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APOD: The View Near a Black Hole (2014 Mar 23)
Posted: Sun Mar 23, 2014 4:07 am
by APOD Robot
The View Near a Black Hole
Explanation: In the center of a swirling whirlpool of hot gas is likely a beast that has never been seen directly: a
black hole. Studies of the bright light emitted by the
swirling gas frequently indicate not only that a
black hole is present, but also likely attributes. The gas surrounding GRO J1655-40, for example, has
been found to display an unusual flickering at a rate of 450 times a second. Given a
previous mass estimate for the
central object of seven times the mass of our
Sun, the rate of the
fast flickering can be
explained by a
black hole that is
rotating very rapidly. What physical mechanisms actually cause the
flickering -- and a slower
quasi-periodic oscillation (QPO) -- in
accretion disks surrounding
black holes and
neutron stars remains a topic of much research.
[/b]
Re: APOD: The View Near a Black Hole (2014 Mar 23)
Posted: Sun Mar 23, 2014 2:56 pm
by Guest
Please tell me how any accretion disk around a black hole could be bowl shaped.
Re: APOD: The View Near a Black Hole (2014 Mar 23)
Posted: Sun Mar 23, 2014 3:09 pm
by Chris Peterson
Guest wrote:Please tell me how any accretion disk around a black hole could be bowl shaped.
It couldn't be. At most, accretion discs can show a bit of warp, like a potato chip.
Unfortunately, the caption here doesn't really describe the image, and there's no link back to the original image where we might find a description of just what's being rendered.
Re: APOD: The View Near a Black Hole (2014 Mar 23)
Posted: Sun Mar 23, 2014 4:02 pm
by RJN
Guest wrote:Please tell me how any accretion disk around a black hole could be bowl shaped.
Interesting question. It's not my subfield, but here are some possibilities that spring to mind:
1. The jet precesses.
2. The jet emits a slight radial wind.
3. Disk material is contained by a poloidal magnetic field component.
- RJN
Re: APOD: The View Near a Black Hole (2014 Mar 23)
Posted: Sun Mar 23, 2014 4:39 pm
by Chris Peterson
RJN wrote:Guest wrote:Please tell me how any accretion disk around a black hole could be bowl shaped.
Interesting question. It's not my subfield, but here are some possibilities that spring to mind:
1. The jet precesses.
2. The jet emits a slight radial wind.
3. Disk material is contained by a poloidal magnetic field component.
Certainly not my field, either. But I did a little research recently about precessing accretion discs, which is where I learned about how they can be very slightly inclined, as well as show several warpage modes (all with low amplitude). Nothing about bowl shapes (I guess that might be considered zero-order warp). And certainly nothing consistent with the degree of warpage today's image
appears to show. So I'm wondering if your suggestions are completely abstract, or if you've encountered actual references to accretion discs warped into bowl shapes (not that they would be "discs" anymore)?
Re: APOD: The View Near a Black Hole (2014 Mar 23)
Posted: Sun Mar 23, 2014 5:05 pm
by geckzilla
Several images at the
black hole illustrations page at the Chandra website depict accretion disks like this. Usually this website has some very good editing and is very good at explaining things. Maybe not this time or at least not for this specific question.
Re: APOD: The View Near a Black Hole (2014 Mar 23)
Posted: Sun Mar 23, 2014 5:09 pm
by RJN
Chris Peterson wrote: So I'm wondering if your suggestions are completely abstract, or if you've encountered actual references to accretion discs warped into bowl shapes (not that they would be "discs" anymore)?
They are all abstract. The artist works with the Chandra X-ray Observatory people and so might have done some research before drawing the image. There appears to me to be an area of "scientific art" that is not well populated that presents the best known illustration of an object or phenomenon given all that is known scientiically. The best scientific art images of some objects would need to adapt as more becomes known. APOD does feature some of this art genre, which is usually tied to press-releases, but I think there is so much more that can be done here.
