Starship Asterisk*

by **Chris Peterson** » Sun Jun 16, 2024 11:54 pm

florid_snow wrote: ↑Sun Jun 16, 2024 11:41 pm Maybe I'm wrong, but that "jet" of material looks exactly like a low Reynolds number smoke simulation. I happen to have more than a decade of painful experience with numerical simulations of turbulence. The rule of thumb for analysis via Reynolds number is that you measure the characteristic length scale of the "blobs" that form when the flow forms vorticies and folds on itself, then multiply by an approximate speed per blob, then divide by the viscosity of the atmosphere into which the jet is flowing. But for a vaccuum, there is no viscosity, so the Reynolds number goes to infinity, and it does not make sense to have any turbulent vorticies in a vacuum, except where the jet material has become so concentrated that it forms a partial atmosphere to have viscosity with itself.

Here is a beautiful image from a SpaceX launch that illustrates the transition from turbulence while the jet plume of the rocket is blown into an atmosphere vs a vacuum, and you can clearly see that how the jet plume is not turbulent in the vacuum of space. Maybe jets from black holes can be concentrated and focused via magnetic fields, but they still can't have significant internal viscosity. I think the animation artists here got a little bit ahead of themselves with some Houdini smoke-in-atmosphere simulations.

GdNRq.jpg

The Reynolds number for the interstellar medium is typically 10⁵ to 10⁷.

by **florid_snow** » Sun Jun 16, 2024 11:41 pm

Maybe I'm wrong, but that "jet" of material looks exactly like a low Reynolds number smoke simulation. I happen to have more than a decade of painful experience with numerical simulations of turbulence. The rule of thumb for analysis via Reynolds number is that you measure the characteristic length scale of the "blobs" that form when the flow forms vorticies and folds on itself, then multiply by an approximate speed per blob, then divide by the viscosity of the atmosphere into which the jet is flowing. But for a vaccuum, there is no viscosity, so the Reynolds number goes to infinity, and it does not make sense to have any turbulent vorticies in a vacuum, except where the jet material has become so concentrated that it forms a partial atmosphere to have viscosity with itself.

Here is a beautiful image from a SpaceX launch that illustrates the transition from turbulence while the jet plume of the rocket is blown into an atmosphere vs a vacuum, and you can clearly see that how the jet plume is not turbulent in the vacuum of space. Maybe jets from black holes can be concentrated and focused via magnetic fields, but they still can't have significant internal viscosity. I think the animation artists here got a little bit ahead of themselves with some Houdini smoke-in-atmosphere simulations.

: SpaceX Launch illustrating transition from turbulent to laminar flow

by **richardschumacher** » Sun Jun 16, 2024 6:14 pm

Chris Peterson wrote: ↑Sun Jun 16, 2024 2:09 pm It probably makes more sense to visualize that scenario the other way around... a black hole falling straight into the star.

Fair enough! With an initial velocity of zero I expect that the BH would fly right through the star, and then fall back. Probably it would make several passes before the star is completely gone (some of it absorbed, the rest flung away).

by **AVAO** » Sun Jun 16, 2024 6:01 pm

Christian G. wrote: ↑Sun Jun 16, 2024 4:04 pm The idea of a black hole tearing a star apart is pretty wild and sure captures the imagination, I'm glad there are at least "attempts" to show what such events might look like. Here's a more sober attempt, for something hugely wild! A massive black hole repeatedly plunging through the disk of a gargantuan black hole and flashing like a trillion stars each time!
https://www.youtube.com/watch?v=HBE8qBt ... kh&index=6

Cool. The referenced video refers to the galaxy OJ 287. This case is really exciting.
and there exists also real pictures ,-)

: Click to view full size image

https://www.astronews.com/news/artikel/2020/04/2004-020a.shtml

Read more: https://www.jpl.nasa.gov/news/spitzer-t ... hole-dance

: Click to view full size image

he curved jet in the active galaxy OJ 287 from radio images taken at the sharpest resolution with RadioAstron (a global array including the space radio telescope Spektr-R in orbit around Earth; top, left), the Global mm-VLBI Array (operating at the short wavelength of 3.5 mm; top, right) and the Very Long Baseline Array (an array of ten antennas across the USA, from the Virgin Islands in the East to Hawaii in the West; bottom). The ellipses at the bottom left indicate the image resolution in each case, a scale bar in milliarcseconds (mas) is also provided. The top panel shows a record-breaking resolution of about 12 microarseconds, achieved when the space radio telescope is 15 earth diameters away from the ground telescopes (a distance of about 190 000 km, comparable to the Moon orbit). Collage: Eduardo Ros (MPIfR), images: Gómez et al. (The Astrophysical Journal, 2022)

