16 ms·

Most images of black holes are illustrations. Here’s what our telescopes capture

335 points by shawndumas 9y ago

corysama 9y ago
Source for the ring of fire image at the bottom of the page: http://eventhorizontelescope.org/simulations-gallery http://eventhorizontelescope.org/simulations-gallery under "> Accretion Disk"
IntronExon 9y ago
Magnificent. I’ve been totally entranced by black holes since I first read A Brief History of Time as a kid. Years and years of trying to wrap my head around them, and they’re still just about the closest thing I get to a spiritual moment. This is a fantastic piece, and even though some images are more visually striking, for me the ones that gives me the most chills are the time-lapse of stellar motion around Sagittarius A. Those are stars* being whipped around like toys. Stars. Over 97% of the mass of the solar system is just Sol, and these stars are more massive, and look at them move! Chills.
ars 9y ago
Keep in mind as well that no observation has yet distinguished between a neutron star and a black hole. i.e. all those photos of super massive objects could be neutron stars, and we would not be able to tell the difference. They are assumed to be black holes because of the mass, but if there is something in the law of physics that prevents black holes from forming we would not know. We do not have a theory on quark degenerative pressure for example, which could possibly exert enough pressure to prevent black holes from forming (you would get quark stars instead, with no event horizon). There are also time dilation issues that might make black holes impossible.
- pdonis 9y ago
  > all those photos of super massive objects could be neutron stars Not if they are more massive than 2.7 times the mass of the Sun. That's the maximum mass for a neutron star (more precisely, it's the upper limit of the range of possible maximum masses, assuming the stiffest possible equation of state). Most of the objects referred to in the article are more massive than that, in some cases much more (the black hole at the center of our galaxy is about 3 million solar masses). > We do not have a theory on quark degenerative pressure for example, which could possible exert enough pressure to prevent black holes from forming No amount of pressure can prevent a black hole from forming, if the mass is large enough. Even for hypothetical quark matter, the equation of state can't get any stiffer than the assumed equation of state that leads to the 2.7 solar mass upper limit for neutron stars. Relativity sets limits to how much an object's pressure can resist gravity, regardless of the source of the pressure. That's where the maximum mass limit comes from. > There are also time dilation issues that might make black holes impossible. No, it doesn't. It just means that light signals from very near the horizon take a long time to get out.
  - ars 9y ago
    > No amount of pressure can prevent a black hole from forming And yet suns with far more mass than is needed to make a black hole exist. Because simple heat pressure keeps the black hole from forming. Remember that the black hole doesn't just suddenly appear - to have enormous gravity the density must go up. If you prevent that from ever happening you can stop the black hole from ever starting in the first place. You are talking assuming the black hole is already there, and saying quark degeneracy can't resist that, but you forget the black hole has to form first. > No, it doesn't. It just means that light signals from very near the horizon take a long time to get out. It also means mass takes a long (infinite) time to get in. So the black hole may never form.
    - podiki 9y ago
      Regarding your last point: that depends on your reference frame. From the outside it does appear to take "forever" to get into a black hole, but if you were the one falling in...it happens much quicker, certainly not taking an infinite amount of time.
      - ars 9y ago
        That's true. But it's things from the outside that are falling in, and that make a black hole. Since they take an infinite amount of time to fall in, the black hole never forms in the first place. (I'm less sure about this paragraph, but I believe that) An object falling in also never sees a black hole, since the other things falling in are dilated relative to him, so there's still not enough mass to make a black hole, even for the object falling in.
        saagarjha 9y ago
        > But it's things from the outside that are falling in, and that make a black hole. Since they take an infinite amount of time to fall in, the black hole never forms in the first place. See this excellent answer on Physics StackExchange: https://physics.stackexchange.com/questions/5031/can-black-holes-form-in-a-finite-amount-of-time#146852 https://physics.stackexchange.com/questions/5031/can-black-h.... In a nutshell (if I'm interpreting this correctly), yes, to an outside observer you never observe the black hole form since it would take an infinite amount of time for light signals from the newly formed black hole to reach you. However, to any observers that fell into the black hole (and so were in the same frame of reference), the black hole would form in finite time.
- IntronExon 9y ago
  I think you’re confusing the lack of knowledge of whether or not singularities really form, with whether or not black holes form. There are very clearly black holes, but of course we can have no way of knowing if they contain singularities. Quark stars could exist, it not with the masses observed in Sag A*. Quark degeneracy pressure isn’t going to support the mass of millions, or even billions of suns. It might be that something other than a singularity is within the event horizon, but there will still be an event horizon. Given that, we’ll never observe the interior of a black hole and be able to communicate those findings, so it’s purely academic at that point. As for time dilation... no. In no way could that magically overcome collapse.
  - ars 9y ago
    What's a black hole without a singularity? A neutron star? Is there a distinction you are making? To me a black hole and a singularity are the same thing. Are you using a different definition? > Quark degeneracy pressure isn’t going to support the mass of millions, or even billions of suns. Why not? If the star is very large the density (and thus gravity) never get high enough. For example, if you consider the milky way as a single object, then that's an object resisting the mass of billions of suns. The mass is irrelevant, what matters is the density. > As for time dilation... no. In no way could that magically overcome collapse. It can keep mass from ever reaching the surface of the black hole (singularity). At least as far as we are concerned. It takes mass an infinite time to actually get to the surface, so the black hole can never grow.
    - podiki 9y ago
      A better definition is a black hole is something with an event horizon. (for your last comment, see my previous response)
      - raattgift 9y ago
