Re: poly: speeding up a star's burn rate

From: carl feynman <>
Date: Thu Jan 08 1998 - 12:10:46 PST

At 12:25 PM 1/7/98 -0800, you wrote:
>On Jan 7, 11:54am, carl feynman wrote:
>> For stars heavier than the Sun, the main hydogen-burning reaction is
>> catalyzed by the elements C, N, O and F. It doesn't matter which one you
>What happens in a big star without CNOF? I suddenly had this image of the
>early universe with lots of red dwarfs and Sols and nothing bigger, because
>there was no CNOF. If the big stars needed CNOF to work but had to wait 10
>billion years for Sols to make carbon and blow up and everyone else has to
>wait for the big stars to blow up themselves before there are any heavy
>elements, then that might put a more specific constraint on when life could

There's two hydrogen-burning reactions, the pp-chain and the CNOF cycle.
The pp-chain gets started at lower temperature and pressure than the CNOF
cycle, but it never gets very fast. The CNOF cycle is dominant at higher
temperatures, and increases rapidly with increasing temperature. But it's
not like the pp-chain doesn't occur in hot stars. So a big star free of
CNOF would burn much cooler than a present-day big star, but burn it would,
and eventually it would blow up, scattering its ashes to the wind.

If you've read Seven Baxter's 'Ring', the stars at the end are the
CNOF-free primordial stars.

>Tangentially, I've heard that dropping mass into a black hole gives you 50%
>conversion. How does that work?


Imagine two big masses in distant orbit about a black hole. They're in the
same orbit, but going opposite directions. One of them is a big magnet and
the other is a loop of wire, so when one of them flies past the other they
act like a generator, and the loop of wire gets a big zotz of current. Use
that electricity for something useful. The masses are slowed by their
encounters, so their orbit shrinks. Eventually their orbit becomes
tangential to the horizon of the black hole, and they silently vanish away.

It's a theorem that you can extract up to half the rest mass as energy this
way. The other half goes to making the hole bigger. Of course, if you
then drop the whole hole into a bigger hole, you can get back half of the
half you lost, etc.

>And is it more efficient to fuse hydrogen
>to iron and drop the iron than to simply drop the hydrogen?\

Yes, but only slightly. Fusion releases a puny 1% of the original mass as
energy. Maybe one is better off not worrying about building stars, etc.
Just drain the universe down black holes.

Received on Thu Jan 8 20:02:01 1998

This archive was generated by hypermail 2.1.8 : Tue Mar 07 2006 - 14:45:29 PST