<p>The <a href="https://eventhorizontelescope.org/" rel="nofollow noreferrer">Event Horizon Telescope</a> or EHT took an image or the black hole at the center of M87 in 2019, and in 2021 it measured the polarization of the light from M87*. Right after the first image of M87* was taken, I had heard that  Sgr A* -- the super massive black hole at the center of our own galaxy -- would be a future target for the EHT. However, it seems the EHT hasn't been used to study Sgr A* yet.</p>
<p>Why hasn't the EHT been used to study Sgr A*?</p>
<p>Based on <a href="https://astronomy.stackexchange.com/a/39341/9527">this answer</a>, Sgr A* is not as bright as M87*. Is Sgr A* not bright enough to be visible? A comment under that same answer also mentions timescale variability as a reason why Sgr A* is harder to see. What does that mean?</p>

CC BY-SA 4.0
2022-04-16T20:14:04.240Z
different questions but related: [How can the Event Horizon Telescope image Sgr A* when it's not visible from all sites at one time?](https://astronomy.stackexchange.com/q/30311/7982) and [Will the first Event Horizon Telescope image of the Milky Way's black hole be just another orange donut?](https://astronomy.stackexchange.com/q/39352/7982) and [How will they know when to start taking the picture of the black hole at the center of the Milky Way?](https://astronomy.stackexchange.com/q/39354/7982) however Peter Erwin's answer to the last may address this as well.
uhoh
CC BY-SA 4.0
2022-04-16T20:31:46.960Z
It's also very possible that some data *has* been taken already. It was quite a lengthy and interesting process between data acquisition and the public release of the first image https://i.sstatic.net/qOKVL.jpg which took two years. Since "our" black hole as a much more fickle personality, and they've been doing upgrades to add more telescopes and possibly go to shorter wavelengths which will need better calibration, it's possible that there will also be a significant delay between acquisition of data and release of an image.
uhoh
CC BY-SA 4.0
2022-04-17T14:08:11.370Z
Answered at https://physics.stackexchange.com/questions/471792/why-was-m87-targeted-for-the-event-horizon-telescope-instead-of-sagittarius-a and https://physics.stackexchange.com/questions/471920/why-couldnt-they-take-pictures-of-a-closer-black-hole
ProfRob
CC BY-SA 4.0
2022-05-24T23:07:58.453Z
https://astronomy.stackexchange.com/q/30313/18054 and a bit of: https://astronomy.stackexchange.com/a/47332/18054
Rob
CC BY-SA 4.0
2022-05-11T22:03:08.433Z
[Event Horizon Telescope collaboration to announce groundbreaking Milky Way results on May 12th, 2022, at 13:00 UT](https://eventhorizontelescope.org/blog/event-horizon-telescope-collaboration-announce-groundbreaking-milky-way-results-may-12th)
uhoh
<observational-astronomy><radio-astronomy><event-horizon-telescope><sagittarius-a>
Why hasn't the EHT taken an image of Sgr A*?
usernumber
# Why hasn't the EHT taken an image of Sgr A*?

(Asked by: username_0 on 2022-04-16)

The [Event Horizon Telescope](https://eventhorizontelescope.org/) or EHT took an image or the black hole at the center of M87 in 2019, and in 2021 it measured the polarization of the light from M87\*. Right after the first image of M87\* was taken, I had heard that Sgr A\* -- the super massive black hole at the center of our own galaxy -- would be a future target for the EHT. However, it seems the EHT hasn't been used to study Sgr A\* yet.

Why hasn't the EHT been used to study Sgr A\*?

Based on [this answer](https://astronomy.stackexchange.com/a/39341/9527), Sgr A\* is not as bright as M87\*. Is Sgr A\* not bright enough to be visible? A comment under that same answer also mentions timescale variability as a reason why Sgr A\* is harder to see. What does that mean?

**Tags:** observational-astronomy, radio-astronomy, event-horizon-telescope, sagittarius-a

> **Comments:**
> **username_1**: different questions but related: [How can the Event Horizon Telescope image Sgr A* when it's not visible from all sites at one time?](https://astronomy.stackexchange.com/q/30311/7982) and [Will the first Event Horizon Telescope image of the Milky Way's black hole be just another orange donut?](https://astronomy.stackexchange.com/q/39352/7982) and [How will they know when to start taking the picture of the black hole at the center of the Milky Way?](https://astronomy.stackexchange.com/q/39354/7982) however Peter Erwin's answer to the last may address this as well.  
> **username_1**: It's also very possible that some data *has* been taken already. It was quite a lengthy and interesting process between data acquisition and the public release of the first image https://i.sstatic.net/qOKVL.jpg which took two years. Since "our" black hole as a much more fickle personality, and they've been doing upgrades to add more telescopes and possibly go to shorter wavelengths which will need better calibration, it's possible that there will also be a significant delay between acquisition of data and release of an image.  
> **username_2**: Answered at https://physics.stackexchange.com/questions/471792/why-was-m87-targeted-for-the-event-horizon-telescope-instead-of-sagittarius-a and https://physics.stackexchange.com/questions/471920/why-couldnt-they-take-pictures-of-a-closer-black-hole  
> **username_1**: [Event Horizon Telescope collaboration to announce groundbreaking Milky Way results on May 12th, 2022, at 13:00 UT](https://eventhorizontelescope.org/blog/event-horizon-telescope-collaboration-announce-groundbreaking-milky-way-results-may-12th)  
> **username_3**: https://astronomy.stackexchange.com/q/30313/18054 and a bit of: https://astronomy.stackexchange.com/a/47332/18054  

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