APOD: Animation: Spiral Disk around a Hole... (2019 Aug 20)

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APOD: Animation: Spiral Disk around a Hole... (2019 Aug 20)

Post by APOD Robot » Tue Aug 20, 2019 4:07 am

Image Animation: Spiral Disk around a Black Hole

Explanation: What would it look like to orbit a black hole? Many black holes are surrounded by swirling pools of gas known as accretion disks. These disks can be extremely hot, and much of the orbiting gas will eventually fall through the black hole's event horizon -- where it will never been seen again. The featured animation is an artist's rendering of the curious disk spiraling around the supermassive black hole at the center of spiral galaxy NGC 3147. Gas at the inner edge of this disk is so close to the black hole that it moves unusually fast -- at 10 percent of the speed of light. Gas this fast shows relativistic beaming, making the side of the disk heading toward us appear significantly brighter than the side moving away. The animation is based on images of NGC 3147 made recently with the Hubble Space Telescope.

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Re: APOD: Animation: Spiral Disk around a Hole... (2019 Aug 20)

Post by bystander » Tue Aug 20, 2019 4:29 am

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Re: APOD: Animation: Spiral Disk around a Hole... (2019 Aug 20)

Post by JohnD » Tue Aug 20, 2019 9:30 am

According to the Wiki page referred to (Relativistic beaming), more photons are emitted in the direction of travel. I'm surprised that this effect is so significant, at a fraction of light speed that causes insignificant Doppler shift. But that's my ignorance speaking.
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Re: APOD: Animation: Spiral Disk around a Hole... (2019 Aug 20)

Post by orin stepanek » Tue Aug 20, 2019 11:54 am

:rocketship: Interesting! :saturn:
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August APOD Animation aberration?

Post by neufer » Tue Aug 20, 2019 12:45 pm

JohnD wrote:
Tue Aug 20, 2019 9:30 am

According to the Wiki page referred to (Relativistic beaming), more photons are emitted in the direction of travel. I'm surprised that this effect is so significant, at a fraction of light speed that causes insignificant Doppler shift. But that's my ignorance speaking.
Of course, everything moves at a fraction of light speed but 1/10 is too small a fraction for any significant relativistic effects (other than aberration) including relativistic beaming.
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Re: APOD: Animation: Spiral Disk around a Hole... (2019 Aug 20)

Post by sillyworm 2 » Tue Aug 20, 2019 3:17 pm

Is there a limit to how big a black hole can become?

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Re: APOD: Animation: Spiral Disk around a Hole... (2019 Aug 20)

Post by Fly_Boy » Tue Aug 20, 2019 3:38 pm

Is there a limit to how big a black hole can become?
I was wondering the same thing. And what happens when they get too big? Is this the ultimate end of the universe, when black holes have absorbed everything?

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Re: APOD: Animation: Spiral Disk around a Hole... (2019 Aug 20)

Post by neufer » Tue Aug 20, 2019 7:13 pm

sillyworm 2 wrote:
Tue Aug 20, 2019 3:17 pm

Is there a limit to how big a black hole can become?
The mass density of large black holes drops off inversely with the square of their mass/radius.

When such black holes approach the size of the known universe they should contain an equivalent density of dark energy that explodes the black hole.

(Very small dense black holes explode due to Hawking radiation.)
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Re: APOD: Animation: Spiral Disk around a Hole... (2019 Aug 20)

Post by Psnarf » Tue Aug 20, 2019 8:45 pm

Does the disk spin like a galaxy, where particles along arbitrary spokes from the center all move with the spokes, or is it like a liquid swirling around a drain, where particles spiral into the black hole?

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Re: APOD: Animation: Spiral Disk around a Hole... (2019 Aug 20)

Post by neufer » Tue Aug 20, 2019 9:56 pm

Psnarf wrote:
Tue Aug 20, 2019 8:45 pm

Does the disk spin like a galaxy, where particles along arbitrary spokes from the center all move with the spokes, or is it like a liquid swirling around a drain, where particles spiral into the black hole?
The emphasis on "gas this fast shows relativistic beaming" would indicate that
the displayed spiral motion is primarily "like a liquid swirling around a drain."

(However, the spokes/arms in a spiral galaxy
constitute a wave through which the particles/stars orbit.)
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Re: APOD: Animation: Spiral Disk around a Hole... (2019 Aug 20)

Post by alter-ego » Wed Aug 21, 2019 3:38 am

neufer wrote:
Tue Aug 20, 2019 7:13 pm
sillyworm 2 wrote:
Tue Aug 20, 2019 3:17 pm

Is there a limit to how big a black hole can become?
The mass density of large black holes drops off inversely with the square of their mass/radius.