        > something with an event horizon. ... where the vast majority of that something's mass and charge are within the event horizon. To keep Birkhoff happy, and to avoid confusion with event horizons that pop up where a black hole clearly isn't, maybe add that in a small region of spacetime mass and charge inside an event horizon is a black hole if after stationarization electromagnetic and gravitational perturbations in the Schwarzschild metric are small compared to those in e.g. the Minkowski or Robertson-Walker metrics. I'm tempted to go the other direction: a physically reasonable arrangement of stress-energy can source a black-hole-like metric and that a black hole metric (i.e., an exact solution for a mathematical black hole, like Kerr-Newman) can usefully approximate such that there is a good match between the geodesics structure around a mathematical black hole and the behaviour of observed matter in the vicinity of a black hole candidate. A practical probe of the null geodesics structure around a BH candidate is surface emissions: we routinely detect them directly and through analyses of radiative efficiency for neutron stars and white dwarfs (whether or not these compact objects are accreting), and a detection of surface emission from a compact BH candidate would rule it out as a source of a BH metric. If all BH candidates have surface emissions, then BH metrics are a poor choice of modelling tool. However candidates which survive this probe and other tests of near-horizon geodesics structure might as well be called black holes, even if we have reasons to hope (or even doubt) that its mass and charge within the apparent horizon is concentrated in the singularity point. You'll note here that I'm taking a "quacks like a duck" view of astrophysical black holes; I'd go even further and want to be agnostic about event horizon vs trapping surface and so forth. Around BH-like objects, arranged by increasing ease of observation, there will be a predictable (set of) ISCO(s) below which free-falling trajectories always decay or plunge inward (or outward if retrograde); there will be very strong gravitational lensing; there will be characteristic outflows from Penrose-like mechanisms; and a characteristic efficiency in conversion of accretion matter into radiation compared to matter accreting onto non-BH objects of similar mass. These all depend on whether the exterior region near the candidate object is like that of an exact BH solution, and when you have all of the above, and no evidence to the contrary, it is pretty safe to assume there is something very similar to an event horizon dividing the near-exterior region from the non-exterior region(s).
- podiki 9y ago
  I'll take your comment in good faith, but there are very good reasons to believe black holes exist and that, for instance, the center of our galaxy contains a very massive black hole and not a neutron star. This is basic general relativity, which only has (physical and theoretical) evidence in support of it. While quantum gravity is still very much uncertain, that would (most likely) only have to do with understanding the possible singularity inside black hole. Otherwise, defining a black hole as "a thing with an event horizon" is purely a general relativity prediction, consistent with all of the other predictions and observations. (Disclaimer: theoretical physicist)
  - ars 9y ago
    You skipped a step. Yes, the general relativity prediction of a black hole is solid once it exists. But you have to construct that black hole in the first place. And it's that part that's on shaky ground.
    - dwaltrip 9y ago
      This seem to be a contrarian view. Do you have any sources you can share with us?
    - AnimalMuppet 9y ago
      You seem to have missed the part where podiki offered the object at the center of the galaxy as evidence that a black hole currently exists. So you're arguing against the evidence when you say (over and over and over) that black holes can't form.
    - podiki 9y ago
      There are indeed people who closely study the process of forming a black hole from collapsing matter, hoping to understand things like the singularity and event horizon. I have not ever heard of any good results that show that a black hole for some reason cannot be formed, but I'm sure people are investigating. This would be very surprising if found, and there doesn't seem to be any evidence against black holes actually forming. So the mainstream, and as far as we can tell, correct, view is that black holes can, do, and have formed.
- KnightOfWords 9y ago
  I'm afraid that's not really accurate. The most massive neutron star observed is just under 2 solar masses, which is difficult to explain if event horizons do not exist. Quark and strange stars are hypothetical objects intermediate in mass between neutron stars and black holes, not suggested replacements for the latter. It is true we don't fully understand neutron stars and we certainly don't understand what happens inside the event horizon.
- marcosdumay 9y ago
  Aren't the detected gravitational waves evidence that black holes exist? I mean, don't the waves measure a merge up to the point that both black holes are inside a single Schwarzschild radius? And if so, isn't that very strong evidence that the things merging are black holes?
  - Ygg2 9y ago
    Gravitational waves are evidence, two extremely large objects merged, not that a black hole was formed. EDIT: If our instruments were precise enough and we could remove the noise, we could theoretically detect gravitational waves of two Sun sized stars merging (2 solar masses shouldn't form a star capable of becoming black hole).
    - marcosdumay 9y ago
      But they can tell the distance between centers of mass and total mass. Haven't we observed that distance shrink until it reaches their Schwarzschild radius? (I really don't know the answer.)
      - 4ad 9y ago
        See my parallel comment, ringdown is different for black hole remnants vs. something else, so in principle we can tell if it resulted in a black hole or not. However, for objects of suitable mass (a.i. small) the current detectors don't work very well at the frequency required to make this assessment accurately, so secondary evidence is required.
    - 4ad 9y ago
      This is not correct, the nature of gravitational waves emitted by the merging of two objects is different in its final stage, depending whether the objects form a black hole or not. Until a black hole is formed, the nature of the emission is the same for all objects (e.g. black holes or neutron stars), but if a black hole forms, the final emission (ringdown) is different. The first LIGO-Virgo events detected black hole mergers which resulted in black holes. The last LIGO-Virgo event detected two neutron star mergers. Unfortunately the sensitivity of the apparatus is not good enough to determine if the merge resulted in a black hole, or a neutron star based purely on gravitational wave measurements. However, we have secondary evidence[1] that the remnant was a black hole. [1] https://arxiv.org/abs/1710.05938 https://arxiv.org/abs/1710.05938
