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HubbleSite Arrested Development: Hubble Finds Relic Galaxy Close to Home

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Space Telescope Science



The adventuring cinema archeologist Indiana Jones would be delighted to find a long-sought relic in his own backyard. Astronomers have gotten lucky enough to achieve such a quest. They identified a very rare and odd assemblage of stars that has remained essentially unchanged for the past 10 billion years. The diffuse stellar island provides valuable new insights into the origin and evolution of galaxies billions of years ago.

As far as galaxy evolution goes, this object is clearly a case of “arrested development.” The galaxy, NGC 1277, started its life with a bang long ago, ferociously churning out stars 1,000 times faster than seen in our own Milky Way today. But it abruptly went quiescent as the baby boomer stars aged and grew ever redder. Though Hubble has seen such “red and dead” galaxies in the early universe, one has never been conclusively found nearby. Where the early galaxies are so distant, they are just red dots in Hubble deep-sky images. NGC 1277 offers a unique opportunity to see one up close and personal.

The telltale sign of the galaxy’s state lies in the ancient globular clusters that swarm around it. Massive galaxies tend to have both metal-poor (appearing blue) and metal-rich (appearing red) globular clusters. The red clusters are believed to form as the galaxy forms, while the blue clusters are later brought in as smaller satellites are swallowed by the central galaxy. However, NGC 1277 is almost entirely lacking in blue globular clusters. The red clusters are the strongest evidence that the galaxy went out of the star-making business long ago. However, the lack of blue clusters suggests that NGC 1277 never grew further by gobbling up surrounding galaxies.

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