Black holes have voracious appetites, consuming all that comes too close, but researchers have discovered each eating session leaves an "echo" as proof of what had transpired.
Passing stars that get too close to black holes end up stretching and compressing as they are swallowed by an immense gravitational force. Called stellar tidal disruption, the process of black holes destroying stars leads to a release of massive energy that brightens the surrounding, an event known as a flare.
Dozens of these flares were observed in recent years but researchers did not know a lot about them. Now, with the help of the Wide-field Infrared Survey Explorer (WISE) from NASA, two studies published in The Astrophysical Journal and The Astrophysical Journal Letters are offering insight into these flares after analyzing how dust around a black hole absorbs and then re-releases light, like light echoes.
According to Sjoert van Velzen, lead author for one of the studies, this is the first time infrared light echoes arising from several tidal disruption events have been clearly seen.
Van Velzen and colleagues' study actually looked at five potential tidal disruption events but only observed the light echoes in three. The other study, led by Ning Jiang, on the other hand, saw one.
Tidal disruption events feature so much radiation, emitting the likes of X-ray and ultraviolet light, that they destroy all dust hanging around close enough to black holes. However, some dust do survive as radiation levels drop after a certain distance.
But once surviving dust gets heat up by a flare, it emits infrared, an emission that the WISE instrument can measure. WISE's measurements not only provide information on the flare but the dust as well, highlighting the delay between the primary flare and the resulting light echo. This then helps in estimating the dust location around a black hole at a galaxy center.
According to Van Velzen's co-author Varoujan Gorjian, the results of their work can be used to determine the level of energy released when a star was destroyed.
Infrared emissions from flare-heated dust leaves signals that are detectable for one year after a flare reaches its peak brightness. The results presented by the researchers are consistent with a dust web found some trillions of miles away from a black hole.
To put it simply, Van Velzen equates the phenomenon to a black hole consuming dust around it to cleaning its room with flames.
WISE is operated and managed by the NASA Jet Propulsion Laboratory for the agency's Science Mission Directorate. It is tasked with mapping the entirety of the sky every half year as part of its mission to aid NASA in identifying near-Earth objects that may be potentially dangerous to the planet.