- raattgift 9y ago
  > Keep in mind as well that no observation has yet distinguished between a neutron star and a black hole. No, that's wrong. Narayan, R. and McClintock, J.E., New Astronomy Reviews, 51, 733–51, 2008 [arxiv: https://arxiv.org/abs/0803.0322 https://arxiv.org/abs/0803.0322 ] has a beautiful chart (Fig. 8) comparing the quiescent bolometric luminosity of star-to-accreting-neutron star binaries and star-to-accreting-black hole binaries. Observed NS binaries are brighter than observed BH (candidate) binaries. This is one test for whether a compact accretor in a binary is a BH rather than an NS. This technique was used by Bennett et al., 2002 and Mao et al., 2002 to find several candidate BHs. - -- Bennett, D.P., Becker, A.C., Quinn, J., et al. (2002). Gravitational microlensing events due to stellar-mass black holes. Astrophysical Journal, 79: 639–59. Mao, S., Smith, M.C., Woz ́niak, P., et al. (2002). Optical Gravitational Lensing Experiment OGLE-1999-BUL-32: the longest ever microlensing event—evidence for a stellar mass black hole? Monthly Notices of the Royal Astronomical Society, 329: 349–54.
booleandilemma 9y ago
If nothing can escape black holes how is it they “spew” things?
- pdonis 9y ago
  The things aren't coming from inside the black hole. They're coming from a region near, but outside, the horizon.
- opcon 9y ago
  The jets shown in the article come from the accretion disk [1], a disk of matter orbiting the black hole, formed as matter 'spirals' in. For reasons we aren't 100% sure about yet (though we suspect it is due to angular momentum and energy transfer through some process [3]), matter (in the form of hot plasma) from this accretion disk can be launched out along the axis of rotation at relativistic speeds (close to the speed of light) in the form of astrophysical jets [2], which we can observe to due the radiation they emit. These jets play a large part in galaxy evolution, and as shown in the article can be huge, extending far beyond the galaxy itself. 1: https://en.wikipedia.org/wiki/Accretion_disk https://en.wikipedia.org/wiki/Accretion_disk 2: https://en.wikipedia.org/wiki/Astrophysical_jet https://en.wikipedia.org/wiki/Astrophysical_jet 3: https://link.springer.com/article/10.1007/s10509-009-9984-y https://link.springer.com/article/10.1007/s10509-009-9984-y
- podiki 9y ago
  They also (are believed to, based on famous calculations by Hawking) radiate like a black body with a temperature related to their mass. And this leads to them losing mass over time, eventually evaporating. (Leaving what is a subject of much debate.)
  - saagarjha 9y ago
    I believe the "spew" that booleandilemma was referring to were the twin perpendicular "jets" that black holes often seem to eject, for which the explanation is probably some sort of angular momentum/near miss close to the event horizon sort of thing.
blackrock 9y ago
I love black holes Between two pillars they lie Dark and mysterious It pulls me in Its gravity is so strong And out comes A new born star.
oevi 9y ago
Black holes are an excellent example for so called "cognitive metaphors". Because we found no better analogy, we named them "holes" despite the fact that they are basically the opposite: an object with enormous mass. This influences our thinking and our language when we discuss problems concerning black holes. We talk about "inside the black hole", "light cannot escape the black hole" or "spitting things out of the black hole". I think it is really interesting how these cognitive metaphors can sometime limit our ability to think about a problem, because they often restrict the properties of the described thing to the properties of the analogy.
- westoncb 9y ago
  I think this is something that deserves much greater general awareness. I think by default we're pretty unaware of the kind of analogizing/metaphoring that takes place when we conceptualize anything—but it's completely pervasive. I see it as a kind of subtle 'dust on the lens' of the microscope which we use to observe things generally. It's an (in a certain sense) inescapable artifact due to the fact the we conceptualize with a definite thing with its own properties and quirks and limitations, which is the human brain. Anyway, I see it as a kind of 'bias' (best I can think of atm, but that term isn't really broad enough to capture the idea) which we could watch for and in doing so make gains in objectivity. Edit: also, another way of looking at it is: when we express any concepts in some concrete form, the particular representation we choose (and we have to choose something) brings its own baggage along with it. And, subsequently, we end up reasoning off of the baggage rather than the thing in itself.
  - dalbasal 9y ago
    One that I think comes up often is the robots/automation metaphor. Technology has reduced 90% or more of farm labour needs, multiplied industrial output many times, etc. We've seen a lot of automation, but it's been vague economics. When we think back on these things, we see technology, tools, & machines like tractors and looms. When we look forward we see robots and automation. Practically this has 2 effects. First, we come back with a Jetsons lime picture, everything is the same as a regular hotel but the maid is a robot, the front desk is an ATM, the barman is a robot arm and the resteraunt is a Japanese conveyor belt. Robots are human shaped metaphors for technology, placeholders for unknowns. Second, we think in terms of replacement. In reality, it's really more like efficiency. A tractor still uses a farmer, but requires a lot less time and effort to get a field ploughed. Again, there's a difference in how we think when looking back or forward.
orf 9y ago
Reminds me of one of my favorite moments[1] in Red Dwarf: > Well, the thing about a black hole - its main distinguishing feature - is it's black. And the thing about space, the colour of space, your basic space colour, is black. So how are you supposed to see them? 1. https://www.quotes.net/show-quote/66989 https://www.quotes.net/show-quote/66989
pbhjpbhj 9y ago
No mention of gravitational lensing (except in a dead comment here)? 20 years ago those images were in all the pop-sci media as evidence of black holes. They seem as strong evidence as x-ray sources.
onion-soup 9y ago
It bugs me how almost never in astronomy-related animated gifs authors never tell explicitly how long is 1 frame. In that blue x-ray burst image, am I looking at 1000 years per frame, 1 second? 1 minute? Really frustrating
- RileyJames 9y ago
  I found this gif particularly amazing because it did. And the others a little underwhelming. https://cdn.vox-cdn.com/uploads/chorus_asset/file/9984865/stars_orbit.gif https://cdn.vox-cdn.com/uploads/chorus_asset/file/9984865/st...
sandworm101 9y ago
Saying we have not "seen" a BH is like saying we haven't seen the core of any other star. We haven't, we cannot and never will. Such things are hidden behind the massively bright regions they power (corona, acretion disks ect). We must calculate the interior of a BH as we calculate the interior of jupiter. That doesnt make thier existance any less real or profound.