Re: APOD: The View Near a Black Hole (2014 Mar 23)
Posted: Sun Mar 23, 2014 5:18 pm
by neufer
Guest wrote:
Please tell me how any accretion disk around a black hole could be bowl shaped.
- It fits certain models of hot high velocity clouds surrounding a narrow dense accretion disk :
http://www.uni.edu/morgans/astro/course/Notes/section3/new13.html wrote:
EarthSci 1100 - Astronomy[/url]
by Dr. Siobahn Morgan
Distant and Weird Galaxies
<<The [standard massive black hole] model is made up of the following components
1) A black hole in the center (this can be as massive as millions or billions of solar masses). Remember, black holes can have a large amount of mass, but they won't cover huge amounts of area (usually smaller than a solar system in radius).
2) An accretion disk forms around the black hole. This would be much larger in size than the black hole and would be very hot and dense near the center - producing UV light and x-rays in most cases or even some gamma-rays. Even though the accretion disk would cover more space than the black hole, it is still relatively small compared to the size of the galaxy that it is located within.
3) Clouds of material would be orbiting around the disk. These clouds will be heated up by the extreme temperatures of the accretion disk. These clouds have to move at pretty high speeds so they don't fall into the accretion disk or, ultimately, into the black hole. They are basically hot, fast, gas clouds near the black hole.
Much more at:
http://www.uni.edu/morgans/astro/index.html
Re: APOD: The View Near a Black Hole (2014 Mar 23)
Posted: Sun Mar 23, 2014 5:22 pm
by Chris Peterson
neufer wrote:- It fits certain models of hot high velocity clouds surrounding a narrow dense accretion disk :
I like that. The image is showing the accretion disc as yellow, or maybe even the interior of that white area, and mostly what we're seeing is surrounding material that's not part of the disc itself.
I'd like to see an original caption for the image if there is one, though.
Re: APOD: The View Near a Black Hole (2014 Mar 23)
Posted: Sun Mar 23, 2014 5:27 pm
by geckzilla
RJN wrote:Chris Peterson wrote: So I'm wondering if your suggestions are completely abstract, or if you've encountered actual references to accretion discs warped into bowl shapes (not that they would be "discs" anymore)?
They are all abstract. The artist works with the Chandra X-ray Observatory people and so might have done some research before drawing the image. There appears to me to be an area of "scientific art" that is not well populated that presents the best known illustration of an object or phenomenon given all that is known scientiically. The best scientific art images of some objects would need to adapt as more becomes known. APOD does feature some of this art genre, which is usually tied to press-releases, but I think there is so much more that can be done here.
Really? I've sometimes wanted to do some illustrations but it looks like there is no shortage of artists, some of them very good. What more could be done? I do sometimes wish they were more accurate. If I ever do any illustrations I swear I will not put star fields behind every bright thing because that makes absolutely no sense. There are stars visible through this accretion disk!!
Re: APOD: The View Near a Black Hole (2014 Mar 23)
Posted: Sun Mar 23, 2014 5:39 pm
by Chris Peterson
geckzilla wrote:Really? I've sometimes wanted to do some illustrations but it looks like there is no shortage of artists, some of them very good. What more could be done? I do sometimes wish they were more accurate. If I ever do any illustrations I swear I will not put star fields behind every bright thing because that makes absolutely no sense. There are stars visible through this accretion disk!!
That may not be inaccurate. If, as Art suggests, we're mainly seeing dusty clouds here, with the accretion disc only at the very center, it's entirely possible they could be tenuous enough, or non-uniform enough, to see stars through them, just as we often can with other types of nebulas.
I do agree with you about how often artist renderings of astronomical scenes are inaccurate, though, sometimes to a cringe-worthy degree. The thing that bothers me the most is the nearly universal failure to capture some sense of actual intensities and relative intensities.
