to spot this extreme system in such a critical transitional phase.

“It shows that the merger of gas-rich and actively star-forming galaxies is a possible mechanism to form the most massive ellipticals that are observed in the young universe,” he said.

Carmel Doyle was a long-time reporter with Silicon Republic