OJ 287 is a BL Lac object 4 billion light-years from Earth that has produced quasi-periodic optical outbursts going back approximately 120 years, as first apparent on photographic plates from 1891. Seen on photographic plates since at least 1887, it was first detected at radio wavelengths during the course of the Ohio Sky Survey. It is a supermassive black hole binary (SMBHB). The intrinsic brightness of the flashes corresponds to over a trillion times the Sun's luminosity, greater than the entire Milky Way galaxy's light output.
The optical light curve shows that OJ 287 has a periodic variation of 11–12 years with a narrow double peak at maximum brightness. This kind of variation suggests that it is a binary supermassive black hole. The double-burst variability is thought to result from the smaller black hole punching through the accretion disc of the larger black hole twice in every 12 years.
In recent models, the mass of the secondary supermassive black hole has been estimated to be approximately 125 million solar masses, although this has been debated through multiple studies.

https://en.wikipedia.org/wiki/OJ_287

by **Chris Peterson** » Sun Jun 16, 2024 5:59 pm

AVAO wrote: ↑Sun Jun 16, 2024 5:49 pm
Chris Peterson wrote: ↑Sun Jun 16, 2024 5:29 pm
johnnydeep wrote: ↑Sun Jun 16, 2024 5:24 pm

And why is that? When I think of this event I picture the likely less massive object - the star - doing the falling into the likely larger object - the black hole.
The black hole is tiny compared with the star, and of similar mass.
Your statement may be true for normal black holes. However, the animation shown in APOD refers to a supermassive black hole. Here the balance of forces is probably somewhat different.

"Tracing back a ghostly particle to a shredded star, scientists have uncovered a gigantic cosmic particle accelerator. The subatomic particle, called a neutrino, was hurled towards Earth after the doomed star came too close to the supermassive black hole at the centre of its home galaxy 2MASX J20570298+1412165 and was ripped apart by the black hole's colossal gravity... Scientists estimate that the enormous black hole is as massive as 30 million suns...It is the first particle that can be traced back to such a 'tidal disruption event' (TDE) and provides evidence that these little understood cosmic catastrophes can be powerful natural particle accelerators, as the team led by DESY scientist Robert Stein reports in the journal Nature Astronomy. The observations also demonstrate the power of exploring the cosmos via a combination of different 'messengers' such as photons (the particles of light) and neutrinos, also known as multi-messenger astronomy.
[...]

https://www.desy.de/news/news_search/in ... nchor=2030

Ok. I looked and didn't see what kind of black hole this was showing. (I didn't look too hard.) I think the collision of a star and a stellar mass black hole is a lot more interesting, though.

And FWIW, the tidal forces around a supermassive black hole are much smaller than around a stellar mass black hole. You could fall through the event horizon of a SMBH without getting torn apart by tides. You can't get that close to a stellar mass BH to prevent that, though.

by **Rauf** » Sun Jun 16, 2024 5:58 pm

Just wanted to say, it's APOD's 29th birthday

Thank you editors, for giving us almost 3 decades of astronomy pictures everyday!

by **AVAO** » Sun Jun 16, 2024 5:49 pm

Chris Peterson wrote: ↑Sun Jun 16, 2024 5:29 pm
johnnydeep wrote: ↑Sun Jun 16, 2024 5:24 pm
Chris Peterson wrote: ↑Sun Jun 16, 2024 2:09 pm

It probably makes more sense to visualize that scenario the other way around... a black hole falling straight into the star.
And why is that? When I think of this event I picture the likely less massive object - the star - doing the falling into the likely larger object - the black hole.
The black hole is tiny compared with the star, and of similar mass.

Your statement may be true for normal black holes. However, the animation shown in APOD refers to a supermassive black hole. Here the balance of forces is probably somewhat different.

"Tracing back a ghostly particle to a shredded star, scientists have uncovered a gigantic cosmic particle accelerator. The subatomic particle, called a neutrino, was hurled towards Earth after the doomed star came too close to the supermassive black hole at the centre of its home galaxy 2MASX J20570298+1412165 and was ripped apart by the black hole's colossal gravity... Scientists estimate that the enormous black hole is as massive as 30 million suns...It is the first particle that can be traced back to such a 'tidal disruption event' (TDE) and provides evidence that these little understood cosmic catastrophes can be powerful natural particle accelerators, as the team led by DESY scientist Robert Stein reports in the journal Nature Astronomy. The observations also demonstrate the power of exploring the cosmos via a combination of different 'messengers' such as photons (the particles of light) and neutrinos, also known as multi-messenger astronomy.
[...]

https://www.desy.de/news/news_search/in ... nchor=2030

by **Chris Peterson** » Sun Jun 16, 2024 5:29 pm

johnnydeep wrote: ↑Sun Jun 16, 2024 5:24 pm
Chris Peterson wrote: ↑Sun Jun 16, 2024 2:09 pm
richardschumacher wrote: ↑Sun Jun 16, 2024 1:56 pm It's quite rare, but it would be fun to see a simulation of a star falling straight into a black hole, a direct hit as it were.
It probably makes more sense to visualize that scenario the other way around... a black hole falling straight into the star.
And why is that? When I think of this event I picture the likely less massive object - the star - doing the falling into the likely larger object - the black hole.

