Starship Asterisk*

Ann wrote: ↑Mon May 06, 2024 4:57 pm

Chris Peterson wrote: ↑Sun May 05, 2024 4:24 pm

johnnydeep wrote: ↑Sun May 05, 2024 4:06 pm

The singularity is small (infinitesimal) but isn't the BH's "size" and hence the gravitational effect - and collision window - determined by how large the event horizon is?

A black hole's "gravitational effect" is determined by its mass. The event horizon isn't a real thing, just a boundary that defines where light can't escape. It really has little physical meaning. We're talking here about stellar mass black holes interacting with stars. That is, objects with event horizons on the order of 10 km and objects with diameters on the order of a million km. So really, we might as well treat the BH as a point source.

All black holes may essentially be point sources, for all I know. But their accretion disks are not the same size. Here is how the accretion disk of Sgr A* (the central black hole of the Milky Way) compares with the accretion disk of the central black hole in M87, the largest elliptical galaxy in the Virgo Cluster (and I apologize for the tiny size of the picture):

Size comparison of the black holes in the Milky Way and M87. The big one is in M87, in case you were wondering. Credit: ESO.

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Ann

Chris Peterson wrote: ↑Sun May 05, 2024 4:24 pm

johnnydeep wrote: ↑Sun May 05, 2024 4:06 pm

Chris Peterson wrote: ↑Sun May 05, 2024 3:53 pm
The mass of the black hole doesn't matter, except to the extent that it's a factor in determining the orbit. Whether it hits the star depends on whether its orbit intersects the interior of the star. This is basically no different than two stars passing by each other, except in the case of the black hole one of the bodies is very small, so there's a smaller collision window.

AFAIK, there is no theoretical limit to how massive a black hole can become.

The singularity is small (infinitesimal) but isn't the BH's "size" and hence the gravitational effect - and collision window - determined by how large the event horizon is?

A black hole's "gravitational effect" is determined by its mass. The event horizon isn't a real thing, just a boundary that defines where light can't escape. It really has little physical meaning. We're talking here about stellar mass black holes interacting with stars. That is, objects with event horizons on the order of 10 km and objects with diameters on the order of a million km. So really, we might as well treat the BH as a point source.

AVAO wrote: ↑Sun May 05, 2024 7:46 pm

APOD Robot wrote: ↑Sun May 05, 2024 4:05 am A Black Hole Disrupts a Passing Star

Explanation: What happens to a star that goes near a black hole? If the star directly impacts a massive black hole, then the star falls in completely -- and everything vanishes. More likely, though, the star goes close enough to have the black hole's gravity pull away its outer layers, or disrupt, the star. Then, most of the star's gas does not fall into the black hole. These stellar tidal disruption events can be as bright as a supernova, and an increasing amount of them are being discovered by automated sky surveys. In the featured artist's illustration, a star has just passed a massive black hole and sheds gas that continues to orbit. The inner edge of a disk of gas and dust surrounding the black hole is heated by the disruption event and may glow long after the star is gone.

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Well. It's still cool that NASA invented a "Black Hole Week", which the APOD team also took up as a topic.
https://science.nasa.gov/universe/black-hole-week

Just a request, if you really want to show such (in my eyes "horrible") visualizations as an APOD to illustrate (with or without AI is the same) real observations, then please provide a prominent link to the corresponding "real APOD". In this case it doesn't look particularly spectacular. A brief brightening (TDE) of a small cloud of pixels near a black hole, such as AT 2020neh.

Click to view full size image

https://www.space.com/black-hole-announ ... tion-event

Space.com (or NASA) wrote:

Astronomers discovered a star being ripped apart by a black hole in the galaxy SDSS J152120.07+140410.5, 850 million light years away. Researchers pointed NASA's Hubble Space Telescope to examine the aftermath, called AT 2020neh, which is shown in the center of the image. Hubble's ultraviolet camera saw a ring of stars being formed around the nucleus of the galaxy where AT 2020neh is located.

