The Event Horizon Telescope has shown us the first picture of the light shadow of the supeemassive black hole in the center of the Milky Way, Sagittarius A*!


It's maybe a bit surprising that they could publish the black hole in another galaxy, M87*, three years before that in our own Milky Way, but that is because even though M87 is much further away, its central black hole is absolutely massive - more than 1000 times heavier than the one in the Milky Way.

Along with the detection of Gravitational Waves in 2015, I think these images are some of the most impressive feats of astrophysics to happen in my time as a researcher. I'm very, very impressed!

The event horizon (also called Schwarzild radius) of M87* ("M-eighty-seven-star"), which is a good deal smaller than the light shadow which we can see in the EHT images, is 2.5 times the orbit of Pluto. Which gives it an average mass density of 2-3% of the air we breathe on Earth!

Such gargantuan black holes fly in the face of all we learned about black holes as kids. Remember "spaghettification" - that you'd be torn apart to atoms by the tidal forces as you approached a Black Hole? Well, at the event horizon of M87*, the tidal forces are weaker than those of the Sun in Earth's orbit!

...Which is to say that if you could survive the radiation (you could not!) at its event horizon, you could drift gently through it in almost-zero gravity and be none the wiser! Pretty darn far from the way it works in black holes with masses of "only" a few massive stars!

In comparison to this, the Milky Way black hole presented today by weighs 1000 times less, "only" the same as 4.5 million suns. That makes a huge difference to its properties!

If you are confused about the difference between Black Hole light shadows and event horizons, and what these images even show (I sure was!), the YouTube channel Veritasium has a great explainer here:

If you are a bit confused about Black Holes in general, the brilliant and mischievously misnamed "Bad Astronomer", Phil Plait, has a great entry-level explainer about Black Holes, including the concept of "spaghettification", here:

CORRECTION: I miscalculated! The density would be as much as about half that of atmospheric air on sea level. Still, the point stands: M87* is less like this:

@thriveth I am still confused, but it's a great video, thanks for sharing!

The difference is interesting though, with the 3 visible lobes.

Does this mean we're seeing SagA* at a higher inclination? (So we can see more accretion disk light "from behind" it, maybe?)

@TerryHancock I'm not well enough informed about this that I can weigh in with anything useful. But I did see someone knowledgeable on the bird site say the SgrA* accretion disk is seen basically face-on, for what it's worth.

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