Yes. A black hole is basically a normal star with normal gravity, but you can't see the gravity source itself. You can detect the motion of all other stuff around it: Imagine our solar system without the sun visible, the planets will still move the same (and not get 'sucked in' or 'gobbled up' etc).
Even if there is no stuff moving around the black hole, we still can detect because the intense gravity bends space and creates lensing effect, which is easily detectable with modern equipment.
That said, we can infer that it is unlikely that a black hole is in our galactic vicinity and most certainly not a monster like in this article. Which, btw, is not only 12 billion light years away, also what we see is 12 billion years ago, putting the whole scene at the beginning of our universe.
If you instead ask, "could we fail to notice if a black hole was near enough to collide", the answer is probably not, at least in this epoch of the universe.
Most astrophysical black holes will tend to have accretion disks that are very bright.
Even if there are really isolated, almost non-accreting black holes in deep space, they will visibly distort (by Einstein lensing) the image of distant light sources behind, and there are many many many of those. We can already in principle use microlensing to find ones that are at the margins of the Milky Way, at distances of tens of kiloparsecs. They will in general be easier to spot at closer distances.
Eventually, thanks to the expansion of the universe, black holes in deep space might not have much to lense: background galaxies will stop being visible (many are already so red and dim that when Einstein-lensed by a black hole they will not be naked-eye visible), so you may be surprised by a black hole that is plainly visible if it is between you and the Milky-Way-Andromeda merged galaxy but has almost nothing to magnify when you are between it and the Milky-Way-Andromeda galaxy.
This is not something to worry about for the next many billion years.
Additionally, if you have reasonably sensitive instrumentation in your spaceship, you are even less likely to be surprised even if a black hole isn't at all naked-eye visible; black holes, even highly isolated ones in the distant future, will still interact with the relic fields like the Cosmic Microwave Background, and can be detected by those interactions.
> sucked into
Black holes don't reach out and grab things gravitationally, really. In general, if you treat them as Eulerian flow observers (as in fluid dynamics) they mostly deflect the trajectory of the "fluid" passing them (tangentially to the horizon), except for the fluid that flows directly onto the horizon or (tangentially) very close to it. In the case of a "fluid" of light, the deflection results in Einstein lensing, although light flowing close enough will be drawn into an orbit that (probably) ultimately leads inwards to the black hole. In the case of "fluids" that are massive -- gas, dust -- the speed at which the flow passes the black hole will always be less than that of light, but the flow is still deflected. Finally, in the case of larger objects like rocky planets or even stars, again their trajectories past the black hole will be deflected, and the result is similar to a hyperbolic orbit. Only the fluid which is aimed very well risks being swept up into an orbit, although some fluid can always be "aimed" directly at the black hole's notional surface (the event horizon), in which case it is on a one-way journey.
A "close call" in a space ship for a very large black hole might produce a large deflection and a significant time dilation, but otherwise is not especially dangerous. A close call for a small black hole might produce enough tidal stresses to compromise the structural integrity of the ship, but otherwise is also not especially dangerous. The more important dangers of black holes would be the intense radiation from their likely accretion disks, and again, that's readily detectable at long distances.
One could consider an analogy with a planet with an atmosphere: if, on a tangential course, you zip by the planet at sufficient distance, you get a pretty view. If you zip by at smaller distances, you might get what rocket scientists call a gravitational boost, but otherwise are probably fine. But if you zip by at smaller distances still, you might collide with the upper atmosphere, which might damage your spaceship (or incinerate it). You generally need an intersecting course to actually hit the rocky surface, although the atmosphere's effects may be relevant for non-intersecting courses. Black holes don't have a rocky surface, but the accretion structures around them can serve as a dangerous atmosphere.
In general, except in binary (and triple and so on) systems where the BH has a stellar partner, black holes tend to grow pretty slowly because not much falls directly on them, things that come close enough to have their trajectories bent into an orbit can stay in orbit for a long time, and not very much tends to come close enough to be drawn into an orbit in the first place. They don't act like the one shown in Disney's _The Black Hole_, for example (the human characters in that film would die of radiation poisoning, mostly, since their ships do not have many-metres-thick lead walls to block the X rays that would be streaming out of the bright accretion structure; turning off the Cygnus's magical station-keeping engine would mostly cause it to fall into a quasi-Keplerian orbit that could be stable for a very long time, so the film did get it kinda right that the Cygnus would need to be steered (with full engines!) directly towards the black hole).