asah 9y ago
serious question: the accretion disk lies flat in the same plane as the earth... so how do we get an image showing the black hole "top-down" ? do they take a guess at what the far side must look like, then rotate the perspective ? either way, how is this new imagery any less synthesized than the old imagery ?
OscarTheGrinch 9y ago
If nothing can escape a black hole how can it have massive jets?
- ahmedalsudani 9y ago
  1. Energy does actually escape black holes 2. The jets are not matter originating inside the black hole. They are are matter that is accelerated by the black hole then slung away. It’s a similar mechanism to how we accelerate some of our spacecraft (by flying them close to the mooon or Jupiter) but with much higher energy levels!
- marcosdumay 9y ago
  The jets come from outside of the hole.
matte_black 9y ago
If the speed of light of this universe was raised significantly, is there some point where black holes would be impossible to form? I assume if the speed of light were lowered black holes would become far more common?
- Sir_Cmpwn 9y ago
  >If the speed of light of this universe was raised significantly, is there some point where black holes would be impossible to form? If the speed of light was infinite, yes, but a lot of physics relies on the speed of light being finite. Pretty much everything breaks (e.g. mass) if you have an infinite speed of light. >I assume if the speed of light were lowered black holes would become far more common? Yep. It might clarify things a bit to say that the "speed of light" is a misleading name - it's really more about being the speed of causality, the speed at which things happen.
- Santosh83 9y ago
  Yeah but if you do that, then you'll get a universe that's not this universe. Speed of light affects much of physics and causality.
  - matte_black 9y ago
    Hard to imagine how different the resulting universe might be, what if the speed of light and causality were say 10x higher than what it is now? Or what if the speed gradually increased over time? Would we just evaporate?
    - Santosh83 9y ago
      I think not, though am just speculating as a layman when I say that. But physicists have theorised this in much detail: https://en.wikipedia.org/wiki/Variable_speed_of_light https://en.wikipedia.org/wiki/Variable_speed_of_light I would imagine that a universe that doesn't obey basic causality will not exist for long, even if it comes into existence, nor will it support complex structures that can observe and reflect (like life). Other universes' physics and evolution might be very different, but whatever its laws, on a macro scale I'd imagine they follow internal consistency. So yes, we might evaporate, but it would be well predicted by the science of that universe. It won't happen inexplicably. :-)
NopeLupe 9y ago
Where could I get that last image 1600x900. Wanna use it as my background picture because this looks incredible!!
Pigo 9y ago
Every time I read articles like this I feel bad about my career choice. How could anything I do compare to the fascination of space exploration? The universe we live in is nothing short of mind-boggling. I'm thankful that I can at least marvel at nebula pictures taken by Hubble. However, I wish they'd switch goals from getting a few people to another planet to getting imaging equipment there that is capable of forming a VR experience we all could share.
- wickawic 9y ago
  But then who would deliver the ads?? /s I completely agree, but with the arts as my object of fixation. I could never live the swanky life I lead without my current job, but damn I would have been a good potter. Luckily, there is still time...
acobster 9y ago
My favorite video about observing black holes: https://youtu.be/iphcyNWFD10 https://youtu.be/iphcyNWFD10 Enjoy :)
dumbfounder 9y ago
When I first loaded the article all of the images were black, and I thought it was just a joke. Then after about 30 seconds they started filling in with actual pictures...
oldandtired 9y ago
Thank you all for the various comments made here, both for and against "black holes". For those who assume that General Relativity is "fact", there is an extension of classical mechanics that gives the same predictions without the space-time curvature aspects. Came out a number of years ago. For those who believe gravity (and relative density) are the causes of the theoretical entity "black hole", a question to think about in relation to fields, what happens as you move towards the centre of any mass? A second question is related to electromagnetic fields strength and approaching atomic nuclei? The same question applies to "neutron stars". For those who see want a change of reference between the external universe and the reference point of approaching the "event horizon", what does the observer see of the external universe when falling towards an "event horizon"? The term "dark star" long predates the GR model and is an entity that is quite different to the "black hole" entity of Einstein's GR theory. Due to inconsistencies between Einstein's SR theory and his GR theory, which model is more correct, if either are correct? All of our models and theories are simplifications of the explanation of how our universe works and as such will be subject to change. They all have limits of applicability. Too often, it is assumed that certain things happen in a specific way because a theory or model has some applicability in explaining observations. What a lot of intelligent people forget is that if you cannot observe some feature of the universe then the explanation of what is going on in that feature is only speculation and belief not "fact", irrespective of how "good" your theory is, including any predictions it makes. At any time, there are competing theories about specific subjects and each will have it proponents and opponents. Which of them is more correct is not the question, the question is are they useful models to help in understanding the universe around us? There is nothing wrong with pushing that a specific model or theory is more applicable than another. What we must be careful of is believing that the theories and models we push and believe in are "truth". When we do this, observations that disagree with or theories and models will (due to human nature) be discarded as irrelevant or faulty. It is interesting to note that there are many observations that have been made that are no longer reported because they do not match the predicted outcomes of the consensus theories and models. This is a shame as we then lose our ability to expand our understanding of the universe about. It is useful to remember that mathematics is a useful tool to help in building our explanations of what we observe, but every field of mathematics has specific premises, axioms etc that are simplifications or generalisations that are not actually matched by the universe around us.

