black hole/gravity questions

[halfeye]

Some not particularly related to each other speculative questions on black holes and things. Of course you are free to add questions of your own.

It sort of feels right that when black holes merge, you can't have a resultant hole smaller than the bigger of the holes that merged, but is there any theoretical proof of this (ideally more detailed than "this would allow perpetual motion", if it would)?

When an orbit increases in energy it becomes wider and takes longer, and is usually slower. This seems to imply that the faster a black hole rotates, the less rotational energy it has. How does a black hole go from the fastest possible rate of rotation to no (no detectable?) rotation?

Is there any way gravity waves can be absorbed, if not how do they get through black holes, but if black holes do absorb them does anything else? is there a potential power source in gravity waves?

[Grey_Wolf_c]

It sort of feels right that when black holes merge, you can't have a resultant hole smaller than the bigger of the holes that merged, but is there any theoretical proof of this (ideally more detailed than "this would allow perpetual motion", if it would)?

Am I missing something? The Schwarzschild radius is dependent on the mass of the object. If you merge two black holes, the resulting black hole will have the combined mass of the two. Therefore, its Schwarzschild radius will be larger.

GW

[halfeye]

Am I missing something? The Schwarzschild radius is dependent on the mass of the object. If you merge two black holes, the resulting black hole will have the combined mass of the two. Therefore, its Schwarzschild radius will be larger.

GW

There were more than one solar masses lost from each of the mergers detected by LIGO, in the form of emitted gravity waves. If that energy came out as non-gravitational radiation, they would be much brighter than supernovae.

[Lord Torath]

There were more than one solar masses lost from each of the mergers detected by LIGO, in the form of emitted gravity waves. If that energy came out as non-gravitational radiation, they would be much brighter than supernovae.That's correct per a Bad Astronomy (http://www.syfy.com/syfywire/ligo-sees-first-ever-gravitational-waves-two-black-holes-eat-each-other) article on the first Ligo detection:

The black holes had masses of 36 and 29 times the mass of the Sun before they merged. After they merged they created a single black hole with a mass of 62 times that of the Sun. You may notice those masses don’t add up right; there’s 3 solar masses missing. That mass didn’t just disappear! It was converted into energy: the energy of the gravitational waves themselves. And the amount of energy is staggering: This single event released as much energy as the Sun does in 15 trillion years.
Some of the energy can also go into accelerating the merged black hole (http://www.syfy.com/syfywire/3-billion-solar-mass-black-hole-rockets-out-galaxy-8-million-kilometers-hour-yes-seriously).

[Leewei]

There were more than one solar masses lost from each of the mergers detected by LIGO, in the form of emitted gravity waves. If that energy came out as non-gravitational radiation, they would be much brighter than supernovae.
Halfeye is right about this. It looks like around 5% of the energy of the black holes is being converted into gravitational waves.

Regarding evidence that the combined size is always bigger than the larger singularity, I'm wondering if thermodynamics is a good starting point. Entropy always increases, and black holes have enormous entropy.

Gravitational waves would also have entropy, but would this be more than a black hole with similar energy? Some brief reading suggests that these waves have very low entropy, similar to light. They dissipate through interaction with matter where the matter is squeezed and stretched by the wave, becoming heat and other higher entropy energies.