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Copernicus
2012-Nov-24, 09:49 PM
Has a black hole formation ever been witnessed?

antoniseb
2012-Nov-24, 11:25 PM
Maybe... there is evidence that SN1987A left a black hole, not a neutron star, but we've haven't seen the black hole to confirm it.

ShinAce
2012-Nov-24, 11:43 PM
but we've haven't seen the black hole to confirm it.

I know you're half serious, and half joking, but that was hilarious!

Would it be possible to be close enough to a newly formed neutron star to detect thermally and not have been toasted by the nova?

antoniseb
2012-Nov-25, 12:33 AM
... Would it be possible to be close enough to a newly formed neutron star to detect thermally and not have been toasted by the nova?
I think so... We can see the much older Geminga, and several other free-roaming neutron stars by their thermal output. A newly formed one, especially if it had a brief accretion disk, should be something Chandra should detect from several, maybe tens of kiloparsecs. Likewise, if a new black hole had an accretion disk and jets, it should leave a detectable trace.

Shaula
2012-Nov-25, 07:01 AM
What do you mean witnessed? I don't mean that in a facetious way. We have seen many supernovae, so yes, we have seen events that will have given rise to black holes. But the problem is that we have never 'seen' a black hole. We have seen evidence for amazingly compact x-ray sources, we have seen accretion disks. The best fit to these observations is a black hole. Most of the detailed, convincing observations of things like variability and accretion come from super-massive black holes. Most of the evidence from stellar mass one are about things like x-ray emissions, gravitational evidence. And sadly supernovae are messy things so getting good measurements of stuff like this tends to happen once the system has settled back down - i.e not in the lifetime of the person who saw the supernnova!

Sadly most of the evidence for a black hole on 1987a seems to be "there isn't a neutron star there"

antoniseb
2012-Nov-25, 12:39 PM
... Sadly most of the evidence for a black hole on 1987a seems to be "there isn't a neutron star there"
... and the event was underluminous compared to models for how San 69-202 should have exploded if it didn't make a black hole.

Copernicus
2012-Nov-25, 02:08 PM
What do you mean witnessed? I don't mean that in a facetious way. We have seen many supernovae, so yes, we have seen events that will have given rise to black holes. But the problem is that we have never 'seen' a black hole. We have seen evidence for amazingly compact x-ray sources, we have seen accretion disks. The best fit to these observations is a black hole. Most of the detailed, convincing observations of things like variability and accretion come from super-massive black holes. Most of the evidence from stellar mass one are about things like x-ray emissions, gravitational evidence. And sadly supernovae are messy things so getting good measurements of stuff like this tends to happen once the system has settled back down - i.e not in the lifetime of the person who saw the supernnova!

Sadly most of the evidence for a black hole on 1987a seems to be "there isn't a neutron star there"

Thats what I meant. Thanks. I was wondering if there was a measure of all the electromagnetic spectrum over time as the black hole was forming in the last days, hours and seconds before the black hole formed.

Shaula
2012-Nov-25, 03:11 PM
Thats what I meant. Thanks. I was wondering if there was a measure of all the electromagnetic spectrum over time as the black hole was forming in the last days, hours and seconds before the black hole formed.
Well, no. You see the problem is while we can point at stars and say "That will go supernova soon" soon means in the next 50 thousand years. And there are a fair few candidates. When you start looking at other galaxies there are huge numbers. 1987a was well studied in that we actually had a name for the precursor star - usually we don't even have that. The monitoring job which would be required to catch a supernova is immense, and until recently not possible. With the advent of neutrino detectors it is a little more possible but still a formidable challenge.

Copernicus
2012-Nov-25, 08:40 PM
Well, no. You see the problem is while we can point at stars and say "That will go supernova soon" soon means in the next 50 thousand years. And there are a fair few candidates. When you start looking at other galaxies there are huge numbers. 1987a was well studied in that we actually had a name for the precursor star - usually we don't even have that. The monitoring job which would be required to catch a supernova is immense, and until recently not possible. With the advent of neutrino detectors it is a little more possible but still a formidable challenge.

Thanks, Maybe we will get lucky some time.

Hornblower
2012-Nov-26, 01:54 AM
Thanks, Maybe we will get lucky some time.

