Black holes Lesson 25 of the space course of Mova's primary school: 19 sentences, each with its syntax tree and pragmatics. The lessons are written for Mova, and their agreed trees are part of Mova corpus 0.4 (CC BY-SA 4.0). How Mova does on its tests: the lesson at school .
0 A black hole is not a hole and not a cosmic vacuum cleaner: it is a huge amount of mass squeezed into a tiny space, so its gravity is so strong that not even light can get out. 1 Its edge is the event horizon, a point of no return: like a waterfall, you can paddle safely far upstream, but once you go over the edge you can never come back. 2 Squeeze the whole Earth down to the size of a marble, about 9 millimetres across, and it would become a black hole. 3 Far from a black hole its pull is just like that of any star of the same mass: if the Sun became a black hole, Earth would keep circling, only cold and dark. 4 We cannot see black holes directly, but we see what they do: stars racing round nothing visible, gas glowing as it falls in, and ripples in space when two of them crash. 5 A black hole is a place where so much mass is squeezed into a small space that its gravity lets nothing, not even light, escape. 6 The edge of a black hole is called the event horizon: anything that crosses it can never come back out. 7 Some very heavy stars collapse into black holes at the end of their lives, usually a few to a few dozen times the mass of the Sun; the Sun is far too light to become one and will end as a white dwarf. 8 The nearest known black holes are more than a thousand light years away, far too far to harm us. 9 Most large galaxies have a supermassive black hole at their centre, millions to billions of times the mass of the Sun. 10 In 2019 the Event Horizon Telescope published the first image of a black hole's shadow, M87*, a dark centre in a glowing orange ring. 11 If the Sun were replaced by a black hole of the same mass, Earth would keep orbiting just as before, only in the cold and dark. 12 Falling feet-first towards a small black hole, the pull on your feet would be so much stronger than on your head that you would be stretched out like spaghetti. 13 To become a black hole, Earth would have to be squeezed to about 9 millimetres across, about the size of a marble. 14 In 2015 the LIGO detectors in the USA first caught gravitational waves, ripples in space from two black holes merging about 1.3 billion light years away. 15 Black holes cannot be seen directly, so astronomers find them by their effects: stars orbiting nothing visible, or hot gas glowing as it falls in. 16 Close to a black hole, time runs more slowly compared with far away, an effect predicted by Einstein. 17 In 1974 Stephen Hawking calculated that black holes should slowly leak tiny amounts of energy and, over unimaginably long times, evaporate. 18 Hawking's leaking, called Hawking radiation, has never been directly observed, because it is far too faint. ← previous Galaxies and the Big Bangnext → Exoplanets and the search for life↑ back to Space This page in Markdown → https://md.mova.elamur.ai/free/en/corpora/school/space/25-black-holes/