<p>You can estimate the main sequence life of a star by an <a href="https://www.maplesoft.com/applications/view.aspx?SID=154326&amp;view=html" rel="nofollow noreferrer">approximate formula</a></p>
<p><span class="math-container">$$ \frac{\text{Mass}}{\text{Luminosity}}×10^{10}\text{years}$$</span></p>
<p>Where the mass and luminosity are both in solar units.</p>
<p>so for Alp-Cen A you get <span class="math-container">$7.2×10^9$</span> or about 1.7 billion years left. For Alp-Cen-B you get <span class="math-container">$1.8×10^{10}$</span> or about 12 billion years left.</p>
<p>The Red Giant phase will then last about a billion years. It will first build up an inert Helium core, then experience a &quot;Helium flash&quot; followed by an &quot;asymptotic-giant&quot; stage, with an inert carbon-oxygen core, and shells of helium burning, and hydrogen burning.</p>

CC BY-SA 4.0
2021-08-16T13:54:43.773Z
α Cen B currently has a mass of $0.907M_\odot$, and is expected to lose $\sim 0.3 M_\odot$ before a possible helium flash, putting it above the $0.5 M_\odot$ threshold for helium fusion.
WarpPrime
CC BY-SA 4.0
2021-08-16T14:00:19.567Z
Right, I was getting luminosity and mass confused in my brain
James K
CC BY-SA 4.0
2021-09-15T20:53:12.230Z
So Alpha Centauri A will become a red giant a few billion years before the Sun does. Of course, the Earth will be uninhabitable well before 1.7 billion years.
PM 2Ring
CC BY-SA 4.0
2021-09-21T07:33:34.757Z
Note that the Sun will not be a red giant for another 7 and a bit billion years.
ProfRob
CC BY-SA 4.0
2021-08-16T10:06:22.373Z
2021-08-16T13:59:50.600Z
2021-08-16T13:59:50.600Z
James K
<p>According to <a href="https://en.wikipedia.org/wiki/Alpha_Centauri" rel="nofollow noreferrer">Wikipedia</a>:</p>
<p>Alpha Centauri A: <span class="math-container">$M=1.100 M_\odot$</span> and <span class="math-container">$L = 1.519 L_\odot$</span></p>
<p>Alpha Centauri B: <span class="math-container">$M=0.907M_\odot$</span> and <span class="math-container">$L=0.5002L_\odot$</span></p>
<p>They are 5-6 billion years old (you can assume they are 5.5 billion years old). How long will they live?</p>
<p>It would be good if you could also give some dates about the red giant phase, thanks.</p>

<stellar-evolution><star-systems>
how much time do Alpha Centauri A and B have?
green_the_planet
# how much time do Alpha Centauri A and B have?

(Asked by: username_0 on 2021-08-16)

According to [Wikipedia](https://en.wikipedia.org/wiki/Alpha_Centauri):

Alpha Centauri A: $M=1.100 M\_\odot$ and $L = 1.519 L\_\odot$

Alpha Centauri B: $M=0.907M\_\odot$ and $L=0.5002L\_\odot$

They are 5-6 billion years old (you can assume they are 5.5 billion years old). How long will they live?

It would be good if you could also give some dates about the red giant phase, thanks.

**Tags:** stellar-evolution, star-systems


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## 1 answers

### Answer by username_1 on 2021-08-16. Score: 2

You can estimate the main sequence life of a star by an [approximate formula](https://www.maplesoft.com/applications/view.aspx?SID=154326&view=html)

$$ \frac{\text{Mass}}{\text{Luminosity}}×10^{10}\text{years}$$

Where the mass and luminosity are both in solar units.

so for Alp-Cen A you get $7.2×10^9$ or about 1.7 billion years left. For Alp-Cen-B you get $1.8×10^{10}$ or about 12 billion years left.

The Red Giant phase will then last about a billion years. It will first build up an inert Helium core, then experience a "Helium flash" followed by an "asymptotic-giant" stage, with an inert carbon-oxygen core, and shells of helium burning, and hydrogen burning.

> **Comments:**
> **username_2**: α Cen B currently has a mass of $0.907M_\odot$, and is expected to lose $\sim 0.3 M_\odot$ before a possible helium flash, putting it above the $0.5 M_\odot$ threshold for helium fusion.  
> **username_1**: Right, I was getting luminosity and mass confused in my brain  
> **username_3**: So Alpha Centauri A will become a red giant a few billion years before the Sun does. Of course, the Earth will be uninhabitable well before 1.7 billion years.  
> **username_4**: Note that the Sun will not be a red giant for another 7 and a bit billion years.  

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