Finally, this entertaining transcript is a bit more chatty-colloquial, and raises some additional points: https://www.nasa.gov/connect/chat/black_hole_chat.html (it might also raise some additional questions, though! For instance, "theoretically could stand at the event horizon point of a blackhole and not be sucked in" doesn't go into how to do this by e.g. constructing a scaffold around the BH that one could use as a platform to stand above it.)
IANAA but here is a wild guess; stars are limited to the sizes we see because they accrete from a swirling gas/dust. after they begin fusion (thousands of years after) and photons are reaching the surface the nascent star begins emitting a stellar wind which pushes back the in-falling gas/dust which limits how big they can get. the important bit is how much more energy is in the stellar wind than the void it is pushing into.
The early universe was hotter less void, solar wind had less advantage and more gas/dust continued to accrete. If ever a still growing star approached black hole mass, solar wind is extinguished and in-fall is in unimpeded forever. (for human values of forever)
but I would go with what raattgift says over this wild speculation
This quasi-stellar object (QSO) is so bright that (with some mild assumptions, including that it's a single supermassive black hole and that its angular momentum is not super-extremal) its outgoing high-energy photons should collide with the electrons in star-forming gas and dust anywhere near it, pushing the electrons outwards from the QSO. In (quasi-)neutral gas, where the electrons are pushed, they drag their protons with them. If all the electron-containing matter is pushed away, how do we reconcile that this QSO [a] grew at all and [b] shines so brightly?
QSOs like this one appear to crash into the Eddington limit, which depends almost entirely on mass (more below). If we assume a "bottom-up" formation for this QSO, with early stellar-collapse black holes merging into this supermassive giant, the problem is that its observed mass is so high that it and its many smaller progenitor BHs should have blasted away all the star-forming dust and gas from their neighbourhood. You need a lot of stellar black holes to merge into this giant, so suppressing star-formation at all is a problem. Moreover, removing much of the matter from neighbourhood then mechanisms like dynamic friction fall off, making the black hole merging process too slow for the relatively short duration (locally to the QSO) between the epoch early star formation and the QSO as we observe it.
A reasonably accessible 40-slide tutorial on the Eddington limit:
Note, however, slide 33, which offers up a couple of hints about how the Eddington limit can be evaded: thick low-density accretion clouds. These are expected in the "dark ages" of the early universe before there are many stars, under the standard structure formation model [1].
If we do the hard computing that slide alludes to and consider a "direct collapse" black hole as the progenitor of this QSO, rather than building it out of smaller stellar black holes, we can explore a class of such "evasions". In essence we need a starless pocket of gas to become dense enough to collapse while relatively cold into a black hole of perhaps a million solar masses. Alternatively we could get perhaps ~10 such pockets to collapse into BHs of a hundred thousand solar masses each, and then rapidly merge. The first approach tends to create a later Eddington problem: such a BH will generically interfere with star formation within kiloparsecs, so its subsequent growth is checked. The second seems to require scenarios like early galaxy-galaxy mergers, where several smaller galaxies with a direct-collapse BH collide in such a way that the BHs rapidly merge. This is even harder to model, but has the advantage of bringing already-formed stars into the neighbourhood of the SMBH, so it can continue growing.
Hypothetical question: Would we be able to detect if we were going to get sucked into a black hole?
Yes. A black hole is basically a normal star with normal gravity, but you can't see the gravity source itself. You can detect the motion of all other stuff around it: Imagine our solar system without the sun visible, the planets will still move the same (and not get 'sucked in' or 'gobbled up' etc).
Even if there is no stuff moving around the black hole, we still can detect because the intense gravity bends space and creates lensing effect, which is easily detectable with modern equipment.
That said, we can infer that it is unlikely that a black hole is in our galactic vicinity and most certainly not a monster like in this article. Which, btw, is not only 12 billion light years away, also what we see is 12 billion years ago, putting the whole scene at the beginning of our universe.
