Fact sheet: Black hole
A black hole is a region of space having a gravitational field so intense that no matter or radiation can escape. A black hole is created after the death of a very massive star. The core of the star collapses in on itself, causing a supernova – a massive explosion of the star's outer layers. All of the former star's matter is then concentrated into a single tiny point (known as a singularity). The gravity of a black hole is so strong that nothing – not even light – can escape its pull.
Black holes are generally categorized according to the mass they contain. There are three main types:
- Stellar black holes, which are the most common and contain about 10 times the mass of our Sun
- Intermediate black holes
- Supermassive black holes, which are found at the centre of most galaxies and can be millions or even billions of times more massive than the Sun
Scientists are still not sure how supermassive black holes are created, although they may be formed through mergers of smaller, stellar black holes.
- The black hole at the centre of our galaxy, the Milky Way, is known as Sagittarius A*.
- The black hole M87* (located at the centre of Messier 87, one of the most massive galaxies in the observable universe) is the subject of the first-ever picture of a black hole, released in .
A black hole's singularity is an infinitely tiny point in its innermost region. The boundary surrounding a black hole, known as the event horizon, varies in size.
Black holes vary in mass. They can range from 10 times to several billion times the mass of our Sun.
The more massive a black hole, the colder it is.
Stellar black holes are very cold: they have a temperature of nearly absolute zero – which is zero Kelvin, or −273.15 degrees Celsius.
Supermassive black holes are even colder.
But a black hole's event horizon is incredibly hot. The gas being pulled rapidly into a black hole can reach millions of degrees.
- Since light cannot escape a black hole, it is impossible to actually see what one looks like. However, black holes that are actively feeding on nearby stars or clouds of gas falling towards their centre will often be surrounded by bright discs or jets. Astronomers can detect and study black holes by finding those discs and jets.
- The image of the black hole M87* at the top of this page was captured by a group of ground-based telescopes around the world acting in unison, effectively creating a single Earth-sized telescope that is called the Event Horizon Telescope.
Because black holes are formed at the end of a large star's life, black holes are scattered throughout galaxies. Supermassive black holes are found at the centre of most galaxies, including our own galaxy, the Milky Way.
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