APOD Robot wrote: ↑Sun May 05, 2024 4:05 am A Black Hole Disrupts a Passing Star

Explanation: What happens to a star that goes near a black hole? If the star directly impacts a massive black hole, then the star falls in completely -- and everything vanishes. More likely, though, the star goes close enough to have the black hole's gravity pull away its outer layers, or disrupt, the star. Then, most of the star's gas does not fall into the black hole. These stellar tidal disruption events can be as bright as a supernova, and an increasing amount of them are being discovered by automated sky surveys. In the featured artist's illustration, a star has just passed a massive black hole and sheds gas that continues to orbit. The inner edge of a disk of gas and dust surrounding the black hole is heated by the disruption event and may glow long after the star is gone.

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Ann wrote: ↑Sun May 05, 2024 10:31 am

Rauf wrote: ↑Sun May 05, 2024 6:44 am

Chris Peterson wrote: ↑Sun May 05, 2024 5:01 am
I fear this is another "artist's representation" that is not very connected to reality.

So what needs to change in order to make it more realistic?

Here's another picture that I like a lot better:

Click to view full size image

Tidal disruption of star near black hole Sophia Dagnello NRAO AUI NSF.png

Tidal disruption of star near black hole. Credit: Sophia Dagnello, NRAO/AUI/NSF

In the picture by Sophia Dagnello, NRAO/AUI/NSF, we can see the star orbiting the black hole. We can't see the star in the APOD.

In the picture by Sophia Dagnello, NRAO/AUI/NSF, we can see gas from the star forming an accretion disk around the black hole. We can't really see that in the APOD.

In the picture by Sophia Dagnello, NRAO/AUI/NSF, we can clearly see a jet from the black hole. In the APOD, the red plume doesn't look much like a black hole jet to me, although I guess that is what it is meant to be.

In the picture by Sophia Dagnello, NRAO/AUI/NSF, there is no debris ring around the black hole. I couldn't understand what that ring was doing in the APOD.

Ann

Edit: Okay. I found a picture that explains what we see in the APOD. I'm not going to annotate this one, just steal the caption:

A disk of hot gas swirls around a black hole in this illustration. The stream of gas stretching to the right is what remains of a star that was pulled apart by the black hole. A cloud of hot plasma (gas atoms with their electrons stripped away) above the black hole is known as a corona. Credit: NASA/JPL-Caltech

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Okay. So the red plume in the APOD is not a jet from the black hole, but the last remnants of the star. D'uh.

Ann

APOD Robot wrote: ↑Sun May 05, 2024 4:05 am If the star directly impacts a massive black hole, then the star falls in completely -- and everything vanishes.

Christian G. wrote: ↑Sun May 05, 2024 3:03 pm

Chris Peterson wrote: ↑Sun May 05, 2024 2:51 pm [...] Still waiting for new physics there.

Thanks, you've made my day!

Chris Peterson wrote: ↑Sun May 05, 2024 4:42 pm

johnnydeep wrote: ↑Sun May 05, 2024 4:36 pm

Chris Peterson wrote: ↑Sun May 05, 2024 4:24 pm
A black hole's "gravitational effect" is determined by its mass. The event horizon isn't a real thing, just a boundary that defines where light can't escape. It really has little physical meaning. We're talking here about stellar mass black holes interacting with stars. That is, objects with event horizons on the order of 10 km and objects with diameters on the order of a million km. So really, we might as well treat the BH as a point source.

"Stellar mass black holes"? I thought these TDE were being caused - at least in the case illustrated here - by super massive BHs of several million solar masses. Those would have much larger event horizon diameters.

Wikipedia has this to say:

https://en.wikipedia.org/wiki/Tidal_disruption_event wrote:A tidal disruption event (TDE) is an astronomical phenomenon that occurs when a star approaches sufficiently close to a supermassive black hole (SMBH) to be pulled apart by the black hole's tidal force, experiencing spaghettification.[1][2] A portion of the star's mass can be captured into an accretion disk around the black hole (if the star is on a parabolic orbit), resulting in a temporary flare of electromagnetic radiation as matter in the disk is consumed by the black hole. According to early papers, tidal disruption events should be an inevitable consequence of massive black holes' activity hidden in galaxy nuclei, whereas later theorists concluded that the resulting explosion or flare of radiation from the accretion of the stellar debris could be a unique signpost for the presence of a dormant black hole in the center of a normal galaxy.[3] Sometimes a star can survive the encounter with an SMBH, and a remnant is formed. These events are termed partial TDEs.[4][5]