335 points by shawndumas 9y ago

Source for the ring of fire image at the bottom of the page: http://eventhorizontelescope.org/simulations-gallery http://eventhorizontelescope.org/simulations-gallery under "> Accretion Disk"

IntronExon 9y ago

Magnificent. I’ve been totally entranced by black holes since I first read A Brief History of Time as a kid. Years and years of trying to wrap my head around them, and they’re still just about the closest thing I get to a spiritual moment. This is a fantastic piece, and even though some images are more visually striking, for me the ones that gives me the most chills are the time-lapse of stellar motion around Sagittarius A. Those are stars* being whipped around like toys. Stars. Over 97% of the mass of the solar system is just Sol, and these stars are more massive, and look at them move! Chills.

ars 9y ago

Keep in mind as well that no observation has yet distinguished between a neutron star and a black hole. i.e. all those photos of super massive objects could be neutron stars, and we would not be able to tell the difference. They are assumed to be black holes because of the mass, but if there is something in the law of physics that prevents black holes from forming we would not know. We do not have a theory on quark degenerative pressure for example, which could possibly exert enough pressure to prevent black holes from forming (you would get quark stars instead, with no event horizon). There are also time dilation issues that might make black holes impossible.

pdonis 9y ago
> all those photos of super massive objects could be neutron stars Not if they are more massive than 2.7 times the mass of the Sun. That's the maximum mass for a neutron star (more precisely, it's the upper limit of the range of possible maximum masses, assuming the stiffest possible equation of state). Most of the objects referred to in the article are more massive than that, in some cases much more (the black hole at the center of our galaxy is about 3 million solar masses). > We do not have a theory on quark degenerative pressure for example, which could possible exert enough pressure to prevent black holes from forming No amount of pressure can prevent a black hole from forming, if the mass is large enough. Even for hypothetical quark matter, the equation of state can't get any stiffer than the assumed equation of state that leads to the 2.7 solar mass upper limit for neutron stars. Relativity sets limits to how much an object's pressure can resist gravity, regardless of the source of the pressure. That's where the maximum mass limit comes from. > There are also time dilation issues that might make black holes impossible. No, it doesn't. It just means that light signals from very near the horizon take a long time to get out.
- ars 9y ago
  > No amount of pressure can prevent a black hole from forming And yet suns with far more mass than is needed to make a black hole exist. Because simple heat pressure keeps the black hole from forming. Remember that the black hole doesn't just suddenly appear - to have enormous gravity the density must go up. If you prevent that from ever happening you can stop the black hole from ever starting in the first place. You are talking assuming the black hole is already there, and saying quark degeneracy can't resist that, but you forget the black hole has to form first. > No, it doesn't. It just means that light signals from very near the horizon take a long time to get out. It also means mass takes a long (infinite) time to get in. So the black hole may never form.
  - podiki 9y ago
    Regarding your last point: that depends on your reference frame. From the outside it does appear to take "forever" to get into a black hole, but if you were the one falling in...it happens much quicker, certainly not taking an infinite amount of time.
    - ars 9y ago
      That's true. But it's things from the outside that are falling in, and that make a black hole. Since they take an infinite amount of time to fall in, the black hole never forms in the first place. (I'm less sure about this paragraph, but I believe that) An object falling in also never sees a black hole, since the other things falling in are dilated relative to him, so there's still not enough mass to make a black hole, even for the object falling in.
      - saagarjha 9y ago
        > But it's things from the outside that are falling in, and that make a black hole. Since they take an infinite amount of time to fall in, the black hole never forms in the first place. See this excellent answer on Physics StackExchange: https://physics.stackexchange.com/questions/5031/can-black-holes-form-in-a-finite-amount-of-time#146852 https://physics.stackexchange.com/questions/5031/can-black-h.... In a nutshell (if I'm interpreting this correctly), yes, to an outside observer you never observe the black hole form since it would take an infinite amount of time for light signals from the newly formed black hole to reach you. However, to any observers that fell into the black hole (and so were in the same frame of reference), the black hole would form in finite time.
IntronExon 9y ago
I think you’re confusing the lack of knowledge of whether or not singularities really form, with whether or not black holes form. There are very clearly black holes, but of course we can have no way of knowing if they contain singularities. Quark stars could exist, it not with the masses observed in Sag A*. Quark degeneracy pressure isn’t going to support the mass of millions, or even billions of suns. It might be that something other than a singularity is within the event horizon, but there will still be an event horizon. Given that, we’ll never observe the interior of a black hole and be able to communicate those findings, so it’s purely academic at that point. As for time dilation... no. In no way could that magically overcome collapse.
- ars 9y ago
  What's a black hole without a singularity? A neutron star? Is there a distinction you are making? To me a black hole and a singularity are the same thing. Are you using a different definition? > Quark degeneracy pressure isn’t going to support the mass of millions, or even billions of suns. Why not? If the star is very large the density (and thus gravity) never get high enough. For example, if you consider the milky way as a single object, then that's an object resisting the mass of billions of suns. The mass is irrelevant, what matters is the density. > As for time dilation... no. In no way could that magically overcome collapse. It can keep mass from ever reaching the surface of the black hole (singularity). At least as far as we are concerned. It takes mass an infinite time to actually get to the surface, so the black hole can never grow.
  - podiki 9y ago
    A better definition is a black hole is something with an event horizon. (for your last comment, see my previous response)
    - raattgift 9y ago
