M87 Black Hole Photos and the Spin Orientations

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Discussion Overview

The discussion focuses on the angular momentum orientations of the M87 black hole and its accretion disk, particularly in relation to the images released by the Event Horizon Telescope (EHT). Participants explore the implications of these orientations on the observed ejection jets and seek to understand the nature of the images, which are not traditional photographs but rather reconstructions from radio telescope data.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants inquire about whether the angular momentum (spin) vectors of the black hole and the accretion disk change over time, referencing the apparent variations in the directions of the ejection jets.
  • There is a question regarding the time scale on which any changes in the angular momentum vectors might occur, with suggestions that the images may simply be displayed in different orientations rather than indicating actual changes.
  • One participant asserts that the ejection jets are nearly collinear with the black hole's spin vector, seeking confirmation of this understanding.
  • Another participant discusses the relationship between the spin of the black hole and the inner radius of the accretion disk, referencing a video that addresses this topic.
  • Clarifications are made regarding the nature of the released images, emphasizing that they are not optical photographs but rather computer-generated reconstructions based on data from radio telescopes.
  • Some participants express the need to avoid using the term "photo" to describe the M87 black hole image, suggesting it may lead to confusion.
  • There is mention of the technique used to create the images, specifically very long baseline interferometry (VLBI), and how this relates to the concept of image reconstruction.

Areas of Agreement / Disagreement

Participants express varying views on the nature of the images and the behavior of the angular momentum vectors. While there is some agreement on the non-optical nature of the images, questions regarding the dynamics of the spin vectors and their implications for the ejection jets remain unresolved, indicating multiple competing perspectives.

Contextual Notes

Participants note that the images are reconstructions and not direct photographs, which introduces complexities in interpretation. There is also uncertainty regarding the time scales of potential changes in angular momentum vectors and the implications of jet orientations.

aabottom
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M87 Black Hole Photos and the Orientations the Angular Momentum of the Black Hole and that of the Accretion Disk.

I’m trying to understand the orientations the angular momentum (let’s call it spin) of the black hole and that of the accretion disk. Veritasium has good video on the topic [1], but it does not relate to the released M87 images. The 5th paper of the EHT [2] (Figures 2, 3, and 5) has some good graphics, but the spins are displayed in 2 dimensions and, for me, are somewhat hard to comprehend. Maybe they are showing projections of the spin vectors.

I’d like to see some good 3-D graphics of the black hole spin and accretion disk spin next to the M87 Black Hole image.

Has anybody seen some good graphics on this topic?

[1] Veritasium, Published on Apr 9, 2019.

[2] The Event Horizon Telescope Collaboration et al. 2019 ApJL 875 L5. https://iopscience.iop.org/journal/2041-8205
 
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I have some follow up questions.

A. Do the angular momentum (spin) vectors change with time? These photos of M87 seem to indicate different directions of the ejection jets. [3] If so, on what time scale- minutes, days, years? Maybe the photos are displayed in different orientations.

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[3] https://www.nationalgeographic.com.au/science/first-ever-picture-of-a-black-hole-unveiled.aspx

B. As I understand it, the ejection jets are nearly collinear with the black hole spin vector. Is this correct?

C. Is the angular momentum (spin) vector of the accretion disk is either parallel or anti-parallel with angular momentum (spin) vector of the black hole?
 
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Also see this Vertasium video. He discusses the relationship between spin and the inner radius of the accretion disk and how that can be used to observe the spin rate.

 
aabottom said:
A. Do the angular momentum (spin) vectors change with time? These photos of M87 seem to indicate different directions of the ejection jets. [3] If so, on what time scale- minutes, days, years? Maybe the photos are displayed in different orientations.
The photos are just rotated. Physical jet rotation at such a scale in such a short time would require matter to travel many times faster than the speed of light.
 
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aabottom said:
M87 Black Hole Photos
Please understand ... the image that has been released is not a photo ... aka optical image
It's a computer generated image created from a large amount of data collected by radio telescopes
 
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aabottom said:
I have some follow up questions.

A. Do the angular momentum (spin) vectors change with time? These photos of M87 seem to indicate different directions of the ejection jets. [3] If so, on what time scale- minutes, days, years? Maybe the photos are displayed in different orientations.

View attachment 241747
From the looks of it, it's different orientations. That M87 jet looks very similar between the two pictures, and given its length and the likely timeframe of observations of it, it likely has not changed much over that time.

But yes, a spinning black hole can precess, and I've found some mention of that in scholar.google.com.
 
davenn said:
Please understand ... the image that has been released is not a photo ... aka optical image
It's a computer generated image created from a large amount of data collected by radio telescopes
Yes, thank you. I know this. The term Photo is just poetic license for the photons at 1.33 mm wavelength (that is 230.6 GHz) of the radio telescope. The image is a radio-graphic image, one might say.

To avoid confusing people, I should stop using the term photo when referring to the M87 black hole "image". But I'm not sure the term "image" would any less confuse the layman.
 
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It is not even a direct image. It is a reconstruction built using VLBI -- very long baseline interferometry.
 
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lpetrich said:
It is not even a direct image. It is a reconstruction built using VLBI -- very long baseline interferometry.
Yes, I have done research in optical/ infrared sparse aperture imaging systems. When the pupil plane data is transformed to the focal plane, the results can be considered a reconstructed image.
 

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