The Calm Before the Storm?

NGC 799 & NGC 800This pair of galaxies, NGC 799 (below) and NGC 800 (above), is located in the constellation of Cetus (The Whale) about 300 million light-years away. Our face-on point of view lets us see these objects are both spiral galaxies with characteristic long arms winding towards a bright bulge at the center.

It may appear that these spiral galaxies are coexisting in an everlasting peace, but that is unlikely. What we see is probably the calm before the storm. Typically, when two galaxies are close enough, they interact over hundreds of millions of years through mutual gravitational attraction. In some cases, only minor interactions occur, causing shape distortions, but sometimes galaxies collide, merging to form a single, new and larger galaxy.

We’ll have to check back in a few hundred million years.

Image Credit: ESO

Black Hole Feedback

The evolution of a galaxy is related to the growth of the supermassive black hole at its center. During the galaxy’s quasar phase, a huge luminosity is released as matter falls onto the black hole, and radiation-driven winds can transfer most of this energy back to the host galaxy. This animation illustrates how black-hole feedback works during that phase. Dense gas and dust in the center simultaneously powers the black hole and hides it from view. The black hole’s radiation wind drives huge outflows of cold gas causing a shock wave that clears gas and dust from the central galaxy.

Video Credit: NASA