Confused Galaxy

For a larger view of this image, embiggen. You can zoom in and take a closer look. Believe me, you’ll want to.

Astronomers recently noticed something incredible behind the elliptical NGC 4696 galaxy. This galaxy lies 150 million light years away in the Centaurus constellation, at the center of the ginormous Centaurus galaxy cluster, a sprawling city of hundreds of galaxies. Astronomers surmise that it was involved in a cataclysmic collision with another galaxy, which must have resulted in its spiral arms being ripped off and most of its interstellar gasses being stripped away, condemning it to a slow death.

Quizzically and astonishingly enough, however, there is a massive swirl of dust behind it that stretches for 30 000 light years and eventually whips back around like a question mark, faintly visible in the above image. It’s very rare for elliptical galaxies to have any dust at all in them. Phil Plait explains the reason for this (along with some additional information beyond the link).

“Clusters of galaxies like this sometimes have one big, fat elliptical sitting in the center. Called the central dominant (or cD*) galaxy, it generally has far more mass than any other galaxy in the cluster and has weird features (like multiple bright cores, an extended halo of stars, and lots and lots of satellite galaxies). We think these galaxies started off relatively normal, but then eat other galaxies that wander too closely — clusters are thick with galaxies, so such encounters are common. The now-heavier galaxy sinks to the center of the cluster through various forces, where it can really let itself go and eat even more galaxies. That explains the multiple cores (undigestible leftovers), their puffy halos (lots of orbital energy can be added to stars in the collision, inflating their paths), and the plenitude of little satellites (again, leftovers from previous galactic meals).”

Observations by the Hubble Space Telescope released today show another first: filaments of ionized, or charged, hydrogen gas branching from the dust swirl. And views in x-ray light reveal super-powerful jets of matter squirting from the galaxy’s central black hole at nearly the speed of light. Together, these features show that NGC 4696 is a galaxy like no other.

It is from these observations, along with its uniquely battered and twisted shape, that has led astronomers to suspect that the filament resulted from some sort of gravitational interaction with another galaxy, possibly a collision.

The above image was the result of a two and a half hour exposure by the Hubble space telescope.

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