Bad astronomy | A star dive towards a huge black hole shows – again! – that Einstein was smart enough

On May 19, 2018, a star in the center of our galaxy shouted in front of a huge black hole at a distance close to the hair and at a ridiculously high speed. It was so close that the light emitted by the star was affected by the warping of the black hole space, in a way so subtle that it could not be detected until it was dark. now, yet so obvious to modern technology that it was easily eradicated from the data.

Surprisingly, all this – and more to come – went exactly as planned. And, like so many trials before her, she showed that Einstein 's theory of relativity is right.

Being able to write something like that is why I love my job. I also love being able to explain it to you, honestly, so let's go, are we going?

We live in the Milky Way, a flat disk of gas, dust, stars and dark matter. At the very center is a monster: a supermassive black hole. Every big galaxy has one, and we think that they are formed at the same time as the galaxies themselves, affecting the growth and evolution of the other. Understanding our own central black hole is a key to understanding the galaxy.

The black hole of the Milky Way – called Sgr A * (said aloud, "Sagittarius A star") – has a mass of 4.1 million times that of the Sun, packed in a space that could easily fit between the Sun and the orbit of Mercury. Black holes have intense gravity because they are massive, of course, and also because they are small . But a side effect of this is that you can get close to a black hole, and as you do, the gravitational effects are going away, much stronger.

It turns out that the center of the Milky Way is busy. Millions of stars make it their home, and a few, just a handful, are on orbits that take them very close to the black hole. One of these stars, called S2 (or sometimes S02), becomes incredibly close to Sgr A *. Its orbit is so tight that it circles the black hole once every 16 years, and at the perimeter (closest approach), it is only 18 billion kilometers away. It's four times the distance that Neptune comes from the Sun! In astronomy, it's a close shave microscopic.

When he passes the black hole, S2 moves to 7,650 kilometers by second or more than 2% of the speed of light! Just writing it made my hair stand up on the back of my neck. This is fast .

S2 is a luminous star that makes it observable from Earth even if it is tens of thousands of light-years away. Astronomers have been observing it for decades and have easily been able to keep up with it. And I mean literally: we can see it moving relative to the stars that surround it. In fact, 45 stars near Sgr A * have been followed over the years, but S2 is the closest and fastest. You can see this movement for yourself in this video, made using real observations of the galactic center :

Whoa. ] S2 passed the black hole in 2002, and by 2018, astronomers were ready for the next one. Let me take a moment to say that I wrote about the preparations for this event in March 2018, and this article has a lot of back story for the most recent observations. Please take a few minutes to read it, then come back here!

OK, so now you have the background. For this periastron, the astronomers had at their disposal three incredible instruments: SINFONI, GRAVITY and NACO, which made it possible to make extremely precise measurements of the position and the speed of S2 when it plunged towards its invisible supermassive and s & # 39; And away from him engaged.

Astronomers observed it in the weeks before the pass, and after. Incredibly, the GRAVITY instrument could detect the movement of the star on a single day! Think about it: The physical movement of this star through space was so fast that a telescope on Earth more than 26,500 light-years away could spot it.

When everything was done, very accurate map of its orbit.

I will not lie to you: seeing that made me smile. This is incredible . You can clearly see the elliptical shape of the orbit, and how they got a lot of observations done near the periosteum. In the space, the top of the orbit in the diagram is inclined towards us, and the bottom is inclined. S2 was moved down and left from the top right over time, then whipped the black hole and moved to the top left.

The movement of the star creates a shift in its light spectrum when it is moving away, and at the blue part of the spectrum that is heading towards us. Before he passed the black hole, he was moving away from us, and after he was moving towards us.

And that's where it gets very cool.

As I wrote in the previous article, in addition to the speed of the star affecting its redshift, the gravity of the black hole too: the light must come out of the gravity well of Sgr A *, and – as the theory of relativity Einstein asks – which steals energy, creating a redshift. In the previous article, I mentioned that this gravitational redshift should be equivalent to a speed of about 200 km / s; in other words, a star whose light must come out of the gravity of the black hole and a star that departs from us at 200 km / s would show the same redshift. So, above the red shift of the star due to its motion, we should see an additional shift of 200 km / sec when it is closest to the black hole

and that Did they see? This :

Oh Yeah . The plot shows the extra redshift due to effects other than orbital speed, and the boom. At periastron, the redshift peaks at 200 km / sec. Just on the money.

So, yes. Einstein was right. As we have always known.

And the astronomers who made these observations have not finished yet. As I wrote in the previous article, the gravity of the black hole affects the entire orbit of S2, causing it to rotate very slightly around (if you draw a line across its major axis, this line turns as the star goes through the black hole). This precession, as it is called, is light, but should be detectable in observations by 2020. There are even more subtle effects that can become clear with deeper observations in the years to come.

Needless to say, I love this. At the present time, no astronomer has serious doubts about relativity. it has been shown correctly millions of times (particle accelerators depend on it, just like your GPS). But what this shows is that our technology has improved to the point where we can detect the scope of Einstein's physics even across space, time and deep in the mouth literally unyielding of a supermassive black hole

. much more complex then we could have thought before Einstein, and even now, after more than a century, we still measure how strange it is. I think we will do it for centuries.