If you instead ask, "could we fail to notice if a black hole was near enough to collide", the answer is probably not, at least in this epoch of the universe.
Most astrophysical black holes will tend to have accretion disks that are very bright.
Even if there are really isolated, almost non-accreting black holes in deep space, they will visibly distort (by Einstein lensing) the image of distant light sources behind, and there are many many many of those. We can already in principle use microlensing to find ones that are at the margins of the Milky Way, at distances of tens of kiloparsecs. They will in general be easier to spot at closer distances.
Eventually, thanks to the expansion of the universe, black holes in deep space might not have much to lense: background galaxies will stop being visible (many are already so red and dim that when Einstein-lensed by a black hole they will not be naked-eye visible), so you may be surprised by a black hole that is plainly visible if it is between you and the Milky-Way-Andromeda merged galaxy but has almost nothing to magnify when you are between it and the Milky-Way-Andromeda galaxy. This is not something to worry about for the next many billion years.
Additionally, if you have reasonably sensitive instrumentation in your spaceship, you are even less likely to be surprised even if a black hole isn't at all naked-eye visible; black holes, even highly isolated ones in the distant future, will still interact with the relic fields like the Cosmic Microwave Background, and can be detected by those interactions.
> sucked into
Black holes don't reach out and grab things gravitationally, really. In general, if you treat them as Eulerian flow observers (as in fluid dynamics) they mostly deflect the trajectory of the "fluid" passing them (tangentially to the horizon), except for the fluid that flows directly onto the horizon or (tangentially) very close to it. In the case of a "fluid" of light, the deflection results in Einstein lensing, although light flowing close enough will be drawn into an orbit that (probably) ultimately leads inwards to the black hole. In the case of "fluids" that are massive -- gas, dust -- the speed at which the flow passes the black hole will always be less than that of light, but the flow is still deflected. Finally, in the case of larger objects like rocky planets or even stars, again their trajectories past the black hole will be deflected, and the result is similar to a hyperbolic orbit. Only the fluid which is aimed very well risks being swept up into an orbit, although some fluid can always be "aimed" directly at the black hole's notional surface (the event horizon), in which case it is on a one-way journey.
A "close call" in a space ship for a very large black hole might produce a large deflection and a significant time dilation, but otherwise is not especially dangerous. A close call for a small black hole might produce enough tidal stresses to compromise the structural integrity of the ship, but otherwise is also not especially dangerous. The more important dangers of black holes would be the intense radiation from their likely accretion disks, and again, that's readily detectable at long distances.
One could consider an analogy with a planet with an atmosphere: if, on a tangential course, you zip by the planet at sufficient distance, you get a pretty view. If you zip by at smaller distances, you might get what rocket scientists call a gravitational boost, but otherwise are probably fine. But if you zip by at smaller distances still, you might collide with the upper atmosphere, which might damage your spaceship (or incinerate it). You generally need an intersecting course to actually hit the rocky surface, although the atmosphere's effects may be relevant for non-intersecting courses. Black holes don't have a rocky surface, but the accretion structures around them can serve as a dangerous atmosphere.
In general, except in binary (and triple and so on) systems where the BH has a stellar partner, black holes tend to grow pretty slowly because not much falls directly on them, things that come close enough to have their trajectories bent into an orbit can stay in orbit for a long time, and not very much tends to come close enough to be drawn into an orbit in the first place. They don't act like the one shown in Disney's _The Black Hole_, for example (the human characters in that film would die of radiation poisoning, mostly, since their ships do not have many-metres-thick lead walls to block the X rays that would be streaming out of the bright accretion structure; turning off the Cygnus's magical station-keeping engine would mostly cause it to fall into a quasi-Keplerian orbit that could be stable for a very long time, so the film did get it kinda right that the Cygnus would need to be steered (with full engines!) directly towards the black hole).
Finally, this entertaining transcript is a bit more chatty-colloquial, and raises some additional points: https://www.nasa.gov/connect/chat/black_hole_chat.html (it might also raise some additional questions, though! For instance, "theoretically could stand at the event horizon point of a blackhole and not be sucked in" doesn't go into how to do this by e.g. constructing a scaffold around the BH that one could use as a platform to stand above it.)
> “How they grew to such mass so early after the Big Bang is a profound puzzle for physics,” the authors say in their paper.
Anyone have any details for this tidbit? Would be interested to know more.
IANAA but here is a wild guess; stars are limited to the sizes we see because they accrete from a swirling gas/dust. after they begin fusion (thousands of years after) and photons are reaching the surface the nascent star begins emitting a stellar wind which pushes back the in-falling gas/dust which limits how big they can get. the important bit is how much more energy is in the stellar wind than the void it is pushing into. The early universe was hotter less void, solar wind had less advantage and more gas/dust continued to accrete. If ever a still growing star approached black hole mass, solar wind is extinguished and in-fall is in unimpeded forever. (for human values of forever)
but I would go with what raattgift says over this wild speculation
This quasi-stellar object (QSO) is so bright that (with some mild assumptions, including that it's a single supermassive black hole and that its angular momentum is not super-extremal) its outgoing high-energy photons should collide with the electrons in star-forming gas and dust anywhere near it, pushing the electrons outwards from the QSO. In (quasi-)neutral gas, where the electrons are pushed, they drag their protons with them. If all the electron-containing matter is pushed away, how do we reconcile that this QSO [a] grew at all and [b] shines so brightly?
QSOs like this one appear to crash into the Eddington limit, which depends almost entirely on mass (more below). If we assume a "bottom-up" formation for this QSO, with early stellar-collapse black holes merging into this supermassive giant, the problem is that its observed mass is so high that it and its many smaller progenitor BHs should have blasted away all the star-forming dust and gas from their neighbourhood. You need a lot of stellar black holes to merge into this giant, so suppressing star-formation at all is a problem. Moreover, removing much of the matter from neighbourhood then mechanisms like dynamic friction fall off, making the black hole merging process too slow for the relatively short duration (locally to the QSO) between the epoch early star formation and the QSO as we observe it.
A reasonably accessible 40-slide tutorial on the Eddington limit:
http://www-astro.physics.ox.ac.uk/~garret/teaching/lecture7-...
Note, however, slide 33, which offers up a couple of hints about how the Eddington limit can be evaded: thick low-density accretion clouds. These are expected in the "dark ages" of the early universe before there are many stars, under the standard structure formation model [1].
If we do the hard computing that slide alludes to and consider a "direct collapse" black hole as the progenitor of this QSO, rather than building it out of smaller stellar black holes, we can explore a class of such "evasions". In essence we need a starless pocket of gas to become dense enough to collapse while relatively cold into a black hole of perhaps a million solar masses. Alternatively we could get perhaps ~10 such pockets to collapse into BHs of a hundred thousand solar masses each, and then rapidly merge. The first approach tends to create a later Eddington problem: such a BH will generically interfere with star formation within kiloparsecs, so its subsequent growth is checked. The second seems to require scenarios like early galaxy-galaxy mergers, where several smaller galaxies with a direct-collapse BH collide in such a way that the BHs rapidly merge. This is even harder to model, but has the advantage of bringing already-formed stars into the neighbourhood of the SMBH, so it can continue growing.
Lastly, I've found a quick non-technical overview of the problem and the direct-collapse idea in the context of the CR7 galaxy: https://www.ras.org.uk/news-and-press/2887-astronomers-find-... (and a further quick article with a pointer to work on the galaxy-galaxy merger idea https://www.simonsfoundation.org/2017/03/17/how-supermassive... )
- --
[1] http://sci.esa.int/planck/51561-the-history-of-structure-for...
Thanks. Great stuff, appreciate the slides.
How can a black hole hunger? Doesn’t its consumption mostly depend on how much matter is around it?
It's an anthropomorphization.
If there is not much matter around it'd be pretty hungry.
"Discovery of the most ultra-luminous QSO using Gaia, SkyMapper and WISE" Publications of the Astronomical Society of Australia (PASA)
free PDF version: https://arxiv.org/pdf/1805.04317.pdf