New Class of Stars Are Totally Metal, Says Astrophysicist 119
KentuckyFC writes Stars form when clouds of gas and dust collapse under their own gravity, generating enough heat and pressure to fuse the atoms inside them together. When this cloud of dust and gas is the remnants of a supernova, it can contain all kinds of heavy elements in addition to primordial hydrogen, helium and lithium. Now one astrophysicist has calculated that a recently discovered phenomenon of turbulence, called preferential concentration, can profoundly alter star formation. He points out that turbulence is essentially vortices rotating on many scales of time and space. On certain scales, the inertial forces these eddies create can push heavy particles into the calmer space between the vortices, thereby increasing their concentration. In giant clouds of interstellar gas, this concentrates heavy elements, increasing their gravitational field, attracting more mass and so on. The result is the formation of a star that is made entirely of heavy elements rather than primordial ones. Astrophysicists call the amount of heavy elements in a star its "metallicity". Including preferential concentration in the standard model of star formation leads to the prediction that 1 in 10,000 stars should be totally metal. Now the race is on to find the first of this new class of entirely metal stars.
One slight problem with that ratio... (Score:5, Interesting)
Hydrogen main sequence stars burn for a a few million years (for the class O supergiants) to literally trillions of years (for the class M all-but-failures). Helium burning, in a star with sufficient mass, lasts between a few hundred thousand to a few dozen million years.
The subject of TFA starts after helium burning normally finishes - Next on a typical star comes carbon, lasting for only a few hundred years; Then comes neon lasting for a single year, oxygen at half a year, and silicon finishes its run in a single day.
So whether or not a star begins life with a high concentration of trans-lithium metals, it will have a very, very short lifetime; That one-in-ten-thousand creation ratio therefore reduces to more like one-in-a-trillion among those stars still shining in our nighttime sky.
We have yet to find a star with this spectrum (Score:4, Interesting)
And we have been studying stellar spectra for a century now. The must be much rarer than 1 in 10,000 or we would have already found one. They must be exceedingly rare.
Re:We have yet to find a star with this spectrum (Score:2, Interesting)
How would you spot them? The stellar spectra you mention are visible because of all the energy that a non-metallic star can generate through fusion. But metal stars don't have that energy available. They'll be dim, which affects the distance at which we can spot them. The lack of light also complicates our ability to determine their spectra. So the fraction of metal stars amongst the stars with a known spectrum will be even lower than that 1:10000.