At the center of the galaxy is a supermassive black hole called Sagittarius A*. It is approximately 27,000 light years away from Earth and is 23.5 million kilometers in diameter.
For the first time in the world, a team of astronomers led by Florian Peisker of the University of Cologne, Germany, has discovered a binary star system orbiting this black hole.
This system is known as D9. Its discovery, announced in a new paper published today in Nature Communications, sheds light on the extreme environment at the center of our galaxy.
It also helps explain the long-standing cosmic mystery of why some stars fly through space much faster than others.
What is a binary star system?
A binary star system is simply two stars orbiting each other.
Our Sun isn’t part of a binary, which is a good thing: We wouldn’t want another star wandering around our solar system. This would disrupt Earth’s orbit; We will fry or freeze.
Observations show that about two-thirds of the stars in the galaxy are single stars, and the remainder are part of a binary or multiple star system. Larger stars are more likely to pair.
Binary star systems are useful to astronomers because their motions contain abundant information. For example, the speed and distance of orbits tell us about the masses of stars.
In contrast, for an individual star, we usually calculate its mass by how bright it is.
technically challenging quest
Although scientists have previously predicted that binary star systems exist near supermassive black holes, they have never actually detected one.
This recent discovery was quite challenging technically. We can’t see the two stars just by looking at the system, because it is too far away. Rather, astronomers used the European Southern Observatory’s Very Large Telescope to measure the shifting of starlight – a phenomenon known as the Doppler effect. This revealed that the stellar system had a characteristic wobble in the light, indicating an orbit.
But the team did much more than that.
Because binary stars contain such an abundant amount of information, astronomers can calculate that this particular system is about 2.7 million years old. That means these stars first ignited 27 million years ago.
They were probably not born in the extreme surroundings of a black hole, so unless they recently arrived in this neighborhood, they have survived in their current environment for about a million years.
This, in turn, tells us about the black hole’s ability to disrupt stars in its orbit. Black holes are mysterious beasts, but clues like these are helping us unravel their nature.
circling a black hole
The situation the astronomers discovered is quite familiar.
Think about the Moon: It orbits the Earth, and the Earth and the Moon together orbit the Sun. Because gravity is an attractive force, it can pull many celestial bodies into complex orbits. The complexity of this scenario inspired a recent book and Netflix series, The Three Body Problem.
If they are complicated, can the whole thing fall apart? The Moon–Earth–Sun arrangement is stable because two of the three bodies – the Earth and the Moon – are much closer together than the other body, the Sun. The Moon and Earth are so close that, as far as the Sun is concerned, it is effectively a two-body system, which is stable.
But if all three bodies interact, the system may fall apart. It is also possible that two bodies completely expel the third body.
unusual motion stars
This mechanism potentially explains a cosmic mystery: hypervelocity stars.
Most stars in the night sky are in a typical, nearly-circular orbit around the center of our galaxy. The orbital speed is about 200 kilometers per second: very fast on Earth, but nothing special in space.
However, since 2005 we have discovered about 20 hypervelocity stars, moving in our galaxy at speeds of more than 1,000 kilometers per second. How?
Our best current idea is that hypervelocity stars were once part of a binary system orbiting our supermassive black hole. Over time, the stars came very close to the black hole and resulted in a complex orbit. In the kerfuffle, with a black hole calling the shots, one of the stars went out. It escaped into the outer galaxy, where we see it as a hypervelocity star.
Finding Hypervelocity Factory
This is an interesting theory.
Theoretical calculations show that the mechanism works and the speed is approximately correct. Observations show that many known hypervelocity stars appear to be moving away from the galactic center, which is another plus for the theory. But how else can we test this idea?
One obvious way is to look for binary stars around our supermassive black holes.
Astronomers have been keeping a close eye on our galaxy’s center for decades. It’s not too difficult to spot in the night sky, as you can see from the image below.
Here are two reliable ways to find Sagittarius A*. First, find Antares (bright and red), which is the center of Scorpio’s back, and then follow the scorpion’s body to the tip of the tail, and that is close to the black hole. Alternatively, get a Good Night Sky app on your phone; They are amazing.
This recent discovery is very important in the context of these theories. Astronomers have found a binary star system around our supermassive black hole. An important piece of the hypervelocity puzzle is in the right place.
,Author: Luke Barnes, Lecturer in Physics, University of Western Sydney)
,disclosure statement: Luke Barnes does not work for, consult to, own shares in, or receive funding from any company or organization that would benefit from this article, and has no relevant affiliations beyond his academic appointment. not disclosed)
This article is republished from The Conversation under a Creative Commons license. Read the original article.
