What happens at the end when a black hole finally disappears?

In one line

The rule

Black holes can slowly lose mass and vanish by giving off energy as Hawking radiation.

There is no simple formula for the final state, but the process is described by: Power = (ħ c⁶) / (15360 π G² M²) where:

• ħ = reduced Planck constant
• c = speed of light
• G = gravitational constant
• M = mass of the black hole

Let's understand it simply

Imagine a pressure cooker on a stove. If you keep heating it, steam slowly leaks out. Over a long time, all the water inside turns to steam and escapes. The cooker is empty, but the steam is now in the air.

A black hole is like that cooker, but instead of steam, it gives off Hawking radiation (a very faint heat). Over a huge amount of time, the black hole shrinks as it loses energy. At the very end, it disappears in a tiny burst of heat. Nothing solid or visible is left—just a little bit of energy spread out in space.

How it works

1. Hawking radiation: Black holes are not completely black. They give off tiny amounts of heat due to quantum effects near their edge (event horizon).
2. Losing mass: This radiation carries away energy, so the black hole slowly loses mass.
3. Shrinking: As it gets lighter, it shrinks and gets hotter, so it radiates even faster.
4. Final burst: In the last moments, the black hole is tiny and very hot. It gives off a quick, strong burst of energy.
5. Nothing left: After this, the black hole is gone. Only its energy (as heat and light) is left, spread out in space.

The story behind it

Stephen Hawking, a British physicist, predicted in 1974 that black holes are not totally black. He used the ideas of quantum mechanics (how tiny particles behave) and general relativity (how gravity works) to show that black holes can slowly evaporate. Hawking’s work surprised everyone, as before this, people thought nothing could escape a black hole.

Where you see it in real life

• Universe’s future: In the far future, all black holes will vanish this way, leaving only faint heat.
• Gamma-ray bursts: The final burst of a tiny black hole could give off a flash of high-energy light.
• No remains: Unlike a star, which leaves behind ashes or a white dwarf, a black hole leaves nothing solid.
• Energy in space: The energy from the vanished black hole becomes part of the background heat in the universe.
• No information: Any matter or information that fell in is lost to us forever (according to current ideas).
• Not seen yet: We have not seen a black hole disappear—this takes longer than the age of the universe for big black holes.

Why it matters

• Fate of the universe: Helps us understand what will happen to everything in the very distant future.
• Physics puzzle: Raises deep questions about whether information is truly lost forever.
• Quantum gravity: Shows where quantum mechanics and gravity must work together—an unsolved area in science.
• Technology: The math behind Hawking radiation is used in advanced physics and may lead to new discoveries.

Worked example

Let’s imagine a tiny black hole with the mass of a mountain (about 10¹¹ kg):

Given:  M = 10¹¹ kg
Step 1: Write the formula for power: Power = (ħ c⁶) / (15360 π G² M²)
Step 2: Plug in the values (using constants):
         ħ ≈ 1.05 × 10⁻³⁴ J·s
         c ≈ 3 × 10⁸ m/s
         G ≈ 6.67 × 10⁻¹¹ N·m²/kg²
         M = 10¹¹ kg
Step 3: Calculate the denominator: (15360 π G² M²)
Step 4: Calculate the numerator: (ħ c⁶)
Step 5: Divide to get Power (very small, but not zero)
Step 6: Over time, the black hole loses mass faster as it gets smaller, until it vanishes in a final burst.

Common mistakes

• Thinking black holes last forever: They slowly evaporate, but it takes a very long time.
• Believing something is left behind: No matter or object remains—only energy as heat.
• Confusing with a star’s death: Stars leave behind white dwarfs or neutron stars; black holes leave nothing.
• Assuming we can see this: The process is too slow for big black holes; we have not observed it yet.

Remember it

When a black hole disappears, it leaves only its energy as faint heat—nothing else.