What is a Black Hole? | Facts & Fictions

Black Holes

Black holes are points in space that are so dense they create deep gravity sinks. Beyond a certain region, not even light can escape the powerful tug of a black hole's gravity. And anything that ventures too close—be it a star, planet, or spacecraft—will be stretched and compressed like putty in a theoretical process aptly known as spaghettification.

Any object with mass warps space-time. But objects with more mass and greater density create greater gravity wells. This illustration compares the relative deformations from different objects. Notice that a black hole essentially rips a hole in the fabric of space-time.

Forging a black hole 

To make a black hole, you need to compress a lot of mass into a very small space. Einstein’s theory says it doesn’t matter what that mass is, but astronomers think nature makes stellar-mass black holes when massive stars die. All-stars spend most of their lives fusing hydrogen into helium in their cores. The energy this produces creates an outward pressure that balances the inward pull of gravity. After a star exhausts its core hydrogen, it eventually starts to fuse helium into carbon. 

More massive stars can tap into additional fuels. Ultimately, silicon fuses into iron and nickel. But the process stops there because fusing heavier elements consumes, rather than releases, energy. The star can no longer support its own weight with radiation pressure from fusion, so it collapses. The implosion triggers a shock wave that tears the star apart in a violent supernova explosion. For stars that begin life with more than 20 solar masses, the core left behind collapses to infinite density and becomes a singularity. An event horizon forms around the singularity, and you have a black hole.

The event horizon — the point of no return — is surprisingly small. The black hole at the centre of the Milky Way Galaxy, known as Sagittarius A* (pronounced A-star), holds about 4 million times the Sun’s mass, but its event horizon is only 15 million miles (24 million kilometres) across. It would fit insideMercury’s orbit with plenty of room to spare. A black hole with 10 times theSun’s mass would have an event horizon that spans 37 miles (60 km) and would fit inside Rhode Island. And if Earth were compressed into a black hole, it would be the size of a marble. The event horizon radius increases in direct proportion to the black hole’s mass, but unlike Hollywood treatments, black holes don't vacuum matter up. If an Earth-mass black hole replaced our planet, the Moon’s orbit wouldn’t change.

The small size matters because the gravitational field changes drastically as one approaches the event horizon. That's why black holes are such good arenas for testing relativity. The gravity wells are steep — a person 3 feet (1 meter) from an Earth-mass black hole would feel a force more than 40 trillion times the gravity at Earth’s surface. In the vicinity of a black hole, the bending of light is easy to spot, and effects like time dilation and deviations from Newtonian mechanics are large enough to observe readily. If relativity stops working, then near a black hole is where we are likely to see it happen.

The sizes of black holes

The diameter of a black hole’s event horizon increases in direct proportion to its mass. A black hole with 10 times the Sun’s mass would span 37 miles (60 km), while the one in the Milky Way’s centre measures 17 Suns across. 

Final Thoughts

These pieces of information are not accurate. Many researchers and scientists are exploring space to get more information about the Black holes.