Can Luminosity Give You a Star's Age?


by chefskitten
Tags: luminosity, star
chefskitten
chefskitten is offline
#1
Oct25-13, 09:33 PM
P: 2
You find two yellow stars at the same distance (but not in a binary system!). They have the same mass, but one is much more luminous than the other.
Which one is older?
Phys.Org News Partner Astronomy news on Phys.org
First potentially habitable Earth-sized planet confirmed: It may have liquid water
A sharp eye on Southern binary stars
Hubble image: A cross-section of the universe
howabout1337
howabout1337 is offline
#2
Oct26-13, 10:58 AM
P: 16
http://en.wikipedia.org/wiki/Stellar_age_estimation:
"As stars grow older, their luminosity increases at an appreciable rate"

So I would assume the more luminous one.
chefskitten
chefskitten is offline
#3
Oct27-13, 08:54 PM
P: 2
Thanks for your input howabout1337! That's what I was thinking, just wanted some confirmation

phinds
phinds is offline
#4
Oct27-13, 09:16 PM
PF Gold
phinds's Avatar
P: 5,677

Can Luminosity Give You a Star's Age?


I don't get it. How would you tell an old modest-sized star from a large younger star, both of which have the same luminosity?
Chronos
Chronos is offline
#5
Oct27-13, 10:46 PM
Sci Advisor
PF Gold
Chronos's Avatar
P: 9,178
The luminosity of a star is strongly dependent on mass, which is known as the mass-luminosity relationship. While the luminosity of a star does increase somewhat with age, the difference is small until it leaves the main sequence. It would be a wildly unreliable way to determine the age of a star.
Drakkith
Drakkith is offline
#6
Oct28-13, 01:35 AM
PF Gold
Drakkith's Avatar
P: 11,012
Quote Quote by phinds View Post
I don't get it. How would you tell an old modest-sized star from a large younger star, both of which have the same luminosity?
The more massive one has a different spectrum. It will be hotter, even if their luminosity is the same.
Drakkith
Drakkith is offline
#7
Oct28-13, 01:37 AM
PF Gold
Drakkith's Avatar
P: 11,012
Quote Quote by Chronos View Post
The luminosity of a star is strongly dependent on mass, which is known as the mass-luminosity relationship. While the luminosity of a star does increase somewhat with age, the difference is small until it leaves the main sequence. It would be a wildly unreliable way to determine the age of a star.
Do you know if this graph is accurate? This seems to be a pretty big change.
From here: http://en.wikipedia.org/wiki/Sun#Main_sequence

Vanadium 50
Vanadium 50 is offline
#8
Oct28-13, 08:16 PM
Mentor
Vanadium 50's Avatar
P: 15,571
It's at least approximately right. When I studied these things, the sun went off the main sequence a little sooner and more quickly (9.1 BY), but there's a factor of ~2 or so luminosity increase over the course of the main sequence.
Chronos
Chronos is offline
#9
Oct28-13, 10:00 PM
Sci Advisor
PF Gold
Chronos's Avatar
P: 9,178
When the sun first entered the main sequence, it was about 70% of its current luminosity. Over the next 4.5 billion years, it's luminosity is expected to increase by about 67%. I do not consider that enough of a luminosity difference to be useful to estimate the age of a star.


Register to reply

Related Discussions
Writing: Input Wanted Star mass/luminosity for a given HZ Science Fiction Writing 30
Help with relative star flux and luminosity Introductory Physics Homework 5
How to change a star's luminosity Astrophysics 4
Luminosity of a star Astrophysics 5
Help to determine the luminosity of a star Introductory Physics Homework 5