Re: APOD: The View Near a Black Hole (2014 Mar 23)
Posted: Sun Mar 23, 2014 5:48 pm
by geckzilla
Chris Peterson wrote:geckzilla wrote:Really? I've sometimes wanted to do some illustrations but it looks like there is no shortage of artists, some of them very good. What more could be done? I do sometimes wish they were more accurate. If I ever do any illustrations I swear I will not put star fields behind every bright thing because that makes absolutely no sense. There are stars visible through this accretion disk!!
That may not be inaccurate. If, as Art suggests, we're mainly seeing dusty clouds here, with the accretion disc only at the very center, it's entirely possible they could be tenuous enough, or non-uniform enough, to see stars through them, just as we often can with other types of nebulas.
I do agree with you about how often artist renderings of astronomical scenes are inaccurate, though, sometimes to a cringe-worthy degree. The thing that bothers me the most is the nearly universal failure to capture some sense of actual intensities and relative intensities.
An active galaxy nucleus is as bright as a supernova. If I were doing it I would hope to capture that effect. Everything within the center should be ionized to hell. This image makes it looks something like a faintly glowing ember except at the very center. Really though, lack of knowledge does keep me from being able to form an idea of an illustration in my head. Maybe my idea is completely wrong.
Re: APOD: The View Near a Black Hole (2014 Mar 23)
Posted: Sun Mar 23, 2014 7:01 pm
by zbvhs
What you would have is a toroidal cloud that's being thinned to something like the thickness of Saturn's rings at the equator of the event horizon. The picture would be bowl-shaped on the other side as well.
Re: APOD: The View Near a Black Hole (2014 Mar 23)
Posted: Sun Mar 23, 2014 11:31 pm
by RJN
geckzilla wrote: Really? I've sometimes wanted to do some illustrations but it looks like there is no shortage of artists, some of them very good. What more could be done? I do sometimes wish they were more accurate. If I ever do any illustrations I swear I will not put star fields behind every bright thing because that makes absolutely no sense. There are stars visible through this accretion disk!!
There are some very good artists, but many times I see a press release accompanied by art that is either scientifically wrong or artistically dull. Yes, the latter reason is subjective, but some of the depicted places are up there with the most interesting in the universe, yet somehow they come off looking boring. And no, I don't really know how to fix them.
Today's illustration is really one of the better ones, in my opinion, in terms of communicating the surroundings of a black hole. Some artists might say that a black hole is just a black spot against a black background, but really the accretion disk and jet and lensing effects can likely be combined to create something both scientifically accurate and visually spectacular -- in a number of wavelengths.
Oh, and if you (plural) do see one of these, please post it to the "Found" thread on the Asterisk's Observation Deck Forum.
- RJN
Re: APOD: The View Near a Black Hole (2014 Mar 23)
Posted: Sun Mar 23, 2014 11:44 pm
by Boomer12k
1. Artists conception. How to depict things.
2. Bowl shaped, well....not so bowl...but VORTEX....think "drain"....the water swirls creating a hole, and the water flows down into the hole of the vortex...only this is very wide, and the Spacetime is not just warped, but also probably spinning and twisting in a vortex itself....next time you are in the bath, swirl your hand around until you get a vortex....
Nasty things.....and utterly fascinating.
:---[===] *
Re: APOD: The View Near a Black Hole (2014 Mar 23)
Posted: Sun Mar 23, 2014 11:56 pm
by Chris Peterson
Boomer12k wrote:1. Artists conception. How to depict things.
2. Bowl shaped, well....not so bowl...but VORTEX....think "drain"....the water swirls creating a hole, and the water flows down into the hole of the vortex...only this is very wide, and the Spacetime is not just warped, but also probably spinning and twisting in a vortex itself....next time you are in the bath, swirl your hand around until you get a vortex...
What's going on around a black hole isn't really a vortex in three dimensions. The rate of inward flow is extremely low. And any effects caused by the rotation of spacetime would only be present very close to the event horizon, and probably would not result in visible effects at this image scale.
