6 Oct 2020 10:46:24 UTC

Topic 223663

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Half to Roger Penrose, UK, for his theoretical research on General Relativity done with Stephen Hawking. The other half to Reinhard Genzel, Germany and Andrea Ghez, USA, for demonstrating the existence of a massive black hole in the center of our Galaxy.

Tullio

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## Hallo! It´s realy a great

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Hallo!

It´s realy a great success. Also my congratulation.

In an TV-interview Reinhard Genzel said, that in conjunction with BH there are still

somemyteries open, that can´t be explained by the GRT. Despite of the question of what happens beyond the eventhorizon, what are the other questions?Kind regards and happy crunching

Martin

## Hallo! Oh, I know another

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Hallo!

Oh, I know another uncleared question about BH : how are the jets formed, we obeserve at active BHs?

And, by theory a BH is charaterizes by it´s mass, it´s spin and, third, by it´s charge. The first two have been clearly obsereved, but I never heared about a charge of a BH. What does this mean? Are there positive and negative charged BHs, and how big is theire charge? And if we don´t obsereve this, is the GRT incomplete ???

Are there even more open questions?

Kind regards and happy crunching

Martin

P.S.: And please stay healthy in these critical times !!!

## According to Paolo Maffei, in

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According to Paolo Maffei, in his book "Monsters in the sky", MIT Press in the translation by Riccardo Giacconi, there are 4 types of black holes:

1 Schwarzschild only mass specified

2 Reissser-Nordstrom, mass and charge specified not rotating

3 Kerr specified by mass and rotation not charged

4 Kerr-Newmann specified by charge mass and rotation

I would add the entropy of a black hole.formula taken by a posthumous book by Stephen Hawking, "Brief answers to the big questions", Spacetimes Publications Limited

S= Akcexp3 divided by 4Ghreduced

where A is the area of the event horizon, k is the Boltzmann constant, G is the Newton constant, c is the speed of light in a vacuum, h is Planck constant

This entropy produces the Hawking radiation emitted by a black hole , and this is still under discussion.

Tullio

## astro-marwil wrote:.....

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astro-marwil wrote:General Relativity is a differential scheme, that is : given an arrangement of mass/energy, then what happens next ? As such GR can describe many universes, not just our observable one. So things like Dark Matter and Dark Energy don't emerge from GR, indeed they are introduced into the GR equations to get a realistic fit to observations. Also GR per se doesn't predict a Big Bang, but if you have one then it will define the evolution of a universe with one.

Then there's quantum mechanics and what phenomena could be described by combining QM with GR. That would include the interior of a black hole, the initial spark of a Big Bang, but also say, the core of a neutron star or as Tullio mentions the radiation from an event horizon.

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

## astro-marwil wrote:Oh, I know

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astro-marwil wrote:In case anyone is interested, there is a project on black hole spins, though not in operation yet:

http://astro.phys.wvu.edu/bhathome/

I was in communication with the project author a few months ago, and he assures me that he is still working on it.

And he sent me this talk which explains it, starting at 1:03 (you need to log in).

https://aps-april.onlineeventpro.freeman.com/live-stream/15336120/D15-Numerical-Relativity-Algorithms-and-Code-Development

## Jim1348 wrote: astro-marwil

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Jim1348 wrote:I hope they get it up and running soon!!