The black hole is tiny compared with the star, and of similar mass.

by **johnnydeep** » Sun Jun 16, 2024 5:24 pm

Chris Peterson wrote: ↑Sun Jun 16, 2024 2:09 pm
richardschumacher wrote: ↑Sun Jun 16, 2024 1:56 pm It's quite rare, but it would be fun to see a simulation of a star falling straight into a black hole, a direct hit as it were.
It probably makes more sense to visualize that scenario the other way around... a black hole falling straight into the star.

And why is that? When I think of this event I picture the likely less massive object - the star - doing the falling into the likely larger object - the black hole.

by **Christian G.** » Sun Jun 16, 2024 4:04 pm

The idea of a black hole tearing a star apart is pretty wild and sure captures the imagination, I'm glad there are at least "attempts" to show what such events might look like. Here's a more sober attempt, for something hugely wild! A massive black hole repeatedly plunging through the disk of a gargantuan black hole and flashing like a trillion stars each time!
https://www.youtube.com/watch?v=HBE8qBt ... kh&index=6

by **AVAO** » Sun Jun 16, 2024 3:51 pm

richardschumacher wrote: ↑Sun Jun 16, 2024 1:56 pm It's quite rare, but it would be fun to see a simulation of a star falling straight into a black hole, a direct hit as it were.

Well - scenarios 1-4 are possible paths to scenario 5. Mouth open - star in - mouth shut

"When a star flies directly into a black hole, dramatic and fascinating processes occur, which can be differentiated depending on the mass of the star and the black hole:

1. Breaking up of the star: If the star is very close to the black hole, immense tidal forces act on it. These enormous forces stretch the star more on the side facing the black hole than on the back. In extreme cases, this can lead to the star breaking into two halves, an event known as "spaghettification". The matter of the torn star then flows into the black hole in a thin spiral disk.

2. Brightness burst: As the star breaks apart and matter falls into the black hole, enormous energy is released. This energy can be emitted in the form of X-rays and gamma rays, creating a short-lived but extremely bright glow in the sky. This event is called a "tidal disruption event" (TDE).

3. Accretion disk: The star's matter that does not immediately fall into the black hole forms a hot, rotating disk around the hole, called the accretion disk. In this disk, the matter rubs against each other, heating it even further and emitting even more radiation.

4. Jets: In some cases, the rotating accretion disk can push jets of matter out of the black hole in opposite directions. These jets can reach enormous speeds and shoot out over great distances.

5. Final consumption: Eventually, all of the star's matter that has fallen into the black hole is pulled out or in beyond the event horizon and can never escape. The star has thus ended its existence and its mass now contributes to the enlargement of the black hole.

It is important to note that these processes occur over long (tbd) timescales due to the extremely strong gravity in the black hole region and involve complex physical phenomena. The exact details may vary from case to case and are the subject of current research in astrophysics."

verified by gemini

by **Chris Peterson** » Sun Jun 16, 2024 2:09 pm

richardschumacher wrote: ↑Sun Jun 16, 2024 1:56 pm It's quite rare, but it would be fun to see a simulation of a star falling straight into a black hole, a direct hit as it were.

It probably makes more sense to visualize that scenario the other way around... a black hole falling straight into the star.

by **richardschumacher** » Sun Jun 16, 2024 1:56 pm

It's quite rare, but it would be fun to see a simulation of a star falling straight into a black hole, a direct hit as it were.

by **xxxmicrobexxx** » Sun Jun 16, 2024 6:11 am

What sort of time frame are we talking about?

by **AVAO** » Sun Jun 16, 2024 6:10 am

shaileshs wrote: ↑Sun Jun 16, 2024 5:43 am I'm sorry to say, to me, this looks more like a sci-fi movie, super exaggerated dramatic, with all kinds of visual and audio effects (music) to make this even waaaaaaaaaaaay more explosive and dramatic than how in reality it'd be (as per many books and articles and scientists and presentations I've seen/read). Of course, NO ONE KNOWS for sure (and i hope people accept and understand that really no one knows), whatever one proposes is all speculation and theory.. Depends on what and who you believe and why. Nothing correct or wrong. Yes ? What do pundits here say/think ?

Well, maybe we can also discuss present events instead of old APODs (http://asterisk.apod.com/viewtopic.php?t=41650) and ridiculous animations.

