Event Horizon Telescope Results Released Yesterday (April 10, 2019)

[Orodruin]

I had a colleague put a rewriting of the Ring Verse from Lord of the Rings so I had to counter with a limerick:

There once was a black hole named Kevan,
so big and far up in heaven,
in the accretion disk
you'll know you're at risk
to be eaten by M87

Edit: He re-countered so I had to write another one ...

In a galaxy far far away
A long time ago, so they say
An enormous black hole
went out of control
its ring was the unwilling prey

 

[pinball1970]

First story on radio 1 and 2 all day beating Brexit and Israeli elections

 

[virgil1612]

Does the light come from the accretion disk?

 

[davenn]

Does the light come from the accretion disk?

Yes, the generated image of the radio signals that you see are coming from the accretion disk

ohhh and it isn't "light" it isn't optically visible ( that is ... this IS NOT an optical image)...
the radio emissions are at very short microwave radio wavelength, 1.3mm ( frequency ~ 230 GHz)Dave

 

[davenn]

but if they used 8 radio telescopes to form this image, where did the visible light colors come from?

Colorization. Somebody picked them.

yes ... so the brighter the colour, the stronger the radio emissionoops, I see @mfb commented the same

 

[berkeman]

So the real colors could be blues and greens? I guess they used the simulations to figure out what the visible colors would probably be, and tuned the radio telescope false color image to try to match?

 

[virgil1612]

Yes, the generated image of the radio signals that you see are coming from the accretion disk

ohhh and it isn't "light" it isn't optically visible ( that is ... this IS NOT an optical image)...
the radio emissions are at very short microwave radio wavelength, 1.3mm ( frequency ~ 230 GHz)Dave

Yes, but I meant... is that luminous ring the accretion disk, or it's just light coming from there and orbiting the black hole (the photon sphere, that's how it's called?), giving us a sense of the shape of the horizon of the black hole?
Virgil.

 

[davenn]

So the real colors could be blues and greens?

well it's a radio signal so it doesn't have a colour. Just in that 144MHz doesn't have a colour or one that is different from, say, 440 MHz

A radio telescope builds up a pattern of signal intensity to give something that looks like the isobars on a weather chart. The astronomers then use different shades of colours to indicate the intensity of the radio signal. They could have just as easily used dark blue to bright blue/white. Dave

 

[davenn]

Yes, but I meant... is that luminous ring the accretion disk, or it's just light coming from there and orbiting the black hole (the photon sphere, that's how it's called?),
Virgil.

It is the accretion disk
From the EHT www site
https://eventhorizontelescope.org/

The EHT image reveals the shadow of M87’s black hole on its accretion disk. Appearing as a fuzzy, asymmetrical ring, it unveils for the first time a dark abyss of one of the universe’s most mysterious objects.

It's not visible light, so not "light" in the way you are thinking of it. It is EM radiation at ~ 230 GHz ( 1.3mm wavelength) a very long way below visible light (much lower frequency and longer wavelength)Dave

 

[berkeman]

well it's a radio signal so it doesn't have a colour. Just in that 144MHz doesn't have a colour or one that is different from, say, 440 MHz

A radio telescope builds up a pattern of signal intensity to give something that looks like the isobars on a weather chart

Yeah, I get that. But how did they map the radio signal frequencies and intensities to those yellows and reds that the popular press is fawning over? Were the simulations earlier in this thread also arbitrary in their color mapping from expected radio emissions, or were they meant to simulate what the visible light emissions would look like?

I'm definitely not meaning to give you and @mfb a hard time at all. Great images. I just prefer to understand where the false color image mappings came from (and I wish astronomy images would be explicitly labeled in the corner "False Color Image" when it's not a true visible light image). Thanks.

 

[davenn]

But how did they map the radio signal frequencies and intensities to those yellows and reds that the popular press is fawning over?

The colours are arbitrary, totally irrelevant to visible light.
darker orange is the lowest intensity radio signal, the brightest colours the strongest signal

I just prefer to understand where the false color image mappings came from

Picked a nice colour ... oranges and shades thereof are aesthetically pleasing to most people
as I said they could have been shades of blue

and I wish astronomy images would be explicitly labeled in the corner "False Color Image" when it's not a true visible light image

you and me both

the number of people on PF and around the net who think these are optical photographs because of the way the press releases have worded it. Us astronomers understand what we are seeing, but the general public are getting easily misled and think that it is optical and not radio telescopes. Because for most people, a telescope is something you look through.D

edited

 

[jedishrfu]

Veritaseum released a new video on it:

 

[Pierre Ordinaire]

Excuse me, but are there not many stars between the black hole and Earth, that should be blocking the view of the black hole?

