Today I will spend most of the day looking at the Event Horizon Telescope image of Sgr A*!

This is the first direct image of the emission immediately outside of our Milky Way’s central supermassive black hole!!!

To some it may look like a blurry doughnut, but this is actually the highest resolution image of our supermassive black hole ever taken. 😮 The EHT is a global network of radio observatories that work together to yield extremely high resolution images.

Resolving the Milky Way’s SMBH at this level is like resolving a doughnut that’s sitting on the moon!


If you remember, the EHT also resolved the emission and shadow of M87 a couple years ago. Although M87 is much further away than Sgr A*, the two supermassive black holes look similar in size because M87 is about 1000 times larger than Sgr A*! (I did not make the graphic and will need to figure out who did)

The shadow that you see in the center of Sgr A*’s image is not actually the event horizon (the radius at which not even light can escape the gravitational pull of the supermassive black hole).

It’s more likely the radius where matter starts directly falling into the SMBH; where the orbits aren’t nice and circular anymore.

Sgr A* is a lot smaller than M87, and its emission is much more variable. It will flicker in intensity on the order of hours, whereas M87 will flicker on the order of ~days. So, for a given exposure time we’re much more sensitive to motion blurring when imaging Sgr A*. This made it a lot harder to clean the data and create the image.

We’ve already learned a few things by comparing this images to *thousands* of simulations! We think Sgr A* is rather quiescent, a chill supermassive black hole that isn’t super hungry. If Sgr A* were a person it would consume a grain of rice every million of years.

It’s likely mis-aligned with the Milky Way’s galactic plane. The orbits of some of the stars in the center of our galaxy also seem mis-aligned with this plane and people like to blame galaxy mergers.

Although a quieter black hole, it’s what most of the supermassive black holes in our Universe look like. It’s the standard. And so, by looking at it we’re learning a lot more about how normal black holes interact with and live in their galaxies.

My favorite meme from today thus far, you ask? This one, made by Dan Galletti

@AdiFoord thanks, this is super cool! Can you already say what those three dense area segments are? Their regularity suggests some kind of geometric behaviour however I fail to come up with a plausible idea. Jets and magnetic fields are polar, and matter in the accretion disk should be homogenized, right?

@phoenix from what I understand, there may not be a lot of significance to the bright patches. It sounds like they align with the directions of where they had a lot of telescope coverage, so it may just be an observational effect.

@AdiFoord oh wow, the regularity is then just a coincidence. Wow. Thanks for the explanation, that makes sense! 😃

@AdiFoord I kind of died laughing at this meme, thank you, it's perfect! 😂🤣🤣🤣

@AdiFoord Question: so if I am looking at the full image found here ( I see a lot, but is that "flat" image all the real world data you get to work with here?

Is it a process of running many simulations and then when one matches the actual image deduct the actual conclusions from the steps involved in that simulation?

@Pepijn the EHT is an array of telescopes that take many images. They are combined to get a final image, which is the image you posted.

To understand the physics, they run thousands of simulations and re-create their observations to see what the final image would look like, assuming various things (temperature of plasma, magnetic field strength, etc). They compare these simulated observations to the actual observation. This allows them to better understand what may be going on in the dataset.

@AdiFoord Thanks. One more question: do I understand it correctly then that image is "all there is" to work with? I was wondering if maybe that image was a flattened version of something with 500 layers of various frequencies or something.

@Pepijn it’s one frequency, but it is a combined image from different radio dishes that did a deep stare at the SMBH at the same time. But by combining them, we are are getting the sharpest image possible.

Hey! Thank you so much for posting this very informative thread @AdiFoord!

@xxyxxyart Aw, thanks! I didn’t prepare it, it all was posted very quickly due to my excitement 😂 so hopefully it made sense!

@AdiFoord theory: do you think that black holes/ gray holes actually create matter ? The information paradox is solved correct? Do you think every galaxy has a super massive black hole?

@AdiFoord ok so as someone who knows very little about black holes, I’m actually wondering now… do black holes make sound?

@AdiFoord Listened to a report on it on the radio today. Interesting!

@AdiFoord Well, I gotta go visit this in elite dangerous now.

Event though it's not real I think it's the closest I'll ever get

@AdiFoord I had no idea M87 was that large... mind-blowing stuff.

@AdiFoord I understand why in M87 there is a light and dark area in the ring due to Doppler shifting. Why are there three bright areas on the Sgr A* ring?

@1dalm from what I understand, there may not be a lot of significance to the bright patches. It sounds like they align with the directions of where they had a lot of telescope coverage, so it may just be an observational effect.

@AdiFoord If we had a radio telescope on the moon, how much could that improve the resolution?

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