First Generation Stars

When the universe began 13.7 billion years ago, the only hydrogen and helium plus a tiny smattering of lithium existed. All other elements, like carbon, nitrogen, oxygen, gold, platinum, all the stuff we and our planet are made of, was created in the nuclear furnaces that power stars.

A star forms when gravity causes a cloud of gas to collapse until the central region is dense enough to support that nuclear fusion which converts hydrogen and helium into other elements. To do that, the cloud must shed heat or the thermal pressure halts the collapse. Hydrogen and helium can’t lose heat very efficiently, so the very first stars had to be huge, with a gravitational pull strong to overpower the thermal pressure. Those first stars were 200 to 400 times the size of our sun.

Huge stars live very short lives, and after only a few million years at best, these stars explode in supernova explosions more powerful than anything this side of the Big Bang. The heavier elements created then blast into space to help form the second generation of stars. Heavier elements shed thermal heat at a higher efficiency, so second generation can be small, even smaller than our sun.

Astronomers have looked for stars as close as possible to that first generation of giant stars. They judge closeness to first generation by the amount of elements heavier than helium, “metals” to astronomers.

A team of astronomers from Johns Hopkins University recently announced the discovery of a star with the lowest known amount of heavy elements of any known star. The star is 13.5 billion years old, and may well be a second generation star. Lead author, Dr. Kevin Schlaufman, commented “The discovery of this star means more stars with very low mass and very low metal content are likely out there – perhaps even the universe’s very first stars.”

The next big step would be discovering a star containing nothing but hydrogen and helium, a first generation star.

On the first Tuesday of each month, I write an astronomy-related column piece for the Oklahoman newspaper. On the following day, I post that same column to my blog page.

This is reprinted by permission form the Oklahoman and www.newsok.com.