Major Findings

  1. Astronomers have observed a tidal disruption event of a black hole consuming a star.
  2. X-ray reverberation is a promising new technique to map the features of black holes.

A View into a Dormant Black Hole

Black holes are often dormant, providing no way to observe any light around them. Sometimes, however, a tidal disruption can set off a black hole to devour nearby stars, giving astronomers a cryptic light show. Researchers from the University of Maryland and University of Michigan observed X-ray radiation in the accretion disk of the black hole. These bursts of visibility give researchers an insight into the 90% of black holes that are dormant.

The discovery used old high-energy X-ray data on Swift J1644+57. Using a method known as X-ray reverberation, researchers were able to map the structure of the black hole’s accretion disk. The process is similar to echo-location. By measuring the delay in X-ray signals, the size, shape, and characteristics of the black hole and its accretion disk were deduced.

“We know how sound echoes in a large auditorium, for example. Because we know the speed of sound, we can use the time delay information to calculate the shape of the auditorium. We are doing the same with X-ray radiation to map out the inner accretion disk.”

Erin Kara, a Hubble Postdoctoral Fellow in astronomy at UMD and the Joint Space-Science Institute and lead author on the study

They concluded that when a star got too close to the center, the black hole rose from its slumber, ripping the star to pieces. The remains now sit in the puffy cloud of the accretion disk. “Most tidal disruption events don’t emit much in the high-energy X-ray band. But there have been at least three known events that have, and this is the first and only such event that has been caught at its peak,” said Kara.

Images from Swift's Ultraviolet/Optical (white, purple) and X-Ray telescopes (yellow and red) were combined in this composite of Swift J1644+57, an X-ray outburst astronomers classify as a tidal disruption event. PHOTO: NASA/SWIFT/STEFAN IMMLER

X-ray reverberation is a relatively new technique, developed in the last six years. It has the potential to uncover the fundamental principles of black holes. The next step for researchers is to continue to monitor tidal disruption events, with a hope of calculating a black hole’s rotation rate.

This view into the peak of a tidal disruption event is the first of its kind. It gives researchers an unprecedented view into a broader black hole population. Since black holes are at the center of galaxies, their study can lead to a better understanding on the evolution of galaxies.

This study was published online in the journal Nature on June 22nd.

Statement from authors and associated researchers.