 

[Orodruin]

Excuse me, but are there not many stars between the black hole and Earth, that should be blocking the view of the black hole?

No. The sky is not as populated as you seem to imagine.

 

[sysprog]

4000x2330 Image available from NSF
https://www.nsf.gov/news/special_reports/blackholes/formedia.jsp

That page uses white text on a black background. I just asked nsf.gov in an email to stop doing that.
To make that page more readable, you can copy and paste the following code into the address bar on your browser, or paste it into a 'bookmarklet' so can you get rid of such color-impairment of readability on any (works on html/css obnoxious colors) page you encounter:

javascript:(function(){var newSS, styles='* { background: white ! important; color: black !important } :link, :link * { color: #0000EE !important } :visited, :visited * { color: #551A8B !important }'; if(document.createStyleSheet) { document.createStyleSheet("javascript:'"+styles+"'"); } else { newSS=document.createElement('link'); newSS.rel='stylesheet'; newSS.href='data:text/css,'+escape(styles); document.getElementsByTagName("head")[0].appendChild(newSS); } })();

The pictures are pretty interesting.

 

[Tom.G]

But how did they map the radio signal frequencies and intensities to those yellows and reds

or were they meant to simulate what the visible light emissions would look like?

It's sort of like asking what the output of an ultrasonic remote control looks like. A frequency-shifted representaion could be used for time-varying data to convert to the audible range, but this Black Hole has spatial signal variation. So they essentially frequency multiplied by a factor of ≈2364 to convert to the visible range of us Humans. Then FM modulated according to intensity (signal strength), just like an FM radio broadcast.

Then the magic occurred when our eyes and brain converted to an image that is somewhat understandable.

Cheers,
Tom

 

[mitchell porter]

I have been searching fruitlessly for a straightforward account of what these pictures show, but the Veritasium videos in #20 and #42 explain it very clearly.

Also, from the papers linked at #14 - paper I, section 4 - I learn that the M87 black hole was observed exactly two years ago. It's interesting that it took so long to process, and that everyone involved maintained a disciplined silence throughout those two years.

 

[DennisN]

A new video about this from one of my favorite channels, Sixty Symbols:

 

[jedishrfu]

And this article on the Comp Sci grad student who helped construct the image from the noisy data:

https://www.sciencealert.com/this-2...lped-bring-us-the-first-image-of-a-black-hole

 

[pinball1970]

Yeah, I get that. But how did they map the radio signal frequencies and intensities to those yellows and reds that the popular press is fawning over? Were the simulations earlier in this thread also arbitrary in their color mapping from expected radio emissions, or were they meant to simulate what the visible light emissions would look like?

I'm definitely not meaning to give you and @mfb a hard time at all. Great images. I just prefer to understand where the false color image mappings came from (and I wish astronomy images would be explicitly labeled in the corner "False Color Image" when it's not a true visible light image). Thanks.

The colours could be are arbitrary? There are other (amazing) images from Hubble of distant galaxies / star nurseries where they overlay infra red and other frequencies out of the visible spectrum. Just so we have a more detailed image of what is there.

Yellow to red could be shorter to longer wavelength? Or difference in intensity.

 

[jedishrfu]

A new video about this from one of my favorite channels, Sixty Symbols:

Did he say "its like taking a picture of a gallstone on the moon"?

I read elsewhere the the 40 uarcsecs was like taking the picture of a DVD on the moon.

Here's more on black holes and the prior illustrations used to represent them to the public:

https://www.vox.com/science-and-health/2018/1/8/16822272/black-hole-looks-like-what

and lastly Kip's excellent book on the Science of Interstellar with their computer simulations:

https://www.amazon.com/dp/0393351378/?tag=pfamazon01-20

 

[jedishrfu]

The colours could be are arbitrary? There are other (amazing) images from Hubble of distant galaxies / star nurseries where they overlay infra red and other frequencies out of the visible spectrum. Just so we have a more detailed image of what is there.

Yellow to red could be shorter to longer wavelength? Or difference in intensity.

Yes, this uis one of the reasons kids get disappointed with Astronomy. They see these fantastic images and don't realize that the colors are describing measured data and aren't the actual colors. In fact, in a telescope you'll see only star brightness ie black and white and it just doesn't look like these amazing works of art.

 

[DennisN]

Did he say "its like taking a picture of a gallstone on the moon"?

I heard "golf ball".

 

[jedishrfu]

I heard "golf ball".

Ahh, okay that makes sense. He really sped through that and I tried listening again at higher volume but just couldn't catch it.