Echoes of Flares from the Milky Way’s Supermassive Black Hole
UNIVERSETODAY.COM | 2024 June 14

Michigan State University researcher Grace Sanger-Johnson found nine previously undiscovered flares from Sagittarius A*, the Milky Way’s central supermassive black hole, by sifting through a decade’s worth of X-ray data. Credit: NuSTAR/NASA
[...]
Searching for Sgr A* X-ray Flares with NuSTAR Sanger-Johnson analyzed ten years’ worth of data looking for X-ray flares generated by Sgr A*’s eating habits. During the search, she found evidence for nine more such outbursts.
[...]
The data Sanger-Johnson collected and analyzed is now a database of flares from Sgr A. “We hope that by building up this bank of data on Sgr A flares, we and other astronomers can analyze the properties of these X-ray flares and infer the physical conditions inside the extreme environment of the supermassive black hole,” Sanger-Johnson said.
[...]
Tracking the Echoes of Flares While Sanger-Johnson was working with the NuSTAR data, undergraduate researcher Jack Uteg studied the activity around the black hole. He analyzed 20 years of data about a giant molecular cloud called “the Bridge”. The data came from observations made by NuSTAR and the European Space Agency’s XMM-Newton observatory. The Bridge lies close to Sgr A* and normally wouldn’t give off its own light.
[...]
What Those Light-echoes from Sgr A* Reveal Thanks to Sanger-Brown and Uteg’s work, astronomers have another way around the difficulties of observing around black holes. “Both flares and fireworks light up the darkness and help us observe things we wouldn’t normally be able to,” she said. “That’s why astronomers need to know when and where these flares occur, so they can study the black hole’s environment using that light.”
[...]
“This is the first time that we have constructed a 24-year-long variability for a molecular cloud surrounding our supermassive black hole that has reached its peak X-ray luminosity,” Zhang said. “It allows us to tell the past activity of Sgr A* from about 200 years ago. Our research team at MSU will continue this ‘astroarchaeology game’ to further unravel the mysteries of the Milky Way’s center.”

These results of the MSU team’s work were presented at the summer 2024 meeting of the American Astronomical Society.

https://www.universetoday.com/167397/ec ... lack-hole/

Astronomers do know about outbursts from Sgr A* from other observations. Here’s a view from NASA’s Imaging X-ray Polarimetry Explorer and Chandra X-ray Observatory. The combination of IXPE and Chandra data helped researchers determine that the X-ray light identified in the molecular clouds originated from Sagittarius A* during an outburst approximately 200 years ago.

: Click to view full size image

Credits: IXPE: NASA/MSFC/F. Marin et al; Chandra: NASA/CXC/SAO; Image Processing: L.Frattare, J.Major & K.Arcand

See more pictures & details under breaking news: viewtopic.php?p=339689#p339689

by **Chris Peterson** » Sun Jun 16, 2024 5:47 am

shaileshs wrote: ↑Sun Jun 16, 2024 5:43 am I'm sorry to say, to me, this looks more like a sci-fi movie, super exaggerated dramatic, with all kinds of visual and audio effects (music) to make this even waaaaaaaaaaaay more explosive and dramatic than how in reality it'd be (as per many books and articles and scientists and presentations I've seen/read). Of course, NO ONE KNOWS for sure (and i hope people accept and understand that really no one knows), whatever one proposes is all speculation and theory.. Depends on what and who you believe and why. Nothing correct or wrong. Yes ? What do pundits here say/think ?

I think it's actually a pretty simple system theoretically, and that means that a numerical simulation like this is likely to be pretty accurate.

by **shaileshs** » Sun Jun 16, 2024 5:43 am

I'm sorry to say, to me, this looks more like a sci-fi movie, super exaggerated dramatic, with all kinds of visual and audio effects (music) to make this even waaaaaaaaaaaay more explosive and dramatic than how in reality it'd be (as per many books and articles and scientists and presentations I've seen/read). Of course, NO ONE KNOWS for sure (and i hope people accept and understand that really no one knows), whatever one proposes is all speculation and theory.. Depends on what and who you believe and why. Nothing correct or wrong. Yes ? What do pundits here say/think ?

by **APOD Robot** » Sun Jun 16, 2024 4:07 am

Animation: Black Hole Destroys Star

Explanation: What happens if a star gets too close to a black hole? The black hole can rip it apart -- but how? It's not the high gravitational attraction itself that's the problem -- it's the difference in gravitational pull across the star that creates the destruction. In the featured animated video illustrating this disintegration, you first see a star approaching the black hole. Increasing in orbital speed, the star's outer atmosphere is ripped away during closest approach. Much of the star's atmosphere disperses into deep space, but some continues to orbit the black hole and forms an accretion disk. The animation then takes you into the accretion disk while looking toward the black hole. Including the strange visual effects of gravitational lensing, you can even see the far side of the disk. Finally, you look along one of the jets being expelled along the spin axis. Theoretical models indicate that these jets not only expel energetic gas, but also create energetic neutrinos -- one of which may have been seen recently on Earth.

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