Green Baron

Imaging a black hole - the EHT

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Sgr A* changes quickly, even during one session, while M87 stays still. That complicates data evaluation.

"very soon" they say

very TM :-)

Edited by Green Baron

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6 hours ago, tater said:

It's the temp as if it was a block body. Doesn't mean that's the actual temp.

Yeah... the scale varies wildly as well.

But still impressively hot.

 

5 hours ago, Green Baron said:

Sgr A* changes quickly, even during one session, while M87 stays still. That complicates data evaluation.

Given how quickly the star very close to Sgr A* goes, it'll be a sight to behold...

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57 minutes ago, Green Baron said:

The dark depression in the image presented is about double the size of the actual event horizon that would fit the mass 6.5 billion solar masses.

Does that mean the M87 black hole is larger than originally estimated, or is it just due to gravitational lensing?

EDIT: upon further reading I found that the EHT images constrained the mass to around 6.5 billion solar masses, so obviously I was wrong and it’s not bigger than expected. 

Edited by ProtoJeb21

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I was interested in what measurements they could take from this image :

The University of Amsterdam's Sera Markoff said that the size of the black hole provided a new estimate of its mass; she called it "really a monster, even by black hole standards." It's roughly the size of the Solar System, but it has a mass that is 6.5 billion times that of our Sun. This actually resolved a conflict between two other measures of its mass, one from the motion of gas clouds nearby, the other from tracking the stars orbiting it. This may help us refine estimates of mass for black holes elsewhere.

from ars

https://arstechnica.com/science/2019/04/event-horizon-telescope-gives-us-first-images-of-what-its-named-for/

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2 hours ago, Starstruck69 said:

Its huge 1.5 light days accross. Wow!!

The Schwarzschild radius is proportional to the mass of the object, unlike ordinary objects, wherein the radius is proportional to the cubed root of the mass given constant density.

I have a tattoo of Earth's schwarzschild radius on my shoulder. It is smaller than a dime.

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[unimportant remark about Schwarzschild deleted]

Edited by Green Baron

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42 minutes ago, sevenperforce said:

The Schwarzschild radius is proportional to the mass of the object, unlike ordinary objects, wherein the radius is proportional to the cubed root of the mass given constant density.

I have a tattoo of Earth's schwarzschild radius on my shoulder. It is smaller than a dime.

 

Now you need to post that.

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Is it just me, or do I read a different description/explanation of the M87* image on every site where it is mentioned?

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Edit: I would interpret this as an evidence that the authors of these articles aren't cleverer than ourselves
:cool:

 

Overview on the EHT homepage:

https://eventhorizontelescope.org/

and special issue of the ApJ Letters, with summary:

https://iopscience.iop.org/journal/2041-8205/page/Focus_on_EHT

Scroll down for the links to the detail papers, which are pretty comprehensible.

--------------

I read that the 2018 observation campaign fell victim to adverse weather conditions, 2019 had technical problems. Hopes are on next year's campaign with added telescopes and probably refined methods of analysis.

 

Edited by Green Baron

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18 hours ago, sevenperforce said:

I have a tattoo of Earth's schwarzschild radius on my shoulder. It is smaller than a dime.

Is it tattoo or birthmark ?

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1 hour ago, Cassel said:

Why is the part of the ring being brighter?

That's actually the cool part.  :)  Doppler shift.

The ring of gas is orbiting at close to lightspeed (makes sense, given that it's not far outside the Schwartzchild radius).  The brighter part is where the gas is orbiting towards us, so gets Doppler-boosted by a lot.

Here's a nice explanatory video:

 

 

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On 12/28/2017 at 3:26 PM, Green Baron said:

Karl Schwarzschild

I can't bear it any more. Many have tried to pronounce it, especially in silly videos, few do it right and many even write it wrong (tz, sh or similar crippledness). For those like me who can't figure out how the international phonetic alphabet really sounds here a try on how to pronounce that name and the corresponding radius correctly:

The German "r" is spoken with an easy tongue instead of a broad retracted one, and the tongue's base is lifted up close to the soft palate. There is no rolling in it like in Italian or Spanish nor chewing gum like sounds or meowing like in American English. Maybe like the British English "barber", but a little more accentuated r, not just a prolonged ah.

