Our own Galactic Black Hole

As I mentioned a while ago the Event Horizon Telescope team held a press conference this afternoon and to nobody’s surprise they used it announce an image of the (shadow of the event horizon around the) black hole at the centre of the Milky Way.

Here it is:

You can read the full press release here.

You may recall a great deal of excitement about three years ago concerning the imaging of the “shadow” of the event horizon of the black hole in the centre of the galaxy M87. The question I was asked most frequently back then is that there’s a much closer black hole in the centre of our own Galaxy, the Milky Way, so why wasn’t that imaged first?

It it true is that the black hole in the centre of M87 is ~103 times further away from us than the black hole in the centre of the Milky Way – known to its friends as Sagittarius A* or SgrA* for short – but is also ~103 times more massive, so its Schwarzschild radius is ~103 times larger. In terms of angular resolution, therefore, the observational challenge of imaging the event horizon is similar in the two cases. However, in the the case of the Milky Way’s black hole the timescales involved are much shorter than in M87 and there is a greater level of obscuration along the line of sight. That’s why it took longer to produce the image.

It’s a very difficult observation of course and I’m not sure of the significance of the “lumps” you can see, but the dark region in the centre is what the image is really about and that seems to be exactly the predicted size. The resolution is about 20 microarcseconds. Congratulations to the Event Horizon Telescope team!

If you’re interested in learning more about how this image was made I recommend this short video:

4 Responses to “Our own Galactic Black Hole”

  1. Are there any more black holes that EHT could take an image of?

  2. Dr. Will Sutherland Says:

    Slight correction: M87* is actually around 2000 times further away than Sgr A* and 1500 times more massive, so about 3/4 of the angular diameter. Unfortunately the third-ranked hole by angle (I forget the name) is many times smaller than the top two, so will need dishes in space to go beyond the current two.

    (Going to 450 microns would gain a factor near 3, but I think that’s not enough for the #3 hole, also the chance of good-enough atmosphere simultaneously at many sites is tiny). Watching time-variability in the two current holes is probably the next step.

  3. […] A blog about the Universe, and all that surrounds it « Our own Galactic Black Hole […]

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: