help with question (mass-luminosity relation law) Watch

iamspiderman
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starry_n3bula
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(Original post by iamspiderman)
Here's the Question:

Sirius A is 2.3 times the mass of the sun and about 20 times as bright. Is this consistent with the mass-luminosity law?

Need help.
Hey again :-)

So this is like the other question with getting you to think about the mass-luminosity relation/law.

As they haven't told you what type of star it is and asked you if it is consistent with the mass-luminosity relation which works for main sequence stars, you can assume its a main sequence star. [fyi Its an Am type star so it is main sequence ]

A stars luminosity is a measure of how 'bright' it is, so they are telling you Sirius A has a luminosity that is about 20 times greater than that of the Suns.

The mass-luminosity equation for main sequence stars is:

(L_star/L_sun) = (M_star/M_sun)^3.5

where M_star=mass of the star, M_sun=mass of the Sun

If you plug the masses they gave you into the equation do you find that Sirius A has a luminosity about 20 times that of the Sun?

Explanation of the mass-luminosity relation here: http://hyperphysics.phy-astr.gsu.edu...ro/herrus.html
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iamspiderman
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(Original post by iamspiderman)
Hey again!
Thanks for replying.

I've filled in the stars mass (2.3) but they didn't give the sun's mass?

L star/ L sun = (2.3/ ? )^3.5
np

'they didn't give the sun's mass'
Its kinda like the other question where you’ll end up not needing to know its value

The question said that Sirius A has a mass 2.3 times the suns, not '2.3' i.e.

M_star=2.3*M_sun

if you substitute that into the equation instead of just '2.3' do you find any terms cancel?
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