Black-hole-triggered star formation in the dwarf galaxy Henize 2-10(nature.com)
nature.com
Black-hole-triggered star formation in the dwarf galaxy Henize 2-10
https://www.nature.com/articles/s41586-021-04215-6
7 comments
To my knowledge nobody has explained how heating in an accretion disc turns into a collimated polar jet thousands of light years long.
"It must be magnets" does not qualify as such an explanation.
"It must be magnets" does not qualify as such an explanation.
It's pretty well accepted that the jets are powered by the Blandford-Znajek mechanism, and MHD simulations of accretion disks do show that the BZ mechanism can in fact generate jets. There are, of course, open questions about the details, in particular where the magnetic fields come from.
I.e., not just heating.
IANAS but:
You were there up until the end. The gas jets aren’t forming stars near the black hole nor are the stars formed using material from around it.
Instead, they are sending out the equivalent of pilot lights that kick off star formation in another part of the galaxy where clouds of star forming gas were already collecting
You were there up until the end. The gas jets aren’t forming stars near the black hole nor are the stars formed using material from around it.
Instead, they are sending out the equivalent of pilot lights that kick off star formation in another part of the galaxy where clouds of star forming gas were already collecting
I believe the jets are compressing the gas clouds that were already there. That definitely could trigger star formation.
Agreed. To go a little further: the main point of the paper is that there is a subtlety with how black hole outflow can effect the neighborhood:
1. the outflow is so energetic that it blows the gas clouds away and shuts down star formation
2. the outflow is energetic enough to compress/raise the temperature of the gas clouds, leading to star formation
This second is the newly observed mode, but there is also yet more subtlety there since this burst of star formation may result a reduction in future star formations, but that is quickly approaching the limit of my layman/enthusiast understanding.
1. the outflow is so energetic that it blows the gas clouds away and shuts down star formation
2. the outflow is energetic enough to compress/raise the temperature of the gas clouds, leading to star formation
This second is the newly observed mode, but there is also yet more subtlety there since this burst of star formation may result a reduction in future star formations, but that is quickly approaching the limit of my layman/enthusiast understanding.
It matters enormously how ionized the gas cloud is. If it is neutral, the ion jet blasts right through, hardly noticing it: it is all, after all, "vacuum". Fully ionized, every particle in the jet interacts with every particle in the cloud.
Most such clouds are partially ionized, often to different degrees in different parts. Even a 0.01% ionized cloud behaves differently to a gas.
The proper name for such a cloud is "plasma". Many astronomers are allergic to this word, probably because the maths for plasma fluid dynamics is all just way too hard, and they steer clear, preferring literally any alternative (heating! gravitation! shocks!) over engaging.
Ordinary fluid dynamics is tricky enough to be often intractable. Plasma fluid dynamics is freaky because usually the positive ions are at least 1836 times as massive as the negative ions. Dust can be ionized, too, either direction. Then the ratio might be 6, 7, 10 orders of magnitude.
Vacuum is usually treated, in astrophysics, as infinitely conductive, and the charge carriers as massless, making static electric fields impossible, and freezing magnetic fields in place. But moving ion clouds (including jets) carry magnetic fields, and thus generate varying local electric fields. And, of course, the carriers are not really massless at all.
Most such clouds are partially ionized, often to different degrees in different parts. Even a 0.01% ionized cloud behaves differently to a gas.
The proper name for such a cloud is "plasma". Many astronomers are allergic to this word, probably because the maths for plasma fluid dynamics is all just way too hard, and they steer clear, preferring literally any alternative (heating! gravitation! shocks!) over engaging.
Ordinary fluid dynamics is tricky enough to be often intractable. Plasma fluid dynamics is freaky because usually the positive ions are at least 1836 times as massive as the negative ions. Dust can be ionized, too, either direction. Then the ratio might be 6, 7, 10 orders of magnitude.
Vacuum is usually treated, in astrophysics, as infinitely conductive, and the charge carriers as massless, making static electric fields impossible, and freezing magnetic fields in place. But moving ion clouds (including jets) carry magnetic fields, and thus generate varying local electric fields. And, of course, the carriers are not really massless at all.
> The proper name for such a cloud is "plasma". Many astronomers are allergic to this word, probably because the maths for plasma fluid dynamics is all just way too hard
I'm an astronomer (or at least used to be) and I don't know any astronomers who are allergic to the word "plasma". MHD simulations are hard, but when it's necessary to do them, astronomers do them. I'm not exactly sure what the point of this comment is. Are you saying that astronomers are not handling the physics of jet-ISM interactions properly?
I'm an astronomer (or at least used to be) and I don't know any astronomers who are allergic to the word "plasma". MHD simulations are hard, but when it's necessary to do them, astronomers do them. I'm not exactly sure what the point of this comment is. Are you saying that astronomers are not handling the physics of jet-ISM interactions properly?
