Chapter 10Science & Nature

What is a black hole?

A region of spacetime where gravity is strong enough that nothing — not even light — can escape. Formed from collapsed massive stars, they range from a few solar masses to billions in galactic centers.

Follow-up questions

Would you actually get spaghettified?

In a small black hole, yes — tidal forces stretch you long before crossing the horizon. Supermassive ones are gentler on the way in.

Is Sagittarius A* the closest one?

The closest supermassive one, at 26,000 light-years. Smaller stellar-mass black holes exist much closer.

Can they die?

Yes — Hawking radiation slowly evaporates them, though a stellar black hole would outlast the current age of the universe by 10^60 times.

Have we ever seen one?

Two so far — M87* (2019) and Sagittarius A* (2022) via the Event Horizon Telescope.

Can we see one?

Not directly. In 2019 the Event Horizon Telescope imaged the shadow one casts on the glowing gas around it.

What if I fell in?

To an outside observer, you'd appear to slow and fade; to yourself, you'd be stretched into a thin string ('spaghettified').

What happens if you fall into a black hole?

For a stellar-mass hole, tidal forces stretch you apart before the horizon. For a supermassive one, you'd cross the horizon without local drama and never return.

Do black holes last forever?

No — Hawking radiation means they evaporate, but a stellar-mass black hole would take roughly 10^67 years, far longer than the universe's current age.

Would a black hole swallow the solar system?

Only if one arrived. From a distance, a black hole's gravity acts like any other mass of the same size.

What's a supermassive black hole?

Millions to billions of solar masses, sitting at the centres of most galaxies including our own (Sagittarius A*).

What happens if you fall in?

Tidal forces stretch you (spaghettification) long before you reach the singularity. Time appears to slow to outside observers.

Do black holes evaporate?

Yes — via Hawking radiation, over timescales far longer than the universe's current age.

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