      > something with an event horizon. ... where the vast majority of that something's mass and charge are within the event horizon. To keep Birkhoff happy, and to avoid confusion with event horizons that pop up where a black hole clearly isn't, maybe add that in a small region of spacetime mass and charge inside an event horizon is a black hole if after stationarization electromagnetic and gravitational perturbations in the Schwarzschild metric are small compared to those in e.g. the Minkowski or Robertson-Walker metrics. I'm tempted to go the other direction: a physically reasonable arrangement of stress-energy can source a black-hole-like metric and that a black hole metric (i.e., an exact solution for a mathematical black hole, like Kerr-Newman) can usefully approximate such that there is a good match between the geodesics structure around a mathematical black hole and the behaviour of observed matter in the vicinity of a black hole candidate. A practical probe of the null geodesics structure around a BH candidate is surface emissions: we routinely detect them directly and through analyses of radiative efficiency for neutron stars and white dwarfs (whether or not these compact objects are accreting), and a detection of surface emission from a compact BH candidate would rule it out as a source of a BH metric. If all BH candidates have surface emissions, then BH metrics are a poor choice of modelling tool. However candidates which survive this probe and other tests of near-horizon geodesics structure might as well be called black holes, even if we have reasons to hope (or even doubt) that its mass and charge within the apparent horizon is concentrated in the singularity point. You'll note here that I'm taking a "quacks like a duck" view of astrophysical black holes; I'd go even further and want to be agnostic about event horizon vs trapping surface and so forth. Around BH-like objects, arranged by increasing ease of observation, there will be a predictable (set of) ISCO(s) below which free-falling trajectories always decay or plunge inward (or outward if retrograde); there will be very strong gravitational lensing; there will be characteristic outflows from Penrose-like mechanisms; and a characteristic efficiency in conversion of accretion matter into radiation compared to matter accreting onto non-BH objects of similar mass. These all depend on whether the exterior region near the candidate object is like that of an exact BH solution, and when you have all of the above, and no evidence to the contrary, it is pretty safe to assume there is something very similar to an event horizon dividing the near-exterior region from the non-exterior region(s).
podiki 9y ago
I'll take your comment in good faith, but there are very good reasons to believe black holes exist and that, for instance, the center of our galaxy contains a very massive black hole and not a neutron star. This is basic general relativity, which only has (physical and theoretical) evidence in support of it. While quantum gravity is still very much uncertain, that would (most likely) only have to do with understanding the possible singularity inside black hole. Otherwise, defining a black hole as "a thing with an event horizon" is purely a general relativity prediction, consistent with all of the other predictions and observations. (Disclaimer: theoretical physicist)
- ars 9y ago
  You skipped a step. Yes, the general relativity prediction of a black hole is solid once it exists. But you have to construct that black hole in the first place. And it's that part that's on shaky ground.
  - dwaltrip 9y ago
    This seem to be a contrarian view. Do you have any sources you can share with us?
  - AnimalMuppet 9y ago
    You seem to have missed the part where podiki offered the object at the center of the galaxy as evidence that a black hole currently exists. So you're arguing against the evidence when you say (over and over and over) that black holes can't form.
  - podiki 9y ago
    There are indeed people who closely study the process of forming a black hole from collapsing matter, hoping to understand things like the singularity and event horizon. I have not ever heard of any good results that show that a black hole for some reason cannot be formed, but I'm sure people are investigating. This would be very surprising if found, and there doesn't seem to be any evidence against black holes actually forming. So the mainstream, and as far as we can tell, correct, view is that black holes can, do, and have formed.
KnightOfWords 9y ago
I'm afraid that's not really accurate. The most massive neutron star observed is just under 2 solar masses, which is difficult to explain if event horizons do not exist. Quark and strange stars are hypothetical objects intermediate in mass between neutron stars and black holes, not suggested replacements for the latter. It is true we don't fully understand neutron stars and we certainly don't understand what happens inside the event horizon.
marcosdumay 9y ago
Aren't the detected gravitational waves evidence that black holes exist? I mean, don't the waves measure a merge up to the point that both black holes are inside a single Schwarzschild radius? And if so, isn't that very strong evidence that the things merging are black holes?
- Ygg2 9y ago
  Gravitational waves are evidence, two extremely large objects merged, not that a black hole was formed. EDIT: If our instruments were precise enough and we could remove the noise, we could theoretically detect gravitational waves of two Sun sized stars merging (2 solar masses shouldn't form a star capable of becoming black hole).
  - marcosdumay 9y ago
    But they can tell the distance between centers of mass and total mass. Haven't we observed that distance shrink until it reaches their Schwarzschild radius? (I really don't know the answer.)
    - 4ad 9y ago
      See my parallel comment, ringdown is different for black hole remnants vs. something else, so in principle we can tell if it resulted in a black hole or not. However, for objects of suitable mass (a.i. small) the current detectors don't work very well at the frequency required to make this assessment accurately, so secondary evidence is required.
  - 4ad 9y ago
    This is not correct, the nature of gravitational waves emitted by the merging of two objects is different in its final stage, depending whether the objects form a black hole or not. Until a black hole is formed, the nature of the emission is the same for all objects (e.g. black holes or neutron stars), but if a black hole forms, the final emission (ringdown) is different. The first LIGO-Virgo events detected black hole mergers which resulted in black holes. The last LIGO-Virgo event detected two neutron star mergers. Unfortunately the sensitivity of the apparatus is not good enough to determine if the merge resulted in a black hole, or a neutron star based purely on gravitational wave measurements. However, we have secondary evidence[1] that the remnant was a black hole. [1] https://arxiv.org/abs/1710.05938 https://arxiv.org/abs/1710.05938
raattgift 9y ago
> Keep in mind as well that no observation has yet distinguished between a neutron star and a black hole. No, that's wrong. Narayan, R. and McClintock, J.E., New Astronomy Reviews, 51, 733–51, 2008 [arxiv: https://arxiv.org/abs/0803.0322 https://arxiv.org/abs/0803.0322 ] has a beautiful chart (Fig. 8) comparing the quiescent bolometric luminosity of star-to-accreting-neutron star binaries and star-to-accreting-black hole binaries. Observed NS binaries are brighter than observed BH (candidate) binaries. This is one test for whether a compact accretor in a binary is a BH rather than an NS. This technique was used by Bennett et al., 2002 and Mao et al., 2002 to find several candidate BHs. - -- Bennett, D.P., Becker, A.C., Quinn, J., et al. (2002). Gravitational microlensing events due to stellar-mass black holes. Astrophysical Journal, 79: 639–59. Mao, S., Smith, M.C., Woz ́niak, P., et al. (2002). Optical Gravitational Lensing Experiment OGLE-1999-BUL-32: the longest ever microlensing event—evidence for a stellar mass black hole? Monthly Notices of the Royal Astronomical Society, 329: 349–54.