We were lucky this time, catching the burst of neutrinos from the core collapse and being able to link them with the subsequent fireworks. I would not have expected to see anything before that moment even if we had been monitoring that star for whatever reason. The response of the photosphere to prior changes in the core during its evolution is very slow on the time scale of a human lifetime.

Copernicus
2012-Nov-27, 11:41 PM
We were lucky this time, catching the burst of neutrinos from the core collapse and being able to link them with the subsequent fireworks. I would not have expected to see anything before that moment even if we had been monitoring that star for whatever reason. The response of the photosphere to prior changes in the core during its evolution is very slow on the time scale of a human lifetime.

These discussions should be on "The Big Bang Theory"

So what was the scene, step by step, when we saw this Black hole form?

Shaula
2012-Nov-28, 06:05 AM
1) we had pre-existing but very sparse data on an unremarkable blue star, one of millions, called Sanduleak -69 202, which we didn't think was a supernovae candidate (cause it was all blue and stuff)
2) 24 extra neutrino events over the background were seen by three detectors around the world (although this was not tied to any particular event at this point
3) 2 hours later the light was seen by an observatory in Chile and monitoring started

At the time it was not thought that blue stars were supernovae candidates so it caused some models to be revised
The neutrino pulse implied that it was core collapse type supernova
Hubble has been on the case since 1990 and no neutron star has been seen
So the odds are it is a black hole

There is loads more interesting phenomena going on throughout this - just Google SN1987A for loads of resources on it

Hornblower
2012-Nov-28, 02:12 PM
Suppose the properties of the star were such that the envelope fell into the collapsing core rather than being blasted into luminous ejecta. In that case we would see it rapidly reddening and fading, and then disappearing entirely. Because of relativistic redshifting and time dilation, from our viewpoint we would not see the surface material cross the event horizon, but instead approach it asymptotically as it fades. It quickly would become unobservably dim.

In a nutshell, this is more about what we would not see than what we would see.

If I am not mistaken, supercomputer models predict just such an event for some extremely supermassive stars.

Copernicus
2012-Dec-01, 02:31 AM
Suppose the properties of the star were such that the envelope fell into the collapsing core rather than being blasted into luminous ejecta. In that case we would see it rapidly reddening and fading, and then disappearing entirely. Because of relativistic redshifting and time dilation, from our viewpoint we would not see the surface material cross the event horizon, but instead approach it asymptotically as it fades. It quickly would become unobservably dim.

In a nutshell, this is more about what we would not see than what we would see.

If I am not mistaken, supercomputer models predict just such an event for some extremely supermassive stars.

As a followup question, lets say, as a possiblity, that black holes are not black, but gravity was sufficient to cause all of the electromagnetic spectrum given off to be redshifted so far that we could not detect those rays. Would there be an indirect way to detect those highly redshifted rays?

Shaula
2012-Dec-01, 06:30 AM
Black holes are not black anyway - Hawking radiation.

It all depends on the flux. If it were high enough you could see one very obvious effect - black holes would not accrete matter or would do so very slowly. Anything infalling would eventually 'see' the radiation and be pushed back out again.

Copernicus
2012-Dec-01, 06:50 PM
Black holes are not black anyway - Hawking radiation.

It all depends on the flux. If it were high enough you could see one very obvious effect - black holes would not accrete matter or would do so very slowly. Anything infalling would eventually 'see' the radiation and be pushed back out again.

Are you suggesting that the nuclear reaction rate of a black hole would be so high and the temperature of the black hole so hot that its radiation would be stronger than its gravity, that the radiation would push infalling objects out?

Shaula
2012-Dec-01, 07:11 PM
Are you suggesting that the nuclear reaction rate of a black hole would be so high and the temperature of the black hole so hot that its radiation would be stronger than its gravity, that the radiation would push infalling objects out?
Of course not, I think black holes are black. You were saying "what if" about them radiating. I merely said that significant amounts of radiation would have an effect on the accretion disk

Copernicus
2012-Dec-01, 11:25 PM
Of course not, I think black holes are black. You were saying "what if" about them radiating. I merely said that significant amounts of radiation would have an effect on the accretion disk

Thanks