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! 😂🤣🤣🤣

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