Merging galaxies could explain large elliptical galaxies

Ars Technica : The largest galaxies in the universe are elliptical, rather than spiral like the Milky Way. Although theory and observation can account for the formation of small elliptical galaxies, how the extremely large ones formed is uncertain. A new set of observations may help to resolve the question. The Herschel Multi-tiered Extragalactic Survey detected a very bright object at a distance of 10 billion light years. Further observations revealed that the object consists of a merging pair of so-called submillimeter bright galaxies (SBGs) and that the exceptional brightness is due to intense star formation, on the order of 1600 to 2400 solar masses worth of stars each year. Researchers estimated that the result of the collision would be a giant elliptical galaxy with a star mass equivalent to 400 billion Suns. Given that giant elliptical galaxies in the nearby universe no longer host much star formation, the collision of a pair of SBGs is consistent with the idea of the giant galaxies forming through mergers that trigger a temporary burst of star formation.