Starship Asterisk*

by **johnnydeep** » Wed May 08, 2024 6:28 pm

Chris Peterson wrote: ↑Tue May 07, 2024 7:19 pm
johnnydeep wrote: ↑Tue May 07, 2024 6:52 pm
Chris Peterson wrote: ↑Tue May 07, 2024 5:19 pm

I don't think the quote is a good description at all. A black hole is an entity which is sufficiently dense that there is a region around it (bounded by the event horizon... which itself isn't a physical thing) where the escape velocity is greater than c. Really, that's all. Every visual aspect of a black hole that we observe takes place outside the event horizon, and in almost all cases can occur (or a similar phenomenon can occur) around any sufficiently dense body, not just a black hole.
What do you mean by that? What "similar phenomenon" around some other "sufficiently dense body" are you referring to?
Accretion disks, jets, energy bursts, complex magnetic and electric fields.

Ok, but what other "sufficiently dense" bodies are there? Neutron stars? White dwarfs? Large stars? Planets? And only BHs have event horizons, right?

by **johnnydeep** » Wed May 08, 2024 6:24 pm

Chris Peterson wrote: ↑Tue May 07, 2024 10:13 pm
Christian G. wrote: ↑Tue May 07, 2024 9:17 pm
Chris Peterson wrote: ↑Tue May 07, 2024 8:12 pm

Photons are just packets of energy. Presumably the energy is converted to its mass form once a photon falls into a black hole. The black hole keeps its energy; it doesn't keep its "light".
That implies a cool idea! All the photons of every star in the sky that reach a black hole are continuously feeding it!
This is already an important part of our understanding. Black holes lose mass due to Hawking radiation, and in theory that will eventually result in their evaporation. But for now, they are acquiring more mass in the form of the radiation they absorb than they lose to Hawking radiation. Most of that radiation being photons from the CMB, at a mere few degrees K. But that's still enough energy to keep them growing. As the Universe cools, that will eventually change, and black holes will start shrinking.

That's very cool! And I presume that fact is taken into account when calculating how long BHs take to evaporate due to Hawking radiation. But about that radiation: I've read it described as happening because of particle/anti-particle pair creation near enough to the BH that one of the pair falls in and the other escapes. But why wouldn't that result in a net gain in mass?

by **Chris Peterson** » Tue May 07, 2024 10:13 pm

Christian G. wrote: ↑Tue May 07, 2024 9:17 pm
Chris Peterson wrote: ↑Tue May 07, 2024 8:12 pm
zendae wrote: ↑Tue May 07, 2024 8:10 pm Is a black hole the brightest thing in the Universe because it keeps its light? In a black hole, things go to infinity, things go to zero, things go we know not. What does light do? Is there a limit to the number of possible photons, or is brightness theoretically infinite?
Photons are just packets of energy. Presumably the energy is converted to its mass form once a photon falls into a black hole. The black hole keeps its energy; it doesn't keep its "light".
That implies a cool idea! All the photons of every star in the sky that reach a black hole are continuously feeding it!

This is already an important part of our understanding. Black holes lose mass due to Hawking radiation, and in theory that will eventually result in their evaporation. But for now, they are acquiring more mass in the form of the radiation they absorb than they lose to Hawking radiation. Most of that radiation being photons from the CMB, at a mere few degrees K. But that's still enough energy to keep them growing. As the Universe cools, that will eventually change, and black holes will start shrinking.

by **Christian G.** » Tue May 07, 2024 9:17 pm

Chris Peterson wrote: ↑Tue May 07, 2024 8:12 pm
zendae wrote: ↑Tue May 07, 2024 8:10 pm Is a black hole the brightest thing in the Universe because it keeps its light? In a black hole, things go to infinity, things go to zero, things go we know not. What does light do? Is there a limit to the number of possible photons, or is brightness theoretically infinite?
Photons are just packets of energy. Presumably the energy is converted to its mass form once a photon falls into a black hole. The black hole keeps its energy; it doesn't keep its "light".