Okay, it's a little different if the BH is massive. But in that case, its event horizon is interesting in different ways. Whereas something will get spaghettified by the tidal force upon getting close to the event horizon of a stellar mass black hole, the tidal forces at the event horizon of a supermassive black hole are small.

johnnydeep wrote: ↑Sun May 05, 2024 4:36 pm

Chris Peterson wrote: ↑Sun May 05, 2024 4:24 pm

johnnydeep wrote: ↑Sun May 05, 2024 4:06 pm

The singularity is small (infinitesimal) but isn't the BH's "size" and hence the gravitational effect - and collision window - determined by how large the event horizon is?

A black hole's "gravitational effect" is determined by its mass. The event horizon isn't a real thing, just a boundary that defines where light can't escape. It really has little physical meaning. We're talking here about stellar mass black holes interacting with stars. That is, objects with event horizons on the order of 10 km and objects with diameters on the order of a million km. So really, we might as well treat the BH as a point source.

"Stellar mass black holes"? I thought these TDE were being caused - at least in the case illustrated here - by super massive BHs of several million solar masses. Those would have much larger event horizon diameters.

Wikipedia has this to say:

https://en.wikipedia.org/wiki/Tidal_disruption_event wrote:A tidal disruption event (TDE) is an astronomical phenomenon that occurs when a star approaches sufficiently close to a supermassive black hole (SMBH) to be pulled apart by the black hole's tidal force, experiencing spaghettification.[1][2] A portion of the star's mass can be captured into an accretion disk around the black hole (if the star is on a parabolic orbit), resulting in a temporary flare of electromagnetic radiation as matter in the disk is consumed by the black hole. According to early papers, tidal disruption events should be an inevitable consequence of massive black holes' activity hidden in galaxy nuclei, whereas later theorists concluded that the resulting explosion or flare of radiation from the accretion of the stellar debris could be a unique signpost for the presence of a dormant black hole in the center of a normal galaxy.[3] Sometimes a star can survive the encounter with an SMBH, and a remnant is formed. These events are termed partial TDEs.[4][5]

Chris Peterson wrote: ↑Sun May 05, 2024 4:24 pm

johnnydeep wrote: ↑Sun May 05, 2024 4:06 pm

Chris Peterson wrote: ↑Sun May 05, 2024 3:53 pm
The mass of the black hole doesn't matter, except to the extent that it's a factor in determining the orbit. Whether it hits the star depends on whether its orbit intersects the interior of the star. This is basically no different than two stars passing by each other, except in the case of the black hole one of the bodies is very small, so there's a smaller collision window.

AFAIK, there is no theoretical limit to how massive a black hole can become.

The singularity is small (infinitesimal) but isn't the BH's "size" and hence the gravitational effect - and collision window - determined by how large the event horizon is?

A black hole's "gravitational effect" is determined by its mass. The event horizon isn't a real thing, just a boundary that defines where light can't escape. It really has little physical meaning. We're talking here about stellar mass black holes interacting with stars. That is, objects with event horizons on the order of 10 km and objects with diameters on the order of a million km. So really, we might as well treat the BH as a point source.

https://en.wikipedia.org/wiki/Tidal_disruption_event wrote:A tidal disruption event (TDE) is an astronomical phenomenon that occurs when a star approaches sufficiently close to a supermassive black hole (SMBH) to be pulled apart by the black hole's tidal force, experiencing spaghettification.[1][2] A portion of the star's mass can be captured into an accretion disk around the black hole (if the star is on a parabolic orbit), resulting in a temporary flare of electromagnetic radiation as matter in the disk is consumed by the black hole. According to early papers, tidal disruption events should be an inevitable consequence of massive black holes' activity hidden in galaxy nuclei, whereas later theorists concluded that the resulting explosion or flare of radiation from the accretion of the stellar debris could be a unique signpost for the presence of a dormant black hole in the center of a normal galaxy.[3] Sometimes a star can survive the encounter with an SMBH, and a remnant is formed. These events are termed partial TDEs.[4][5]

johnnydeep wrote: ↑Sun May 05, 2024 4:06 pm

Chris Peterson wrote: ↑Sun May 05, 2024 3:53 pm

zendae wrote: ↑Sun May 05, 2024 3:48 pm

I edited my post with more queries...

