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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

#231

Post by JacobThreeThree »

dotnet00 wrote: post #212
JacobThreeThree wrote: post #183

Earlier quoted context omitted.

>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.…

If general relativity based models have struggled to help predict or explain planetary system formation and exoplanet observations, I think we should have the same level of expectation about how helpful a general relativity based black hole model will be.

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

#232

Post by jankovicsandras »

hbrav wrote: post #219
jankovicsandras wrote: post #136

Earlier quoted context omitted.

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 horizo…

Thanks for your reply!

I also think it's scientifically interesting and appreciate the work.

But it should be called a model or illustration, because a human could never see this with bare eyes.

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

#233

Post by sandworm101 »

ISL wrote: post #188
hammock wrote: post #155

Earlier quoted context omitted.

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

The edge should be quite sharp. Any deformation or movement in the edge will be smoothed extremely quickly, on timescales comparable to the light-crossing time of the object -- in this case ten seconds or so. If you're a photon and you're in, you stay in. If you're out and heading out, you get out. (if you skim the surface, you might make an orbit and then leave :) ). It is that fact that makes the edge quite sharp.

I disagree. The edge of a BH is essentially an asymptote. While there is a mathematical bright line, when looking at it you should see light in all manner of red/blue-shifted colors near the event horizon. Since that light is coming in from a variety of directions it leaves in a variety of directions too. Everything would look soft and fuzzy around the edges. Out of focus.

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

#234

Post by dotnet00 »

JacobThreeThree wrote: post #231
dotnet00 wrote: post #212

Earlier quoted context omitted.

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.…

If general relativity based models have struggled to help predict or explain planetary system formation and exoplanet observations, I think we should have the same level of expectation about how helpful a general relativity based black hole model will be.

You might as well be saying that if fluid dynamics models have struggled to help predict or explain CPU performance increases, we should have the same level of expectation about how helpful a fluid dynamics based model of aerodynamics will be, i.e. complete nonsense

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

#235

Post by raattgift »

quasarj wrote: post #217
raattgift wrote: post #81

Earlier quoted context omitted.

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"?

Unexpected question from someone whose nickname starts with "quasar"! :-)

Active in the sense of (from https://en.wikipedia.org/wiki/Active_galactic_nucleus>) "much higher than normal ... excess non-stellar emission" from the region very close to the central black hole. Our central parsec is simply dim in practically every wavelength compared to its enclosing central bulge. An active galactic nucleus in our galaxy would be very noticeable to the naked human eye: it would "light up" (with far ultraviolet to gamma radiation) lots of interstellar material that, having been heated, would glow very brightly in the reds and oranges.

The luminosity of AGNs and quasars (especially luminous AGNs) is mostly from matter-matter collisions between gas and dust on intersecting geodesics (a fancy sort of friction that becomes enormous in the material nearest the black hole), with a contribution from daughter products of those collisions.

There isn't much matter circulating close to Sgr A*. It's "starving". In the panel they tried to put it in terms of a human diet: if you were eating like Sgr A* is, scaled down to human size, you'd be eating a grain of rice every few million years. Good luck keeping your body heat up on that diet. :-)

In the past -- tens of thousands to many millions of years ago -- there might have been a lot of matter circulating around Sgr A*, being swept up into luminous jets, which generated the Fermi bubbles https://en.wikipedia.org/wiki/Galactic_Center#Gamma-_and_X-r...>. That's an area of current research: do central black holes eventually go radio-quiet in general? Is there a active-quiet-active-quiet cycle in central black holes in general? Or is this all an ultraviolet herring with the Fermi bubbles being produced by some mechanism that doesn't involve (or only very weakly depends upon) Sgr A*?

ETA: I forgot to re-read my own (grandparent) comment. The "luminous structures nearby" are not just an accretion disc. Jets count, too. Also anything that they strike (molecular gas clouds, for instance) will tend to become luminous in some part of the spectrum (sometimes this results in "frustrated lobes", sometimes "light echoes" or ionization echoes from flares).

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

#236

Post by holoduke »

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?

Aren't these black hole images based on ultra sensitive radio telescopes?

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

#237

Post by nojonestownpls »

yawz wrote: post #35

> EHT team members talk about a sharpness of vision akin to being able to see a bagel on the surface of the Moon. This is truly amazing!

Scientists discover a bagel on the surface of the Moon!

Search for black hole ends with a bagel hole?!

[Become a paid subscriber to read the full story.]

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

#239

Post by dekhn »

hammock wrote: post #215
dekhn wrote: post #164

Earlier quoted context omitted.

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?

I couldn't really say for sure but I think macroscopically (viewed from a low-resolution telescope) it would look fuzzy, but close up, it would look very spiky and dynamic with all sorts of stochastic events happening.

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

#240

Post by kloch »

ramigb wrote: post #148

Can the smart people in here confirm if we are getting sucked into this someday or not?

Some perspective that may help:

If the Sun were replaced by black hole with the same mass as the Sun at the center of the Solar System we wouldn't automatically get sucked into it. A very cold Earth would continue to orbit the black hole exactly as it does the Sun today. Only if the Earth's orbit were perturbed by some other body would it have a chance of joining the black hole.

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