Astronomers spot 3,000 light-year 'light echo' of dying supermassive black hole

At the dark hearts of galaxies like the Milky Way lie supermassive black holes, with millions or even billions of times the sun's mass.

Some of those supermassive black holes are what scientists call active galactic nuclei (AGN), which spew out copious amounts of radiation like X-rays and radio waves. AGN are responsible for the twin jets of ionized gas you see shooting away in pictures of many galaxies.

As all things must pass, so too must every AGN one day shut off. But scientists have never quite understood how or when that happens. Now, researchers led by Kohei Ichikawa, an astronomer at Tohoku University in Sendai, Japan, may have found a clue. Looking at the distant galaxy Arp 187, those researchers have seen what they think is an AGN in its very last days.