[HN Gopher] Physicists identify the engine powering black hole e...
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Physicists identify the engine powering black hole energy beams
Author : theafh
Score : 96 points
Date : 2021-05-20 16:43 UTC (6 hours ago)
(HTM) web link (www.quantamagazine.org)
(TXT) w3m dump (www.quantamagazine.org)
| hcrisp wrote:
| I want to know if the jets are made up of material that is
| swirling towards the black hole from the accretion disk but get
| caught up in the magnetic helix (a) before it reaches the event
| horizon, or (b) after it passes the event horizon. If the former,
| then it's not as impressive since then nothing can escape a black
| hole except via Hawking radiation. If the latter, then this seems
| like quite a novel mechanism to prevent infinite black hole
| growth.
|
| The illustrations in the article don't provide an answer, though,
| since the details ends right where it ought to provide insight.
| The article does mention that the new paper puts doubt on the
| idea that nothing can escape a black hole, but I still didn't see
| any direct mention of the event horizon question.
| db48x wrote:
| Nothing can return after having crossed the event horizon.
| Gravity bends space and time, and in particular it changes
| which direction the time axis points. In a black hole, the time
| axis is bent all the way over so that it points directly at the
| singularity. All paths that enter the black hole must end at
| the singularity, because to do otherwise would require going
| backwards in time or faster than the speed of light.
| vmception wrote:
| How does one get to be the "artist" in astronomy article "artist
| renditions"?
| mhh__ wrote:
| If you've read Brian May's (of Queen fame) PhD thesis, he is
| the artist of his own pretty sketches
| RosanaAnaDana wrote:
| Well if its anything like biology, your first bet would be to
| get a degree in astrophysics. Doesn't necessarily need to be an
| advanced degree, but enough to know how to ask the right
| questions of those doing the work. Second step would be to
| maintain a continuous love for art/ drawing/ illustration.
| Third step is to get your work out there/ build a portfolio.
|
| Several colleagues of mine have ended up down the road of
| scientific illustration in biology. Most of them had BS in
| biology, botany, zoo, etc..
|
| Also:
|
| https://work.chron.com/become-scientific-illustrator-17160.h...
| kryptn wrote:
| Looks like they have a position open for an Interactive Web
| Developer [1] but it seems like the header animation is sourced
| (and attributed) from a youtube video from 2018 [2]
|
| [1] https://www.quantamagazine.org/about/
|
| [2] https://www.youtube.com/watch?v=S4a45z36EU4
| wumpus wrote:
| That animation was made by an EHT collaboration scientist,
| Andrew Chael. The EHT has outsourced some animations to a
| firm named CrazyBridge, but only occasionally.
| lsllc wrote:
| The spiral picture appears to actually be a "photo" of a black
| hole, from this article linked in the OP:
|
| https://eventhorizontelescope.org/blog/astronomers-image-mag...
| wumpus wrote:
| The spiral is an overlay telling you which way the magnetic
| fields point.
| ineedasername wrote:
| Unobtainium. Probably literally.
| arbitrage wrote:
| i mean their hypothesis is pretty convincing. have you read the
| article?
| eloff wrote:
| Simulation theory speculation:
|
| If the universe is a simulation, when there gets too much matter
| in an area to simulate all the interactions, a black hole is the
| way programmers fixed that - it gets turned into a singularity
| and isn't simulated anymore except as one point source of gravity
| (or in a more complex way if black holes preserve entropy - jury
| is still out on that one.)
|
| Silly and untestable, but fun to think about, like the rest of
| simulation theory. It would be required to do something like that
| if you're running a simulation with finite resources. You
| couldn't just keep piling matter into a finite area without
| bound, eventually you'd overwhelm what you can compute. Same
| reason one might want a hard speed limit like the speed of light.
|
| Interestingly this is a not a discrete function, time slows near
| large masses, which would allow the computer to keep up as matter
| in an area increased, much as you'd expect in a simulation.
| cout wrote:
| It's all fun and games until someone underflows velocity.
|
| In all seriousness, finding such a bug in the software would be
| the best possible evidence of living in a simulation. The hard
| part is demonstrating that it is a a bug an not a feature.
| wise0wl wrote:
| Delayed choice quantum eraser.
| infogulch wrote:
| Agree! This is my favorite crazy pet theory: spacetime is
| simulated on a flat 3d substrate with constant compute and
| memory per volume, which runs at a fixed rate in time (c) [1],
| and to account for a high density of mass requiring more
| compute the simulation is slowed down proportionally. Then,
| black holes are just the extreme end of this slowing down of
| the simulation.
|
| [1]: You always move at a constant speed: the speed of light.
