Most images of black holes are illustrations. Here’s what our telescopes capture • Hacker News Board

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

#61

Post by grkvlt » Wed, Feb 28, 2018, 12:51 PM UTC

teamonkey wrote: post #28

ars wrote: post #25

Earlier quoted context omitted.

No, that's exactly what I understand. But we don't care about the infalling object. We care about the observer, because any infalling object initially is an observer, and because we (us humans) are observing the black holes. Since from an observers POV nothing can actually fall into the black hole, no black hole can form. The fact that an infalling object reaches the black hole makes no difference to us. Because of t…

> Since from an observers POV nothing can actually fall into the black hole, no black hole can form. The event horizon isn't really a physical boundary in that sense. It's the mathematical boundary at which, according to general relativity, a particle must have velocity equal to the speed of light in order to escape. A density change inside the star can change the size and shape of that boundary without things fallin…

A better way of thinking about the event horizon is that it is the boundary beyond which events happening cannot be assigned a 'when' in our universe - i.e. the object falling 'in' to the black hole is never seen to pass this horizon, but to the object it seems that they do, however those events happen to it after an infinite time in our universe, i.e. never, due to time dilation. The contents of a black hole are the events that occur outside/after our universe relative to that boundary. I found these explanations on an awesome PBS youtube video [0] about black holes and space-time.

0. https://youtu.be/vNaEBbFbvcY

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

#62

Post by NopeLupe » Wed, Feb 28, 2018, 1:00 PM UTC

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

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

#63

Post by pvg » Wed, Feb 28, 2018, 1:03 PM UTC

oevi wrote: post #24

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 b…

Is it really an [excellent] example of that? We don't use much of the language we use for holes in general for 'black holes'. The term may have been influenced by 'Black hole of Calcutta', itself a metaphorical use.

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

#64

Post by qubex » Wed, Feb 28, 2018, 1:05 PM UTC

oevi wrote: post #24

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 b…

On the topic of how languages and metaphors affect (and might even form the fundamental substrate of) our thinking, I highly recommend Douglas Hofstadter (he of Godel, Escher, Bach fame) 's book Surfaces and Essences (2010).

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

#65

Post by qubex » Wed, Feb 28, 2018, 1:08 PM UTC

Santosh83 wrote: post #49

blackrock wrote: post #38

Earlier quoted context omitted.

I would prefer if black holes were called "Dark Stars". Because that really is what they are. A weird star that is so massive, its gravitational field distorted the fabric of its local space, that not even light can escape it. It is theoretically possible that the black hole is still performing fusion, and emitting light and heat, like a regular star. But its gravitational field is so intense, that even light cannot…

Gravitational collapse overwhelms fusion pressure much before the black hole stage is reached, i.e., neutron stars. Also general relativity seems to indicate unambiguously that the in-falling matter collapses to a singularity, which obviously cannot have any kind of structure or process inside it. I guess only a quantum theory of gravity can clear up this enigma.

(Not to mention that once one has crossed the Schartzchild Radius time dilation becomes infinite from the perspective of the outer universe, and time freezes, so any process becomes frozen in its tracks, at least from the perspective of external observers.)

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

#66

Post by zaarn » Wed, Feb 28, 2018, 1:14 PM UTC

ars wrote: post #10

pdonis wrote: post #6

Earlier quoted context omitted.

> 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…

> 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…

>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.

A star has internal fusion/fission that keeps it's mass from collapsing. Once a supermassive star runs out of energy, the entire thing comes rushing centerwards (and some of it gets explodified as supernova)

>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.

Blackholes aren't magic. To form, a certain matter density must be reached in a certain volume of space (which can be surprisingly low; the blackhole at the center of the milkyway is not much more dense than water at normal atmospheric pressure). Once you have reached this specific point, you get a black hole.

From an outside perspective, being pulled into a blackhole looks like being redshifted out of existence and torn apart, for the infalling object, nothing happens (unless the BH is small enough).

The black horizon around a black hole is not a simple line, it's a smort of smudge leading up to the real border; the closer you get the more redshifted everything becomes. Thus, for the naked observer, it might appear as though the object has been swallowed even though it might not have yet crossed the event horizon.

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

#67

Post by qubex » Wed, Feb 28, 2018, 1:18 PM UTC

marcosdumay wrote: post #58

akvadrako wrote: post #44

Earlier quoted context omitted.

