Giant galaxy hides its secrets

Galaxy NGC 4696

A supermassive black hole beats at the heart of huge elliptical galaxy NGC 4696.

This picture, taken by Hubble’s Advanced Camera for Surveys, shows NGC 4696, the largest galaxy in the Centaurus Cluster (also known as galaxy cluster Abell 3526).

NGC 4696 is an elliptical-shaped galaxy with a difference. Lacking the complex structure and active star formation of their spiral galaxy cousins, elliptical galaxies are usually little more than shapeless, albeit huge, collections of ageing stars.

Most likely formed by collisions between spiral galaxies, elliptical galaxies experience a brief burst of star formation triggered as interstellar dust and gas clouds crash into each other.

But this burst of star formation activity quickly leaves young elliptical galaxies exhausted. With no more gas to form new stars from, the galaxies grow older and fainter.

But NGC 4696 is more interesting than most elliptical galaxies.

A huge dust lane, around 30,000 light-years across, sweeping 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 gas are visible within it.

Looking at NGC 4696 at 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 to “clear out” large volumes of space of their gas and dust.

Adapted from information issued by ESA / Hubble and NASA.

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