Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

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

vox.com

Post reply on HN
Print view View original

111–120 of 167 posts

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

#111

Post by 4ad »

marcosdumay wrote: post #105
Ygg2 wrote: post #73

Earlier quoted context omitted.

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).

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.)

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.

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

#112

Post by oldandtired »

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.

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

#113

Post by trophycase »

pnut wrote: post #68
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…

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 sp…

I personally subscribe to this theory. I also think it's plausible that the development of intelligent life may be a part of the universe's reproductive process and may end up facilitating it in some way

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

#114

Post by nikofeyn »

dsacco wrote: post #100
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. No, they actually are holes. We don’t need analogies or metaphors to describe black holes. Their mathematical properties are quite complicated to define and we have to reason about what happens around or inside them using figurative thought experiments, but their action does…

does it make sense to you that a "hole" has mass, electric charge, and angular momentum and is completely characterized by these properties?

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

#115

Post by wallace_f »

podiki wrote: post #14
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…

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 understandin…

OP's claim is that black holes infinite amount of time to form, because matter would take an infinite amount of time to fall into it.

Personally, as a layman on the subject of black holes, what I understand is that mass does take infinite amount of time to fall into an event horizon. But I don't know about the formation process of how/when that event horizon is formed.

Perhaps you can help me, and him, understand why his claim is false--that it would happen in finite time?

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

#116

Post by 4ad »

nikofeyn wrote: post #114
dsacco wrote: post #100

Earlier quoted context omitted.

> Because we found no better analogy, we named them "holes" despite the fact that they are basically the opposite: an object with enormous mass. No, they actually are holes. We don’t need analogies or metaphors to describe black holes. Their mathematical properties are quite complicated to define and we have to reason about what happens around or inside them using figurative thought experiments, but their action does…

does it make sense to you that a "hole" has mass, electric charge, and angular momentum and is completely characterized by these properties?

Notice how an electron hole also has all those properties. That's because those properties are due to specific symmetries of various fields (in space), or symmetries of space itself. Those properties are not "in" the particle, they do not belong to it, rather they are constraints over what kind of interactions can happen in all space that is causally-connected.

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

#117

Post by Santosh83 »

matte_black wrote: post #110
Santosh83 wrote: post #96

Earlier quoted context omitted.

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.

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?

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

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. :-)

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

#118

Post by JoeAltmaier »

wallace_f wrote: post #115
podiki wrote: post #14

Earlier quoted context omitted.

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 understandin…

OP's claim is that black holes infinite amount of time to form, because matter would take an infinite amount of time to fall into it. Personally, as a layman on the subject of black holes, what I understand is that mass does take infinite amount of time to fall into an event horizon. But I don't know about the formation process of how/when that event horizon is formed. Perhaps you can help me, and him, understand why…

Maybe they never finish forming (keep collapsing forever). But once you have an event horizon, you have a black hole, right?

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

#119

Post by hackerman12345 »

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 is my understanding that black holes create new stars. It's also my understanding that small mass will eventually be drawn towards bigger mass. Does this mean the eventual "heat death of the universe" won't actually happen as stray light/heat/RF/particles/whatever will always get drawn in back towards a mass like a blackhole and reformed?

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

#120

Post by monocasa »

saagarjha wrote: post #19
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…

> 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-h... . In a nutshell (if I'm interpreting this correctly), yes, to an outside observer you never observe the black hole for…

Except Hawking radiation means that it doesn't exist for an infinite amount of time.

So an observer falling in would just see it fizzle away as they get closer to it.

Post reply on HN