That implies a cool idea! All the photons of every star in the sky that reach a black hole are continuously feeding it!

by **Chris Peterson** » Tue May 07, 2024 8:12 pm

zendae wrote: ↑Tue May 07, 2024 8:10 pm Is a black hole the brightest thing in the Universe because it keeps its light? In a black hole, things go to infinity, things go to zero, things go we know not. What does light do? Is there a limit to the number of possible photons, or is brightness theoretically infinite?

Photons are just packets of energy. Presumably the energy is converted to its mass form once a photon falls into a black hole. The black hole keeps its energy; it doesn't keep its "light".

by **zendae** » Tue May 07, 2024 8:10 pm

Is a black hole the brightest thing in the Universe because it keeps its light? In a black hole, things go to infinity, things go to zero, things go we know not. What does light do? Is there a limit to the number of possible photons, or is brightness theoretically infinite?

edit: I did find this, tho it's not entirely in the layman's realm:

https://www.fabiopacucci.com/resources/ ... alculator/

by **Chris Peterson** » Tue May 07, 2024 8:06 pm

Christian G. wrote: ↑Tue May 07, 2024 7:44 pm
Chris Peterson wrote: ↑Tue May 07, 2024 5:19 pm
Christian G. wrote: ↑Tue May 07, 2024 5:11 pm From the link posted just above: "You can roughly think of a black hole as a star that traps all of its light". I like the "its" light. We normally read that "even light" can't escape a black hole, but saying "its" own light makes me wonder further. For instance gamma-ray bursts generated when black holes form (provided it is indeed the case), appear to last just a few seconds; but could it be that they last much longer but simply stay trapped? Might newborn black holes shine in powerful gamma-rays for a while but hold them back? Not sure if this makes any sense but it's a nice idea to entertain!
I don't think the quote is a good description at all. A black hole is an entity which is sufficiently dense that there is a region around it (bounded by the event horizon... which itself isn't a physical thing) where the escape velocity is greater than c. Really, that's all. Every visual aspect of a black hole that we observe takes place outside the event horizon, and in almost all cases can occur (or a similar phenomenon can occur) around any sufficiently dense body, not just a black hole.
I get that every visual aspect takes place outside the event horizon, and whatever may take place inside can't travel out and so can not be detected. But to the point of those gamma-ray bursts: A core-collapse lasts a second or so in the process leading to a black hole, and gamma-ray bursts associated to the process are deemed to also last brief seconds, so is it possible that those GRBs are only visible for brief seconds but may well go on much longer inside the newly-formed event horizon? (undetected obviously)

Not very long, I expect! Whatever is trapped inside the event horizon is going to spiral very quickly into the black hole. I don't think much survives long between the black hole and the event horizon.

by **Christian G.** » Tue May 07, 2024 7:44 pm

Chris Peterson wrote: ↑Tue May 07, 2024 5:19 pm
Christian G. wrote: ↑Tue May 07, 2024 5:11 pm From the link posted just above: "You can roughly think of a black hole as a star that traps all of its light". I like the "its" light. We normally read that "even light" can't escape a black hole, but saying "its" own light makes me wonder further. For instance gamma-ray bursts generated when black holes form (provided it is indeed the case), appear to last just a few seconds; but could it be that they last much longer but simply stay trapped? Might newborn black holes shine in powerful gamma-rays for a while but hold them back? Not sure if this makes any sense but it's a nice idea to entertain!
I don't think the quote is a good description at all. A black hole is an entity which is sufficiently dense that there is a region around it (bounded by the event horizon... which itself isn't a physical thing) where the escape velocity is greater than c. Really, that's all. Every visual aspect of a black hole that we observe takes place outside the event horizon, and in almost all cases can occur (or a similar phenomenon can occur) around any sufficiently dense body, not just a black hole.

