APOD: A Black Hole Disrupts a Passing Star (2024 May 05)

[zendae]

Thanks Chris. Interesting stuff. Black holes are really something. We can visually observe a something in which Relativity no longer holds; looking into a darkness not at all dark, and very undefinable.

[Ann]

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

Thanks, Jac! You provided us with a Hubble image of a real TDE, or at least its aftermath, called (as your picture showed) AT 2020neh. The caption to the image you posted reads like this:

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.

Okay. That explains the totally weird ring of dark debris seen in the APOD. The person behind the illustration had obviously seen the Hubble picture of a TDE showing a ring around the black hole, but the illustrator didn't understand that the ring was made up of massive stars, and therefore showed us a ring made of large clumps of murky space dust.

The presence of newborn stars very close to the black hole also makes it more likely that one of those stars might fall in, causing a TDE.

Ann

[VictorBorun]

IMHO this APOD means that the star is going away moving the other way than suggested in the comments above.
The accretion disk has been dark but now there is a bright trail through it; we can't see the disk in this pic, just the glowing trail through it.

What makes me think that the exit is broad hazy red part of the trail is the thing that on its way down to the perinegron the star should not leave a bright trail; the star before the ordeal was still strong at containing itself

[Ann]

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.

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

[VictorBorun]

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

I guess not a single brown dwarf happened to be disrupted during the Event Horizon Telescope exposure so all we see is a tiny inner part of the accretion disk (and a dark shadow twice the size of the event horizon where the gravity stopped the light and radio going our way). Both for M87 and for the Milky Way