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

#71

Post by r-bryan » Wed, Feb 28, 2018, 2:05 PM UTC

4ad wrote: post #34

ars wrote: post #16

Earlier quoted context omitted.

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 hol…

You keep repeating this misconception even though you have been repeatedly been corrected over and over again. What you don't seem to realize is that the choice of coordinates in GR is arbitrary and local. There are types of coordinates that are singular at the event horizon, and there are others which are not. This has nothing to do with infalling vs. the exterior observer. You seem to think that time is somehow fix…

I can recommend:

Bernard F. Schultz, _A first course in general relativity_

It's accessible to undergrads! (who have studied SR, vector calculus, electrostatics).

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

#72

Post by pault » Wed, Feb 28, 2018, 2:17 PM UTC

qubex wrote: post #67

marcosdumay wrote: post #58

Earlier quoted context omitted.

> 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 p…

You could go into the black hole yourself but you'd need to communicate the results of your experiment by twitching the second hand on your daughter's watch who, conveniently, works for NASA.

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

#73

Post by Ygg2 » Wed, Feb 28, 2018, 2:19 PM UTC

marcosdumay wrote: post #60

ars wrote: post #4

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 d…

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?

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).

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

#74

Post by asah » Wed, Feb 28, 2018, 2:19 PM UTC

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 ?

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

#75

Post by Sir_Cmpwn » Wed, Feb 28, 2018, 2:21 PM UTC

blackrock wrote: post #38

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…

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's a lot more complicated than this and a lot of your assumptions are not true. So far as our universe is concerned, the inside of a black hole literally doesn't exist and events in there literally don't happen. Once you get inside, spacetime is warped so severely that a lot of our fundamental assumptions about how space and time work change. It's not reasonable to assume that normal processes observed outside of the event horizon are still happening inside (plus, black holes form from supernovas, which happen precisely because fusion ceased in the star (simplified explanation)).

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

#76

Post by Sir_Cmpwn » Wed, Feb 28, 2018, 2:24 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…

"Hole" is accurate. The "object" with enormous mass would be the singularity, whereas "black hole" refers to the nature of spacetime near the singularity, for which "hole" is an apt name from our reference frame. Also, we don't talk about "spitting things out of the black hole".

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

#77

Post by whyever » Wed, Feb 28, 2018, 2:27 PM UTC

blackrock wrote: post #38

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…

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…

I would argue that calling them "dark stars" is just as misleading and "limiting thinking". In fact, I think you are a victim of this in your post: you incorrectly ascribe nuclear fusion (which is typical for many stars) to a black hole.

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

#78

Post by Sir_Cmpwn » Wed, Feb 28, 2018, 2:30 PM UTC

matte_black wrote: post #57

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?

>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.

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

#79

Post by Pigo » Wed, Feb 28, 2018, 2:31 PM UTC

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.

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

#80

Post by dragonwriter » Wed, Feb 28, 2018, 2:33 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…

> Because we found no better analogy, we named them "holes" despite the fact that they are basically the opposite: an object with enormous mass.

Strictly speaking, the defining character is enormous density, not mass. And the black hole is arguably a name for an effect of the object, not the object itself; the object itself is (or is in the process of becoming; verb tenses get weird when time gets weird) infinitesimally small, but the “black hole” generally refers to the space bounded by the event horizon.