When such black holes approach the size of the known universe they should contain an equivalent density of dark energy that explodes the black hole.

(Very small dense black holes explode due to Hawking radiation.)
Interesting concept. I see the appeal in wanting DE to exist inside a black hole but it's pure speculation. I'm not aware of any accepted theory predicting BH instability as it's mass increases. Suggesting any "interior" dynamics of that nature is a real stretch. We can't see, and have no understanding any physical processes within the BH event horizon other than a mathematical singularity. Someday I believe we'll eliminate the singularity problem, but today, frankly, you're just dreaming. Hey not to say you couldn't be right though :wink:
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Re: APOD: Animation: Spiral Disk around a Hole... (2019 Aug 20)

Post by FLPhotoCatcher » Wed Aug 21, 2019 4:51 am

I'd have to give this movie two thumbs down. :thumb_down: :thumb_down:
I don't see any relativistic beaming near the center, I don't see any gravitational lensing near the center, nor is there any hint of a polar jet. :facepalm:
And it's so short that I only ate two pieces of popcorn.

And, only three emojis allowed??
>:-(

Ok, rant over.

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Re: APOD: Animation: Spiral Disk around a Hole... (2019 Aug 20)

Post by neufer » Wed Aug 21, 2019 12:17 pm

FLPhotoCatcher wrote:
Wed Aug 21, 2019 4:51 am

I'd have to give this movie two thumbs down. :thumb_down: :thumb_down:
I don't see any relativistic beaming near the center,
Don't think of synchrotron X-ray radiation beaming :!:

This is just plain old Poynting–Robertson effect zodiacal cloud drag on steroids:
https://en.wikipedia.org/wiki/Zodiacal_light#Origin wrote:
<<The first fully dynamical model of the zodiacal cloud demonstrated that only if the dust was released in orbits that approach Jupiter, is it stirred up enough to explain the thickness of the zodiacal dust cloud. The dust in meteoroid streams is much larger, 300 to 10,000 micrometres in diameter, and falls apart into smaller zodiacal dust grains over time. The Poynting–Robertson effect forces the dust into more circular (but still elongated) orbits, while spiralling slowly into the Sun. Hence a continuous source of new particles is needed to maintain the zodiacal cloud.

The Poynting–Robertson effect is a process by which solar radiation causes a dust grain orbiting a star to lose angular momentum relative to its orbit around the star. This is related to radiation pressure tangential to the grain's motion.

This causes dust that is small enough to be affected by this drag, but too large to be blown away from the star by radiation pressure, to spiral slowly into the star. In the case of the Solar System, this can be thought of as affecting dust grains from 1 μm to 1 mm in diameter. Larger dust is likely to collide with another object long before such drag can have an effect.

Poynting initially gave a description of the effect in 1903 based on the luminiferous aether theory, which was superseded by the theories of relativity in 1905–1915. In 1937 Robertson described the effect in terms of general relativity.>>
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Re: APOD: Animation: Spiral Disk around a Hole... (2019 Aug 20)

Post by Psnarf » Fri Aug 30, 2019 3:03 pm

If the particles in the accretion disk are "like a liquid swirling around a drain," does it not then follow that all of the stars in the galaxy behave in much the same way? That is, will the stars orbiting the central super-massive black hole eventually approach and fall into the hole? Is the rate at which the distance between a star and the galactic center decreases offset by expansion? Are the two forces, gravitational attraction of the black hole vs expansion of the universe, in balance? Will galaxies contract eventually collapsing into the hole or expand and fly apart?
Speaking of empty space expanding, does not the space-time inside a black hole horizon expand as well?

Obquote: "Holey Space-Time, Batman!" -Robin.

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Re: APOD: Animation: Spiral Disk around a Hole... (2019 Aug 20)

Post by neufer » Fri Aug 30, 2019 4:07 pm

Psnarf wrote:
Fri Aug 30, 2019 3:03 pm

If the particles in the accretion disk are "like a liquid swirling around a drain," does it not then follow that all of the stars in the galaxy behave in much the same way? That is, will the stars orbiting the central super-massive black hole eventually approach and fall into the hole?
Just because tiny zodiacal dust grains spiral into the Sun (from Poynting–Robertson effect) doesn't mean that planets do too.

