Hawking may be right after all

Stephen Hawking predicted black holes eventually disappear thanks to the vagaries of quantum mechanics. Seems preliminary evidence from BH mergers shows his take may be right after all. 

In 1974 Stephen Hawking theorized that black holes are not black but slowly emit thermal radiation. Hawking’s prediction shook physics to its core because it implied that black holes cannot last forever and that they instead, over eons, evaporate into nothingness—except, however, for one small problem: there is simply no way to see such faint radiation. But if this “Hawking radiation” could somehow be stimulated and amplified, it might be detectable, according to some astrophysicists. And they are now claiming to have seen signs of it in the aftermath of the most massive collision of black holes ever observed.

Two massive black holes spiral together and emit copious gravitational waves moments before colliding in this image from a numerical simulation of the merger known as GW190521. Credit: N. Fischer, H. Pfeiffer, A. Buonanno (Max Planck Institute for Gravitational Physics), Simulating eXtreme Spacetimes (SXS) Collaboration

It's all about echoes.

Exactly what such echoes would look like depends on the exact physics being modeled. For example, the region just outside a black hole’s horizon is thought to be a bustling place, abuzz with pairs of virtual particles popping in and out of existence. Sometimes one of the pair falls into the black hole, and the other escapes. These escaping particles constitute Hawking radiation. This is an agonizingly slow process. In the case of the GW190521, Abedi and his colleagues argue that the production of Hawking radiation by the remnant could be sped up substantially—stimulated, in other words—by the infalling gravitational waves.

The principle is somewhat similar to what occurs during stimulated emission of radiation in atoms. In this process, photons of light hit “excited” electrons in atoms, causing the electrons to drop to lower energy levels while spitting out photons that have the same wavelength as the incident photons. In certain situations, this stimulated emission can far exceed the spontaneous “background” emission of radiation (where an electron, on its own, drops from a higher energy level to a lower one and emits a photon). Abedi and his colleagues theorize that gravitational waves interacting with a black hole’s event horizon should similarly stimulate the production of Hawking radiation to levels that far exceed spontaneous emissions, thus making it detectable. This radiation would constitute gravitational waves of the same wavelength as the incident waves, albeit with much lower intensity.

As per the title of this blurb ... Hawking may be right after all.

Stephen Hawking at NASA's StarChild Learning Center, c. 1980s