Do you ever wake up grumpy? No, I usually just let him sleep.
That classic joke is good advice for humans and now it looks like it’s a good policy for stars as well. For the first time ever, astronomers report seeing a dormant black hole wake up and consume a passing star, ripping it apart and belching out photons like your dad with a thick, juicy steak at the first barbecue of the year.
Black hole eating contests like these are technically known as “tidal disruption events” and this particular one was detected by NASA’s Swift satellite in March 2011, earning it the name Swift J1644+57. Dormant black holes, although they make up 90 percent of all black holes, are rarely seen because – you guessed it - they’re dormant. Fortunately, Swift’s detection of this activated surveillance by two other satellites: the ESA’s XMM-Newton satellite and the Japanese Aerospace Exploration Agency and NASA's Suzaku satellite.
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.
Erin Kara, a Hubble Postdoctoral Fellow in astronomy at the University of Maryland and the Joint Space-Science Institute and lead author of a study on Swift J1644+57 published this week in the journal Nature, says the key to viewing this tidal disruption events was the use of a new technique called x-ray reverberation mapping which allows analysis of delays in the x-rays spewed while the black hole consumed a star, thus indicating the event’s occurrence and the star’s demise.
The star’s death by black hole consumption created an accretion disk of particles around the black hole which reflected and amplified the X-ray emissions. This differs from previous theories that the black hole itself created the huge X-ray beams and this new information will help astronomers detect more total disruption events as they occur.
Although dormant black holes make up 90 percent of the black hole population, little is known about them, making Swift J1644+57 even more important, says study co-author Chris Reynolds.
If we only look at active black holes, we might be getting a strongly biased sample.
Based on what we now know, it’s beneficial to study one but it’s not a good idea to wake up dormant.