Science

Black hole: What is a black hole? Could a black hole swallow the Sun? What is inside one?


A black hole is an almost impossibly dense object in space, exhibiting gravitational acceleration so strong even light cannot escape. Although black holes are undoubtedly mysterious, they are simply a consequence of how gravity works – when enough mass is compressed into a small enough space, the resulting object rips the very fabric of space and time, becoming what is called a singularity.

How are black holes formed?

A stellar-mass black hole, with a mass of tens of times the mass of the Sun, can likely form in seconds, after the collapse of a massive star.

These relatively small black holes can also be made through the merger of two dense stellar remnants called neutron stars.

A neutron star can also merge with a black hole to make a bigger black hole, or two black holes can collide.

Mergers like these also make black holes quickly, and produce ripples in space-time called gravitational waves.

More mysterious are the supermassive black holes found at the centre of galaxies.

It can take less than a billion years for one to reach a very large size, but it is unknown how long it takes them to form, generally.

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Could a black hole swallow the Sun?

Supermassive black hole M87 lies 50 million light-years from our Earth and is one of the largest black holes discovered so far, thought to contain a mass equal to 6.6 billion of our suns.

A black hole this huge would have a very wide event horizon – the edge from which nothing can escape.

Light from our Sun takes eight minutes to travel to Earth and four hours to travel to Neptune, the solar system’s most distant planet.

M87’s black hole has an event horizon about four times as large as Neptune’s orbit, meaning it could theoretically swallow our solar system – and our Sun – whole.

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If black holes are “black”, how do we know they exist?

A black hole invisible because their powerful pulls all light into the black hole’s core.

However, scientists can see the effects of its strong gravity on the surrounding stars and gases.

If a star is orbiting a certain point in space, scientists can study the star’s motion to find out if it is orbiting a black hole.

When a black hole and a star are orbiting close together, high-energy light is produced, capable of being detected by sensitive scientific instruments.

A black hole’s gravity can sometimes be strong enough to suck a star’s outer gases and grow a disk around itself called the accretion disk.

As gas from the accretion disk spirals into the black hole, the gas heats to very high temperatures and releases measurable X-ray energy.

Will the entire Universe eventually be swallowed by a black hole?

A region where a black hole has exerts gravitational influence is quite limited compared to the size of a galaxy.

This applies even to supermassive black holes like the one sitting in the Milky Way’s centre.

This black hole has probably already devoured most or all of the stars that formed nearby and stars further out are mostly safe from being pulled in.

Since this black hole already weighs a few million times the mass of the Sun, there will only be small increases in its mass if it swallows a few more Sun-like stars.

There is consequently little danger of Earth, located 26,000 light years away from the Milky Way’s black hole, being pulled in.

Future galaxy collisions will cause black holes to grow in size, for example by merging of two black holes.

But collisions will not happen indefinitely because the Universe is infinite and expanding, meaning any sort of black hole runaway effect is highly unlikely.



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