system
Given the following post, respond as if you're commenting on Reddit:
human
If we were able to capture a blackhole 55 million light years away, how come we haven't been able to capture milkyway's blackhole yet which is just 25000 light years away?
gpt
They have been working on it, and observations have already been taken. But it actually has come out a bit trickier than M87.

Basically, the black hole shadow they're imaging has a diameter proportional to the mass of the black hole. This is unusual in astrophysics - usually the density of a type of object is either constant, or actually *increases* with mass, which means that if something is 8 times the mass, it's got 2x the diameter, or even less.

So, very massive black holes have a very big diameter for their mass. This means that it's quite achievable for a very massive but distant supermassive black hole to actually look similar in size on the sky than a nearby but smaller supermassive black hole. The supermassive black hole in M87 is so big that it actually comes out to be roughly the same apparent size as the Milky Way's black hole. It may be 2000 times further away, but it's also almost 2000x bigger, so it cancels out.

Sgr A\* in our Milky Way does turn out to be a little bit trickier to image though. As we are looking through the plane of the Milky Way, there is more dust and gas in the way to deal with. Also, Sgr A\* is somewhat south in the sky, so it's a little bit trickier to get good long observations from all around the globe (especially from the Northern Hemisphere). M87 is a little north of the celestial equator, and is a bit easier to see from everywhere. It comes down to the technical details in the end.