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Unveiling the first-ever image of a black hole [video]

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Re: Unveiling the first-ever image of a black hole [video]

#61

Post by typon »

jessriedel wrote: post #53
ragebol wrote: post #25

Earlier quoted context omitted.

Note that the prediction of the light being brighter on one side did come out.

What are you basing that on? (Edit:) From one of the papers released today: > The ring is brighter in the south than the north. This can be explained by a combination of motion in the source and Doppler beaming. As a simple example we consider a luminous, optically thin ring... Then the approaching side of the ring is Doppler boosted, and the receding side is Doppler dimmed...This sense of rotation is consistent with…

It's confirmed in the press conference by the scientists. They said its the Doppler beam effect

Re: Unveiling the first-ever image of a black hole [video]

#63

Post by posix_me_less »

nukeop wrote: post #42
acl777 wrote: post #17

There are people that can't believe the Earth is round... I can't imagine what "alternative explanation" will be made to explain a black hole...

There is still zero evidence that there exists such a thing as a black hole with all its fantastic properties. We have a picture of a red-yellow accretion disk and that's it. Black holes remain a mathematical artifact of general relativity and there is as much evidence of their existence as of crystal healing and astral travel. There is at best some evidence of very massive objects at certain points.

How do you explain observed gravitational wave observed by LIGO? It is almost the same as the one calculated for coalescence of two black holes in GR.

Re: Unveiling the first-ever image of a black hole [video]

#64

Post by hacker_9 »

gigatexal wrote: post #29

Any word if Einstein's predictions are correct or refuted? There was word that if the shadow looked a certain way it could mean that relativity is incomplete.

General relativity predicted the event horizon, but it breaks down when trying to predict what is going on in the center, as all equations go to infinity, which is likely to be more a problem with our current understanding than what is actually happening.

Re: Unveiling the first-ever image of a black hole [video]

#66

Post by mercwear »

gigatexal wrote: post #29

Any word if Einstein's predictions are correct or refuted? There was word that if the shadow looked a certain way it could mean that relativity is incomplete.

USA Today is live streaming a presentation about this from the National Science Foundation and they seem to be taking the point of view that Einstein's theory of general relativity has held up SO FAR. There is still quite a bit of research to do on the image / data which means the theory could be further proven or disproven.

Re: Unveiling the first-ever image of a black hole [video]

#68

Post by thatcherc »

zeristor wrote: post #45

How big a VLBI baseline would they need to see much more detail? Are there any plans for a space based VLBI; not easy when you consider the utterly huge amounts of information they have to transfer, a radio telescope in a L5 would be a start. Also I'd be interested to read how they got around scintallation of the Interstellar Medium.

Space VLBI is a thing already! Seems to have been around for a while [0][1]. I imagine that the challenge with during EHT-style VLBI in space is downlink bandwidth... there's just no way to get the petabytes of data they talk about down from a satellite. It's already so much data that it's easier to fly hard drives around the world than to send it over the internet, so the transfer would probably take ages over a microwave link. Maybe with laser communication in the near future but even then... it's a lot of data.

Resolution-wise, the angular resolution is inversely proportional to the farthest baseline, as given by the Rayleigh criterion. [2] To get twice the resolution, you "just" need to double the size of your baseline (and do that in both dimensions, otherwise the angular resolution will be different in x & y). We've maxed out the Earth's baseline, so it seems like orbital radio telescopes are the only way to better resolution. Pretty exciting!

[0] - https://www.jpl.nasa.gov/missions/space-very-long-baseline-i...

[1] - https://asd.gsfc.nasa.gov/blueshift/index.php/2016/07/25/thi...

[2] - https://en.wikipedia.org/wiki/Angular_resolution

Re: Unveiling the first-ever image of a black hole [video]

#69

Post by privong »

zeristor wrote: post #45

How big a VLBI baseline would they need to see much more detail? Are there any plans for a space based VLBI; not easy when you consider the utterly huge amounts of information they have to transfer, a radio telescope in a L5 would be a start. Also I'd be interested to read how they got around scintallation of the Interstellar Medium.

> Are there any plans for a space based VLBI; not easy when you consider the utterly huge amounts of information they have to transfer, a radio telescope in a L5 would be a start.

There is space-based VLBI at lower radio frequencies, with the "Radio Astron" project[0]. That effort works at frequencies which are roughly a factor of ~10 lower than that of the EHT. I'm not aware of any plans for millimeter Space VLBI, but the higher frequency would require higher data rates.

[0] http://www.asc.rssi.ru/radioastron/

Re: Unveiling the first-ever image of a black hole [video]

#70

Post by huffmsa »

So is a black hole 3 dimensional? Is it a sphere? Or does it only work in certain directions? Does everything "fall" the same direction?

I ask because even in a brief history of time, the diagrams are very "single plane of space-time, pulled infinitely deep by the black hole"

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