# Black hole lifespan

1. Jul 14, 2012

### thequestioner

how long do black holes last before they vaporize?

2. Jul 14, 2012

### Janus

Staff Emeritus
That depends on a number of factors: The size of the black hole and how fast other stuff is falling into the black hole etc.

If you ignore incoming mass, you can use the formula

$$T_{evap} = 5120 \pi \sqrt{\frac{\hbar G}{c^5}}$$

For example, a black hole the mass of the Sun would take ~2e67 years to evaporate.

3. Jul 14, 2012

### Nabeshin

Janus: That is the result for a black hole of the Planck mass. The generic result for a black hole of mass M is,
$$T_{\rm evap} = 5120 \pi \frac{ G^2 M^3}{\hbar c^4}$$

4. Jul 16, 2012

### ibysaiyan

Are the formula for the time that it takes for a BH to evaporate and for an object of same mass to gravitationally collapse alike , or would the latter give rise to BH that is expressed by aforementioned ^ formula ?

5. Jul 16, 2012

### Chronos

It takes a very long time. In fact, it will take way longer than the age of the universe before any black hole of a solar mass or more can actually radiate more energy than it absorbs from the environment.

6. Jul 16, 2012

### Naty1

The evaporation time of a black hole and the time of 'collapse' of mass are not related. Most mass is not dense enough to 'collapse'....but before the end of the universe most mass may be consumed by black holes. In other words, a lot of mass may is likely to be consumed by existing black holes rather than form new black holes.

7. Jul 16, 2012

### ibysaiyan

Thanks for the clarification.

8. Jul 16, 2012

### Staff: Mentor

9. Jul 26, 2012

### rcttsoul2

This is something I learned today; I always thought that a black hole was actually an extremely large nuclear explosion in progress….
And due to the time dilation of a black hole, it would never come to a conclusion.

10. Jul 26, 2012

### Staff: Mentor

That is not the case. A black hole is an object whose escape velocity exceeds the speed of light.