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Galactic bull's-eye came naturally

A strange cosmic object isn't the result of a galactic crash

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2:34pm, August 24, 2011
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A galactic oddball may have spun itself into its strange bull’s-eye shape, report astronomers probing the origins of Hoag’s Object.

The galaxy, made up of a golden sphere of stars in the middle of a much bigger star-studded hula hoop, had once been thought to have formed as the result of a cosmic smashup.

Now, using both ground- and space-based observations, Israeli and Russian astronomers propose that the object formed that way on its own. The golden core formed first, at least 10 billion years ago. Soon after, the core skirted itself with a disk of hydrogen gas that it pulled from surrounding material. The disk’s spiral pattern could be caused by rotation of the core, if the central cluster isn’t quite spherical.

That setup would also explain the ongoing star formation that dots the ring with young, massive stars, the team reports in an upcoming Monthly Notices of the Royal Astronomical Society.

When Arthur Hoag first discovered the object in 1950, he thought the ring was the image of a distant galaxy smeared into a circular halo of light by the gravity of the dense central orb. Not until 1987 did researchers confirm that the orb and ring were actually part of the same galaxy. Theories about why Hoag’s Object looks so weird have ranged since then from a transient evolutionary phase to a galactic collision or near miss, but none has wholly satisfied.

The object could be a good test bed for understanding how important gas-snatching is in already formed galaxies, the researchers say.

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