The earliest known galaxy merger occurred shortly after the Big Bang

The earliest known galaxy smashup happened less than a billion years after the Big Bang, a study affirms.

Mergers have helped build galaxies up from smaller clumps of stars to the elegant spirals seen in the modern universe. Our own Milky Way galaxy has eaten some of its smaller neighbors (SN: 11/24/18, p. 8), and is expected to collide with the giant Andromeda galaxy in some 4 billion years (SN: 7/14/12, p. 10).

Astronomers didn’t know when these galaxy pileups started — until a team spotted galaxy B14-65666, nearly 13 billion light-years away. Images taken with the Hubble Space Telescope showed that the galaxy’s stars cluster in two distinct blobs, astronomer Rebecca Bowler of the University of Oxford and colleagues reported in 2016. The lobed shape suggested that the galaxy, one of the earliest ever observed, was actually two galaxies mid-merge.

That assessment was supported by recent observations with the Atacama Large Millimeter/submillimeter Array in Chile, which showed the object’s gas split into two blobs that overlap with the stars’ clumps. The new data also revealed that the blobs were moving at different speeds with respect to each other, another hint they were merging galaxies, Takuya Hashimoto of Waseda University in Tokyo and colleagues report June 17 in Publications of the Astronomical Society of Japan.

The team concludes that B14-65666 is a pair of galaxies that were merging by about 760 million years after the Big Bang, if not earlier, triggering a burst of star formation. The galaxies’ combined gas was making the equivalent of about 200 solar-mass stars per year, more than 100 times as many stars as the Milky Way currently makes, the researchers estimate.

“Although this galaxy is a fascinating window into how galaxies form in the early universe, it is only one object,” Bowler says. “More work is needed to understand if all galaxies like B14-65666 are mergers in the early universe, or whether it is an unusual monster.”