8 ms·

One of the findings they announced at the press conference is that the spin of the black hole is not aligned with the galactic plane but is tilted "towards us"

by kloch 4y ago

One of the findings they announced at the press conference is that the spin of the black hole is not aligned with the galactic plane but is tilted "towards us" so that it is viewed face on. How unexpected is that?

deleted 4y ago
[deleted]
zeven7 4y ago
For quasars, don't the beams shoot out of the poles? Let's hope our nearby buddy doesn't become that active.
- raattgift 4y ago
  There is vanishingly small likelihood of Sgr A* becoming active (in the sense of developing highly luminous structures nearby it). There is little in the central parsec to feed it, and it is low in mass for a central black hole. There is a lot of astronomical hunting to be done to find the weak polar jet from Sgr A*. We only look down on its north pole approximately. Extending the spin axis of Sgr A* could miss our solar system by thousands of light years. A polar jet, moreover, can be slightly unaligned from the extended spin axis, and over a 27 kilolightyear distance, that can be even more significant. Finally, we don't know whether the spin axis of the black hole will keep pointing roughly towards us, or whether it sweeps through (up or down) or around the midplane of the galaxy (or on what time scale such "precession", if any, occurs: for all we know, in a few years we might have an image that evidences an Earth-based view almost perpendicular to the spin axis).
  - quasarj 4y ago
    So I have a question about that.. I thought it would only have an accretion disk if it was active. So what gives? I guess I'm wrong? What constitutes "active" if not "stuff is falling in"?
    - raattgift 4y ago
      Unexpected question from someone whose nickname starts with "quasar"! :-) Active in the sense of (from <https://en.wikipedia.org/wiki/Active_galactic_nucleus https://en.wikipedia.org/wiki/Active_galactic_nucleus>) "much higher than normal ... excess non-stellar emission" from the region very close to the central black hole. Our central parsec is simply dim in practically every wavelength compared to its enclosing central bulge. An active galactic nucleus in our galaxy would be very noticeable to the naked human eye: it would "light up" (with far ultraviolet to gamma radiation) lots of interstellar material that, having been heated, would glow very brightly in the reds and oranges. The luminosity of AGNs and quasars (especially luminous AGNs) is mostly from matter-matter collisions between gas and dust on intersecting geodesics (a fancy sort of friction that becomes enormous in the material nearest the black hole), with a contribution from daughter products of those collisions. There isn't much matter circulating close to Sgr A*. It's "starving". In the panel they tried to put it in terms of a human diet: if you were eating like Sgr A* is, scaled down to human size, you'd be eating a grain of rice every few million years. Good luck keeping your body heat up on that diet. :-) In the past -- tens of thousands to many millions of years ago -- there might have been a lot of matter circulating around Sgr A*, being swept up into luminous jets, which generated the Fermi bubbles <https://en.wikipedia.org/wiki/Galactic_Center#Gamma-_and_X-ray_emitting_Fermi_bubbles https://en.wikipedia.org/wiki/Galactic_Center#Gamma-_and_X-r...>. That's an area of current research: do central black holes eventually go radio-quiet in general? Is there a active-quiet-active-quiet cycle in central black holes in general? Or is this all an ultraviolet herring with the Fermi bubbles being produced by some mechanism that doesn't involve (or only very weakly depends upon) Sgr A*? ETA: I forgot to re-read my own (grandparent) comment. The "luminous structures nearby" are not just an accretion disc. Jets count, too. Also anything that they strike (molecular gas clouds, for instance) will tend to become luminous in some part of the spectrum (sometimes this results in "frustrated lobes", sometimes "light echoes" or ionization echoes from flares).
      - quasarj 4y ago
        Thanks for the reply! And yes, given my name I thought I should know more about it. Especially since this was not in line with my previous understanding.
- Mehringotio 4y ago
  The distance should be that far away that a potential spread would be relatively wide I would argue.
- willis936 4y ago
  The "us" in "let us" are humans that are alive 30,000 years after a hypothetical quasar starts at SgrA*. The image would look realtime to us. Just weird relativity things.
- db48x 4y ago
