Quiz, myth or fact, and squash-it
Test yourself. Every answer comes with its source.
How to play. Pick an answer and the fact behind it appears, with a link to where it comes from. Without JavaScript, open “Show the answer” under each question.
The black hole quiz
1 What is the edge of a black hole called?
Show the answer
The event horizon. The edge of a black hole is the event horizon. It isn’t a solid surface like Earth’s: it is a boundary that contains all of the black hole’s matter. NASA
2 Can light escape from inside the event horizon?
Show the answer
No, no light of any kind. No light of any kind, not even X-rays, can get out from inside the event horizon. NASA, 10 questions
3 What is the black hole at the centre of the Milky Way called?
Show the answer
Sagittarius A*. The supermassive black hole at the centre of the Milky Way is called Sagittarius A*, said “ay-star”. NASA
4 About how heavy is Sagittarius A*?
Show the answer
About 4 million Suns. It has about 4 million times the mass of the Sun. NASA
5 When was the first picture of a black hole revealed?
Show the answer
2019. On 10 April 2019 the Event Horizon Telescope team revealed the first direct visual evidence of a supermassive black hole and its shadow. ESO, 2019
6 How many radio telescopes made up the Event Horizon Telescope for the first picture?
Show the answer
Eight. The Event Horizon Telescope linked eight radio telescopes on the ground into one virtual telescope the size of Earth. ESO, 2019
7 What did LIGO detect on 14 September 2015?
Show the answer
Gravitational waves from two colliding black holes. On 14 September 2015 gravitational waves were observed for the very first time. They came from a collision between two black holes. Nobel Prize, 2017
8 Who lost a bet that Cygnus X-1 did not contain a black hole?
Show the answer
Stephen Hawking. Stephen Hawking lost a bet, first placed in 1974, that Cygnus X-1 did not contain a black hole. NASA Chandra, 2011
9 Who described ‘dark stars’ in 1783?
Show the answer
John Michell. In 1783 the clergyman and astronomer John Michell described ‘dark stars’ whose light could not reach us, in a letter to Henry Cavendish that the Royal Society published. Royal Society
10 What would happen to the planets if the Sun became a black hole of the same mass?
Show the answer
They would stay in their orbits. If the Sun were swapped for a black hole of the same mass, the planets would stay in their orbits, though the solar system would get a lot colder. NASA
11 Will the Sun ever become a black hole?
Show the answer
No, it isn’t massive enough. The Sun will never become a black hole. It isn’t massive enough to explode, and will end its life as a white dwarf. NASA, 10 questions
12 What is the nearest known black hole?
Show the answer
Gaia BH1. The nearest known black hole, Gaia BH1, is about 1,500 light-years away. NASA
Myth or fact?
Eight statements. Some are true, some are myths.
1 Black holes suck in everything around them, like cosmic vacuum cleaners.
Show the answer
Myth. Black holes are not cosmic vacuum cleaners. They don’t suck in other matter: from far enough away, their gravity acts just like that of anything else with the same mass. NASA
2 All black holes spin.
Show the answer
Fact. All black holes spin. The fastest known, GRS 1915+105, turns more than 1,000 times a second. NASA
3 Black holes are shortcuts to other universes.
Show the answer
Myth. Black holes are not wormholes. They don’t give shortcuts between places in space, or portals to other dimensions or universes. NASA
4 Most Milky Way-sized galaxies have a giant black hole at their centre.
Show the answer
Fact. Black holes are not rare. Most galaxies the size of the Milky Way have a giant one at their centre. NASA
5 A black hole could eat a whole galaxy.
Show the answer
Myth. A black hole cannot eat a whole galaxy. Even a supermassive one’s reach is nowhere near big enough. NASA, 10 questions
6 Black holes bend light from things behind them.
Show the answer
Fact. Black holes bend light from things behind them. This gravitational lensing can reveal lonely black holes that would otherwise be invisible. NASA
7 Telescopes can see a black hole itself.
Show the answer
Myth. Telescopes don’t see black holes themselves. They see what happens around them: hot gas, orbiting stars and bent light. NASA
8 Gravitational waves were first detected about a hundred years after Einstein predicted them.
Show the answer
Fact. Einstein predicted gravitational waves about a hundred years earlier, but was convinced they could never be measured. Nobel Prize, 2017
Squash-it: how small to make a black hole?
Anything would become a black hole if it were squashed small enough. The size it has to fit inside is its Schwarzschild radius, and it grows in step with the mass.
For a star like the Sun, the Schwarzschild radius is about 3 km (2 miles). Britannica The Schwarzschild radius goes up in proportion to the mass: twice the mass, twice the radius. Britannica
Pick an example or type a mass.
Our own rough calculation: about 3 km of radius for each Sun’s worth of mass (Britannica’s figure for the Sun), doubled for the width. For a person we use Britannica’s figure directly. As a check, it gives M87* about 39 billion km across; Britannica says 38 billion km.