<p>There are several causes for mass loss.</p>

<p>One is transformation of mass into energy by means of nuclear fusion, and the energy is radiated away.</p>

<p>But the big one is stellar winds: particles ejected from the star surface.</p>

CC BY-SA 3.0
2014-04-23T13:20:07.387Z
Thanks for the answer. I think that transformation of mass into energy does not play a big role, as you said. I tried to estimate: Regarding to HS-diagram and mass-luminosity, the sun must lose 8.66 e29 kg of it's mass during upcoming 9 e10 years, but if the sun keeps radiating energy with current rate (in fact this rate will decrease by time, but we ignored that) the sun will lose only 1.22 e28 kg during this time (E=mc^2). This is less than 1.5% of all lost mass. Therefore, stellar winds are the main cause of mass loss. However I'm still looking for more answers and ideas.
Mostafa Farzán
CC BY-SA 3.0
2014-04-23T14:34:29.257Z
Hi again. I'm sorry but I'm not satisfied. The sun must lose 8.66 e29 kg during upcoming 9 e10 years (see my last comment). But in the [Solar Wind page of Wikipedia](http://en.wikipedia.org/wiki/Solar_wind#cite_ref-20), I've found this: "the total mass loss each year is about (2–3)×10 e−14 solar masses" which means only 5.35 e27 kg during this time (considering 3 e-14 solar masses each year). This amount of mass is less than 0.7% of total mass loss. What's wrong? My estimation? Or the Wikipedia data? Or maybe these are right, and there's some else mass ejection way for stars?
Mostafa Farzán
CC BY-SA 3.0
2014-04-23T12:33:01.837Z
2014-04-23T12:33:01.837Z
Envite
<p>There is an alternative interpretation: Massive stars burn their fuel much faster than tiny ones. Hence massive stars are short-lived in comparison to tiny stars.</p>

<p>The <a href="http://www.astro.umd.edu/~ssm/ASTR100/lecture20.pdf" rel="noreferrer">lifetime of a star</a> is proportional to about the inverse of the cube of its mass.
The Sun's lifetime is about $10^{10}$ years, hence for stars with 10 solar masses the lifetime is about $10^7$ years, and for stars with 0.1 solar masses it's about $10^{13}$ years.</p>

<p>But stars also loose mass, e.g. by <a href="http://en.wikipedia.org/wiki/Solar_wind" rel="noreferrer">stellar wind</a> and <a href="http://en.wikipedia.org/wiki/Coronal_mass_ejection" rel="noreferrer">coronal mass ejections</a>. Heavy stars may <a href="http://www.astro.ru.nl/~onnop/education/stev_utrecht_notes/chapter12-13.pdf" rel="noreferrer">loose mass</a> (parts of their envelope) e.g. by <a href="http://en.wikipedia.org/wiki/Variable_star#Eruptive_variable_stars" rel="noreferrer">pulsation</a> or <a href="http://en.wikipedia.org/wiki/Radiation_pressure" rel="noreferrer">radiation pressure</a> during their <a href="http://en.wikipedia.org/wiki/Red_giant" rel="noreferrer">red giant</a> or their <a href="http://en.wikipedia.org/wiki/Wolf%E2%80%93Rayet_star" rel="noreferrer">Wolf-Rayet</a> phases, before they explode as a supernova.</p>

CC BY-SA 3.0
2017-06-12T11:19:31.570Z
Oh I see... I confused average life-time with age.
Mostafa Farzán
CC BY-SA 3.0
2018-01-06T21:54:31.543Z
@MostafaFarzán I suspect the term "Main Sequence" is partly responsible for this confusion, in that it is [not a time sequence](https://astronomy.stackexchange.com/q/11082/71). So an individual star is not necessarily more luminous when it's young than when that same star is old.
Bob Stein
CC BY-SA 3.0
2014-04-23T23:04:28.460Z
2014-04-23T23:04:28.460Z
Gerald
<p>I think that the title is completely clear, but here's an expansion:</p>

<p>I was just reading about <a href="http://en.wikipedia.org/wiki/Mass%E2%80%93luminosity_relation" rel="nofollow">Mass-luminosity relation</a> that says <strong>massive stars are more luminous than tiny ones</strong>. Well, let's talk about main-sequence stars for now. This relation becomes interesting when it's mixed with the <a href="http://en.wikipedia.org/wiki/Hertzsprung%E2%80%93Russell_diagram" rel="nofollow">Hertzsprung-Russel diagram</a> that says <strong>young stars are more luminous than older ones</strong> (Originally says that <em>hotter</em> stars are more luminous and we know that hotter stars are younger).</p>

<p>So mixing these two relations produces some kind of <em>Mass-age relation</em> which says <strong>young stars are more massive</strong>, that is a star loses its mass over time, right? (Please tell me if I'm going wrong)</p>

<p>If this Mass-age relation is right, how do stars lose this extra mass during their evolution? And where does this stray matter go?</p>

