Our Galaxy's Monster Black Hole Is Spinning Almost As Fast As Physics Allows (sciencealert.com) 41
alternative_right shares a report from ScienceAlert: The colossal black hole lurking at the center of the Milky Way galaxy is spinning almost as fast as its maximum rotation rate. That's just one thing astrophysicists have discovered after developing and applying a new method to tease apart the secrets still hidden in supermassive black hole observations collected by the Event Horizon Telescope (EHT). The unprecedented global collaboration spent years working to give us the first direct images of the shadows of black holes, first with M87* in a galaxy 55 million light-years away, then with Sgr A*, the supermassive black hole at the heart of our own galaxy. [...]
Their results show, among other things, that Sgr A* is not only spinning at close to its maximum speed, but that its rotational axis is pointed in Earth's direction, and that the glow around it is generated by hot electrons. Perhaps the most interesting thing is that the magnetic field in the material around Sgr A* doesn't appear to be behaving in a way that's predicted by theory. M87*, they discovered, is also rotating rapidly, although not as fast as Sgr A*. However, it is rotating in the opposite direction to the material swirling in a disk around it -- possibly because of a past merger with another supermassive black hole. The findings have been detailed in three papers published in the journal Astronomy & Astrophysics. They can be found here, here, and here.
Their results show, among other things, that Sgr A* is not only spinning at close to its maximum speed, but that its rotational axis is pointed in Earth's direction, and that the glow around it is generated by hot electrons. Perhaps the most interesting thing is that the magnetic field in the material around Sgr A* doesn't appear to be behaving in a way that's predicted by theory. M87*, they discovered, is also rotating rapidly, although not as fast as Sgr A*. However, it is rotating in the opposite direction to the material swirling in a disk around it -- possibly because of a past merger with another supermassive black hole. The findings have been detailed in three papers published in the journal Astronomy & Astrophysics. They can be found here, here, and here.
Six terabytes (Score:5, Informative)
The study of the black hole in our galaxy has taken years to analyze.
A large number of images were taken during an observing campaign in 2017, producing six terabytes of data. These data had to be processed and analyzed – a process that took years, and the development of new algorithms to compensate for the rapid changeability.
They also found we are at about 90 degrees from the accretion disc, almost on the axis of rotation. This should provide an interesting viewpoint for observation and analysis.
13.25: Christian Fromm of Würzburg University in Germany is now stepping up to tell us what the image tells us about Sgr A*.
The team used supercomputers around the world to model black holes. When compared with their models, the image tells us that Sgr A* is rotating and that we are looking at it face-on. https://www.sciencealert.com/l... [sciencealert.com]
Re:Six terabytes (Score:5, Informative)
Yeah I think the rotating bit is to be taken for granted. It would be *very* strange to find a black hole without any angular momentum (being that its one of only three properties a black hole has, angular momentum, electrical charge and mass, aka the no-hair theorem).
The text of the actual papers is a little terse and mathematical for my brain, did you manage to figure out what that "close to the maximum allowed by physics" speed actually was, the pop-sci article seemed a bit short on details.
Re:Six terabytes (Score:5, Informative)
did you manage to figure out what that "close to the maximum allowed by physics" speed actually was, the pop-sci article seemed a bit short on details.
I didn't understand exactly, but a quick summary of a few articles indicated that when stars collapse into smaller objects (white dwarfs, neutron stars, etc) their angular momentum is preserved so the smaller objects must rotate faster. With Sgr A* containing mass 4.3 million times the mass of the Sun, the angular momentum is huge and the mass spins extremely fast. The limiting factor seems to be the outer edge of the mass exceeding the speed of light which instead gets converted into gravity waves, keeping the mass from spinning any faster. Slower rotational speeds have been observed on other black holes, but Sgr A* seems to be spinning near the theoretical maximum as it absorbs more mass and rotational energy.
That was my layman's understanding of what was happening. Other stellar experts can probably explain it better.
Re: Six terabytes (Score:2)
Do you know whether this might relate to the masses of those galaxies or whether faster speeds have been observed?
Re: Six terabytes (Score:5, Informative)
Re: Six terabytes (Score:4, Informative)
Think of an iceskater pirouetting on the rink with their arms stretched out. If they pull their arms in, they start to spin faster, thereby conserving angular momentum, but they don't gain any additional mass from doing so.
Kids that grew up on playgrounds with those little merry-go-rounds that held only one or two people knew about this phenomenon. You'd push yourself to get going as fast as you could by hanging out as far as you could on the bars, then pull yourself in once spinning, increasing the spin as you neared the center of the rotation. If you got really god at it, you could come to a point where you wouldn't have the arm strength to pull yourself all the way into the center, because the centrifugal force would be too much to pull through.
I'm sure those were deemed unsafe sometime not long after I got too big for them, but there were valuable lessons on such dangerous toys.
Black hole maximum rotation speed (Score:2)
That intuitively makes sense, but I thought part of the black hole cheat is that it doesn't have an edge. I thought they were literally singularities, with a circumference of zero. Apparently not the case?