I get that every visual aspect takes place outside the event horizon, and whatever may take place inside can't travel out and so can not be detected. But to the point of those gamma-ray bursts: A core-collapse lasts a second or so in the process leading to a black hole, and gamma-ray bursts associated to the process are deemed to also last brief seconds, so is it possible that those GRBs are only visible for brief seconds but may well go on much longer inside the newly-formed event horizon? (undetected obviously)

by **Chris Peterson** » Tue May 07, 2024 7:19 pm

johnnydeep wrote: ↑Tue May 07, 2024 6:52 pm
Chris Peterson wrote: ↑Tue May 07, 2024 5:19 pm
Christian G. wrote: ↑Tue May 07, 2024 5:11 pm From the link posted just above: "You can roughly think of a black hole as a star that traps all of its light". I like the "its" light. We normally read that "even light" can't escape a black hole, but saying "its" own light makes me wonder further. For instance gamma-ray bursts generated when black holes form (provided it is indeed the case), appear to last just a few seconds; but could it be that they last much longer but simply stay trapped? Might newborn black holes shine in powerful gamma-rays for a while but hold them back? Not sure if this makes any sense but it's a nice idea to entertain!
I don't think the quote is a good description at all. A black hole is an entity which is sufficiently dense that there is a region around it (bounded by the event horizon... which itself isn't a physical thing) where the escape velocity is greater than c. Really, that's all. Every visual aspect of a black hole that we observe takes place outside the event horizon, and in almost all cases can occur (or a similar phenomenon can occur) around any sufficiently dense body, not just a black hole.
What do you mean by that? What "similar phenomenon" around some other "sufficiently dense body" are you referring to?

Accretion disks, jets, energy bursts, complex magnetic and electric fields.

by **johnnydeep** » Tue May 07, 2024 6:52 pm

Chris Peterson wrote: ↑Tue May 07, 2024 5:19 pm
Christian G. wrote: ↑Tue May 07, 2024 5:11 pm From the link posted just above: "You can roughly think of a black hole as a star that traps all of its light". I like the "its" light. We normally read that "even light" can't escape a black hole, but saying "its" own light makes me wonder further. For instance gamma-ray bursts generated when black holes form (provided it is indeed the case), appear to last just a few seconds; but could it be that they last much longer but simply stay trapped? Might newborn black holes shine in powerful gamma-rays for a while but hold them back? Not sure if this makes any sense but it's a nice idea to entertain!
I don't think the quote is a good description at all. A black hole is an entity which is sufficiently dense that there is a region around it (bounded by the event horizon... which itself isn't a physical thing) where the escape velocity is greater than c. Really, that's all. Every visual aspect of a black hole that we observe takes place outside the event horizon, and in almost all cases can occur (or a similar phenomenon can occur) around any sufficiently dense body, not just a black hole.

What do you mean by that? What "similar phenomenon" around some other "sufficiently dense body" are you referring to?

by **Chris Peterson** » Tue May 07, 2024 5:19 pm

Christian G. wrote: ↑Tue May 07, 2024 5:11 pm From the link posted just above: "You can roughly think of a black hole as a star that traps all of its light". I like the "its" light. We normally read that "even light" can't escape a black hole, but saying "its" own light makes me wonder further. For instance gamma-ray bursts generated when black holes form (provided it is indeed the case), appear to last just a few seconds; but could it be that they last much longer but simply stay trapped? Might newborn black holes shine in powerful gamma-rays for a while but hold them back? Not sure if this makes any sense but it's a nice idea to entertain!

I don't think the quote is a good description at all. A black hole is an entity which is sufficiently dense that there is a region around it (bounded by the event horizon... which itself isn't a physical thing) where the escape velocity is greater than c. Really, that's all. Every visual aspect of a black hole that we observe takes place outside the event horizon, and in almost all cases can occur (or a similar phenomenon can occur) around any sufficiently dense body, not just a black hole.

by **Christian G.** » Tue May 07, 2024 5:11 pm

From the link posted just above: "You can roughly think of a black hole as a star that traps all of its light". I like the "its" light. We normally read that "even light" can't escape a black hole, but saying "its" own light makes me wonder further. For instance gamma-ray bursts generated when black holes form (provided it is indeed the case), appear to last just a few seconds; but could it be that they last much longer but simply stay trapped? Might newborn black holes shine in powerful gamma-rays for a while but hold them back? Not sure if this makes any sense but it's a nice idea to entertain!

by **Chris Peterson** » Tue May 07, 2024 3:38 pm

Fred the Cat wrote: ↑Tue May 07, 2024 3:31 pm Let's say a black hole is a four-dimensional object.

What about its jet?

