We’re taking a page from the best nature guide books and bringing you a Field Guide to Black Holes this week. Check back each day for a new page in the book.
First up? The basic black hole.

A black hole is an object whose main characteristics are mass and spin. https://abs.twimg.com/emoji/v2/... draggable="false" alt="⚖️" title="Waage" aria-label="Emoji: Waage">https://abs.twimg.com/emoji/v2/... draggable="false" alt="💫" title="Symbol für Benommenheit" aria-label="Emoji: Symbol für Benommenheit"> It also has a “surface,” called an event horizon. This boundary defines the place where an object has to go faster than light – faster than anything can go – to escape. http://go.nasa.gov/2OozGm4 ">https://go.nasa.gov/2OozGm4&q...

Since light can’t escape from inside a black hole, these objects can be hard to detect. But one thing black holes can’t hide is their gravity. https://abs.twimg.com/emoji/v2/... draggable="false" alt="🙈" title="Nichts sehen-Affe" aria-label="Emoji: Nichts sehen-Affe"> They affect their environment just like any other mass in the universe.

For decades, scientists have tracked stars orbiting the black hole at the center of our galaxy. https://abs.twimg.com/emoji/v2/... draggable="false" alt="🔭" title="Teleskop" aria-label="Emoji: Teleskop"> Using those observations, they’ve estimated the black hole weighs 4 million times the Sun’s mass!

Black holes can also act as a lens. https://abs.twimg.com/emoji/v2/... draggable="false" alt="🔍" title="Nach links zeigende Lupe" aria-label="Emoji: Nach links zeigende Lupe"> They can cause light from distant objects to bend around them. By looking for signatures of warped light, we can tell where there’s something with a lot of mass.

Follow us throughout the day to learn more about these basic black holes. And come back tomorrow to hear about fancier ones with accretion disks and jets — and how we detect them!