Understanding black holes and galaxies

[Highburymark]

It seems generally accepted today that most galaxies have a large black hole at their core. Yet also that new black holes are created whenever a larger star explodes as a supernova. Considering that galaxies contain hundreds of billions of stars, shouldn't that mean that new black holes are emerging relatively regularly, and competing with the central supermassive black star as new sources of gravity? 

Supplementary but linked question. If the closest supergiant star to the solar system were to go supernova tomorrow, how would that impact our area of the Milky Way? How far would it interact with surrounding stars, planets and gas? 

[Alien 13]

A black hole that is produced by an imploding star will have less mass than the star that produced it (some matter will be expelled as it collapses) so as far as the overall gravity in that general area nothing much will have changed. I often wonder though which came first, the black hole or the galaxy..

Alan

[Stu]

I attended a very interesting talk the other day in Guildford on this very subject! Wish I had access to the presentation that was given. The relationship between galaxies and their black holes is not as obvious as you might think. I will trawl my memory to see if I can explain!

Some comments though, the Black holes in the centre of galaxies are super massive ones, thousands of solar masses, vs the much smaller ones cause by SN events. Also, because of the inverse square law, the gravitational effect falls off relatively quickly I think so despite their massive gravity they do not dominate as far out as you might think.

[Highburymark]

31 minutes ago, Alien 13 said:

A black hole that is produced by an imploding star will have less mass than the star that produced it (some matter will be expelled as it collapses) so as far as the overall gravity in that general area nothing much will have changed. I often wonder though which came first, the black hole or the galaxy..

Alan

So a galaxy might contain thousands of black holes?

[Alien 13]

2 minutes ago, Highburymark said:

So a galaxy might contain thousands of black holes?

I expect it could if its old enough, its a similar situation with stars that go small like red dwarfs, they can still hold a planetary system much like they did before the collapse.

Alan 

[Handy_Andy]

Side note the stars that form black holes create the heavy elements including gold and uranium during their supernova phases

[Highburymark]

39 minutes ago, Stu said:

I attended a very interesting talk the other day in Guildford on this very subject! Wish I had access to the presentation that was given. The relationship between galaxies and their black holes is not as obvious as you might think. I will trawl my memory to see if I can explain!

Some comments though, the Black holes in the centre of galaxies are super massive ones, thousands of solar masses, vs the much smaller ones cause by SN events. Also, because of the inverse square law, the gravitational effect falls off relatively quickly I think so despite their massive gravity they do not dominate as far out as you might think.

 The science of black holes seems so cataclysmic - but I suppose the vast distances between stars limit their influence.

Alan's point about which came first is interesting. Can galaxies have two or more supermassive black holes, and if so how would it affect their evolution? We see lots of galaxies merging, but could competing supermassive black holes break a single galaxy up?

[Handy_Andy]

Not sure about breaking up a galaxy but there are several simulations showing what we think will happen when the Milky Way and Andromeda collide. They  show both galaxies shedding large numbers of stars as the two black holes slingshot each other. Though none of us will be around to see it unfortunately 

[Highburymark]

1 hour ago, Handy_Andy said:

Not sure about breaking up a galaxy but there are several simulations showing what we think will happen when the Milky Way and Andromeda collide. They  show both galaxies shedding large numbers of stars as the two black holes slingshot each other. Though none of us will be around to see it unfortunately 

Sadly not. But maybe Betelgeuse or Antares might put on a show for us instead over the next few years? Still about as likely as winning the Eurolottery, but still, possible. Suspect UK skies might be cloudy for a few decades were it to happen.

[Stu]

I'm trying to get a copy of the presentation I saw, but in the meantime I think this may be along similar lines, it's an audio file.

https://commons.swinburne.edu.au/items/c138d764-363e-4572-b52c-db40eaa76b56/1/

[Highburymark]

On 27/01/2018 at 21:11, Stu said:

I'm trying to get a copy of the presentation I saw, but in the meantime I think this may be along similar lines, it's an audio file.

https://commons.swinburne.edu.au/items/c138d764-363e-4572-b52c-db40eaa76b56/1/

Thanks for posting this Stu - will give it a listen later - much appreciated

[Tiki]

On ‎27‎/‎01‎/‎2018 at 17:11, Highburymark said:

 

 If the closest supergiant star to the solar system were to go supernova tomorrow, how would that impact our area of the Milky Way? How far would it interact with surrounding stars, planets and gas? 

The only gravitational effects of the formation of a new and relatively nearby black-hole would would be a barely perceptible ripple in space-time. Hopefully our gravitational wave detectors would be able to detect it .

On ‎27‎/‎01‎/‎2018 at 18:10, Stu said:

....Also, because of the inverse square law, the gravitational effect falls off relatively quickly I think so despite their massive gravity they do not dominate as far out as you might think.

Tidal forces are at the heart of Einstein's gravitational theory and they fall off according to an inverse cube law. This means that all the gnarling of space-time that occurs in the vicinity of compact objects fall off even more quickly than might be at first suspected.

[robin_astro]

Unlike the asymmetric events we have observed gravitational waves from (colliding black holes and neutron stars), Spherically symmetric events (such as the collapse of a stellar core of a massive star to produce a black hole) do not produce gravitational waves. 

Robin

[Tiki]

On ‎11‎/‎02‎/‎2018 at 15:21, robin_astro said:

Unlike the asymmetric events we have observed gravitational waves from (colliding black holes and neutron stars), Spherically symmetric events (such as the collapse of a stellar core of a massive star to produce a black hole) do not produce gravitational waves. 

Robin

 Whilst I agree that a spherically symmetric stellar core collapse would not produce any gravitational waves, real-world stellar cores are axisymmetric objects and are expected to produce gravitational waves. There has been a fair amount of research into predicting the precise nature of these emitted waves.

"Stellar core collapse events are expected to produce gravitational waves via several mechanisms, most of which are not yet fully understood due to the current limitations in the numerical simulations of these events." From the abstract of https://arxiv.org/abs/1701.02638

[Ags]

As far as I understand it, Gold, Platinum and other very heavy elements are not formed in supernovae but in colliding neutron stars, as in the recently detected gravitational wave which was confirmed optically and spectrographically.