Can black holes ever shrink or disappear?

In one line

The rule

Black holes can lose mass and energy over time by a process called Hawking radiation, which can eventually make them shrink and vanish.

There is no simple formula for all black hole evaporation, but the basic idea is: Power = (ħ c⁶) / (15360 π G² M²) where:

• ħ (h-bar) = reduced Planck's constant
• c = speed of light
• G = gravitational constant
• M = mass of the black hole

Let's understand it simply

Imagine a pressure cooker on your kitchen stove. If you leave it on, steam slowly escapes from the whistle. Over a long time, the water inside will reduce. Now, think of a black hole as a container that is not just holding water, but everything—even light. For a long time, nothing seems to come out. But scientists found that, just like steam, a tiny bit of energy can slowly escape from a black hole. This is called Hawking radiation (named after Stephen Hawking). It's like the black hole is leaking, but very, very slowly.

How it works

1. Quantum effects near the edge: Near the black hole's edge (event horizon), space is not empty. Tiny pairs of particles and antiparticles pop in and out of existence.
2. One particle falls in: Sometimes, one particle falls into the black hole, and the other escapes into space.
3. Energy is lost: The escaping particle carries away a tiny bit of energy.
4. Black hole loses mass: Because of Einstein's E = mc², losing energy means the black hole loses mass.
5. Shrinking and vanishing: Over a huge amount of time, the black hole gets smaller and smaller, until it disappears in a final burst of energy.

The story behind it

For a long time, scientists thought nothing could escape a black hole. In 1974, British physicist Stephen Hawking used quantum physics and Einstein's ideas to show that black holes are not completely black. He found that black holes can give off a tiny amount of heat and energy—now called Hawking radiation. This was a big surprise to everyone, even Hawking himself. It changed how we think about black holes and the universe.

Where you see it in real life

• Space telescopes: Scientists look for signs of Hawking radiation from black holes, but it is too weak to see with current technology.
• The early universe: Tiny black holes, formed just after the Big Bang, might have already evaporated and disappeared.
• Particle accelerators: Some theories suggest tiny black holes could be made in high-energy experiments, and they would vanish quickly.
• Science fiction: Many stories imagine black holes shrinking or exploding at the end of their lives.
• Physics classrooms: Teachers use Hawking radiation to show how quantum physics and gravity work together.
• Theoretical research: Scientists use these ideas to study the fate of the universe and the laws of physics.

Why it matters

• Shows quantum physics and gravity together: Hawking radiation is one of the few ideas that uses both quantum mechanics and Einstein's gravity.
• Tells us about the end of black holes: It helps us know what happens to black holes over billions of years.
• Helps explain the fate of the universe: If all black holes can disappear, the universe will look very different in the far future.
• Drives new research: This idea pushes scientists to find a theory that explains everything (a "theory of everything").

Worked example

Let's see how long a small black hole would take to vanish:

Given: Mass of black hole (M) = 10¹² kg (about the mass of a big mountain)
Step 1: The time to evaporate (T) ≈ (5120 × π × G² × M³) / (ħ × c⁴)
Step 2: Plug in the numbers (using constants):
         G = 6.674 × 10⁻¹¹ m³/kg/s²
         ħ = 1.055 × 10⁻³⁴ J·s
         c = 3 × 10⁸ m/s
Step 3: Calculate T (skip detailed math here)
Step 4: Result: T ≈ 2 × 10⁶⁸ years (for a black hole with the mass of the Sun)
Step 5: For our small black hole (10¹² kg), T ≈ 2 × 10¹⁰ years (about the age of the universe)

So, even a small black hole takes longer than the age of the universe to disappear!

Common mistakes

• Thinking nothing can escape a black hole: Actually, Hawking radiation lets a tiny bit of energy escape.
• Believing black holes vanish quickly: In reality, big black holes take much, much longer than the age of the universe to disappear.
• Confusing Hawking radiation with normal light: It's not normal light, but a special quantum effect.
• Forgetting that only tiny black holes might vanish soon: Large ones will last for billions of years more.

Remember it

Black holes can slowly leak energy and shrink, but this takes so long that even the universe is young compared to their lifetime.