  Nobody really knows the exact mechanism that forms the beams, but the beams definitely do not shoot out of the black hole. Of course that’s usually what you see in an artist’s depiction of them, but that’s a whole different problem. The beams come from the accretion disk. There are two opposing beams because the disk has two opposing faces. The profile of the disk is narrow, so it stands to reason that very little radiation would leak out around the edge. On the other hand, there is a black hole in the middle of the disk and that should be smearing the beam out quite a lot. Somehow the magnetic fields and currents within the disk must conspire to keep the beam fairly narrow.
raattgift 4y ago
For a small-mass central black hole (CBH), the spin-spin coupling of the CBH and the bulk matter of a relatively small and sparse galaxy is so small that it the orientation of the spin axis is almost unconstrained. That from Earth we look down on the CBH's north pole (right-hand-rule: the bright features appear to circulate counter-clockwise, and there is decent evidence in them that the black hole's spin is in the same direction (i.e., the accretion structure is prograde rather than retrograde)) is probably just a funny coincidence. M87 and its CBH M87* are much more massive than the Milky Way and its respective CBH Sgr A*, but it M87 a giant elliptical galaxy that is almost circular (as far as we can tell from the highly random orbital motions of constituent parts like hydrogen and molecular gas clouds, resolvable globular and other star clusters, and so forth). So there is essentially no (bulk) galactic spin for M87* to couple to. M87*, the black hole, has significant spin however. For a galaxy with strong axisymmetry to the point of a thin disc, there are still open questions about spin-spin coupling with a sufficiently massive CBH, under the assumption that the CBH spin and the galactic spin were identical in the early universe and that the CBH spin has not become perturbed (e.g. by black hole mergers, which may change the spin parameter, which translates to a CBH spin axis unaligned with the galactic spin axis, or a counter-rotating CBH, or some combination), and that the galactic spin has not become perturbed (by close-encounters or mergers with other galaxies). There are additional reasons why a jet and counter-jet may not trace out the extended spin axis of a CBH. Finally, the spin-spin coupling is probably driven by the galactic spin imposing its "will" upon the CBH, rather than the other way around, because of the large mass-ratio and the distribution of mass at significant spatial remove from the CBH. However, there is a chicken/egg conundrum for very large CBHs, since we don't know if they become so huge (principally) primordially or by hierarchical mergers or by some other mechanism. The biggest CBHs may drive the initial angular momentum in the early protogalaxy, and then both the CBH and the later-time bulk galaxy will influence each others' spins. That is, the spin-spin can be correlated without any significant direct linking (in terms of forcing a drifting spin to realign), because the coupling can be arbitrarily weak. So, we should not be surprised by central black holes spinning differently from their enclosing galaxies. But, we have a lot to learn about your question from further observations of CBHs!
- foobarian 4y ago
px43 4y ago
Kind of makes me nervous that both black holes we've imaged are pointing right at us. I'm imagining some super advanced civilization somehow using black holes as powerful telescopes that are for some reason intent on mapping out our region of space. I know M87 is 55 million light years away, so that makes no sense, but I'd really like to see some black holes that are looking in some other direction. Is it at all possible that the glow is more of a spherical cloud and the black spot would be visible from any angle you look at it?
- edgyquant 4y ago
  From our perspective would not all black holes we can see appear the same? Considering that what we seek is simply light not escaping.
queuebert 4y ago
It may also precess, so that the axis of rotation is changing with time. Previous galactic collisions may also have caused two holes to merge into this one, with a net spin not orthogonal to the Galactic plane.
jakeogh 4y ago
https://www.youtube.com/watch?v=8URdhSigzjs https://www.youtube.com/watch?v=8URdhSigzjs
Sirvadi 4y ago
Your question stuck in my head and I found this video today which gives a good explanation of the alignment (around 12:45). https://youtu.be/BtnFwNKEmyY?t=765 https://youtu.be/BtnFwNKEmyY?t=765

by kloch 4y ago

deleted 4y ago

[deleted]

zeven7 4y ago

For quasars, don't the beams shoot out of the poles? Let's hope our nearby buddy doesn't become that active.

