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

Astronomers reveal first image of the black hole at the heart of our galaxy

public.nrao.edu

Post reply on HN
Print view View original

211–220 of 329 posts

Re: Astronomers reveal first image of the black hole at the heart of our galaxy

#211

Post by whoopdedo »

adgjlsfhk1 wrote: post #207
whoopdedo wrote: post #145

Earlier quoted context omitted.

Where can I read more about how that volume of data is generated? I'm looking at the description of ALMA right now. So is each "node" a cluster of antennas? And each antenna is collecting a high-resolution snapshot across a wide frequency band. And each snapshot has to be timestamped. What's the sampling rate? It says the frequency range is 31GHz to 950GHz but how wide can a single snapshot be? Then to move it around…

much faster than infiniband. A suitcase full of hard drives.

That's for moving between sites. I'm talking about the link between the antennas to each observatory's main computer.

Re: Astronomers reveal first image of the black hole at the heart of our galaxy

#212

Post by dotnet00 »

JacobThreeThree wrote: post #183
dotnet00 wrote: post #75

Earlier quoted context omitted.

Checking against callibration measurements isn't the only way to do things. With M87's SMBH for instance, they had a simulated image of what they ought to see given general relativity and what they knew about M87. The extracted data matches that fairly closely, thus lending credibility to the result for obtaining parity with physics without actually applying those physics to the data.

>With M87's SMBH for instance, they had a simulated image of what they ought to see given general relativity and what they knew about M87. How confident are we that our current simulations accurately reproduce the universe? Given how many unpredicted and supposedly impossible exoplanet and star configurations that keep being found, I'd say the current model is not doing so well on the prediction front. https://www.sc…

Those configurations aren't "impossible" due to fundamental well tested physics like general relativity. They're "impossible" from the perspective of our understanding of the formation of planetary systems, which is understandably less well developed given how much more difficult it is to study since as a science, exoplanet detection is just 30 years old, with the majority of detections being less than 15 years old.

In comparison, general relativity is one of the most well tested theories in physics, having been undergoing rigorous testing for over a century, and regardless, the point stands that the results were close to the model, thus providing evidence for the model's validity.

Re: Astronomers reveal first image of the black hole at the heart of our galaxy

#213

Post by boringg »

guelo wrote: post #204
wthomp wrote: post #91

For those wondering if we could get sharper images with JWST, here’s the previously imaged black hole (same angular size as our own) compared to a single pixel from Hubble’s wide field camera 3: https://twitter.com/alex_parker/status/1116070667068170240?s... JWST will have smaller “pixels” but is in the same ballpark.

There is so much post processing that the telescope resolution barely matters. Personally I'm skeptical of these images since the algorithms have a lot of data fitting to "what it should look like" built in to them.

How much post processing is happening? This isn't raw co-ordinated but rather fit data?

Re: Astronomers reveal first image of the black hole at the heart of our galaxy

#214

Post by quasarj »

fasteddie31003 wrote: post #29

I am very skeptical of the Event Horizon Telescope (EHT) images because they are not following a scientific method that results in a true representative image of their target. In my opinion astronomy is jumping the shark with these images by making this a big PR stunt. I've looked at their methods for their earlier images and they seem to be hunting for a circle that looks like a black hole in their data. The EHT's f…

Thank you! I read over their process from the first one and it sounded like they were just using ML to make up most of the image! I need to read a lot more of the details but I am quite skeptical of these images...

Re: Astronomers reveal first image of the black hole at the heart of our galaxy

#215

Post by hammock »

dekhn wrote: post #164
hammock wrote: post #155

Earlier quoted context omitted.

Should have clarified. Does a black hole have fuzzy edges or sharp edges?

this is sort of getting into the definition of black holes and event horizons. I don't think they really have solid surfaces, I would expect all imaging here to show fuzzy samples.

Like, would it be a gradient from dense-to-fuzzy as you move outward from the center, until you reach the event horizon outside of which is nothing?

Re: Astronomers reveal first image of the black hole at the heart of our galaxy

#216

Post by hbrav »

SkyMarshal wrote: post #157
wthomp wrote: post #91

For those wondering if we could get sharper images with JWST, here’s the previously imaged black hole (same angular size as our own) compared to a single pixel from Hubble’s wide field camera 3: https://twitter.com/alex_parker/status/1116070667068170240?s... JWST will have smaller “pixels” but is in the same ballpark.

