Black Holes
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Abstract
The unlucky star that wanders too close to a supermassive black hole faces a catastrophic end. Initially, it bulges slightly due to tidal forces, just as Earth’s oceans bulge in response to the Moon’s gravity. Over the next half-hour or so, increasing gravitational stress rips the star apart. Stellar remains spread in a wide spiral; the gas that isn’t ejected at high speeds circles back to feed the black hole, glowing brighthot before it disappears into its gaping maw. Astronomers first proposed that stars could become victim to tidal shredding by black holes in 1975, but it took two decades for astronomers to observe the first convincing candidates. In the past five years, two developments have substantially widened the discovery potential. First we have found several events emitting light at optical wavelengths, where the next, most powerful surveys will soon scan the sky for transient and variable phenomena. And astronomers have also detected X-rays and radio waves from brief, spectacular jets that can form when the shredded star funnels into the black hole. These developments are guiding future searches for these rare events. We are able to see black holes despite what their name suggests because when they devour a meal, they become beacons of light. Snared gas releases its gravitational potential energy as light and heat, rendering black holes visible even when they’re billions of light-years away. In luminous active galactic nuclei, huge disks of gas feed supermassive black holes millions or billions of times Star-Shredding