| But that speed can be broken down into two component directions
| which you can trade off: time and space. You typically move
| near the speed of light in the _time_ direction, meaning your
| speed through the space direction is comparatively low.
| shaded-enmity wrote:
| My crazy pet theory: computational bandwidth is constant for
| any spacetime coordinate. According to Bekenstein bound the
| lower the temperature of the system the cheaper it is to flip
| a bit of information. As time progresses the CMBR gets
| colder, so it's cheaper to flip a bit, but conversely, as
| time progresses our Hubble volume gets smaller, limiting our
| total available energy budget to perform a bit flip.
| goldenkey wrote:
| None of these theories are crazy at all. Special relativity
| is directly derivable from energy causing a fixed amount of
| change (action) per unit time.
|
| When the information/computational changes that the energy
| is allocated, is used for non-local movement, then we
| consider this to be an aspect of velocity, and the amount
| of changes leftover for internal changes, which effectively
| are internal time, is decreased by a ratio equivalent to
| the standard time dilation formulas.
|
| Movement is change...change requires energy allocation,
| movement diminishes other interactions, hence time
| dilation, hence special relativity.
|
| Wolfram talks about this in his new graph based model of
| physics. Mass is an emergent metric of the amount of
| internal changes occurring in an object per unit time.
| Essentially, causal loops in the graph. Feynman had a toy
| model called the checkerboard model where the amount of
| bouncing in an area represented mass.
|
| https://youtu.be/xQafZ3CvBUs
| Strilanc wrote:
| Why would gravity follow an inverse square law in this model?
| Wouldn't you expect there to be a hard cutoff as you moved
| away from a busy region, instead of a gradual decrease?
| whoisburbansky wrote:
| Wouldn't it have to be a 4d substrate for c to be the "time"
| step-rate of the simulation? What does flat mean in this
| context?
| m3kw9 wrote:
| And how do they simulate us having consciousness?
| wpasc wrote:
| Would any knowledgeable HNers mind providing an ELI5 for this
| discovery?
| omrjml wrote:
| There has been lost of theories to explain how jets from black
| hole systems form. New observations of light polarization from
| M87 jet show twisting magnetic field lines which suggest one of
| the theories might be right. That theory says that spinning
| black hole's energy can be extracted by these twisting magnetic
| field lines and therefore power these jets.
| ISL wrote:
| For many decades, people have observed jets of hot gas spewing
| from the centers of some galaxies. There are multiple theories
| as to how those jets form.
|
| Radio astronomers got together and built a synthetic telescope
| the size of the Earth in order to be able to take a picture of
| the gas near the black hole at the center of a nearby galaxy,
| M87.
|
| When they did, and looked at the polarization of the light,
| they saw twisting lines, which agreed with the prediction of
| one of the most-favored theories for how these jets are
| produced.
| FredPret wrote:
| Things like the above makes me so grateful to be alive in
| this day and age
| prichino wrote:
| Quanta magazine is not a journal and is meant for general
| public divulgation; it is written in a very accessible style,
| starting from the title.
| arbitrage wrote:
| some people do not speak English as their native language.
| hi41 wrote:
| >> "The black hole in M87 is about the size of our solar system,"
| Issaoun said, yet it produces a 5,000-light-year-long current of
| white-hot plasma
|
| Do both jets put together have a length of 5000 light years or
| does each of the two jets have a length of 5000 light years
| making a total lenght of 10000 light years?
|
| Can someone please clarify. I have had this question for a ling
| time and it is eating me up.
|
| Edit: grammar.
| omrjml wrote:
| That's just one of the jets. In fact, I think only one side is
| observable as it pointed close to our direction, making the
| other side very difficult to observe.
| wumpus wrote:
| Yes. The forward jet is already faint despite being enhanced
| because it's pointed towards us. We can't see the backward
| one until it's way way outside the galaxy.
| [deleted]
| nvader wrote:
| This reminds me of the Hairy Ball Theorem:
| https://en.wikipedia.org/wiki/Hairy_ball_theorem
| eevilspock wrote:
| If these jets are narrow, and if the radiation is directed in the
| same direction as these jets (That's my understanding. Am I
| wrong?), how do we (1) see these jets in the first place and (2)
| if the answer is that we only see the ones pointed at us, how do
| we know they are (narrow) jets since we can't observe them from
| other angles?
| omrjml wrote:
| The radiation is not pointed in the same direction as jets like
| a laser. There is bulk motion of the plasma in a given
| direction, but the radiation is emitted from particles that are
| moving in a different directions within that plasma. So the
| radiation spread is wider than the jet direction.