All bodies with mass are 4D objects. Black holes. Stars. Atoms. So jets, too.

by **Fred the Cat** » Tue May 07, 2024 3:31 pm

Let's say a black hole is a four-dimensional object.

What about its jet?

by **Christian G.** » Tue May 07, 2024 12:27 pm

Black holes are often depicted as devouring cosmic cannibals that destroy everything, even equations! In my book however they are of an all-mighty beauty. Black holes are the ultimate objets, the ultimate manifestation of gravity, the ultimate evolution of stars (leaving aside galactic ones), we call them "black" but they generate the brightest lights of the universe, their interiors turn spacetime into spacelessness and timelessness, - I mean, they are everything but boring! A continuous source of mind-boggling fascination...

(and yes indeed AVAO, this week is a very cool idea on APOD's part following NASA, especially with you chiming in!)

by **AVAO** » Tue May 07, 2024 5:04 am

APOD Robot wrote: ↑Tue May 07, 2024 4:06 am Black Hole Accreting with Jet

Explanation: What happens when a black hole devours a star? Many details remain unknown, but observations are providing new clues. In 2014, a powerful explosion was recorded by the ground-based robotic telescopes of the All Sky Automated Survey for SuperNovae (Project ASAS-SN), with followed-up observations by instruments including NASA's Earth-orbiting Swift satellite. Computer modeling of these emissions fit a star being ripped apart by a distant supermassive black hole. The results of such a collision are portrayed in the featured artistic illustration. The black hole itself is a depicted as a tiny black dot in the center. As matter falls toward the hole, it collides with other matter and heats up. Surrounding the black hole is an accretion disk of hot matter that used to be the star, with a jet emanating from the black hole's spin axis.

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It's cool that the APOD team also adopted the NASA motto "It's Black Hole Week at NASA!".

But...
I personally love "real" pictures.

Today's illustration is a good example of the dilemma an illustrator faces when no one knows exactly, what the immediate enviroment of a black hole really looks like? So, he has to be really creative!

Where else are there jets? Yeea e.g. at the Crab Nebula

: Click to view full size image

: Click to view full size image 1 or image 2

jac berne (flickr) Original data: JWST

: Click to view full size image 1 or image 2

Original data: Chandra (X-ray)/HST/JWST

well, unfortunately a pulsar and not a black hole

But by the way, the visualization is from 2017 without AI, the image of the Crab Nebula is from 2023 from the WEBB space telescope

...not so bad after all.

Now on to the topic of jets in reality.
I took a closer look at M87 a while ago...

: Click to view full size image

: Click to view full size image

: Click to view full size image

: Click to view full size image

jac berne (flickr) Original data: HST

: Click to view full size image

jac berne (flickr) Original data: HST

: Click to view full size image

: Click to view full size image

: Click to view full size image

This sequence of images is intended to give a sense of how big black holes in the centers of galaxies and their jets really are. In the first images you can also see the full extent of the ejected gas masses in the radio (red).

by **Ann** » Tue May 07, 2024 4:42 am

Well, you know, that's a beautiful, ethereal, whimsical aerial dance of the remnants of a ripped-apart star, like the dance of the seven veils! It reminds me a little bit - not a lot, but a little bit - of the recent APOD showing Mt. Etna blowing smoke rings.

Black Hole Accreting with Jet.
Illustration Credit: NASA, Swift, Aurore Simonnet

Click to play embedded YouTube video.

And that's all I have to say about it!

Ann

by **APOD Robot** » Tue May 07, 2024 4:06 am

Black Hole Accreting with Jet

Explanation: What happens when a black hole devours a star? Many details remain unknown, but observations are providing new clues. In 2014, a powerful explosion was recorded by the ground-based robotic telescopes of the All Sky Automated Survey for SuperNovae (Project ASAS-SN), with followed-up observations by instruments including NASA's Earth-orbiting Swift satellite. Computer modeling of these emissions fit a star being ripped apart by a distant supermassive black hole. The results of such a collision are portrayed in the featured artistic illustration. The black hole itself is a depicted as a tiny black dot in the center. As matter falls toward the hole, it collides with other matter and heats up. Surrounding the black hole is an accretion disk of hot matter that used to be the star, with a jet emanating from the black hole's spin axis.

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