Throwback Thursday: How Fast Do Stars Run Out Of Fuel? (Synopsis)

“Man loves company — even if it is only that of a small burning candle.” -Georg C. Lichtenberg

The Sun, like all stars initially, burns hydrogen fuel into helium through the process of nuclear fusion. But as the Sun ages, as do all stars over a certain mass, it starts burning those heavier elements in its core, going through different phases of its life cycle and eventually ending in a planetary nebula/white dwarf combination.

Image credit: NASA, W. Sparks (STScI) and R. Sahai (JPL). Image credit: NASA, W. Sparks (STScI) and R. Sahai (JPL).

But are these transitions sharp or gradual, and what of even more massive stars that start burning carbon, oxygen, silicon and so on? What do the different phases in a star's life cycle really look like, and how does the transition work at every stage?

Image credit: S&T: Casey Reed / Source: J. Hester & others. Image credit: S&T: Casey Reed / Source: J. Hester & others.

The answers are right here for you on today's Throwback Thursday!

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Do we know any star which is converting O->Si?

By Piyush Gupta (not verified) on 16 Jul 2015 #permalink

Ethan, is there any way short of being able to measure the energy spectrum of neutrinos that we could diagnose how far along the sequence a massive giant star is? Or will we be forever uncertain and continue to have to say, Giant star XXX, could supernova .1second from now -or maybe not for a million years?

I could think of some milestones marking a star like the sun reaching middle age, here are a few:
(1) When the hydrogen fraction at the center reaches half of what it started out as.
(2) When the (fusion) energy production rate at the center drops below the rate further out*, (i.e. its starting to transition to shell burning.
(3) When the cumulative energy released from fusion is half the total for the stars entire lifespan.
Would you happen to know when these milestones will be crossed for the sun?

*Because too little hydrogen is left.

By Omega Centauri (not verified) on 16 Jul 2015 #permalink

How long until "wow" starts an argument over something on this thread?

By Wow caller (not verified) on 17 Jul 2015 #permalink

How long till trolls stop trying to derail conversations with argumentative claims?

Never, I reckon.

You should know.

By Ragtag Media (not verified) on 17 Jul 2015 #permalink

I know lots, Raggie.

What, specifically, do you want to know?

Which came first the chicken or the egg?

By Ragtag Media (not verified) on 17 Jul 2015 #permalink

If the star is fusing silicon into iron for only one day, how long does the degenerate iron core exist?

Normally much less time than it takes to fall in at the local gravitational speed.

There's little keeping the star up when it turns to iron.