How a thing with a circumference of zero could meaningfully "rotate" is beyond me, but I thought this (and many other suspected properties of rotating black holes) was supposed to be beyond my ignorant layman understanding!
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Very few physicists really believe that a black hole has a singularity. Things like infinite density and zero size usually indicate you've pushed your theory too far. And from the outside everything looks like its piled up on the horizon, so it would be pretty strange to observe it whipping around at faster than the speed of light.
The singularity comes from an interpretation of an infalling observer's point of view, and Roy Kerr, the guy who came up with the solution for a rotating black hole, pretty veheme
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Here's more on the subject in lay terms: How Does the Event Horizon Affect Black Hole Spin and Space-Time? [medium.com]
Re: Black hole maximum rotation speed (Score:2)
Do you disagree with Eddington that the universe is not only stranger than you imagine, but stranger than you can imagine?
Re: Black hole maximum rotation speed (Score:2)
If we went back in time to the 1980s would you be saying even a non-singular black hole is just too far outside the Overton Window for most physicists? How do you know the limits you set now, which have moved so far, won't move towards zero size and infinite densities in another few decades?
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No.
Because infinities in a physical theory aren't "oh, that's very extreme, I don't know," they signify a breakdown in the predictive capability of a theory: i.e. the one thing it's supposed to do.
Re: Black hole maximum rotation speed (Score:2)
"The concept that explains black holes was so radical, in fact, that Einstein, himself, had strong misgivings. He concluded in a 1939 paper in the Annals of Mathematics that the idea was âoenot convincingâ and the phenomena did not exist âoein the real world.â"
Are you saying we're smarter than Einstein, and future evidence won't move us in favor of concepts such as infinite density that are simply emotionally too costly for the consensus to accept at the moment?
Re: galaxy rotational speed variation (Score:2)
Do you know how this might relate to the masses of those galaxies and whether faster speeds have been observed?
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Not simply.
M87 and M87* are considerably larger than the Milky Way and SgrA* (though I don't know which way the SMBH:galaxy mass ratio goes), yet rotates slower. So the obvious "more infalling mass means more accumulated angular momentum, means more rotation" argument doesn't work, or is overcome by effects you'd expect to be second-order.
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But if the singularity inside is a point how can it have any angular momentum?
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Yeah, I'm hung up on that too. You can come up with some outrageously huge numbers for mass and angular velocity, but once I multiply them by zero distance... I'm missing something.
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So are electrons. But they have both spin, and angular momentum.
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> They also found we are at about 90 degrees from the accretion disc, almost on the axis of rotation. This should provide an interesting viewpoint for observation and analysis.
I assume this is temporary, albeit in a context where "temporary" is measured in millions of years? But regardless, this suggests it's not rotating in the same plane as the Milky Way?
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Neither are we.
In a relatively simple system - the Solar system - with only a few interacting components compared to the galaxy, we have an angular momentum budget dominated by Jupiter's orbiting around the Sun (then Saturn, and some change). But we have one planet rotating "on it's side" (Uranus, rotation axial tilt 98 to the rotation axis of the whole system), and another planet rotating retrograde (Venus, axial tilt 178).
Nice (Score:3)
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Latch one to the moon first, it is also rotating. With appropriate choice of gears, you can turn a generator as fast as you want.
Re: Nice (Score:2)
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Hardly any at first, there is a lot of rotational energy there. But eventually yeah, just like the global warming.
Re: Nice (Score:2)
The moon is moving away from us though so it has energy to spare.
Need to make sure that our Ringworld... (Score:1)
Rotates in the right plane so that the scrith can block as much of the astrophysical jets as possible.
Just saying :-)
Beowulf Shaeffer should know (Score:2)
They should ask him.
Looking down the barrel (Score:5, Funny)
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That much energy should have an effect on objects between us and Sagittarius A*, some of which may output light. Therefore we may see the affect of that much energy on those objects before it hits us, but depending on distance it's not going to be a lot of warning of our impending extinction.
How fast is that? (Score:3)
I'm having trouble finding out how fast is "maximum speed".
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I'm having trouble finding out how fast is "maximum speed".
I thought it was just me. I'm going to be pretty disappointed when I find out the maximum rotation speed of a black hole is 47mph.
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After punching GoogAI in the LLM for a bit there's no minimum nor maximum "mass" needed to achieve that rotational speed. There are several factors that contribute to that number, of which mass (as far as I can tell) is not a primary player.
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The Kerr metric is 0 to 1. With 0=non-rotating to 1=c (c=299,792,458 m/s). The theoretical maximum is 0.998 c.
But rotation is measured in rad/s, c is m/s, so how does it fits?
Clarification: Physics diesnt "allow" anything... (Score:2)
... of anything, its just the science of measurement/observation of cosmic occurrences.
Clarification: Physics doesnt "allow" anything... (Score:2)
Clarification: Physics doesnt "allow" anything... ... if anything, it is just the science of measurement/observation of cosmic occurrences.
(corrected typos)