booleandilemma 9y ago

If nothing can escape black holes how is it they “spew” things?

pdonis 9y ago
The things aren't coming from inside the black hole. They're coming from a region near, but outside, the horizon.
opcon 9y ago
The jets shown in the article come from the accretion disk [1], a disk of matter orbiting the black hole, formed as matter 'spirals' in. For reasons we aren't 100% sure about yet (though we suspect it is due to angular momentum and energy transfer through some process [3]), matter (in the form of hot plasma) from this accretion disk can be launched out along the axis of rotation at relativistic speeds (close to the speed of light) in the form of astrophysical jets [2], which we can observe to due the radiation they emit. These jets play a large part in galaxy evolution, and as shown in the article can be huge, extending far beyond the galaxy itself. 1: https://en.wikipedia.org/wiki/Accretion_disk https://en.wikipedia.org/wiki/Accretion_disk 2: https://en.wikipedia.org/wiki/Astrophysical_jet https://en.wikipedia.org/wiki/Astrophysical_jet 3: https://link.springer.com/article/10.1007/s10509-009-9984-y https://link.springer.com/article/10.1007/s10509-009-9984-y
podiki 9y ago
They also (are believed to, based on famous calculations by Hawking) radiate like a black body with a temperature related to their mass. And this leads to them losing mass over time, eventually evaporating. (Leaving what is a subject of much debate.)
- saagarjha 9y ago
  I believe the "spew" that booleandilemma was referring to were the twin perpendicular "jets" that black holes often seem to eject, for which the explanation is probably some sort of angular momentum/near miss close to the event horizon sort of thing.

blackrock 9y ago

I love black holes Between two pillars they lie Dark and mysterious It pulls me in Its gravity is so strong And out comes A new born star.

oevi 9y ago

Black holes are an excellent example for so called "cognitive metaphors". Because we found no better analogy, we named them "holes" despite the fact that they are basically the opposite: an object with enormous mass. This influences our thinking and our language when we discuss problems concerning black holes. We talk about "inside the black hole", "light cannot escape the black hole" or "spitting things out of the black hole". I think it is really interesting how these cognitive metaphors can sometime limit our ability to think about a problem, because they often restrict the properties of the described thing to the properties of the analogy.

westoncb 9y ago
I think this is something that deserves much greater general awareness. I think by default we're pretty unaware of the kind of analogizing/metaphoring that takes place when we conceptualize anything—but it's completely pervasive. I see it as a kind of subtle 'dust on the lens' of the microscope which we use to observe things generally. It's an (in a certain sense) inescapable artifact due to the fact the we conceptualize with a definite thing with its own properties and quirks and limitations, which is the human brain. Anyway, I see it as a kind of 'bias' (best I can think of atm, but that term isn't really broad enough to capture the idea) which we could watch for and in doing so make gains in objectivity. Edit: also, another way of looking at it is: when we express any concepts in some concrete form, the particular representation we choose (and we have to choose something) brings its own baggage along with it. And, subsequently, we end up reasoning off of the baggage rather than the thing in itself.
- dalbasal 9y ago
  One that I think comes up often is the robots/automation metaphor. Technology has reduced 90% or more of farm labour needs, multiplied industrial output many times, etc. We've seen a lot of automation, but it's been vague economics. When we think back on these things, we see technology, tools, & machines like tractors and looms. When we look forward we see robots and automation. Practically this has 2 effects. First, we come back with a Jetsons lime picture, everything is the same as a regular hotel but the maid is a robot, the front desk is an ATM, the barman is a robot arm and the resteraunt is a Japanese conveyor belt. Robots are human shaped metaphors for technology, placeholders for unknowns. Second, we think in terms of replacement. In reality, it's really more like efficiency. A tractor still uses a farmer, but requires a lot less time and effort to get a field ploughed. Again, there's a difference in how we think when looking back or forward.

orf 9y ago

Reminds me of one of my favorite moments[1] in Red Dwarf: > Well, the thing about a black hole - its main distinguishing feature - is it's black. And the thing about space, the colour of space, your basic space colour, is black. So how are you supposed to see them? 1. https://www.quotes.net/show-quote/66989 https://www.quotes.net/show-quote/66989

pbhjpbhj 9y ago

No mention of gravitational lensing (except in a dead comment here)? 20 years ago those images were in all the pop-sci media as evidence of black holes. They seem as strong evidence as x-ray sources.

onion-soup 9y ago

It bugs me how almost never in astronomy-related animated gifs authors never tell explicitly how long is 1 frame. In that blue x-ray burst image, am I looking at 1000 years per frame, 1 second? 1 minute? Really frustrating

RileyJames 9y ago
I found this gif particularly amazing because it did. And the others a little underwhelming. https://cdn.vox-cdn.com/uploads/chorus_asset/file/9984865/stars_orbit.gif https://cdn.vox-cdn.com/uploads/chorus_asset/file/9984865/st...

sandworm101 9y ago

Saying we have not "seen" a BH is like saying we haven't seen the core of any other star. We haven't, we cannot and never will. Such things are hidden behind the massively bright regions they power (corona, acretion disks ect). We must calculate the interior of a BH as we calculate the interior of jupiter. That doesnt make thier existance any less real or profound.

asah 9y ago

serious question: the accretion disk lies flat in the same plane as the earth... so how do we get an image showing the black hole "top-down" ? do they take a guess at what the far side must look like, then rotate the perspective ? either way, how is this new imagery any less synthesized than the old imagery ?