raattgift 4y ago
There is vanishingly small likelihood of Sgr A* becoming active (in the sense of developing highly luminous structures nearby it). There is little in the central parsec to feed it, and it is low in mass for a central black hole. There is a lot of astronomical hunting to be done to find the weak polar jet from Sgr A*. We only look down on its north pole approximately. Extending the spin axis of Sgr A* could miss our solar system by thousands of light years. A polar jet, moreover, can be slightly unaligned from the extended spin axis, and over a 27 kilolightyear distance, that can be even more significant. Finally, we don't know whether the spin axis of the black hole will keep pointing roughly towards us, or whether it sweeps through (up or down) or around the midplane of the galaxy (or on what time scale such "precession", if any, occurs: for all we know, in a few years we might have an image that evidences an Earth-based view almost perpendicular to the spin axis).
- quasarj 4y ago
  So I have a question about that.. I thought it would only have an accretion disk if it was active. So what gives? I guess I'm wrong? What constitutes "active" if not "stuff is falling in"?
  - raattgift 4y ago
    Unexpected question from someone whose nickname starts with "quasar"! :-) Active in the sense of (from <https://en.wikipedia.org/wiki/Active_galactic_nucleus https://en.wikipedia.org/wiki/Active_galactic_nucleus>) "much higher than normal ... excess non-stellar emission" from the region very close to the central black hole. Our central parsec is simply dim in practically every wavelength compared to its enclosing central bulge. An active galactic nucleus in our galaxy would be very noticeable to the naked human eye: it would "light up" (with far ultraviolet to gamma radiation) lots of interstellar material that, having been heated, would glow very brightly in the reds and oranges. The luminosity of AGNs and quasars (especially luminous AGNs) is mostly from matter-matter collisions between gas and dust on intersecting geodesics (a fancy sort of friction that becomes enormous in the material nearest the black hole), with a contribution from daughter products of those collisions. There isn't much matter circulating close to Sgr A*. It's "starving". In the panel they tried to put it in terms of a human diet: if you were eating like Sgr A* is, scaled down to human size, you'd be eating a grain of rice every few million years. Good luck keeping your body heat up on that diet. :-) In the past -- tens of thousands to many millions of years ago -- there might have been a lot of matter circulating around Sgr A*, being swept up into luminous jets, which generated the Fermi bubbles <https://en.wikipedia.org/wiki/Galactic_Center#Gamma-_and_X-ray_emitting_Fermi_bubbles https://en.wikipedia.org/wiki/Galactic_Center#Gamma-_and_X-r...>. That's an area of current research: do central black holes eventually go radio-quiet in general? Is there a active-quiet-active-quiet cycle in central black holes in general? Or is this all an ultraviolet herring with the Fermi bubbles being produced by some mechanism that doesn't involve (or only very weakly depends upon) Sgr A*? ETA: I forgot to re-read my own (grandparent) comment. The "luminous structures nearby" are not just an accretion disc. Jets count, too. Also anything that they strike (molecular gas clouds, for instance) will tend to become luminous in some part of the spectrum (sometimes this results in "frustrated lobes", sometimes "light echoes" or ionization echoes from flares).
    - quasarj 4y ago
      Thanks for the reply! And yes, given my name I thought I should know more about it. Especially since this was not in line with my previous understanding.
Mehringotio 4y ago
The distance should be that far away that a potential spread would be relatively wide I would argue.
willis936 4y ago
The "us" in "let us" are humans that are alive 30,000 years after a hypothetical quasar starts at SgrA*. The image would look realtime to us. Just weird relativity things.
db48x 4y ago
Nobody really knows the exact mechanism that forms the beams, but the beams definitely do not shoot out of the black hole. Of course that’s usually what you see in an artist’s depiction of them, but that’s a whole different problem. The beams come from the accretion disk. There are two opposing beams because the disk has two opposing faces. The profile of the disk is narrow, so it stands to reason that very little radiation would leak out around the edge. On the other hand, there is a black hole in the middle of the disk and that should be smearing the beam out quite a lot. Somehow the magnetic fields and currents within the disk must conspire to keep the beam fairly narrow.