The mass of the black hole doesn't matter, except to the extent that it's a factor in determining the orbit. Whether it hits the star depends on whether its orbit intersects the interior of the star. This is basically no different than two stars passing by each other, except in the case of the black hole one of the bodies is very small, so there's a smaller collision window.

AFAIK, there is no theoretical limit to how massive a black hole can become.

The singularity is small (infinitesimal) but isn't the BH's "size" and hence the gravitational effect - and collision window - determined by how large the event horizon is?

Chris Peterson wrote: ↑Sun May 05, 2024 3:53 pm

zendae wrote: ↑Sun May 05, 2024 3:48 pm

Chris Peterson wrote: ↑Sun May 05, 2024 3:47 pm

The tidal force of a black hole, because it is so small, is also small. Something doesn't feel tidal distortion around a black hole until it's about to fall in. (And with supermassive black holes, after it's fallen past the event horizon.)

I edited my post with more queries...

The mass of the black hole doesn't matter, except to the extent that it's a factor in determining the orbit. Whether it hits the star depends on whether its orbit intersects the interior of the star. This is basically no different than two stars passing by each other, except in the case of the black hole one of the bodies is very small, so there's a smaller collision window.

AFAIK, there is no theoretical limit to how massive a black hole can become.

zendae wrote: ↑Sun May 05, 2024 3:48 pm

Chris Peterson wrote: ↑Sun May 05, 2024 3:47 pm

zendae wrote: ↑Sun May 05, 2024 3:29 pm Can a black hole cause a star to supernova? Is the tidal force of a black hole more powerful than a supernova, either squelching it or, like Q, not being affected by it at all other than merely sucking it in like anything else?

The tidal force of a black hole, because it is so small, is also small. Something doesn't feel tidal distortion around a black hole until it's about to fall in. (And with supermassive black holes, after it's fallen past the event horizon.)

I edited my post with more queries...

Chris Peterson wrote: ↑Sun May 05, 2024 3:47 pm

zendae wrote: ↑Sun May 05, 2024 3:29 pm Can a black hole cause a star to supernova? Is the tidal force of a black hole more powerful than a supernova, either squelching it or, like Q, not being affected by it at all other than merely sucking it in like anything else?

The tidal force of a black hole, because it is so small, is also small. Something doesn't feel tidal distortion around a black hole until it's about to fall in. (And with supermassive black holes, after it's fallen past the event horizon.)

zendae wrote: ↑Sun May 05, 2024 3:29 pm Can a black hole cause a star to supernova? Is the tidal force of a black hole more powerful than a supernova, either squelching it or, like Q, not being affected by it at all other than merely sucking it in like anything else?

Chris Peterson wrote: ↑Sun May 05, 2024 2:51 pm

Christian G. wrote: ↑Sun May 05, 2024 2:44 pm

Chris Peterson wrote: ↑Sun May 05, 2024 1:45 pm

If a black hole is, indeed, a singularity, then by definition it has zero volume. No matter what its mass. As we have no physics at this point that can describe the details of the actual black hole, though... who knows?

I appreciate your answer! I imagine mathematicians being comfortable with singularities, since they deal with them on paper, but physicians less so, because they deal with nature! Singularities have zero volume, "by definition", in other words on paper! But are they realistic? By which I don't mean intuitive - I mean: can such singularities correspond to a physical reality, however weird? I'm over my head here but the idea that we can find a "singularity" in nature almost seems like a category mistake.
In any case I remember reading here a while ago that a black hole may be "some form of elementary particle", I think it was you who said that! (apologies if my memory's wrong). Should you feel like elaborating, please don't hesitate!

