Starts With A Bang

Nothing Escapes From A Black Hole, And Now Astronomers Have Proof (Synopsis)

If event horizons are real, then a star falling into a central black hole would simply be devoured, leaving no trace of the encounter behind. Image credit: Mark A. Garlick/CfA.

“Where we’re going, we won’t need eyes to see.” -Sam Neill, Event Horizon

Are event horizons real? With data taken from around a dozen observatories earlier this year, simultaneously, the Event Horizon Telescope is poised to put together the first-ever direct image of the black hole at the center of our galaxy Sagittarius A*. If event horizons are real, this data should be able to create the first-ever image of it, proving that nothing escapes from inside a black hole once you’ve been swallowed.

Five different simulations in general relativity, using a magnetohydrodynamic model of the black hole’s accretion disk, and how the radio signal will look as a result. Note the clear signature of the event horizon in all the expected results. Image credit: GRMHD simulations of visibility amplitude variability for Event Horizon Telescope images of Sgr A*, L. Medeiros et al., arXiv:1601.06799.

But why wait? Through a very clever technique, a team of astronomers used data from the Pan-STARRS telescope to test the alternative: that there’d be a hard surface exterior to where the event horizon is supposed to be. If that were the case, stars that collided with these hard surfaces would create a transient signal in the visible and infrared, which is exactly what Pan-STARRS is sensitive to.

If a hard surface, rather than an event horizon, exists around a supermassive object, a collision should result in a luminous burst that telescopes like Pan-STARRS should easily perceive. Image credit: Mark A. Garlick.

The lack of such signals, even though a significant number would be expected, shows that the alternative to event horizons cannot stand. Event horizons are real, and now we have indirect proof!