Have a look at the linked documents giving the popular science background.

They led the teams that gave the decisive proof that there is black hole at the galactic centre. The teams developed techniques to precisely measure the orbits of the stars which orbit the central black hole. Looking at the speed of the stars, particularly as they pass close to the object, you can measure its mass and put a constraint on its size. The only thing which is small enough and heavy enough is a black hole. Doing this required lots of advances in data analysis and adaptive optics to be able to measure the stars orbits to enough precision.

Now that's an answer. Thanks for the detailed reply!

We already know it because Genzel and Ghez discovered it.

Their work goes back 30 years.

When I heard about this, I seriously thought we just only discovered Sagittarius A* this year and that I must have fucked up my memories. Thanks for the clarification!

The Penrose-Hawking singularity theorems go back 55 years to work starting in 1965. No joke. This has be to near a record in time lag between the work the Nobel committee recognized and when that work was first published. Better late than never I guess (but too late for Hawking, as has been mentioned elsewhere..) EDIT - a detailed analysis: https://physicstoday.scitation.org/do/10.1063/PT.5.2012/full...

I've always thought Nobel prizes are awarded based on the winners' works in that particular year so this came as huge surprise.

Too late for Hawking indeed, he could've very well been one of the winners today.

There's a huge backlog of people who deserve Nobel prizes. The committee is also conservative, and doesn't want to give out a prize for something that turns out to be wrong. Both factors mean that it takes years from discovery to the awarding of a Nobel prize.

It's one thing to allow enough time to pass before a given theory/experiment can be considered as "accepted" by science, and therefore eligible to the award.

However, the Nobel committee's rules can be considered archaic to a fault: 3 winners at most, all winners must be living at the time of the award.

If you want an egregious example of exclusion, look at the 2013 Nobel prize for the discovery of the Higgs boson. The prize was given to Higgs and Englert [0], but by any measure it should have been awarded to the five living scientists who made the discovery [1].

Was there really any reason to exclude Guralnik, Hagen and Kibble, who were all alive at the time of the award, other than a strict adherence to the "rule of three"?

[0]: https://web.archive.org/web/20131008193310/http://www.nobelp...

[1]: https://en.wikipedia.org/wiki/1964_PRL_symmetry_breaking_pap...

Even increasing it to 5 people wouldn't solve the problem. The Nobel prize could be awarded at the institution level rather than invidually but I'm sure there'll be objections to that as well.

The opposite, really. Nobel prizes are given out for major works which are now well-accepted. This can take decades, so typically the Nobel is given to now-old scientists as recognition for work done when they were young.

Made this cool video?

https://www.youtube.com/watch?v=u_gggKHvfGw

Back in the day they each led research to detect irrefutable evidence of it. This isn't anything new and groundbreaking.

I think that's rather unfair. The measurements are still ongoing with ever-increasing accuracy. In 2018 they managed to record the closest approach of the star S2, measuring a velocity of 7000 km/s at its maximum. This was after mapping the full 16 year orbit. I know that Genzel is still actively researching this topic with his group, see e.g. https://www.mpe.mpg.de/7433286/news20200416

Ghez is very active. Both her group and Genzel's group are at the very leading edge.

I haven't found an updated GIF, but even when I first saw images like this around 2002, it was clear she was chasing something awesome.

https://www.physicscentral.com/explore/people/images/2008orb...

That is true, but the prize was awarded to Genzel for “for the __discovery__ of a supermassive compact object at the centre of our galaxy” (emphasis mine), not for the (impressive no doubt) follow-up work, so my comment was done in that context. That being said, I should have been a bit more enthusiastic about the infrared group's work to not appear dismissive on their ongoing contribution.

Fun fact: looks like we're both in MPE (although I left two years ago).