NASA's WISE Satellite Observes Flares from Stellar Tidal Disruption Events

Posted on September 19, 2016

When a black hole destroys a star it is known as stellar tidal disruption. The stellar material gets stretched and compressed as it is consumed by the black hole. An enormous amount of energy is also released during these events which brightens the surroundings.

Astronomers have been using new data from NASA's WISE satellite to learn more about these tidal disruption flares. They have studied how surrounding dust absorbs and re-emits their light, like echoes.

Sjoert van Velzen, a postdoctoral fellow at Johns Hopkins University, Baltimore, is lead author of a study finding three such events, to be published in the Astrophysical Journal. Data from a fourth potential light echo based on WISE data was published here in an independent study.

Flares from the tidal disruption destroy any dust that hangs around near the black hole but dust farther away survives the flare's radiation. The surviving dust gives off infrared radiation as it is heated by the flare. WISE measures this infrared emission from the dust. This information gives astronomers clues about tidal disruption flares and the nature of the dust itself.

Astronomers also use a technique called "photo-reverberation" or "light echoes" to characterize the dust. Van Velzen's study looked at five possible tidal disruption events, and saw the light echo effect in three of them. The researchers found that the infrared emission from dust heated by a flare causes an infrared signal that can be detected for up to a year after the flare is at its most luminous. The dust can be located as far away as a few trillion miles (half a light-year) from the black hole itself.

Van Velzen says in a statement, "The black hole has destroyed everything between itself and this dust shell. It's as though the black hole has cleaned its room by throwing flames."

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