CC BY-SA 3.0
2015-05-26T17:39:47.413Z
Where do you get from the HR diagram that "hotter stars are younger"? All stars in the MS have the same age. What varies is their mass and radius, see http://ia.terc.edu/images/mod_05/H-R%20Diagram.jpg (@RobJeffries I believe he meant a 'HR' diagram, ie: a Hertzsprung-Russel diagram)
Gabriel
CC BY-SA 3.0
2015-05-26T19:29:27.847Z
@Gabriel *On average* hotter stars on the main sequence *are* younger. All stars on the MS certainly do *not* have the same age.
ProfRob
CC BY-SA 3.0
2015-05-26T19:36:53.617Z
@RobJeffries would you mind explaining what you mean? References would be great. A star is called a *MS star* when it begins to fuse H into He, are you talking about the time spent as pre-MS stars?
Gabriel
CC BY-SA 3.0
2015-05-26T20:26:08.643Z
@Gabriel, Gerald's answer explains. For a uniform star formation rate then a bunch of main sequence B stars would have an average age of about 100 million years. A random bunch of main sequence G stars would have an average age of about 5 billion years.
ProfRob
CC BY-SA 3.0
2015-05-26T20:30:54.507Z
Better to say that more massive main sequence stars cannot be very old, so their *average* age is younger.
ProfRob
CC BY-SA 3.0
2015-05-26T20:33:56.927Z
@RobJeffries not following you and I don't see how Gerald's answer explains your statement. Massive stars will stay less time _on the MS_ but that's not the issue here. We are talking about MS stars _exclusively_, meaning (to my knowledge) that they will all have the same age. Care to expand on your cmmts a bit?
Gabriel
CC BY-SA 3.0
2015-05-26T20:37:24.160Z
@Gabriel A random set of MS stars have ages between almost zero and their maximum age as MS stars. This latter is much less for massive stars, so a random set of high mass MS stars will be younger than a random set of low mass MS stars. I can't be any clearer. End of discussion.
ProfRob
CC BY-SA 3.0
2015-05-26T20:49:27.793Z
@RobJeffries I see the confusion now. I'm talking about MS stars belonging to _the same_ stellar formation event; you are talking about random MS stars.
Gabriel
CC BY-SA 3.0
2015-05-26T23:39:06.633Z
@Gabriel That's the first indication I see that you are interested in stars belonging to the same "formation event".  It's hard to even know stars are from the same event, since they don't tend to stick around each other on long time scales.  We've basically no idea which of the stars in our galaxy were formed with our sun.
zibadawa timmy
CC BY-SA 3.0
2015-05-26T23:42:25.767Z
@zibadawatimmy I'm not the user who made the question.
Gabriel
CC BY-SA 3.0
2015-05-26T23:54:30.767Z
@Gabriel That was the first specification of "same formation event" by any user at any point that I can see.  Did an earlier version of the OP suggest restricting it to such a collection of stars?  I otherwise don't see why you would restrict it to the same formation event.  Perhaps there are some things we need the OP to clarify?
zibadawa timmy
<star><mass><stellar-evolution>
Putting mass-luminosity relation and Hertzsprung-Russel diagrams together leads us to a mass-age relation; so how do stars lose their mass over time?
Mostafa Farzán
# Putting mass-luminosity relation and Hertzsprung-Russel diagrams together leads us to a mass-age relation; so how do stars lose their mass over time?

(Asked by: username_0 on 2014-04-23)

I think that the title is completely clear, but here's an expansion:

I was just reading about [Mass-luminosity relation](http://en.wikipedia.org/wiki/Mass%E2%80%93luminosity_relation) that says **massive stars are more luminous than tiny ones**. Well, let's talk about main-sequence stars for now. This relation becomes interesting when it's mixed with the [Hertzsprung-Russel diagram](http://en.wikipedia.org/wiki/Hertzsprung%E2%80%93Russell_diagram) that says **young stars are more luminous than older ones** (Originally says that *hotter* stars are more luminous and we know that hotter stars are younger).

So mixing these two relations produces some kind of *Mass-age relation* which says **young stars are more massive**, that is a star loses its mass over time, right? (Please tell me if I'm going wrong)

If this Mass-age relation is right, how do stars lose this extra mass during their evolution? And where does this stray matter go?