Re: APOD: The View Near a Black Hole (2014 Mar 23)
Posted: Mon Mar 24, 2014 2:58 am
by Boomer12k
Chris Peterson wrote:Boomer12k wrote:1. Artists conception. How to depict things.
2. Bowl shaped, well....not so bowl...but VORTEX....think "drain"....the water swirls creating a hole, and the water flows down into the hole of the vortex...only this is very wide, and the Spacetime is not just warped, but also probably spinning and twisting in a vortex itself....next time you are in the bath, swirl your hand around until you get a vortex...
What's going on around a black hole isn't really a vortex in three dimensions. The rate of inward flow is extremely low. And any effects caused by the rotation of spacetime would only be present very close to the event horizon, and probably would not result in visible effects at this image scale.
Then I chalk it up to Number 1....as from your description, it would not be such a dramatic effect....
:---[===] *
Re: APOD: The View Near a Black Hole (2014 Mar 23)
Posted: Mon Mar 24, 2014 1:15 pm
by FloridaMike
The artist seems to be depicting the invisible gravity well of the black hole as opposed to an actual visual representation. The eye is poised dangerously close to certain destruction in this image. Be careful, you may fall in. The image invokes the “feeling” of being near a black hole if not the actual visual experience.
Re: APOD: The View Near a Black Hole (2014 Mar 23)
Posted: Mon Mar 24, 2014 2:12 pm
by DavidLeodis
In the information brought up through the 'central object' link I was quite surprised to read (my underlining) "Black holes have a bad reputation for sucking in entire galactic neighborhoods. Yet...their evil clutches only reach so far. After all, gravity's strength is determined by mass and distance.
If the Sun suddenly collapsed into a black hole, Earth would keep right on orbiting. We wouldn't suddenly fall in. A year would still be 365 days, however chilly."
Re: APOD: The View Near a Black Hole (2014 Mar 23)
Posted: Mon Mar 24, 2014 2:28 pm
by Chris Peterson
DavidLeodis wrote:In the information brought up through the 'central object' link I was quite surprised to read (my underlining) "Black holes have a bad reputation for sucking in entire galactic neighborhoods. Yet...their evil clutches only reach so far. After all, gravity's strength is determined by mass and distance. If the Sun suddenly collapsed into a black hole, Earth would keep right on orbiting. We wouldn't suddenly fall in. A year would still be 365 days, however chilly." :o
I credit lots of bad science fiction.
Of course, in terms of influence, there's almost no difference between a black hole and any other object of the same mass. Gravitationally, the only difference is that you can get closer to black hole because it is smaller, and that means you can experience much stronger tidal effects. In general, it's only the mass that is important, not the density. If you wanted to study one, you could fly up in your spaceship, enter orbit a few tenths of an AU away, and it would be no different from orbiting any star... just cooler. Same with a supermassive black hole, except you'd want to be a little further away to avoid tidal effects. But an orbit is an orbit. Things in orbit can't get sucked into the thing they're orbiting. Good thing for us!
Re: APOD: The View Near a Black Hole (2014 Mar 23)
Posted: Mon Mar 24, 2014 3:16 pm
by DavidLeodis
Chris Peterson wrote:DavidLeodis wrote:In the information brought up through the 'central object' link I was quite surprised to read (my underlining) "Black holes have a bad reputation for sucking in entire galactic neighborhoods. Yet...their evil clutches only reach so far. After all, gravity's strength is determined by mass and distance.
If the Sun suddenly collapsed into a black hole, Earth would keep right on orbiting. We wouldn't suddenly fall in. A year would still be 365 days, however chilly."
I credit lots of bad science fiction.