It is very rare to encounter the word "plasma", at all, in any astro article, and vanishingly rare to encounter any mention of any plasma fluid dynamics phenomenon, as such, except in solar physics. Usually we read "hot gas". There has been some progress: x-radiation is not militantly insisted to be blackbody radiation from stuff at absurdly high temperatures, anymore.
MHD is the trivial, sanitized subset of plasma fluid dynamics that rarely occurs in nature, and is hard enough to maintain even artificially. But MHD maths are easier.
I am saying that astronomers seem, from any remove, to try hard to avoid discussing things that seem to require treatment with PFD. Polar jets are embarrassing because they cannot be ignored. So, how they work is just never mentioned in the popular press.
MHD is the trivial, sanitized subset of plasma fluid dynamics that rarely occurs in nature, and is hard enough to maintain even artificially. But MHD maths are easier.
I am saying that astronomers seem, from any remove, to try hard to avoid discussing things that seem to require treatment with PFD. Polar jets are embarrassing because they cannot be ignored. So, how they work is just never mentioned in the popular press.
So... they recycle matters into stars?
Can we say black holes are in fact... green?
Can we say black holes are in fact... green?
I mean, they are the best trash compactors known to us...
What goes in must come out.
1st law of common sense LoL
The title here:
> “Black Hole Gives Birth to New Stars Rather Than Devouring Them”
is misleading. The black hole is still devouring matter, in fact it must have been to cause the outflow that triggered star formation in another region.
Removing “Rather Than Devouring Them” would improve the title, but better would be to simply use the title from the paper.
is misleading. The black hole is still devouring matter, in fact it must have been to cause the outflow that triggered star formation in another region.
Removing “Rather Than Devouring Them” would improve the title, but better would be to simply use the title from the paper.
Over-anthropomorphizing for self-amusement: perhaps it's merely playing with its food, creating new stars that it fully intends to devour in the future.
Ok, changed above. Thanks!
I was going to suggest, "Black Holes Provide Umbilical Cords to New Stars"
After I posted I was thinking and came up with “Black Hole Exhaust (Can) Breathe Life Into New Star Formation,” but I also like yours
previous thread https://news.ycombinator.com/item?id=30027502
> Black-hole-driven outflows ... probably play a role in heating and expelling gas (thereby suppressing star formation)
I feel like there is a neat science-fiction story in here somewhere :) A hyper-advanced space civilization embarks on a multi-million-year mission to tow black holes into neighboring galaxies in order to suppress star formation there and thus reduce the chances of competing civilization appearing in the next few billion years
I feel like there is a neat science-fiction story in here somewhere :) A hyper-advanced space civilization embarks on a multi-million-year mission to tow black holes into neighboring galaxies in order to suppress star formation there and thus reduce the chances of competing civilization appearing in the next few billion years
If your tech can do that, I wonder if it may be more efficient to just throw neutron stars around to disrupt star formation
My first question would be why such a civilization isn't just colonizing that galaxy. If the reason is that those distances are too hard to cross, then my question is why they're concerned about other civilizations developing. Of the top of my head, the best reason they would be worried about it is because it is something they would do themselves; but ever for an advanced civilization that seems like an expensive project with limited return. Or maybe they're as fearful as Larry Niven's puppeteers.
It also would be more efficient to go to that galaxy, tow its stars around, and form new black holes there. You'd move much less mass a much shorter distance. You could probably even pick a relative handful of stars and just nudge them and wait; they're already moving after all. Might as well use that momentum.
It also would be more efficient to go to that galaxy, tow its stars around, and form new black holes there. You'd move much less mass a much shorter distance. You could probably even pick a relative handful of stars and just nudge them and wait; they're already moving after all. Might as well use that momentum.
> My first question would be why such a civilization isn't just colonizing that galaxy.
Super advanced AI civilization spreads in all directions. Eventually the loyalty and purpose bits flip and the far-flung frontiers no longer share the same mission profile or allegiances.
Super advanced AI civilization spreads in all directions. Eventually the loyalty and purpose bits flip and the far-flung frontiers no longer share the same mission profile or allegiances.
Ah, yes, creating black holes in-situ does sound more reasonable.
As for the motivations of this civilization, I'm not sure, no one has written this story yet :)
As for the motivations of this civilization, I'm not sure, no one has written this story yet :)
Maybe they can’t colonize it due to multi-year gestation periods? Thus they can’t grow the population fast enough.
Maybe any civilization it can create there is bound to become a competitor for the same resources.
A moat of black holes.
Black holes pull in matter, but as the matter falls into the black hole, before it reaches the event horizon, it starts to collide into other matter, which can cause a lot of heating, which can cause gas jets to erupt outward. In the case of a supermassive black hole (such as the one theorized to be at the center of our galaxy), the gas jets could be so massive and hot that the gas could pull itself together (via gravity) and become one or more stars.