> It is theoretically possible that the black hole is still performing fusion, and emitting light and heat, like a regular star. I don't think that's a useful picture. It's closer to the truth to say that from the outside perspective, all the information and energy sits on the border and there is not even an inside to speak about. In other words, it's the edge of the universe and what's past the event horizon is anot…

> From the outside perspective, all the information and energy sits on the border Are you sure that's known? What kind of experiment would settle that?

Since at the event horizon (schardzchild radius) time dilation becomes infinite, essentially time ceases there. That's why it's called an “event horizon”: because events (four-dimensional coordinates) become disconnected there. As time is frozen (from an external observer's perspective) stuff ceases to move and just “piles up” there. From the in-falling matter's perspective, however, the transition occurs in finite proper time. Once it has crossed the horizon, it finds itself inside the hole where the direction of space pointing towards the horizon (inwards) becomes ‘timelike’ (in the sense that its flow cannot be arrested and it is unidirectional) and time becomes ‘spacelike’ (in the sense that it could be negotiated at will).

No experiment that I know of could confirm this because everything will depend on extrapolation from less extreme and finite scenarios.

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

#68

Post by pnut » Wed, Feb 28, 2018, 1:22 PM UTC

akvadrako wrote: post #44

blackrock wrote: post #38

Earlier quoted context omitted.

I would prefer if black holes were called "Dark Stars". Because that really is what they are. A weird star that is so massive, its gravitational field distorted the fabric of its local space, that not even light can escape it. It is theoretically possible that the black hole is still performing fusion, and emitting light and heat, like a regular star. But its gravitational field is so intense, that even light cannot…

> It is theoretically possible that the black hole is still performing fusion, and emitting light and heat, like a regular star. I don't think that's a useful picture. It's closer to the truth to say that from the outside perspective, all the information and energy sits on the border and there is not even an inside to speak about. In other words, it's the edge of the universe and what's past the event horizon is anot…

Lee Smolin proposed a really compelling concept in "Life of the Cosmos" - that the reason our universe has the universal constants that it does, is the product of natural selection at the cosmological level.

https://en.wikipedia.org/wiki/Lee_Smolin#Fecund_universes

His idea is that production of black holes is the universe producing offspring, and our perception that a black hole is constrained within a coordinate space in our own universe, is an illusion.

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

#69

Post by qubex » Wed, Feb 28, 2018, 1:27 PM UTC

ars wrote: post #10

pdonis wrote: post #6

Earlier quoted context omitted.

> 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…

> 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…

First and foremost: GR guarantees that an event horizon will form. Oddball exotic states of matter (quark stars, fuzz balls, whatever) might form in proper time within the event horizon, halting collapse before it reaches the singularity state of infinite compaction. (Since time freezes at the event horizon, these states would occur infinitely far in the future from the perspective of any external observer and might therefore very reasonably be considered ‘unphysical’.)

Second, and this is surprisingly subtle: we often discuss black-hole formation in terms of mass, but it's really a matter of relative density: the 2.7 solar mass limit only pertains when one is considering a mass in a void, if for example one found oneself in an infinite universe with an undisturbed uniform density of (say) 2.7 solar masses per metre cubed the tug of gravity would be uniform in all directions and there would be no impetus to initiate gravitational collapse towards any specific point. Once perturbed, however, average density somewhere would rise, and the collapse would begin.

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

#70

Post by thathappened » Wed, Feb 28, 2018, 1:31 PM UTC

chrisweekly wrote: post #54

oevi wrote: post #24

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 b…

Great comment -- but while I agree w/ your point about metaphors, I respectfully mildly disagree about this one in particular. For context, I associate it with the popular analogy of timespace as an elastic "sheet" of sorts, with marble-like objects resting on (and sinking into) its surface, with their mass dictating how "deep" their gravity "well" is. With that metaphor in mind, black holes really do approximate hol…

But even how we illustrate a sheet of spacetime we show it dip when it should stay flat and pinch, closing the gap between atoms as they get more dense.

All of these inaccurate descriptions assume we have the concept already in mind to recursively look up. Describing more accurately let's the reader get a clearer picture and thats where real concepts get conceived.

I like heavy/dark star/planet for a vague description. I also think the fact that humans rely on visuals now and we can't get more than a single angle of one of these we can show anyone a 3D view of how it's not just nothing.