**Tags:** star, mass, stellar-evolution
> **Comments:**
> **username_1**: Where do you get from the HR diagram that "hotter stars are younger"? All stars in the MS have the same age. What varies is their mass and radius, see http://ia.terc.edu/images/mod_05/H-R%20Diagram.jpg (@RobJeffries I believe he meant a 'HR' diagram, ie: a Hertzsprung-Russel diagram)  
> **username_2**: @Gabriel *On average* hotter stars on the main sequence *are* younger. All stars on the MS certainly do *not* have the same age.  
> **username_1**: @RobJeffries would you mind explaining what you mean? References would be great. A star is called a *MS star* when it begins to fuse H into He, are you talking about the time spent as pre-MS stars?  
> **username_2**: @Gabriel, Gerald's answer explains. For a uniform star formation rate then a bunch of main sequence B stars would have an average age of about 100 million years. A random bunch of main sequence G stars would have an average age of about 5 billion years.  
> **username_2**: Better to say that more massive main sequence stars cannot be very old, so their *average* age is younger.  
> **username_1**: @RobJeffries not following you and I don't see how Gerald's answer explains your statement. Massive stars will stay less time _on the MS_ but that's not the issue here. We are talking about MS stars _exclusively_, meaning (to my knowledge) that they will all have the same age. Care to expand on your cmmts a bit?  
> **username_2**: @Gabriel A random set of MS stars have ages between almost zero and their maximum age as MS stars. This latter is much less for massive stars, so a random set of high mass MS stars will be younger than a random set of low mass MS stars. I can't be any clearer. End of discussion.  
> **username_1**: @RobJeffries I see the confusion now. I'm talking about MS stars belonging to _the same_ stellar formation event; you are talking about random MS stars.  
> **username_3**: @Gabriel That's the first indication I see that you are interested in stars belonging to the same "formation event".  It's hard to even know stars are from the same event, since they don't tend to stick around each other on long time scales.  We've basically no idea which of the stars in our galaxy were formed with our sun.  
> **username_1**: @zibadawatimmy I'm not the user who made the question.  
> **username_3**: @Gabriel That was the first specification of "same formation event" by any user at any point that I can see.  Did an earlier version of the OP suggest restricting it to such a collection of stars?  I otherwise don't see why you would restrict it to the same formation event.  Perhaps there are some things we need the OP to clarify?  

---

## 2 answers

### Answer by username_5 on 2014-04-23. Score: 5 | Accepted answer

There is an alternative interpretation: Massive stars burn their fuel much faster than tiny ones. Hence massive stars are short-lived in comparison to tiny stars.

The [lifetime of a star](http://www.astro.umd.edu/~ssm/ASTR100/lecture20.pdf) is proportional to about the inverse of the cube of its mass.
The Sun's lifetime is about $10^{10}$ years, hence for stars with 10 solar masses the lifetime is about $10^7$ years, and for stars with 0.1 solar masses it's about $10^{13}$ years.

But stars also loose mass, e.g. by [stellar wind](http://en.wikipedia.org/wiki/Solar_wind) and [coronal mass ejections](http://en.wikipedia.org/wiki/Coronal_mass_ejection). Heavy stars may [loose mass](http://www.astro.ru.nl/~onnop/education/stev_utrecht_notes/chapter12-13.pdf) (parts of their envelope) e.g. by [pulsation](http://en.wikipedia.org/wiki/Variable_star#Eruptive_variable_stars) or [radiation pressure](http://en.wikipedia.org/wiki/Radiation_pressure) during their [red giant](http://en.wikipedia.org/wiki/Red_giant) or their [Wolf-Rayet](http://en.wikipedia.org/wiki/Wolf%E2%80%93Rayet_star) phases, before they explode as a supernova.

> **Comments:**
> **username_0**: Oh I see... I confused average life-time with age.  
> **username_6**: @MostafaFarzán I suspect the term "Main Sequence" is partly responsible for this confusion, in that it is [not a time sequence](https://astronomy.stackexchange.com/q/11082/71). So an individual star is not necessarily more luminous when it's young than when that same star is old.  

---

### Answer by username_4 on 2014-04-23. Score: 1

There are several causes for mass loss.

One is transformation of mass into energy by means of nuclear fusion, and the energy is radiated away.

But the big one is stellar winds: particles ejected from the star surface.

> **Comments:**
> **username_0**: Thanks for the answer. I think that transformation of mass into energy does not play a big role, as you said. I tried to estimate: Regarding to HS-diagram and mass-luminosity, the sun must lose 8.66 e29 kg of it's mass during upcoming 9 e10 years, but if the sun keeps radiating energy with current rate (in fact this rate will decrease by time, but we ignored that) the sun will lose only 1.22 e28 kg during this time (E=mc^2). This is less than 1.5% of all lost mass. Therefore, stellar winds are the main cause of mass loss. However I'm still looking for more answers and ideas.  
> **username_0**: Hi again. I'm sorry but I'm not satisfied. The sun must lose 8.66 e29 kg during upcoming 9 e10 years (see my last comment). But in the [Solar Wind page of Wikipedia](http://en.wikipedia.org/wiki/Solar_wind#cite_ref-20), I've found this: "the total mass loss each year is about (2–3)×10 e−14 solar masses" which means only 5.35 e27 kg during this time (considering 3 e-14 solar masses each year). This amount of mass is less than 0.7% of total mass loss. What's wrong? My estimation? Or the Wikipedia data? Or maybe these are right, and there's some else mass ejection way for stars?  

---

