Question 1 of 12Correct: 0
Why can't light escape beyond the event horizon?
What appears as a bright ring in images of a black hole?
Why might you not notice crossing the event horizon?
Why is the dark spot in an image not the event horizon?
How do stellar-mass black holes form?
What remains an open question?
What is known about what happens inside a black hole?
What would a person feel crossing a supermassive black hole's horizon?
How did they get an image of a black hole's shadow?
What exactly can you see in the image?
What does Hawking radiation predict?
Are large black holes evaporating now?
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Why light can't escape a black hole0/2What Happens at a Black Hole's Edgein the app0/2Where Black Holes Come From0/2What Happens Inside a Black Hole0/2How We Photographed a Black Holein the app0/2What Is Hawking Radiationin the app0/2
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Answers and explanations12 questions
- Why can't light escape beyond the event horizon? There is no direction leading outwardBeyond the horizon, every available path leads inward, even though light still travels at its usual speed.From “Why light can't escape a black hole”
- What appears as a bright ring in images of a black hole? Hot gas and rays that curved around the holeThe black hole itself doesn't glow: you see the hot gas around it and some rays bent by its gravity.From “Why light can't escape a black hole”
- Why might you not notice crossing the event horizon? There is no matter or local sign at the boundaryThe horizon is not a surface but a boundary of causality, so instruments on a falling spacecraft would not register it.From “What Happens at a Black Hole's Edge”
- Why is the dark spot in an image not the event horizon? It is an optical shadow created by curved lightThe shadow's edge is set by light bent near the black hole, so the dark spot is noticeably wider than the horizon.From “What Happens at a Black Hole's Edge”
- How do stellar-mass black holes form? When a massive star's core collapses after it runs out of fuelWhile reactions continue, outward pressure balances gravity; when the fuel runs out, the balance disappears.From “Where Black Holes Come From”
- What remains an open question? Where supermassive objects in galactic centers came fromThey are found in the early universe, when there was not enough time for gradual growth from stellar size.From “Where Black Holes Come From”
- What is known about what happens inside a black hole? The equations stop producing a meaningful result: there is no answerWe need a theory that combines gravity and quantum mechanics, and we still don't have one.From “What Happens Inside a Black Hole”
- What would a person feel crossing a supermassive black hole's horizon? Nothing unusual: there is no wall or flashFor these objects, the difference in gravity across the length of a body is small, unlike with small black holes.From “What Happens Inside a Black Hole”
- How did they get an image of a black hole's shadow? By combining observatories on different continents into one virtual antennaThey later combined recordings with atomic timestamps as if they were pieces of one mirror.From “How We Photographed a Black Hole”
- What exactly can you see in the image? A shadow: a dark circle against glowing matterLight cannot escape from beneath the event horizon, while the hot gas around it creates a ring.From “How We Photographed a Black Hole”
- What does Hawking radiation predict? That black holes glow faintly and lose massThe energy for the escaping particle comes from the black hole itself.From “What Is Hawking Radiation”
- Are large black holes evaporating now? No: they are colder than the cosmic background and therefore growEvaporation will become possible only after the Universe has cooled more than they have.From “What Is Hawking Radiation”