Of course, in terms of influence, there's almost no difference between a black hole and any other object of the same mass. Gravitationally, the only difference is that you can get closer to black hole because it is smaller, and that means you can experience much stronger tidal effects. In general, it's only the mass that is important, not the density. If you wanted to study one, you could fly up in your spaceship, enter orbit a few tenths of an AU away, and it would be no different from orbiting any star... just cooler. Same with a supermassive black hole, except you'd want to be a little further away to avoid tidal effects. But an orbit is an orbit. Things in orbit can't get sucked into the thing they're orbiting. Good thing for us!
Thanks for that reply Chris, which is appreciated.
I seem to have misunderstood what the quote that I underlined meant. I took it to mean that the Sun (taking the Earth with it) collapsed/fell into a black hole that was already there, not that the Sun itself suddenly became a black hole! My mistake, though I do think the quote that I underlined is not that clear.
Re: APOD: The View Near a Black Hole (2014 Mar 23)
Posted: Mon Mar 24, 2014 3:19 pm
by Chris Peterson
DavidLeodis wrote:I seem to have misunderstood what the quote that I underlined meant. I took it to mean that the Sun (taking the Earth with it) collapsed/fell into a black hole that was already there, not that the Sun itself suddenly became a black hole! My mistake, though I do think the quote that I underlined is not that clear. :?
Ah. I missed that ambiguity. Certainly, if a black hole passed through our system closely enough to the Sun to suck it in, the Earth would either accompany it, or be flung into a radically different orbit- either around the black hole, or out of the Solar System completely.
Re: APOD: The View Near a Black Hole (2014 Mar 23)
Posted: Mon Mar 24, 2014 10:57 pm
by Guest
Guest wrote:Please tell me how any accretion disk around a black hole could be bowl shaped.
Chris Peterson is right. Mass, large amounts of it create a gravity "well" in the space-time continuum. They do not create a well shape in a two or three dimensional surface, such as a disk. The surface of the disk may appear slightly like a well as the disk maybe compressed, and therefore thinner, near the center.
And, yes, it will appear to have a warped shape like a potato chip. This would be caused by light, as it leaves the far side of the disk, to be bent toward the center of the black hole, much like light coming from objects below the surface of water are bent toward the observer.
Sorry, I'm just tired of artist's conceptions of black holes that seem to have not been reviewed by astro-physicists who understand them.
Re: APOD: The View Near a Black Hole (2014 Mar 23)
Posted: Mon Mar 24, 2014 11:12 pm
by Chris Peterson
Guest wrote:And, yes, it will appear to have a warped shape like a potato chip. This would be caused by light, as it leaves the far side of the disk, to be bent toward the center of the black hole, much like light coming from objects below the surface of water are bent toward the observer.
I think at this scale we're much too far away from the black hole to visually detect any light aberration due to gravity. An noted elsewhere, the image is almost certainly not showing a bowl shaped accretion disc, but rather, a toroidal dust structure above the accretion disc, with the disc itself only visible at the very center.
Sorry, I'm just tired of artist's conceptions of black holes that seem to have not been reviewed by astro-physicists who understand them.
Given the source of this image, I think it is very likely to have been well reviewed by astrophysicists specializing in black holes and accretion discs.
Re: APOD: The View Near a Black Hole (2014 Mar 23)
Posted: Mon Mar 24, 2014 11:34 pm
by DavidLeodis
Regarding the illustration I notice that it is at least almost 13 years old according to its use in previous APODs.
As the credit did not have a direct link to information on April Hobart I searched the CXC website and found in an entry in a 'Women in the High-Energy Universe' section (dated March 28th 2012) that she may now be called April Jubett and that “April Jubett creates animations and videos to help explain Chandra’s discoveries in a visual way”. The entry (which also contained the illustration) was however confusingly signed by April Hobart. To add to my confusion I found a 'Web, Multimedia, Imaging & Support' section (dated August 22nd 2013) in the CXC website in which in a list of staff it had “April Hobart, Animator” but did not list an April Jubett.
