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Wednesday January 18th 2012

A cosmic question mark

NGC 4696 poses a question

To truly appreciate this picture you have to click to see the larger image. It represents an unusual shaped galaxy never before documented.  The galaxy is curling around itself like a question mark.

This picture was taken by Hubble’s Advanced Camera for Surveys. It is NGC 4696, the largest galaxy in the Centaurus Cluster. NGC 4696 is an elliptical galaxy lacking the complex structure and active star formation of other elliptical galaxies.

Most likely formed by collisions between spiral galaxies, elliptical galaxies experience a brief burst of star formation triggered as the interstellar dust and gas crash into each other, but which quickly leaves the young elliptical galaxies exhausted. With no more gas to form new stars from, the galaxies gradually grow older and fainter.

But NGC 4696 is more interesting than most elliptical galaxies.

The huge dust lane, around 30 000 light-years across, that sweeps across the face of the galaxy is one way in which it looks different from most other elliptical galaxies. Viewed at certain wavelengths, strange thin filaments of ionised hydrogen are visible within it. In this picture, these structures are visible as a subtle marbling effect across the galaxy’s bright centre.

Looking at NGC 4696 in the optical and near-infrared wavelengths seen by Hubble gives a beautiful and dramatic view of the galaxy. But in fact, much of its inner turmoil is still hidden from view in this picture. At the heart of the galaxy, a supermassive black hole is blowing out jets of matter at nearly the speed of light. When looked at in X-ray wavelengths, such as those visible from NASA’s Chandra X-ray Observatory, huge voids within the galaxy become visible, telltale signs of these jets’ enormous power.

The picture was created from images taken using the NASA/ESA Hubble Space Telescope’s Advanced Camera for Surveys.

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