 

Schwarz: sh like in shambles, v like Vladimir (Harkonnen, not Putin), a long "a" like the second one in banana, (not an "äi" like baby) the z is like a ts, spoken with some time. A "tz" exists in German as well ("Platz"), but this is shorter and harder. "Schwarz" is the colour "black".

-schild: this one is easier. Like the "shield" (that's what in means), but the i is shorter like the one in mill and the trailing d is pronounced between d and t, not as soft as in building and not as hard as in mattress.

And take your time, there is a short reconfiguration of the speech organ between the two words, even for a native speaker.

 

I want you all to practice that, exam next week.

:o:cool::D

 

I'll never understand the stubborn cultural insularity of USA. (I'm not criticizing you per se, just commenting on the whole annoying thing of butchering people's names and surnames in videos online, basically same reason that made you write your post. LOL)

Most people in the world learn at least basic IPA in schools. Even better, today we have the Internet and we can hear the sounds denoted by IPA signs. And everything is linked and so easily accessible. I remember when I learned this in school. We'd have little notebooks and learned how to pronounce it.

It's pronounced as:

[ˈʃvaɐ̯tsʃɪlt]

(https://en.wikipedia.org/wiki/Help:IPA/Standard_German)

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31 minutes ago, Snark said:

That's actually the cool part.  :)  Doppler shift.

The ring of gas is orbiting at close to lightspeed (makes sense, given that it's not far outside the Schwartzchild radius).  The brighter part is where the gas is orbiting towards us, so gets Doppler-boosted by a lot.

Here's a nice explanatory video:

 

 

It does not make sense if something has been fired by a black hole in the opposite direction, why do we see it?
Did he say that the magnetic waves from this black hole are directed towards us? It's probably a big threat?
I watched another video from his channel and showed the horizon of events there, but here you can not see the event horizon.
Well, it reminds me of https://en.wikipedia.org/wiki/Synestia

Edit:

What is on the right side of the hole does not move away from us, it only gets towards us. What you see on the left is moving away from us. Why then is the bottom lighter, and what is behind the black hole is darker?

Edited by Cassel

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19 minutes ago, Cassel said:

It does not make sense if something has been fired by a black hole in the opposite direction, why do we see it?

It's not going to disappear if it's heading away from us-- it's not going faster than light, after all.  Towards us = brighter, away from us = dimmer.

20 minutes ago, Cassel said:

Did he say that the magnetic waves from this black hole are directed towards us? It's probably a big threat?

Nope.  Remember just how staggeringly far away this thing is.  That's why it took a years-long effort combining data from ultra-sensitive radio telescopes all over the world over a period of years, generating petabytes of data that then had to be sifted through by powerful computers to separate the tiny, tiny signal from all of the noise.

Far from being a danger to us, it's a miracle of science and concerted effort that we can even detect it, it's so faint.  The apparent size of this thing in the sky is only 40-50 micro-arc-seconds across.  That's equivalent to taking a picture of a one-centimeter object from 50,000 km away.

22 minutes ago, Cassel said:

What is on the right side of the hole does not move away from us, it only gets towards us. What you see on the left is moving away from us. Why then is the bottom lighter, and what is behind the black hole is darker?

Not sure of all the details.  The "right towards us, left away from us" that you cite, news to me-- is that actually the case?

Also, do bear in mind that what we're seeing is not just a simple "here's a photo of a disk of stuff, as it would appear taken from a camera".  It's a black hole.  Even outside the Schwartzchild radius, light's gonna get bent all to heck-- there's all kinds of gravitational lensing going on that distorts the image in various ways.  Nice simulated animation is in the video linked above.

 

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Yeah, well, it was written with some humour :-) If people like Ainsteene more, i know who's meant.

To be clear: the ring does not show optical data from an imaging optical telescope, it is processed data from overlaid radio signals, obtained by receivers all around the world. What is so outstanding is the resolution.

