This illustration of a black hole, surrounded by X-ray emitting gas, showcases one of the major ways black holes are identified and found. Based on recent research, there may be as many as 100 million black holes in the Milky Way galaxy alone. Image credit: ESA.

Milky Way Houses Up To 100 Million Black Holes, With Big Implications For LIGO

That number is far bigger than anyone expected, but physics doesn’t lie.

“Our first priority was making sure we weren’t fooling ourselves.”
-Keith Riles, LIGO team member

How many black holes are there in the Milky Way? This straightforward question has proven extremely difficult to answer, since black holes are so difficult to directly detect. However, scientists not only have developed indirect methods for locating and even weighing them, we also understand how the Universe forms them: from stars and stellar remnants. If we can understand the different stars that existed at all different times in our galaxy’s history, we should be able to infer exactly how many black holes — and of what mass — exist in our galaxy today. Thanks to a comprehensive study by a trio of researchers from UC Irvine, the first accurate estimates of the number of black holes found in Milky Way-like galaxy have now been made. Not only is our galaxy filled with hundreds of billions of stars, but we also are home to up to 100 million black holes.

Black holes themselves are not visible, but emissions in the radio and X-ray from matter outside of them can clue us into their locations and physical properties. Image credit: J. Wise/Georgia Institute of Technology and J. Regan/Dublin City University.