A Tour of RGG 118

Narrator (April Hobart, CXC): Oxymorons are often thought of as gaffes in language, but a new black hole discovery shows they can also represent important scientific advances. Astronomers using NASA's Chandra X-ray Observatory and the 6.5-meter Clay Telescope in Chile have identified the smallest giant black hole known. This oxymoronic object could provide clues to how much larger black holes formed along with their host galaxies billion of years in the past.

Astronomers estimate this supermassive black hole is about 50,000 times the mass of the Sun. This is less than half the previous lowest mass for a black hole at the center of a galaxy. The tiny heavyweight black hole is located at the center of a dwarf disk galaxy, called RGG 118, about 340 million light years from Earth.

Researchers estimated the mass of the black hole by studying the motion of cool gas near the center of the galaxy using visible light data from the Clay Telescope. They used the Chandra data to figure out the brightness in X-rays of hot gas swirling toward the black hole. They found that the outward push of radiation pressure of this hot gas is about 1% of the black hole's inward pull of gravity. This matches the properties of other supermassive black holes.

The black hole in RGG 118 is nearly 100 times less massive than the supermassive black hole found in the center of the Milky Way. It is also about 200,000 times less massive than the heaviest black holes found in the centers of other galaxies.

Researchers will keep looking for other supermassive black holes that are comparable in size or even smaller than the one in RGG 118. It is important to gather a large sample because black holes of this size might be seeds that lead to the formation of much larger supermassive black holes.