Where the ring is brighter, the radio signals have been stronger. The edge of the dark centre is where photons are going around the event horizon very closely (like 2 Schwarzschild radii). The black hole itself is rotating very fast, and together with the doppler effect this causes the southwest of the ring to appear brighter (signals being stronger) than the northeast.

Spoiler

(4) 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 rotating with speed v and an angular momentum vector inclined at a viewing angle i > 0° to the line of sight. Then the approaching side of the ring is Doppler boosted, and the receding side is Doppler dimmed, producing a surface brightness contrast of order unity if v is relativistic. The approaching side of the large-scale jet in M87 is oriented west–northwest (position angle $\mathrm{PA}\approx 288^\circ ;$ in Paper VI this is called ${\mathrm{PA}}_{\mathrm{FJ}}$), or to the right and slightly up in the image. Walker et al. (2018) estimated that the angle between the approaching jet and the line of sight is 17°. If the emission is produced by a rotating ring with an angular momentum vector oriented along the jet axis, then the plasma in the south is approaching Earth and the plasma in the north is receding. This implies a clockwise circulation of the plasma in the source, as projected onto the plane of the sky. This sense of rotation is consistent with the sense of rotation in ionized gas at arcsecond scales (Harms et al. 1994; Walsh et al. 2013). Notice that the asymmetry of the ring is consistent with the asymmetry inferred from 43 GHz observations of the brightness ratio between the north and south sides of the jet and counter-jet (Walker et al. 2018).

The ring is seen almost face on, the upper-right being tilt a little away from us (~17°), and rotating clockwise. That makes the lower part of it moving slightly towards us, the upper part moving away. This, plus to large degree spacetime distortions explains the observed differences in signal strengths.

Spoiler

Despite these uncertainties, many of the models produce images with similar morphology that is consistent with EHT2017 data. This suggests that the image shape is controlled mainly by gravitational lensing and the spacetime geometry, rather than details of the plasma physics.

(citings from paper V)

 

Oops, ninja'd

Edited by Green Baron
clarification

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44 minutes ago, Snark said:

It's not going to disappear if it's heading away from us-- it's not going faster than light, after all.  Towards us = brighter, away from us = dimmer.

If even the photons are moving away from us, how do we see them? What provides us with information that they exist?
Here is an additional obstacle between these photons and our telescope, there is a black hole that should intercept anything that would try to turn back. From this first video cover photo, I imagine that we should see something like a photo of SgrA *. So what moves away from us is invisible to us.

Quote

Nope.  Remember just how staggeringly far away this thing is.  That's why it took a years-long effort combining data from ultra-sensitive radio telescopes all over the world over a period of years, generating petabytes of data that then had to be sifted through by powerful computers to separate the tiny, tiny signal from all of the noise.

I hope you're right.

Quote

 

Not sure of all the details.  The "right towards us, left away from us" that you cite, news to me-- is that actually the case?

I see it that way, after all this ring is orbiting around the black hole, so the bottom is the closest to us, the top farthest, and the right and left sides move towards us or on the contrary, move away, depending on which direction the ring rotates. Either the picture is rotated 90 degrees or something does not fit.

edit:
Although I probably do not understand it correctly. If the magnetic waves of the black hole are directed towards us, then this picture does not make any sense at all. What we should see is the ring of exactly the same brightness like

yUYWB.png

because we are looking at it as if from above and not from the perspective, so there is nothing going away from us and nothing comes towards us any faster.

 

Quote

Also, do bear in mind that what we're seeing is not just a simple "here's a photo of a disk of stuff, as it would appear taken from a camera".  It's a black hole.  Even outside the Schwartzchild radius, light's gonna get bent all to heck-- there's all kinds of gravitational lensing going on that distorts the image in various ways.  Nice simulated animation is in the video linked above.

 

I know, I watched the conferences and there they said that you can clearly see the horizon of events, and I can not see anything in this picture, so I do not know if I am watching the right picture.

Edited by Cassel

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