Astronomy and Space
Re: Astronomy and Space
The black bit of the shadow* is about the size of the orbit of Mercury - but it contains as much material as 4,000,000 Suns.
* I roughly recall that the shadow is 1 point something times the size of the black hole itself,but I can't remember whether it's the black hole or the shadow that's the size of orbit of Mercury (60m km)
* I roughly recall that the shadow is 1 point something times the size of the black hole itself,but I can't remember whether it's the black hole or the shadow that's the size of orbit of Mercury (60m km)
My avatar was a scientific result that was later found to be 'mistaken' - I rarely claim to be 100% correct
ETA 5/8/20: I've been advised that the result was correct, it was the initial interpretation that needed to be withdrawn
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ETA 5/8/20: I've been advised that the result was correct, it was the initial interpretation that needed to be withdrawn
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Re: Astronomy and Space
How do we even describe the size of a black hole? Is the event horizon a useful measure? We can know the mass.
where once I used to scintillate
now I sin till ten past three
now I sin till ten past three
Re: Astronomy and Space
Not sure whether it's interesting, but although we can calculate the volume enclosed by the event horizon, the volume inside the event horizon is indeterminate.
My avatar was a scientific result that was later found to be 'mistaken' - I rarely claim to be 100% correct
ETA 5/8/20: I've been advised that the result was correct, it was the initial interpretation that needed to be withdrawn
Meta? I'd say so!
ETA 5/8/20: I've been advised that the result was correct, it was the initial interpretation that needed to be withdrawn
Meta? I'd say so!
Re: Astronomy and Space
The ratio of the radius of the ISCO (innermost stable circular orbit for massive particles) to the Schwarzchild radius (radius of the event horizon) is 3 for a non-rotating black hole, but there are unstable circular orbits down to 2 times the Schwarzchild radius - which is where the inner edge of an accretion disk lies.Gfamily wrote: ↑Thu May 12, 2022 2:38 pmThe black bit of the shadow* is about the size of the orbit of Mercury - but it contains as much material as 4,000,000 Suns.
* I roughly recall that the shadow is 1 point something times the size of the black hole itself,but I can't remember whether it's the black hole or the shadow that's the size of orbit of Mercury (60m km)
For spinning black holes, those radii get smaller for prograde orbits, and can reduce down to the same as the Schwarzchild radius for a maximally spinning black hole.
Re: Astronomy and Space
The Schwarzchild radius is the usual measure - that's the distance from the singularity within which photons cannot escape - i.e. the event horizon.
The Schwarzchild radius is just GM/c², so directly proportional to the mass.
Last edited by dyqik on Thu May 12, 2022 2:50 pm, edited 1 time in total.
Re: Astronomy and Space
That’s the sort of statement that breaks my brain
where once I used to scintillate
now I sin till ten past three
now I sin till ten past three
Re: Astronomy and Space
Yeah, but is the black hole itself the singularity, which presumably doesn’t really have a volume?
where once I used to scintillate
now I sin till ten past three
now I sin till ten past three
Re: Astronomy and Space
I think it's undefined. You'd need to integrate over a infinitesimally small point of infinite curvature of spacetime.Grumble wrote: ↑Thu May 12, 2022 2:50 pmYeah, but is the black hole itself the singularity, which presumably doesn’t really have a volume?
Last edited by dyqik on Thu May 12, 2022 2:54 pm, edited 1 time in total.
Re: Astronomy and Space
Going to stop thinking about this now ![Laughing :lol:](./images/smilies/icon_lol.gif)
![Laughing :lol:](./images/smilies/icon_lol.gif)
where once I used to scintillate
now I sin till ten past three
now I sin till ten past three
Re: Astronomy and Space
Happy to be corrected, but my understanding is that a Black Hole is generally understood to be everything inside the Event Horizon (the Schwarzchild Radius). I am not sure whether that should include the Event Horizon itself.
My avatar was a scientific result that was later found to be 'mistaken' - I rarely claim to be 100% correct
ETA 5/8/20: I've been advised that the result was correct, it was the initial interpretation that needed to be withdrawn
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ETA 5/8/20: I've been advised that the result was correct, it was the initial interpretation that needed to be withdrawn
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Re: Astronomy and Space
I edited that post, but the interior of the event horizon includes the singularity, so all bets are off.
