What Happens When Two Black Holes Collide?

    18
    0

    What Happens When Two Black Holes Collide?

    For the first time, we’ve observed a 50-year-old theorem from Stephen Hawking in the natural world. Scientists from the Massachusetts Institute of Technology (MIT), California Institute of Technology, Cornell University, and Stony Brook University analyzed the gravitational wave data of two inspiraling black holes. What they found in the collision proved Hawking’s Area Theorem: The area of a black hole’s event horizon cannot shrink.

    When a binary black hole system inspirals, the orbits of the two black holes shrink, and the system begins emitting gravitational waves. The emission rate increases as the orbits shrink further and gain speed, and when a merger finally occurs, wave emission peaks. The two black holes become a single, new black hole, and according to Hawking’s theorem, that new black hole should be equal in area to the total area of the original two black holes. That’s exactly what the researchers found per the wave data of the observed inspiraling system.

    “Hawking showed that when quantum mechanical effects are taken into account, a black hole can spontaneously reduce its surface area over time by emitting radiation.”

    The confirmation brings us closer to understanding the intricacies of black hole functions, says Riccardo Penco, Ph.D., assistant Professor of High Energy Physics Theory at Carnegie Mellon University. “The detection of gravitational waves allows us to test black holes directly (as opposed to just inferring their existence indirectly by studying the motion of other objects around them). For the longest time, we have studied black holes as mathematical objects endowed with a remarkable set of properties (Hawking’s area law being one of them). We are now in a position to test these properties experimentally.”

    Per Hawking’s calculations, if a black hole changes in area, its event horizon would stretch or constrict in correspondence with its new size. The event horizon, the area of effect for a black hole’s gravitational field, is the point of no return for anything—including light—orbiting the black hole. An object would need to travel faster than the speed of light in order to escape.

    Penco says Hawking’s Theorem holds true for the black holes observed by the Laser Interferometer Gravitational-Wave Observatory (LIGO)—a pair of U.S. facilities built to study gravitational waves—whose work these researchers used for their findings. But Hawking’s Theorem could apply to other black holes as well, those that at first seem to defy the Theorem until they prove applicable to another concept hypothesized by the physicist.

    “Hawking showed that when quantum mechanical effects [like the behavior of subatomic matter and light] are taken into account, a black hole can spontaneously reduce its surface area over time by emitting radiation,” says Penco. Black hole evaporation, also called Hawking radiation (see sidebar), is theorized electromagnetic radiation spontaneously expelled by black holes. So Hawking’s Area Theorem has an exception, Hawking radiation, touted by Hawking himself.


    ☢️ The Lowdown on Hawking Radiation

    Proposed in 1974, Hawking radiation might cause a black hole to shrink. Subatomic particle pairs near the event horizon might split, with one particle—a photon or neutrino, perhaps—escaping and another, of negative energy, disappearing into the black hole. This influx of negative energy could eventually reduce the black hole’s mass until it disappears. This means a black hole’s size is inversely proportional to its temperature—the smaller the black hole, the warmer it is.

    —Daisy Hernandez


    LIGO detected the first gravitational wave signal in this study—essentially a ripple in space-time resulting from cosmic interactions—in 2015. The signal, they discovered, was the product of two merging black holes (which typically cause the stronger gravitational waves), along with a vast amount of energy that rippled across the space-time continuum.

    The researchers posited that if Hawking’s Area Theorem held up, the event horizon area of the new black hole created from the merger would not be smaller than the total event horizon area of its parent black holes. To test their hypothesis, they split up the gravitational wave data from the system into two sections—before the merger and after the merger—then analyzed both sections to see how their event horizon areas compared. The scientists then reanalyzed the wave data and found that the two areas are statistically the same—the total event horizon area did not decrease post-collision—within a 95 percent confidence margin.

    It would seem from the analysis, then, that the laws of “regular” physics, such as the law of conservation of mass, can still be applied to the study of black holes, where physics can become more theoretical in situations unfamiliar to the Earth-bound human experience. Working in reverse, observing real-life data to interrogate the laws that might govern black hole behavior, could be a practical way to advance the entire field of cosmology. With this black hole mergence, other scientists now have a concrete example to reference as they continue to study space.

    Still, Penco says this “doesn’t fundamentally alter our understanding of black holes [just] because it confirms our theoretical expectations.” Confirming a theory helps us better understand the mechanics of mysterious cosmic phenomena such as black holes, but it also creates a more important tie between the tactile scientific experience on Earth and the theoretical science of space. “It’s always important to be able to confirm experimentally,” Penco says. “It’s another step forward toward a deeper understanding of black holes.”


    🎥 Now Watch This:

    This content is created and maintained by a third party, and imported onto this page to help users provide their email addresses. You may be able to find more information about this and similar content at piano.io

    Published at Wed, 03 Nov 2021 21:15:00 +0000

    https://www.popularmechanics.com/space/deep-space/a36970402/hawkings-area-theorem-black-holes/

    Previous articleMinimalist architecture: homes that inspire calm
    Next article‘Reality check’: Global CO2 emissions shooting back to record levels