# Luminosity and power?

1. Apr 27, 2012

### Mafia

If one star is say 10 times more luminous than another star would that mean it would have 10 times more power as in W? And would that relationship continue with increased luminousity as in a star 1000 times more luminous would have 1000 times more power?

2. Apr 27, 2012

### phyzguy

Basically, yes. Luminosity has units of energy per time, and is typically measured in ergs/sec(CGS) or joules/sec(MKS), with joules per second being the same as watts.

3. Apr 28, 2012

### Dotini

As a layman, the way I read the H-R diagram, white dwarfs have less luminosity and less absolute visual magnitude than most main sequence stars, yet can have higher surface temperature, higher frequency color index (B-V), and higher surface current density. But perhaps this has nothing to do with power?

Respectfully submitted,
Steve

4. Apr 28, 2012

### phyzguy

It does have to do with power. The luminosity is the power of the radiation that the stars emit. Since a star is roughly a blackbody, the total luminosity of a star is $$L =4\pi r^2 * \sigma T^4$$
where sigma is the Stefan-Boltzmann constant. White dwarfs emit a lot of radiation per square cm of surface area because their temperature is high, but their total luminosity is low because their radius is so small.