So you’re saying no, JWST won’t provide significantly sharper images of black holes than the Event Horizon Telescope?

JWST would be unable to resolve the black hole at all.

Re: Astronomers reveal first image of the black hole at the heart of our galaxy

#217

Post by quasarj »

raattgift wrote: post #81
zeven7 wrote: post #56

Earlier quoted context omitted.

For quasars, don't the beams shoot out of the poles? Let's hope our nearby buddy doesn't become that active.

There is vanishingly small likelihood of Sgr A* becoming active (in the sense of developing highly luminous structures nearby it). There is little in the central parsec to feed it, and it is low in mass for a central black hole. There is a lot of astronomical hunting to be done to find the weak polar jet from Sgr A*. We only look down on its north pole approximately. Extending the spin axis of Sgr A* could miss our s…

So I have a question about that.. I thought it would only have an accretion disk if it was active. So what gives? I guess I'm wrong? What constitutes "active" if not "stuff is falling in"?

Re: Astronomers reveal first image of the black hole at the heart of our galaxy

#218

Post by KAMSPioneer »

kloch wrote: post #129
KAMSPioneer wrote: post #126

Earlier quoted context omitted.

So I work at one of the participating institutes, and you're very much dead-on about transfer speeds/logistics limiting options here. I'm not an astronomer, so grain of salt, but the data is generated at a bit of an unwieldy pace: there are four collector nodes at each site, each of which generates ~16Gbps of raw data (though read speeds from disk after observation is more like 8Gbps). This, as you say, forces most l…

How many seconds of observation data are required for one of these images?

For the entire image? I'm not sure, but a lot. Usually an EHT observing session is days in length, and the responsible astronomer(s) will reside at the telescope for a week or so...but I don't believe that 100% of that time is spent feeding data into the collectors. I can ask my coworker tomorrow for clarification on the actual observing time and post an update.

Re: Astronomers reveal first image of the black hole at the heart of our galaxy

#219

Post by hbrav »

jankovicsandras wrote: post #136
fasteddie31003 wrote: post #29

I am very skeptical of the Event Horizon Telescope (EHT) images because they are not following a scientific method that results in a true representative image of their target. In my opinion astronomy is jumping the shark with these images by making this a big PR stunt. I've looked at their methods for their earlier images and they seem to be hunting for a circle that looks like a black hole in their data. The EHT's f…

I share your skepticism. To others: Before voting me down, please consider these arguments. As I understand, this image is not from visible light, not a photo, more like plotting radio measurements. "black holes" are the brightest objects in the universe. It's a bit like an alien scientist showing an X-ray picture of a skeleton:"This is a human!" Some quotes from https://en.m.wikipedia.org/wiki/Black_hole : "Moreover…

I think there's some confusion on your part about what the image purports to show.

I shall put aside the parent comments concern about the signal analysis techniques. Those may be valid concerns, and I don't know enough to assess them.

> I'm not sure it's physically possible to take a visible light picture of a "naked" event horizon The event horizon telescope isn't purporting the image emission from the event horizon itself. While the theory of those emissions (Hawking radiation) is very persuasive, they would be incredibly weak for a black hole of even stellar mass, and even weaker for a supermassive black hole. What is being imaged here is hot around the black hole, which is heated due fluid dynamic effect (compression or viscosity, I'm not sure which dominates) as it spiral in to the black hole. The 'image' of the event horizon is the 'shadow' where the black hole blocks our view of the hot gas on the far side.

The fact that this shadow is compatible with the expected size given the mass of this black hole is a scientifically interesting result.

Re: Astronomers reveal first image of the black hole at the heart of our galaxy

#220

Post by fsh »

amelius wrote: post #180
fsh wrote: post #125

Earlier quoted context omitted.

The resolution of these telescopes is limited by diffraction, not by the number of pixels on the sensors. The achievable angular resolution is roughly the wavelength divided by the aperture diameter [1]. JWST works in the few µm wavelength range and has a 6.5 m aperture, such that the angular resolution is ~0.1 arcsec. The EHT works with 1.3 mm wavelength and has an effective aperture of roughly the earth diameter (~…

Can we invert the diffraction process numerically?

No, this is fundamentally impossible. There are infinitely many possible objects that would produce the same blurry image.
Post reply on HN