Age of stars is pinned to their spin | Hacker News Reader

Age of stars is pinned to their spin

bbc.co.uk

26 pointssjcsjc9 comments

> Astronomers use sun spots, travelling across the surface, and these only dim its brightness by much less than 1%.

How do they know they are sun spots and not a very small planets? I'd assume planets have a more regular schedule, but unless you watch a star for years (Julian), how can you tell?

Where does the angular momentum in a star go?

To orbiting planets? If so, I wonder if they can use that 10% error to infer things about the planets orbiting that star.

Stars eject their outer atmosphere into space during their lifetime.

Consider that the visible surface of our sun isn't actually it's surface, it's just the point that the temperature is low enough that electrons can bind to protons, yielding hydrogen gas that is transparent to light. Underneath the photosphere, the charged particles are dissociated; photons scatter off of them.

Outside the photosphere there is still lots of hydrogen gas.

The outermost boundary of the sun is regarded by astronomers as the heliopause. It's the point at which the solar wind as deflected by the flow of interstellar gas. Voyager 1 crossed into the heliopause a few years ago - it's way beyond the orbit of pluto.

The most obvious candidate is http://en.wikipedia.org/wiki/Magnetic_braking.

Good question, I wonder where their angular momentum comes in the first place

The same method that cause water in a drain to swirl. A star is a gravity well, like a hole, where particles fall into. A randomly variable number of particles are hitting each side -- the side that gets more particles sets the spin in motion, which in turn gives influence to the rest of the particles falling in, accelerating spin.

It's also conservation of angular momentum--- a very slow spin that's spread out will become much faster when it's pulled tightly in. You can watch ice skaters do the same thing--- moving their limbs in or out to speed up or slow down their rotation.

I'd bet that the 10% error isn't unknown variation of the stars' rotation, rather it's error in our equipment and observations.

There are a very few candidate population 3/population 2.5-ish stars that have been discovered in past years, classification based on extremely low metallicity. It would be interesting to see what the spin methodology has to say about their ages.

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