What is a black hole, can we see one, and could one swallow Earth? Short answers to common questions.
1. What is a black hole?
A region of space where matter is so compressed that its gravity does not let anything escape, not even light.
2. How do black holes form?
Stellar black holes form when very massive stars collapse at the end of their lives. How the supermassive black holes in the centres of galaxies grew so large is still being studied.
3. Can we see a black hole?
Not directly, but we can see its effects: hot gas swirling around it, stars orbiting it, or its "shadow". The first image of a black hole's shadow was published in 2019.
4. Is there a black hole in our galaxy?
Yes. At the centre of the Milky Way sits Sagittarius A*, with a mass of about 4 million Suns.
5. Could a black hole swallow Earth?
No. The nearest known black holes are more than a thousand light-years away. And from a distance, a black hole attracts objects just like a star of the same mass would.
Image: First Image of a Black Hole. Credit: EHT Collaboration. Source, CC BY 4.0.