Hubble photographs stellar trail of runaway black hole

This archival image from the NASA/ESA Hubble Space Telescope captures a curious linear feature that is so unusual it was first dismissed as an imaging artifact from Hubble’s cameras. But follow-up spectroscopic observations reveal it is a 200 000-light-year-long chain of young blue stars. A supermassive black hole lies at the tip of the bridge at lower left. The black hole was ejected from the galaxy at upper right. It compressed gas in its wake to leave a long trail of young blue stars. Nothing like this has ever been seen before in the Universe. This unusual event happened when the Universe was approximately half its current age.

This intergalactic skyrocket is likely the result of multiple collisions of supermassive black holes. Astronomers suspect the first two galaxies merged perhaps 50 million years ago. That brought together two supermassive black holes at their centers. They whirled around each other as a binary black hole. When the single black hole took off in one direction, the binary black holes shot off in the opposite direction. There is a feature seen on the opposite side of the host galaxy that might be the runaway binary black hole. Circumstantial evidence for this is that there is no sign of an active black hole remaining at the galaxy’s core. The next step is to do follow-up observations with the NASA/ESA/CSA James Webb Space Telescope and NASA’s Chandra X-ray Observatory to confirm the black hole explanation.

These results are featured in the paper published on 6 April 2023 in the Astrophysical Journal Letters.

[Image description: This image shows a wide field of galaxies and stars against a black background. A callout box is used to highlight a specific linear feature that appears as a streak of small blue stars.]