The Anomalous X-Ray Arms of the Galaxy Known as NGC 4258

At the heart of galaxy NGC 4258 lies a black hole that's 10 times more massive than the one in our galaxy — and it's blasting gas out of the galactic plane, creating those purple galactic arms that astronomers dub "anomalous" because of their peculiar orientation.

Now, thanks in part to this image, we have a theory about what made those arms arch out of the galactic plane, emitting tons of x-rays. They've been shaped by enormous, galaxy-spanning shockwaves.

Here's what the Chandra X-Ray Observatory has to say about what you're seeing:

The anomalous arms are seen in this new composite image of NGC 4258, where X-rays from NASA's Chandra X-ray Observatory are blue, radio data from the NSF's Karl Jansky Very Large Array are purple, optical data from NASA's Hubble Space Telescope are yellow and blue, and infrared data from NASA's Spitzer Space Telescope are red.

A new study of these anomalous arms made with Spitzer shows that shock waves, similar to sonic booms from supersonic planes, are heating large amounts of gas - equivalent to about 10 million Suns. What is generating these shock waves? Radio data shows that the supermassive black hole at the center of NGC 4258 is producing powerful jets of high-energy particles. Researchers think that these jets strike the disk of the galaxy and generate shock waves. These shock waves, in turn, heat some of the gas - composed mainly of hydrogen molecules - to thousands of degrees. As shown in our additional, composite image, part of the evidence for this heating process comes from the similarity in location between the hydrogen and X-ray emission, both thought to be caused by shocks, and the radio jets.

The Chandra X-ray image reveals huge bubbles of hot gas above and below the plane of the galaxy. These bubbles indicate that much of the gas that was originally in the disk of the galaxy has been heated to millions of degrees and ejected into the outer regions by the jets from the black hole.

Here's the x-ray image:

The Anomalous X-Ray Arms of the Galaxy Known as NGC 4258

Possibly because NGC 4258 has such a large black hole, there is far less gas at the galactic core than astronomers expected. As a result, the galaxy is forming at a rate that's "about 10 times less than the Milky Way." If the black hole keeps ejecting gas from its galaxy, astronomers estimate, all the gas will be gone in about 300 million years — which is very fast in cosmic time.

Read more, and see each layer of the composite image above, at the Chandra X-Ray Observatory