Galaxies are often seen as islands of stars in the vast empty universe, but during their long life, they do in fact interact and merge. And these interactions are key to understanding how galaxies evolve.
An extremely fine example of such a galaxy merger is NGC 5256, an interacting system located 350 million light-years from Earth. The merger, also known as Markarian 266, is between two disk galaxies (not unlike the Milky Way) and in an advanced state. Most of the original shapes of the galaxies are gone, with the two galactic cores now just 13,000 light-years apart.
Hubble has pretty much caught these two galaxies in the most heated moment of the collision, which is also the most interesting time to study these objects. NGC 5256 is undergoing star formation due to the intense gravitational forces that slosh and compress the gas into brand new stars.
The gas moving around has also been feeding the supermassive black holes at the core of each of the two galaxies. These are now classified as active galactic nuclei. The gas, which accumulated around the black hole's accretion disk under extreme gravity, is emitting powerful X-rays that were previously detected by Chandra, NASA’s X-ray observatory.
Although it is advanced, the merging process is far from over, and it will continue for quite some time. Over millions of years, the two cores will continue to orbit each other until their eventual collision. In the meantime, the gas and stars around them will have settled down in a more stable arrangement. NGC 5256 will then be an elliptical galaxy.
The image is also a fantastic hallmark of how much Hubble has improved over the last decade. The first image of NGC 5256 by the space telescope was taken in 2008 with another 58 merging galaxies to celebrate Hubble’s 18th birthday. Just a year later, Hubble received an important upgrade with the installation of the Wide-Field Camera 3, which significantly expanded the capabilities of the telescope. It can now see further into infrared wavelengths, hence the highlighted appearance of the tendrils of gas thrown around by the galaxy.
Hubble’s successor, the James Webb Space Telescope, will be even better equipped to look at the gas of galaxies. Its keener eye will also be able to snap detailed images of mergers even further away.