Left: Galaxies 12 million light-years away in the constellation Ursa Major. Right: The Hubble Space Telescope shows bright blue star clusters along a wispy bridge of gas stretched between the two galaxies, and a third companion galaxy not seen in this picture. The so-called "blue blobs" are clumped together in a structure called Arp's Loop.
Credit: NASA, ESA, and D. de Mello (Catholic University of America/GSFC)
AUSTIN, Texas — Brilliant blue blobs weighing tens of thousands of solar masses have been found lurking in the seemingly barren expanse of intergalactic space. The "eyes" of the Hubble Space Telescope resolved the objects, which appear to be clusters of stars born in the swirls and eddies of a galactic smashup some 200 million years ago.
The mysterious star clusters are considered orphaned, as they don't belong to any particular galaxy. Instead, they are clumped together into a structure called Arp's Loop along a wispy bridge of gas stretched like taffy between three colliding galaxies — M81, M82 and NGC 3077. These galaxies are located about 12 million light-years from us in the constellation Ursa Major.
"We could not believe it, the stars were in the middle of nowhere," said Duilia de Mello of the Catholic University of America in Washington, D.C., and NASA's Goddard Space Flight Center.
De Mello reported the findings here today at a meeting of the American Astronomical Society.
Astronomers had not considered the gas tendrils thick enough to accumulate enough material needed to build so many stars. But the new images reveal they hold the star-equivalent of five Orion Nebulae.
While more massive than most open clusters housed inside galaxies, the blue blobs are just a fraction of the mass of globular star clusters that orbit a galaxy. The astronomers estimate that many of the clusters' stars are as young as 10 million years and younger. Our sun, for comparison, is 4.6 billion years old.
De Mello and her colleagues suggest galactic collisions and the turbulent aftermaths might have triggered the starbirth. In fact, it was about 200 million years ago that M81 and M82 had their last encounter.
Galaxy collisions like this one, which would enhance locally the density of gas streams, were much more common in the early universe, they say. And so such blue blobs would have been more common as well in the early universe.
Once the clustered stars had burned out or exploded, the heavier elements would have been ejected into intergalactic space. The fact that the blue-blob clusters are not associated with any galaxy means such elements produced during fusion in their nuclear furnaces would be easily expelled.
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