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

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

#221

Post by jrgd »

yellow_postit wrote: post #134
jrgd wrote: post #32

I find the whole thing amazing and captivating - yet the image is … huh … slightly underwhelming. It looks like some gaussian blurred random image. I wish it could be the kind of crisp image JWST ‘sent’. It’s difficult to force oneself to not romanticise these un-visible things based on artists visualisation we got accustomed to.

There’s a good Video from Kip Thorne showing why the “real” images differ from the idealized one that made much fanfare in Interstellar (Edit) to add that it’s about 22minutes in. https://youtu.be/GlmMxmWHEfg

Hey that’s amazing; thanks.

My comments was more about the culturally idealised images we have in mind rather than criticising the work and the tech (far from it actually, but given the downvotes I might have not expressed myself really clearly -> apologies to anyone who felt bad/sad about what i wrote).

I really appreciate the small animation you pointed at 22min.

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

#222

Post by denton-scratch »

I am impressed.

I have a few ignorant questions:

1. There are three bright blobs on the image; I assume they are the same object, behind the BH. What are they/is it? They said the image was averaged; so presumably whatever the blobs are wasn't moving?

2. Is it correct that the rest of the ring, ignoring the three blobs, is the far side of the accretion disk? Why can't I see this side of the accretion disk?

3. According to the article, at least one submillimeter telescope was important. But submillimeter is infrared, isn't it? I thought infrared was blocked by dust, and if there's one thing there's a lot of at the centre of the galaxy, it's dust?

[Edit] Questions 1 and two were prompted by this remark in the article:

  "The new view captures light bent by the powerful gravity of the black hole"
The only "light" I can see is a ring with blobs in it; that's why I suppose the ring in the image is not the accretion disk, at least, not as viewed from the pole. Most other commenters here assume (or know) that it is the accretion disk, and we are looking at a pole.

But if that is indeed the accretion disk, then that isn't light that's been bent by the gravity of the black hole.

Perhaps the explanation is that many other commenters haven't actually read the article, possibly because they already know the story.

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

#223

Post by KAMSPioneer »

whoopdedo wrote: post #145
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…

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…

So ALMA, being an array, is a bit of a different beast than single-dish telescopes like the one where I'm employed; they do indeed have an array of antennae and correlate all the collected data at a central correlator (at least, for normal observations). My institute has a single, much larger primary reflector (30 meter diameter) and does not require such a process during normal observation. However, during VLBI observations, which EHT is, the receiver is dumping data to four collector computers, which is what I was referring to as "nodes" generating ~16Gbps of data apiece.

I wish I could shed some more light on the ins-and-outs of exactly how these observations work, but I just run the computers, man. :) What I can tell you is that in order to move data off of the collector machines, they typically use m5copy, which is a part of the JIVE project (they have a Github repo: https://github.com/jive-vlbi/jive5ab). All communication between the control computer and the collectors happens within a private, physically-distinct network, but it's just standard commodity networking equipment between the control computer and the collectors. The folks in charge of the node's design are in the process of removing some of the bottlenecks to make electronic transfers more viable (the current spec doesn't even include a 10Gbps uplink!).

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

#225

Post by gilbetron »

hammock wrote: post #155
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 (~…

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

Does the sun have fuzzy or sharp edges?

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

#226

Post by fsh »

quasarj wrote: post #214
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...

The papers do not mention any machine learning.

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

#227

Post by nyc111 »

Matt Strassler: «The details of the reconstructed image depend on exactly what assumptions are made.» https://profmattstrassler.com/2022/05/12/in-our-galaxys-cent...

What does this mean? If they assembled an image to fit their assumptions, that would be circular reasoning. I don't understand.

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

#228

Post by gilbetron »

Mehringotio wrote: post #107
fasteddie31003 wrote: post #42

Earlier quoted context omitted.

I did read them and I'm not satisfied with their methods.

Either you are an expert in this field than it should be you who writes a clear argument and present it or you are not an expert. Aren't they are peer reviewed? What is your expertise in astrophysics?

He has a theoretical degree in astrophysics.

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

#229

Post by fasteddie31003 »

queuebert wrote: post #201
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…

The point spread function of the detector is pretty well characterized, and from there the image is basically just a Fourier transform. It's not as magical as you might think. Then it looks like they average a bunch of these images to get a maximum likelihood image. What is your issue with that? Besides, to calibrate on a known celestial body, they'd have to have another micro-arcsecond resolution radio telescope to…

Could they not zoom out and take a picture of the stars around Sagittarius A* to compare that to the knowns locations of these stars?

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

#230

Post by sandworm101 »

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 is nowhere near the caliber of telescopes necessary to resolve black holes. Very literally, we would need an optical telescope bigger than new york city to even make an attempt.
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