| Interestingly, depending on if the jet we are viewing is
| pointed towards us or not can impact on the radiation signature
| in the form of blue shift and red shift. If the orientation is
| just right, bits of jet appear to move faster than to the speed
| of light, but it's just a geometric effect.
| FredPret wrote:
| I'm speculating, but maybe it lights up a conveniently located
| dust cloud
| ISL wrote:
| I believe that this is generally correct. Relativistic
| particles impinging upon even dilute gas will have bright
| signatures in many bands.
| gotstad wrote:
| Perhaps reflection from other bodies? Or simply some kind of
| radiation emitted from the jets?
| btilly wrote:
| How do you see the beam of a flashlight in the dark? Because it
| hits stuff in the air and bounces off.
|
| And the particles previously in the beam that already hit
| something are likely to hang around and be candidates for being
| hit themselves. And eventually they wind up as part of a big
| glowing cloud that you can see in the pictures. See
| https://d2r55xnwy6nx47.cloudfront.net/uploads/2021/05/cyga_v...
| linked in the picture for what it looks like. And for evidence
| that we can still see the beam when it isn't pointed directly
| at us.
| ectopod wrote:
| > Many jets are thin and bright all along their length. "How
| does it shine? How do we see it?" Chen wonders.
|
| It looks like nobody knows for sure.
| eloff wrote:
| Noob question: if not even light can escape from a black hole,
| magnetism can't either, right?
|
| So these fields must be produced by matter falling into the black
| hole, but before it crosses the event horizon?
| nostromo wrote:
| Another noob question I've never heard explained in a way I can
| understand:
|
| How does gravity escape from a black hole? It, like light,
| travels at the speed of light. So if light cannot escape, how
| does gravity?
| ncmncm wrote:
| That one, anyway, is easy. Sort of. Gravity is our perception
| of space itself being stretched, squeezed, even twisted. So,
| no gravity is escaping; instead, the black hole is warping
| the space it is in.
|
| The mathematics describing this process are intractable
| except in very special cases. In most cases, physicists are
| obliged to use an approximation that produces an answer that
| they hope has much of the character of the correct answer. At
| one extreme, they just use Newtonian gravity, which produces
| almost-exactly correct answers for small-scale systems
| involving just regular stars and planets. It is only when
| warpage gets very large compared to the size of the system,
| or when e.g. galaxy-scale mass is involved, or the
| differences between Newtonian gravity and reality are what is
| interesting, that they have to resort to more complicated
| approximations.
|
| It was recently discovered that calculations of the motion of
| galaxies were using an insufficiently accurate approximation
| that made it seem like stuff is orbiting too fast for the
| visible mass, requiring "dark matter"-extra, invisible mass-
| to hold the galaxy together. But using a more accurate
| approximation makes the need for dark matter evaporate. This
| created a problem because astrophysicists and cosmologists
| have come up with lots more uses for dark matter, to explain
| lots of other things. Without dark matter, they have dug
| themselves into a hole. The response has generally been to
| ignore the more accurate galactic gravitational model, and
| double down on dark matter. They can do this because
| ultimately it is all just a matter of papers being published
| and careers advanced or blighted; there are no other real-
| world consequences.
| willhslade wrote:
| Can you point us to something to illustrate this more
| accurate gravity estimate reducing the need for dark
| matter? Sounds fascinating.
| ncmncm wrote:
| It was on HN a few weeks ago.
|
| https://news.ycombinator.com/item?id=26450664
|
| https://news.ycombinator.com/item?id=26442021
| neom wrote:
| PBS Space Time to the rescue:
|
| What Happens at the Event Horizon? -
| https://www.youtube.com/watch?v=mht-1c4wc0Q
|
| What's On The Other Side Of A Black Hole? -
| https://www.youtube.com/watch?v=T4oYvSH6jJ8
|
| How Time Becomes Space Inside a Black Hole -
| https://www.youtube.com/watch?v=KePNhUJ2reI
|
| The Black Hole Information Paradox -
| https://www.youtube.com/watch?v=9XkHBmE-N34
| tzs wrote:
| I'd recommend the two episodes released right before the
| one about the black hole information paradox too. They set
| up for what is covered in the information paradox episode.
|
| "Why Quantum Information is Never Destroyed" -
| https://www.youtube.com/watch?v=HF-9Dy6iB_4
|
| "What Survives Inside A Black Hole?" -
| https://www.youtube.com/watch?v=GscfuQWZFAo
|
| Maybe the episode before those two also. I vaguely recall
| that something from the information paradox episode used
| something from that (and if I'm misremembering, it was
| still a neat episode):
|
| "Noether's Theorem and The Symmetries of Reality" -
| https://www.youtube.com/watch?v=04ERSb06dOg
|
| I have a question about the episodes you cited. They cover
| how beyond the event horizon space becomes time and time
| becomes space. They go over how that means that inside you
| can't go backwards in space for the same reason that out
| here in the normal universe you can't go backwards in time.
