Testing the Black-Hole Area Law with GW150914

in hive-160342 •  3 years ago 

One of Stephen Hawking's predictions about black holes was just confirmed by gravitational wave astronomy recently. Hawking believed that the area of ​​a black hole's event horizon can only grow, never shrink.

ABSTRACT

We present observational confirmation of Hawking’s black-hole area theorem based on data from GW150914, finding agreement with the prediction with 97% (95%) probability when we model the ringdown including (excluding) overtones of the quadrupolar mode. We obtain this result from a new time-domain analysis of the pre- and postmerger data. We also confirm that the inspiral and ringdown portions of the signal are consistent with the same remnant mass and spin, in agreement with general relativity.

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This is surprising:

Hawking believed that the area of ​​a black hole's event horizon can only grow, never shrink.

Because I thought that Hawking Radiation implied that a blackhole could (theoretically) decay away to nothing. I'm too tired to read more about it tonight, but I'm going to try to understand this sometime.

Hawking said many interesting theories related to black holes, but none had been proven so far, Hawking was guided by some laws that a black hole was subject to and one of those laws was that event horizons could never decrease. To put it this way, the region or zone of gravity of the black hole exerts such an influence that if we go beyond it, we will no longer be able to escape from it since not even light can escape from there.

Hawking said that this event horizon a hole can only grow, because they are gaining mass as it devours everything in its path and the scientists realized that this theory was true, when they observed that gravitational waves were detected as a consequence of the fusion of two black holes after merging the volume or size of the black hole never decreased.

So I read the abstract and the link you included, and now I understand (at a high level) what they did. Basically, they measured the areas of two black holes before a merger and the area of the combined black hole after the merger. They concluded with >95% certainty that the area before the merge was not bigger than the area after the merge.

I am still confused about the apparent conflict between this theorem of Hawking's and the idea of Hawking Radiation, though. Wikipedia says this:

Hawking radiation reduces the mass and rotational energy of black holes and is therefore also theorized to cause black hole evaporation. Because of this, black holes that do not gain mass through other means are expected to shrink and ultimately vanish.

And this says:

Black holes are not decaying because there's an infalling virtual particle carrying negative energy; that's another fantasy devised by Hawking to "save" his insufficient analogy. Instead, black holes are decaying, and losing mass over time, because the energy emitted by this Hawking radiation is slowly reducing the curvature of space in that region. Once enough time passes, and that duration is enormous for realistic black holes, they will have evaporated entirely.

So on one hand, we have Hawking's theorem saying that black holes' area cannot get smaller, but on the other hand we have him saying that they will eventually evaporate and vanish.

I guess there would be a way to reconcile this if I understood it in more depth, but for now, I remain confused.

Hawking handled several theories in ocations I think that these theories is like saying I am going to say several even if it is one I have to get it right.
By the theory that I understood from wikipedia if a black hole is not devouring a star or planet this usually disappears with time, of course this contradicts a bit the latest study on the theory that a black hole never diminishes.

But it can also be that an active black hole gains mass because it is constantly devouring and that a hole that has nothing nearby to devour loses mass and disappears.

As the saying goes, if I eat well I grow healthy and strong, but if I don't eat anything, I die and disappear.