Why Isn't There More Helium than Hydrogen in the Universe?

Eventually there will, but not enough time has passed for converting most hydrogen IN STARS (it also exists elsewhere, e.g. cold molecular clouds) to helium.

Two parts:

1) There is more hydrogen than helium because the universe is still pretty young. Not much hydrogen has been used yet.

2) Stars are almost entirely hydrogen. Eventhough we say that they die when they run out of hydrogen for fuel, this is a little misleading. They actually die out when there is insufficient hydrogen density for sustained nuclear fusion. This occurs when stars are still about 90% hydrogen and 9.9% helium. At this point the star will cool off and die, or go nova.

If you figure that a star lives about 10 billion years on average, and that each cycle reduces the hydrogen by 10% or so, you can estimate it will take about 70billion years before 50% of the hydrogen in the universe is transformed in to helium. The universe is only about 14 billion years old, so we have a long way to go.

The universe isn't old enough for all of the hydrogen to have been fused into helium yet. Or even a substantial amount to sway the numbers in favor of haevier elements.

Keep in mind, most of the stars in the universe are red dwarfs, which use up their fuel much slower than the more massive stars. The first red dwarfs to form are likely still around, 13 billion years after they formed, while stars as massive as our Sun only fuse hydrogen for 10 billion years... and supergiants use it up even faster than that.

Sure, at some point in time, a few hundred quadrillion years from now, there may be less hydrogen than helium in the universe, but remember, stars fuse heavier elements during the later stages of their lives too.

At some point in time, perhaps 10^100,000 years from now, there will be so little fusable atoms in t he universe that star formation will slow down and become rare, possibly stop altogehter.

The simplest answer is: there will be, but enough time hasn't passed yet.

The simplest answer to your second: They don't, which is why they die.

The more direct answer would be that it just takes longer than we observe the universe to have existed to burn through so much hydrogen, converting it to Helium, then heavier elements. That's another thing: everything up to (probably) iron is fused into heavier elements, so you don't just have a start that stops at helium and burns out.

If you imagine a 1st generation star, meaning that it formed from the original hydrogen clouds early on, as it fuses heavier elements it gets less energy for its buck, until it either collapses under its own gravitational pull, or simply dies out and sheds its large gas envelope (what The Sun will do) leaving a White Dwarf (cooling through brown to black).

In the latter case, you have that gas envelope which mixes with interstellar hydrogen, and over a LOOOONG time another collapse event occurs and ignites a new start with "bits" of the old in there. It's NOT recycling fuel for the most part, although there is some leftover hydrogen. In fact, as time goes on stars have less light elements to fuse, and that would mean that given time and many generations of supernovae or other "deaths" you won't heve enough H, or He (or anything light) to form a star at all.

Once again, that is FAR in the future, and beyond that you probably have everything ending up in black holes until THEY radiate (a trillion+ years) Hawking Radiation and the universe suffers what is called, "heat death".

The free helium in the universe is not a result of fusion inside stars, it's a result of fusion occuring everywhere in the universe when it was once as hot and dense as the inside of a star. As the universe expanded and cooled, hydrogen stopped fusing into helium.

Big stars burn faster and die quickly, but use very little of their fuel before exploding. This is because big stars have very tiny inner cores compared to small stars, in proportion to their diameters, so when the fuel is exhausted in the inner core, BOOM, yet the outer core and every level above is 90% hydrogen or more.

Only red dwarf stars will burn ALL the available fuel, but each one will take trillions of years to do so. We have a long wait.

In addition to the other answers you got, most stars never burn all their hydrogen. With the sun for example, the outer layers will never get hot enough to fuse the hydrogen into anything else. If the sun eventually forms a planetary nebula, most of that out layer of unused hydrogen will get "puffed off" into space.

The supply of hydrogen is still quite immense out there, much of it hiding as "dark matter". While a star consumes a lot of hydrogen, fusing into helium, the supply of hydrogen gas in space is still quite enormous. No matter how "sparse" you may think space is, it is also very, very expansive.

If you read the article referred to, you my get a better understanding.

www.newtonphysics.on.ca/hydrogen/index.html