Re: Astronomy and Space
My bad
The Accretion disc is about the size of Mercury's orbit
My avatar was a scientific result that was later found to be 'mistaken' - I rarely claim to be 100% correct
ETA 5/8/20: I've been advised that the result was correct, it was the initial interpretation that needed to be withdrawn
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Re: Astronomy and Space
That's rubbish, surely. That picture implies we're looking at the accretion disk exactly face on, which is extremely unlikely. The disk is most likely roughly parallel to the rest of the galaxy, which means we'd be seeing it edge-on. Have they done some jiggery-pokery to create an image as if we were looking at it face on? Or is it some gravitational lensing thing? Or what?
Fake edit: OK, it's sort of the last of those. I was forgetting that the light gets bent so much that we are seeing behind the black hole as well as/more than classical line-of-sight.
https://www.eso.org/public/blog/spot-th ... ius-a-m87/
Re: Astronomy and Space
Whatevs. You're just jealous because Krispy Kreme donuts didn't celebrate your last paper with free donuts for everyone*.
https://twitter.com/krispykreme/status/ ... AXY_g&s=19
https://twitter.com/krispykreme/status/ ... AXY_g&s=19
Re: Astronomy and Space
The EHT got a picture 3 years ago of a different black hole which was in the centre of a whole different galaxy. Can anyone explain why that was easier than this picture of a black hole that is so much closer to us?
Well, actually I'm just assuming the other one was easier cause they did it first - I mean why wouldn't you do the Milky Way one if you had a choice?
Well, actually I'm just assuming the other one was easier cause they did it first - I mean why wouldn't you do the Milky Way one if you had a choice?
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Re: Astronomy and Space
I've seen an explanation that the M87 BH is 1000 times bigger, so material in its accretion disc orbits in a matter of days, whereas the material orbiting Sgr A* does so in minutes, so the timescale for capturing data is much shorter.jaap wrote: ↑Fri May 13, 2022 8:02 amThe EHT got a picture 3 years ago of a different black hole which was in the centre of a whole different galaxy. Can anyone explain why that was easier than this picture of a black hole that is so much closer to us?
Well, actually I'm just assuming the other one was easier cause they did it first - I mean why wouldn't you do the Milky Way one if you had a choice?
The date of the observations is the same (i think) so it's the processing that has taken so much longer.
My avatar was a scientific result that was later found to be 'mistaken' - I rarely claim to be 100% correct
ETA 5/8/20: I've been advised that the result was correct, it was the initial interpretation that needed to be withdrawn
Meta? I'd say so!
ETA 5/8/20: I've been advised that the result was correct, it was the initial interpretation that needed to be withdrawn
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Re: Astronomy and Space
There's a whole sh.t load of dust between us and the centre of our own galaxy. That's why you can't actually see it optically but have to use the radio wavelengths.jaap wrote: ↑Fri May 13, 2022 8:02 amThe EHT got a picture 3 years ago of a different black hole which was in the centre of a whole different galaxy. Can anyone explain why that was easier than this picture of a black hole that is so much closer to us?
Well, actually I'm just assuming the other one was easier cause they did it first - I mean why wouldn't you do the Milky Way one if you had a choice?
having that swing is a necessary but not sufficient condition for it meaning a thing
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Re: Astronomy and Space
Interesting - a suggestion that the appearance may be an artefact of the processing.
https://twitter.com/apontzen/status/1525027622874398720
associated paper preprint
https://arxiv.org/abs/2205.04623
https://twitter.com/apontzen/status/1525027622874398720
associated paper preprint
https://arxiv.org/abs/2205.04623
The ring-like structures of the EHTC can be created not only from the public data, but also from the simulated data of a point image
My avatar was a scientific result that was later found to be 'mistaken' - I rarely claim to be 100% correct
ETA 5/8/20: I've been advised that the result was correct, it was the initial interpretation that needed to be withdrawn
Meta? I'd say so!
ETA 5/8/20: I've been advised that the result was correct, it was the initial interpretation that needed to be withdrawn
Meta? I'd say so!