raattgift 4y ago

For a small-mass central black hole (CBH), the spin-spin coupling of the CBH and the bulk matter of a relatively small and sparse galaxy is so small that it the orientation of the spin axis is almost unconstrained. That from Earth we look down on the CBH's north pole (right-hand-rule: the bright features appear to circulate counter-clockwise, and there is decent evidence in them that the black hole's spin is in the same direction (i.e., the accretion structure is prograde rather than retrograde)) is probably just a funny coincidence. M87 and its CBH M87* are much more massive than the Milky Way and its respective CBH Sgr A*, but it M87 a giant elliptical galaxy that is almost circular (as far as we can tell from the highly random orbital motions of constituent parts like hydrogen and molecular gas clouds, resolvable globular and other star clusters, and so forth). So there is essentially no (bulk) galactic spin for M87* to couple to. M87*, the black hole, has significant spin however. For a galaxy with strong axisymmetry to the point of a thin disc, there are still open questions about spin-spin coupling with a sufficiently massive CBH, under the assumption that the CBH spin and the galactic spin were identical in the early universe and that the CBH spin has not become perturbed (e.g. by black hole mergers, which may change the spin parameter, which translates to a CBH spin axis unaligned with the galactic spin axis, or a counter-rotating CBH, or some combination), and that the galactic spin has not become perturbed (by close-encounters or mergers with other galaxies). There are additional reasons why a jet and counter-jet may not trace out the extended spin axis of a CBH. Finally, the spin-spin coupling is probably driven by the galactic spin imposing its "will" upon the CBH, rather than the other way around, because of the large mass-ratio and the distribution of mass at significant spatial remove from the CBH. However, there is a chicken/egg conundrum for very large CBHs, since we don't know if they become so huge (principally) primordially or by hierarchical mergers or by some other mechanism. The biggest CBHs may drive the initial angular momentum in the early protogalaxy, and then both the CBH and the later-time bulk galaxy will influence each others' spins. That is, the spin-spin can be correlated without any significant direct linking (in terms of forcing a drifting spin to realign), because the coupling can be arbitrarily weak. So, we should not be surprised by central black holes spinning differently from their enclosing galaxies. But, we have a lot to learn about your question from further observations of CBHs!

foobarian 4y ago

px43 4y ago

Kind of makes me nervous that both black holes we've imaged are pointing right at us. I'm imagining some super advanced civilization somehow using black holes as powerful telescopes that are for some reason intent on mapping out our region of space. I know M87 is 55 million light years away, so that makes no sense, but I'd really like to see some black holes that are looking in some other direction. Is it at all possible that the glow is more of a spherical cloud and the black spot would be visible from any angle you look at it?

edgyquant 4y ago
From our perspective would not all black holes we can see appear the same? Considering that what we seek is simply light not escaping.

queuebert 4y ago

It may also precess, so that the axis of rotation is changing with time. Previous galactic collisions may also have caused two holes to merge into this one, with a net spin not orthogonal to the Galactic plane.

jakeogh 4y ago

https://www.youtube.com/watch?v=8URdhSigzjs https://www.youtube.com/watch?v=8URdhSigzjs

Sirvadi 4y ago

Your question stuck in my head and I found this video today which gives a good explanation of the alignment (around 12:45). https://youtu.be/BtnFwNKEmyY?t=765 https://youtu.be/BtnFwNKEmyY?t=765