| You are doomed to only go forward, which inside means
| toward the singularity.
|
| (Much better than the ridiculous analogy often given that
| you can't get out of a black hole because the escape
| velocity equals or exceeds the speed of light. That's a
| ridiculous analogy because it only explains why you can't
| get out ballistically).
|
| But all their explanations used a simplified black hole in
| a spacetime with just 1 space dimension and 1 time
| dimension. We've actually got 3 space dimension. Does that
| mean that in a real block hole past the event horizon, you
| end up in a spacetime with 3 time dimensions and 1 space
| dimension?
|
| If so, does anything interesting happen due to having more
| than one time dimension?
| neom wrote:
| I think that's the million dollar question. :)
|
| This episode touches on that a bit, and we're getting
| into holographic universe theory -
| https://www.youtube.com/watch?v=klpDHn8viX8
| Jun8 wrote:
| Exactly your question is answered here:
| https://physics.stackexchange.com/questions/937/how-does-
| gra...
|
| Quick summary: gravitational field is different from
| gravitational radiation.
| thaumaturgy wrote:
| There are a handful of replies already and I'm not any sort
| of authority on this subject. But, I'd like to share a few of
| the things about this that have made sense to me; maybe
| someone will add to or correct one of them and I'll learn
| something more.
|
| Black holes and gravity are hard to get a satisfactory grasp
| on for laymen (like me) because they behave in ways that are
| unlike anything else in the natural, observable world around
| us. People try to understand difficult concepts by relating
| them to familiar things, but gravity and black holes don't
| relate to anything we're familiar with.
|
| Gravity for example isn't, we think, a "thing". It's a
| property, or a consequence. [1] Lots of people are looking
| for some way to relate it to the physics of particles and
| electromagnetic forces, but that hasn't happened yet. So,
| gravity doesn't escape, or travel, because it isn't a
| "thing". There's no particle of gravity. There is a force, in
| that when we observe large masses, they seem to be acted upon
| by some kind of invisible action, but that force is actually
| a consequence of things attempting to travel in straight
| lines along a curved surface.
|
| _Changes_ in gravity do travel, apparently at the speed of
| light. So, in that sense, the gravitational _effect_ of a
| black hole does extend beyond its event horizon. But, that 's
| totally okay, because gravity itself isn't a thing and
| doesn't travel and therefore doesn't need to escape a black
| hole.
|
| Rather, a black hole is a consequence of gravity, or
| relativity. It's a division-by-zero [2] in the equations that
| describe matter, gravity, and curved spacetime. Thinking of
| black holes as being somehow similar to really really dense
| planets is one of the misconceptions that misled me for a
| long time. They are instead more of a place where physics, as
| we understand it so far, stops working.
|
| That place has a boundary region where physics still mostly
| works, and things happen there that we can sort of understand
| and relate to. We can observe some of the effects of this
| extreme curvature of spacetime in this boundary region.
|
| But beyond that, the curvature goes to infinity and volume
| goes to 0 and time stops existing.
|
| [1]: https://www.youtube.com/watch?v=xdIjYBtnvZU -- A video
| with 3 Blue 1 Brown on Feynman's "lost lecture", which
| describes gravity in geometrical terms. There is also a
| Feynman lecture on this:
| https://www.feynmanlectures.caltech.edu/II_42.html
|
| [2]: https://old.reddit.com/r/askscience/comments/1dox03/phys
| ics_...
| curtainsforus wrote:
| From the perspective of an outside observer, nothing ever
| reaches past the event horizon- it just asymptotically
| approaches it. The same goes for the whole mass of the black
| of hole- from an outside perspective, it's smeared across the
| surface.
|
| There isn't an object that messes with the warping of
| spacetime- the black hole IS the warp in spacetime. If
| changes in spacetime couldn't propagate away from the black
| hole, it wouldn't exist.
| bollu wrote:
| As best as I understand: light travels in space. Thus, if
| space is scrunched up, light can't escape. Gravity IS space.
| The scrunching up IS gravity. There is no "escaping", because
| gravity is literally the substrate.
| Koshkin wrote:
| > _Gravity IS space_
|
| More accurately, gravity is the curvature of _spacetime_.
| whoisburbansky wrote:
| "The scrunching up IS gravity" seems to imply that fairly
| adequately.
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