Star runs out of hydrogen, then ...?

Question

When the core of a star runs out of hydrogen, the star contracts (due to a decrease in the core temperature) and this causes the core to heat up again and start fusing helium. Why doesn't the He start fusing smoothly as the H runs out? Why the bounce / oscillation?

Answer 1

Helium needs a lot more heat to start fusion than hydrogen does. So the core has to heat up (and the only way for a star to heat up is from gravitational contraction).

Answer 2

While the star burns hydrogen, it is not hot enough at the core to burn helium. But when the hyrdogen runs out and the star collapses, the pressure and temperature at the core increases, and only until then can the helium begin to fuse into heavier elements, like carbon.

Answer 3

The helium will fuse smoothly for a while, then when it runs out, the helium will be fused into oxygen and carbon, which will in turn be fused into sodium, sulphur, silicon, magnesium, neon and then these will be turned into iron, calcium, nickel, chromium, copper etc. and other heavy elements. These will then be spewed into space together with the outer layer, causing the star to become unstable and collapse on itself.

Answer 4

Because at that pressure and temperature there is not enough energy to fuse helium until it collapses a bit more and gets hotter and more dense. Once it collapses a bit, it is then able to fuse helium into carbon.

Answer 5

it may be. until of direction, the reason of hydrogen present isn't because of what we understand. Hydrogen being the 1st element to style, because of fact many sub atomic types got here mutually to make it, then what appropriate to the sub atomic structures? the place did they arrive from? If we are able to appreciate how hydrogen got here into existence? then in step with danger this is consistently being created without us understanding? no longer in stars, yet interior the vacuum it is self? that should mean that no hydrogen could be exhausted to 0. that should mean the universe could stay around perpetually and in no way bypass dark. Black holes, of direction, recycling remember to potential...and then potential being converted back into the sub atomics and hydrogen.... A perpetually cycle........ sounds good to me......

Answer 6

You just missed a show on The History Channel called The Universe. Look it up in your TV directory. Friday's show talked about the life of a star and explained everything from beginning to end. Look up the program for a listing and possible repeat showing. Check here.
http://www.history.com/minisite.do?content_type=mini_home&mini_id=54036

Answer 7

Think about it how much more heat it takes to fuse Helium. You can't be serious asking this question.

Answer 8

Well....... It actually does take a few hundred years to happen (during which time the star is highly unstable). But that's a -very- quick blink in the overall scheme of things.

Doug

Answer 9

you need a second element for the molecules to bind to cause a fusion