The main orbital loss of star sized bodies is probably due to gravitational radiation.
Psnarf wrote:
Fri Aug 30, 2019 3:03 pm

Is the rate at which the distance between a star and the galactic center decreases offset by expansion? Are the two forces, gravitational attraction of the black hole vs expansion of the universe, in balance? Will galaxies contract eventually collapsing into the hole or expand and fly apart?

Speaking of empty space expanding, does not the space-time inside a black hole horizon expand as well?
Gravitationally bound objects are thought to be exempt from expansion of the universe. Dark energy reduces the attraction of orbiting objects but since the space between the bound objects isn't increasing the reduction in the attraction shouldn't increase as well. (Ditto with the space-time inside a black hole horizon.)
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Re: APOD: Animation: Spiral Disk around a Hole... (2019 Aug 20)

Post by BDanielMayfield » Fri Aug 30, 2019 4:09 pm

Psnarf wrote:
Fri Aug 30, 2019 3:03 pm
If the particles in the accretion disk are "like a liquid swirling around a drain," does it not then follow that all of the stars in the galaxy behave in much the same way? That is, will the stars orbiting the central super-massive black hole eventually approach and fall into the hole?
No. As has often been explained here, objects orbit black holes in the same manner that planets orbit stars. Conservation of momentum insures that orbits don't decay unless there is a loss of energy somehow, as when low orbit satellites experience atmospheric drag.
Is the rate at which the distance between a star and the galactic center decreases offset by expansion?
No. The universe's expansion is occurring because the voids between galactic clusters are expanding. The distance between objects inside gravitationally bound systems are not affected by this expansion. Over its whole orbit, the average distance between a typical star and the galactic center remains unchanged.

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Re: APOD: Animation: Spiral Disk around a Hole... (2019 Aug 20)

Post by Chris Peterson » Fri Aug 30, 2019 5:33 pm

Psnarf wrote:
Fri Aug 30, 2019 3:03 pm
If the particles in the accretion disk are "like a liquid swirling around a drain," does it not then follow that all of the stars in the galaxy behave in much the same way? That is, will the stars orbiting the central super-massive black hole eventually approach and fall into the hole? Is the rate at which the distance between a star and the galactic center decreases offset by expansion? Are the two forces, gravitational attraction of the black hole vs expansion of the universe, in balance? Will galaxies contract eventually collapsing into the hole or expand and fly apart?
Speaking of empty space expanding, does not the space-time inside a black hole horizon expand as well?
An accretion disk is dense enough that the material in it can interact hydrodynamically (via collisions and electromagnetic effects). This results in a loss of energy and reduction in orbit size (i.e spiraling into the center). Stars in a galaxy only interact gravitationally, and only very weakly. The result is that stars don't generally lose their orbital momentum, and when they do (as with near passes) one star gains a little and the other loses a little.
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Re: APOD: Animation: Spiral Disk around a Hole... (2019 Aug 20)

Post by neufer » Fri Aug 30, 2019 11:23 pm

Chris Peterson wrote:
Fri Aug 30, 2019 5:33 pm

An accretion disk is dense enough that the material in it can interact hydrodynamically (via collisions and electromagnetic effects). This results in a loss of energy and reduction in orbit size (i.e spiraling into the center). Stars in a galaxy only interact gravitationally, and only very weakly. The result is that stars don't generally lose their orbital momentum, and when they do (as with near passes) one star gains a little and the other loses a little.
To the extent electrohydrodynamics (EHD) is acting here it is probably redirecting the equatorial influx into polar jets. However, there is no indication anything like that is taking place in the APOD video.
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Re: APOD: Animation: Spiral Disk around a Hole... (2019 Aug 20)

Post by Chris Peterson » Fri Aug 30, 2019 11:54 pm

neufer wrote:
Fri Aug 30, 2019 11:23 pm
Chris Peterson wrote:
Fri Aug 30, 2019 5:33 pm

An accretion disk is dense enough that the material in it can interact hydrodynamically (via collisions and electromagnetic effects). This results in a loss of energy and reduction in orbit size (i.e spiraling into the center). Stars in a galaxy only interact gravitationally, and only very weakly. The result is that stars don't generally lose their orbital momentum, and when they do (as with near passes) one star gains a little and the other loses a little.
To the extent electrohydrodynamics (EHD) is acting here it is probably redirecting the equatorial influx into polar jets. However, there is no indication anything like that is taking place in the APOD video.
My understanding is that hydrodynamics are always an important factor in accretion disks- whether around a black hole, or around a new star.
Chris

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