Re: Astronomy and Space
This isn't peer reviewed, and this scenario is tested in the original papers, as well as in the new papers - the analysis includes Bayesian model selection among multiple source models, and a non-ring like structure only works with very low probability.Gfamily wrote: ↑Fri May 13, 2022 11:41 amInteresting - a suggestion that the appearance may be an artefact of the processing.
https://twitter.com/apontzen/status/1525027622874398720
associated paper preprint
https://arxiv.org/abs/2205.04623
The ring-like structures of the EHTC can be created not only from the public data, but also from the simulated data of a point image
This is shown in the first image in yesterday's special issue of The Astrophysical Journal Letters - https://iopscience.iop.org/journal/2041 ... _A_Results
See also Fig 6. and associated text (particularly section 7) in https://iopscience.iop.org/article/10.3 ... 213/ac6429
Re: Astronomy and Space
Whilst that is the "size of the black hole", we have an astronomical object which is arguably more than a black hole. That very extensive accretion disk is, in a sense, part of "it". The accretion disk might be considered as being a bit like an "atmosphere" of a planet, in that it surrounds it from the very "surface" of the event horizon, without a gap.
There is a degree of inconsistency here in saying where the edge of an object is, to say how big it is. When asking "how big is the earth", we tend to give the diameter of solid and liquid part of it, and ignore the atmosphere. But when asking how big are the ice and gas giant planets, we assuredly include the atmosphere. Indeed we may be uncertain of the precise size of the solid/liquid part. And it is possible that the lower atmospheres of some of them are supercritical so that gas gradually becomes liquid without a defined surface. But we wouldn't include Saturn's rings, or the satellites. Saturn's rings are at a distance from the top of the atmosphere of the planet. The accretion disk of a black hole is a bit like an atmosphere, in that it is right up against the event horizon, albeit not in spherical distribution around it.
Re: Astronomy and Space
No, the accretion disk is much more like Saturn's rings or the asteroid belt than an atmosphere. It's gravitationally attracted into an orbit about the BH, with an orbital plane that's determined by the net angular momentum of the infalling material - much like the formation of the Solar System as the Sun collapsed and ignited. In contrast, an atmosphere is supported entirely by gas pressure - you can't go ballooning in an accretion disk.IvanV wrote: ↑Mon May 16, 2022 1:00 pmWhilst that is the "size of the black hole", we have an astronomical object which is arguably more than a black hole. That very extensive accretion disk is, in a sense, part of "it". The accretion disk might be considered as being a bit like an "atmosphere" of a planet, in that it surrounds it from the very "surface" of the event horizon, without a gap.
There is a degree of inconsistency here in saying where the edge of an object is, to say how big it is. When asking "how big is the earth", we tend to give the diameter of solid and liquid part of it, and ignore the atmosphere. But when asking how big are the ice and gas giant planets, we assuredly include the atmosphere. Indeed we may be uncertain of the precise size of the solid/liquid part. And it is possible that the lower atmospheres of some of them are supercritical so that gas gradually becomes liquid without a defined surface. But we wouldn't include Saturn's rings, or the satellites. Saturn's rings are at a distance from the top of the atmosphere of the planet. The accretion disk of a black hole is a bit like an atmosphere, in that it is right up against the event horizon, albeit not in spherical distribution around it.
The accretion disk stops at around twice the size of the Event Horizon, and inside that is virtually empty until you get to the Event Horizon.
Re: Astronomy and Space
Thank you. You've just completely changed the image I've always had of a black hole being surrounded by the stuff that was just outside and soon to fall in.
Re: Astronomy and Space
That's the difference between the ISCO (3 Rs), the unstable orbits within the ISCO (down to 2 Rs), and the Schwarzchild Radius (Rs).
The first two numbers get smaller for rapidly spinning black holes with a prograde accretion disk.
Re: Astronomy and Space
Boeing's long delayed Starliner space capsule launched yesterday, on its second test flight. (The second test flight was necessary because the first one did not go well in 2019). The failure of 2 thrusters on yesterday's flight is being downplayed, but it does indicate that Boeing has a long way to go before it can re-establish its reputation for competence.