Do you think a gallstone is comparable to a golf ball in size? haha

Turns out yes.

https://www.webmd.com/digestive-disorders/understanding-gallstones-basics#1

 

[mfb]

Yeah, I get that. But how did they map the radio signal frequencies and intensities to those yellows and reds that the popular press is fawning over? Were the simulations earlier in this thread also arbitrary in their color mapping from expected radio emissions, or were they meant to simulate what the visible light emissions would look like?

I'm definitely not meaning to give you and @mfb a hard time at all. Great images. I just prefer to understand where the false color image mappings came from (and I wish astronomy images would be explicitly labeled in the corner "False Color Image" when it's not a true visible light image). Thanks.

They chose a color code that some software package provided, the publication will have some details. You'll find a similar color scheme in many other publications. The simulations used the same scheme, sure.

This has absolutely nothing to do with whatever visible light the accretion disk emits.

 

[DennisN]

Do you think a gallstone is comparable to a golf ball in size? haha

Turns out yes.

Ouch. And if we hit a golf ball into Sagittarius A* would it count as a hole-in-one?

 

[Orodruin]

Do you think a gallstone is comparable to a golf ball in size? haha

Turns out yes.

Fermi estimate it! A golf ball is not order 0.1 cm and not order 10 cm in radius, so order 1 cm. A gall stone is not order 0.1 cm and not order 10 cm in radius, so order 1 cm. The exact same size!

 

[russ_watters]

Yeah, I get that. But how did they map the radio signal frequencies and intensities to those yellows and reds that the popular press is fawning over? Were the simulations earlier in this thread also arbitrary in their color mapping from expected radio emissions, or were they meant to simulate what the visible light emissions would look like?

I'm definitely not meaning to give you and @mfb a hard time at all. Great images. I just prefer to understand where the false color image mappings came from (and I wish astronomy images would be explicitly labeled in the corner "False Color Image" when it's not a true visible light image). Thanks.

It's totally arbitrary. These colors were probably picked because they "look right", but radio waves are used here because there is little or no visible light to determine a color. Insofar as "color" is just a name for different bands of wavelengths, the "color" of this image is "microwave".

Usually false color images are labeled, but not always, and I agree it is a bit irritating when it is way off. There are a lot of Hubble photos that are visible or near ir where the colors are purposely way off.

Most of my photos are taken in greyscale, with filters. Indeed even a consumer camera gets its color with a grid of filters and software to map the colors to the proper pixels.

For many of my solar photos I used narrow-band Hydrogen Alpha spectral line filter - which is deep red - and mapped it to a yellow I chose because it looked right.

Hydrogen alpha also works really well for the moon by cutting down the glare. So those photos I just leave greyscale since the moon is an almost perfect grey (black) even though I took the images in red light.

 

[russ_watters]

...
FYI, there is actually a defined "Hubble Palette" for color mapping:

...A composite of narrowband image data, the telescopic view captures the characteristic emission from ionized sulfur, hydrogen, and oxygen atoms mapped to red, green, and blue hues in the popular Hubble Palette.

https://apod.nasa.gov/cgi-bin/apod/apod_search?tquery="hubble palette"
http://www.mcwetboy.com/mcwetlog/2010/04/falsecolour_astrophotography_explained.php

There's a chart in the second one that shows for example the Ha filter, which is red, mapped to Green and the O-III, which is green, mapped to blue.

I suppose it is most common to see wavelengths larger than visible to be red and smaller than visible to be blue in false color images.

 

[OmCheeto]

A new video about this from one of my favorite channels, Sixty Symbols:

Did you watch the video on M87 they recommended at the end?
I thought it was interesting that the Earth orbits M87.

​

M87 - Infinity in your Hand - Deep Sky Videos​

DeepSkyVideos​

Video by Brady Haran​

Published on Oct 9, 2018​

Becky Smethurst discusses the massive and superfreaky M87.​

Recorded with Dr Becky Smethurst as part of the Sixty Symbols Ogden Fellowship at the University of Nottingham.​

​

"The Earth goes round the Sun​

The Sun goes round the Milky Way​

The Milky Way goes round the center of the Local Group​

And the Local Group goes round the center of the Virgo Supercluster​

​

The center of the Virgo Supercluster is M87​

​

Technically, the Earth is going round M87"​

Paraphrased for brevity.​

​

Livestream e.g. here at ESO.

I wonder how many livestreams there were. I watched both that one, and the following:



National Science Foundation/EHT Press Conference Announcing First Image of Black Hole
National Science Foundation
Published Apr 10, 2019

I found the following information interesting, and somewhat entertaining:

​

@13:40​

Dan Marrone, AP of Astronomy, Univ of AZ​

"It took 7 days to collect 5 petabytes of data​

recorded on >100 toasterish sized modules​

HALF A TON of hard drives"​

​

Just notes I scribbled while watching. "toasterish sized modules" are my words.​

​

That's a lot of hard drives!