OscarTheGrinch 9y ago

If nothing can escape a black hole how can it have massive jets?

ahmedalsudani 9y ago
1. Energy does actually escape black holes 2. The jets are not matter originating inside the black hole. They are are matter that is accelerated by the black hole then slung away. It’s a similar mechanism to how we accelerate some of our spacecraft (by flying them close to the mooon or Jupiter) but with much higher energy levels!
marcosdumay 9y ago
The jets come from outside of the hole.

matte_black 9y ago

If the speed of light of this universe was raised significantly, is there some point where black holes would be impossible to form? I assume if the speed of light were lowered black holes would become far more common?

Sir_Cmpwn 9y ago
>If the speed of light of this universe was raised significantly, is there some point where black holes would be impossible to form? If the speed of light was infinite, yes, but a lot of physics relies on the speed of light being finite. Pretty much everything breaks (e.g. mass) if you have an infinite speed of light. >I assume if the speed of light were lowered black holes would become far more common? Yep. It might clarify things a bit to say that the "speed of light" is a misleading name - it's really more about being the speed of causality, the speed at which things happen.
Santosh83 9y ago
Yeah but if you do that, then you'll get a universe that's not this universe. Speed of light affects much of physics and causality.
- matte_black 9y ago
  Hard to imagine how different the resulting universe might be, what if the speed of light and causality were say 10x higher than what it is now? Or what if the speed gradually increased over time? Would we just evaporate?
  - Santosh83 9y ago
    I think not, though am just speculating as a layman when I say that. But physicists have theorised this in much detail: https://en.wikipedia.org/wiki/Variable_speed_of_light https://en.wikipedia.org/wiki/Variable_speed_of_light I would imagine that a universe that doesn't obey basic causality will not exist for long, even if it comes into existence, nor will it support complex structures that can observe and reflect (like life). Other universes' physics and evolution might be very different, but whatever its laws, on a macro scale I'd imagine they follow internal consistency. So yes, we might evaporate, but it would be well predicted by the science of that universe. It won't happen inexplicably. :-)

NopeLupe 9y ago

Where could I get that last image 1600x900. Wanna use it as my background picture because this looks incredible!!

Pigo 9y ago

Every time I read articles like this I feel bad about my career choice. How could anything I do compare to the fascination of space exploration? The universe we live in is nothing short of mind-boggling. I'm thankful that I can at least marvel at nebula pictures taken by Hubble. However, I wish they'd switch goals from getting a few people to another planet to getting imaging equipment there that is capable of forming a VR experience we all could share.

wickawic 9y ago
But then who would deliver the ads?? /s I completely agree, but with the arts as my object of fixation. I could never live the swanky life I lead without my current job, but damn I would have been a good potter. Luckily, there is still time...

acobster 9y ago

My favorite video about observing black holes: https://youtu.be/iphcyNWFD10 https://youtu.be/iphcyNWFD10 Enjoy :)

dumbfounder 9y ago

When I first loaded the article all of the images were black, and I thought it was just a joke. Then after about 30 seconds they started filling in with actual pictures...

oldandtired 9y ago

Thank you all for the various comments made here, both for and against "black holes". For those who assume that General Relativity is "fact", there is an extension of classical mechanics that gives the same predictions without the space-time curvature aspects. Came out a number of years ago. For those who believe gravity (and relative density) are the causes of the theoretical entity "black hole", a question to think about in relation to fields, what happens as you move towards the centre of any mass? A second question is related to electromagnetic fields strength and approaching atomic nuclei? The same question applies to "neutron stars". For those who see want a change of reference between the external universe and the reference point of approaching the "event horizon", what does the observer see of the external universe when falling towards an "event horizon"? The term "dark star" long predates the GR model and is an entity that is quite different to the "black hole" entity of Einstein's GR theory. Due to inconsistencies between Einstein's SR theory and his GR theory, which model is more correct, if either are correct? All of our models and theories are simplifications of the explanation of how our universe works and as such will be subject to change. They all have limits of applicability. Too often, it is assumed that certain things happen in a specific way because a theory or model has some applicability in explaining observations. What a lot of intelligent people forget is that if you cannot observe some feature of the universe then the explanation of what is going on in that feature is only speculation and belief not "fact", irrespective of how "good" your theory is, including any predictions it makes. At any time, there are competing theories about specific subjects and each will have it proponents and opponents. Which of them is more correct is not the question, the question is are they useful models to help in understanding the universe around us? There is nothing wrong with pushing that a specific model or theory is more applicable than another. What we must be careful of is believing that the theories and models we push and believe in are "truth". When we do this, observations that disagree with or theories and models will (due to human nature) be discarded as irrelevant or faulty. It is interesting to note that there are many observations that have been made that are no longer reported because they do not match the predicted outcomes of the consensus theories and models. This is a shame as we then lose our ability to expand our understanding of the universe about. It is useful to remember that mathematics is a useful tool to help in building our explanations of what we observe, but every field of mathematics has specific premises, axioms etc that are simplifications or generalisations that are not actually matched by the universe around us.