Closer than ever: a big flash reveals a black hole devouring a star

Astronomers at MIT and elsewhere have observed infrared signs of the closest tidal disruption event (TDE) to date. A bright flare was detected from the galaxy NGC 7392 in 2015 (top left panel). Observations of the same galaxy were taken in 2010-2011 (top right), prior to the TDE. The bottom left shows the difference between the first two images, representing the actual, detected TDE. For comparison, the bottom right panel shows the same galaxy in the optical waveband. Credit: MIT

With the closest proximity to date, astronomers captured the rarely seen moment when a supermassive black hole first ripped apart and then swallowed a star in the galaxy NGC 7392, located 137 million light-years from Earth.

This is the first event of its kind captured with unconventional light. Instead of optical or X-ray radiation, the event, dubbed WTP14adbjsh, was seen as a bright infrared flare. The discovery suggests that there could be tidal disruption events (TDEs) that we are missing simply because we are looking in the wrong part of the electromagnetic spectrum.

The scientists found WTP14adbjsh, which was not detected by any of the telescopes set up to view the optical and X-ray flares, in data collected in 2014 and 2015 by the Neowise Space Infrared Telescope. turned on and off exactly matched the evolution of a TDE around a supermassive black hole about 30 million times the mass of the Sun.

Another important aspect is that most of the TDEs detected to date were found in a relatively rare type of galaxies, the oldest and most static ones, which do not have much gas or dust in the space between the stars. The WTP14adbjsh might explain why this is so. Star-forming galaxies have a lot of dust that obscures their centers. X-rays and optical light could not penetrate this dust. But infrared light, with its longer wavelengths, does not scatter in dust particles the way shorter wavelengths do, and can pass through them unimpeded. So it’s not that TDEs prefer galaxies that don’t have dust, but that they didn’t look for them in dusty galaxies with the right tools. This means that there could be a whole new universe of dismembered stars in infrared light.

Journal Reference:

  1. Christos Panagiotou, Kishalay De, et al. A Luminous Dust-obscured Tidal Disruption Event Candidate in a Star-forming Galaxy at 42 Mpc. The Astrophysical Journal Letters. DOI 10.3847/2041-8213/acc02f