You are viewing content which is not in your chosen language.
Classroom visuals
Film info
Film summary
Scientists believe there is a supermassive black hole 26,000 light years away at the centre of our Galaxy. But how do they know, when they can't see it?Key facts
- Black holes are formed when massive stars collapse in on themselves to a single point.
- Black holes are so dense that not even light can escape their immense gravitational pull, making them invisible.
- By studying the motion of stars, scientists believe they have detected a black hole at the centre of the Milky Way, known as Sagittarius A*.
- Sagittarius A* is 26,000 light years from Earth.
Transcript
It is believed that at the centre of most galaxies lies something violent and destructive, and our own galaxy is no different.
It's home to a supermassive black hole.
Black holes are formed when massive stars collapse in on themselves to a single point.
They are so dense that not even light can escape their immense gravitational pull.
But if we can't see it, how can we tell that there is a black hole at the centre of our galaxy?
The Keck telescope in Hawaii is one of the most powerful telescopes in the world.
The Keck Telescope
Astronomer Andrea Ghez has been using it to observe the faint stars close to the centre of the Milky Way.
Dr Andrea Ghez, University of California – "Here's an example of one of the images we got just last night, we actually see that there are fainter stars towards the centre of our field of view and these stars are extremely important. It's the motion of these stars that reveal the presence of the black hole."
These stars are orbiting a central mass very quickly.
6000 km per second
They are travelling around this mass in the same way that the Earth orbits the Sun.
But their speed tells us that they are orbiting something 4 million times as heavy.
4 million solar masses
The size of the orbits mean that the mass must be condensed into a very small space, so Ghez amongst others, believes that they are orbiting around a supermassive black hole called Sagittarius A*.
Sagittarius A*
It is located 26,000 light years from Earth.
This means that we are over 1.5 billion times further from its event horizon than we are from the Sun.
The galaxy circles this supermassive black hole, but it sits dormant in the centre.
The stars that make up the Milky Way aren't being pulled towards it and the black hole won't have anything to devour until something crosses its path.