I prefer not to assess what is possible in nature with what my intuition (something evolved over millions of years of observing macroscopic nature and avoiding falling from trees) tells me makes sense. I'm fine with black holes being true singularities in the mathematical sense, or being particles (and modern physics doesn't even treat particles as particles, but rather, as complex fields... again defying intuition). Or being something else. For now, we're quite far along in our ability to describe the effect of a black hole on its surrounds, how it distorts spacetime, how it behaves gravitationally, what's going on at the event horizon. But the object itself? Still waiting for new physics there.

Christian G. wrote: ↑Sun May 05, 2024 2:44 pm

Chris Peterson wrote: ↑Sun May 05, 2024 1:45 pm

Christian G. wrote: ↑Sun May 05, 2024 1:27 pm
I suppose the "everything vanishes" part is a manner of speaking. Everything falls out of sight perhaps, but nothing "vanishes", rather what's left of the star's mass is added to the black hole's mass, increasing very slightly the event horizon radius, and dare I add: increasing ever so slightly the elusive singularity's volume? Say from the size of an atomic nucleus to a minuscule notch above? Surely a 5 solar mass BH singularity has a different volume than a 50 solar mass one?

If a black hole is, indeed, a singularity, then by definition it has zero volume. No matter what its mass. As we have no physics at this point that can describe the details of the actual black hole, though... who knows?

I appreciate your answer! I imagine mathematicians being comfortable with singularities, since they deal with them on paper, but physicians less so, because they deal with nature! Singularities have zero volume, "by definition", in other words on paper! But are they realistic? By which I don't mean intuitive - I mean: can such singularities correspond to a physical reality, however weird? I'm over my head here but the idea that we can find a "singularity" in nature almost seems like a category mistake.
In any case I remember reading here a while ago that a black hole may be "some form of elementary particle", I think it was you who said that! (apologies if my memory's wrong). Should you feel like elaborating, please don't hesitate!

Chris Peterson wrote: ↑Sun May 05, 2024 1:45 pm

Christian G. wrote: ↑Sun May 05, 2024 1:27 pm

APOD Robot wrote: ↑Sun May 05, 2024 4:05 am A Black Hole Disrupts a Passing Star

If the star directly impacts a massive black hole, then the star falls in completely -- and everything vanishes.

I suppose the "everything vanishes" part is a manner of speaking. Everything falls out of sight perhaps, but nothing "vanishes", rather what's left of the star's mass is added to the black hole's mass, increasing very slightly the event horizon radius, and dare I add: increasing ever so slightly the elusive singularity's volume? Say from the size of an atomic nucleus to a minuscule notch above? Surely a 5 solar mass BH singularity has a different volume than a 50 solar mass one?

If a black hole is, indeed, a singularity, then by definition it has zero volume. No matter what its mass. As we have no physics at this point that can describe the details of the actual black hole, though... who knows?

Rauf wrote: ↑Sun May 05, 2024 6:44 am

Chris Peterson wrote: ↑Sun May 05, 2024 5:01 am

Ann wrote: ↑Sun May 05, 2024 4:27 am Okay, cool, but...

A Black Hole Disrupts a Passing Star. Illustration Credit: NASA, JPL-Caltech

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APOD 5 May 2024 annotated.png

Can anyone answer my questions?

Ann

I fear this is another "artist's representation" that is not very connected to reality.

So what needs to change in order to make it more realistic?

Christian G. wrote: ↑Sun May 05, 2024 1:27 pm

APOD Robot wrote: ↑Sun May 05, 2024 4:05 am A Black Hole Disrupts a Passing Star

If the star directly impacts a massive black hole, then the star falls in completely -- and everything vanishes.

I suppose the "everything vanishes" part is a manner of speaking. Everything falls out of sight perhaps, but nothing "vanishes", rather what's left of the star's mass is added to the black hole's mass, increasing very slightly the event horizon radius, and dare I add: increasing ever so slightly the elusive singularity's volume? Say from the size of an atomic nucleus to a minuscule notch above? Surely a 5 solar mass BH singularity has a different volume than a 50 solar mass one?

APOD Robot wrote: ↑Sun May 05, 2024 4:05 am A Black Hole Disrupts a Passing Star

If the star directly impacts a massive black hole, then the star falls in completely -- and everything vanishes.