New Class of Stars Are Totally Metal, Says Astrophysicist

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.

Comments

Look in Decibel Magazine

[Anonymous Coward]

or Kerrang! They're full of metal stars

We have a name for these already...

[Guano_Jim]

... they're called Class \m/ stars.

Re:Made of Led?

[TarPitt]

name it Ozzy

One slight problem with that ratio...

[pla]

Let's take TFA at face value, and assume one in 10k stars start their evolution as count as "metallic" stars.

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.

Re:One slight problem with that ratio...

[ArcadeMan]

You're right, heavy metal stars usually have short lifespans.

Re:One slight problem with that ratio...

[kenwd0elq]

Fusion of hydrogen into helium produces a LOT of energy. Fusion of helium into carbon produces less. In physics terms, it's the "packing fraction" curve, which can show you what energy you'd get out if you fuse elements together.

Iron is at the bottom of the packing fraction curve; when you fuse other stuff into iron, you're getting out the dregs of the fusion energy, partly because it takes higher and higher pressures and temperatures for fusion to occur for heavier elements.

When you get to the pressure and temperature points where iron fuses into still heavier elements, it begins to EXTRACT energy - from the core of the star. Stars exist in a delicate balance between the heat and pressure that tries to blow them apart, and the gravity that tries to crush them together. Take heat OUT of the core of the star, and there's less internal pressure - and gravity starts to win. The core will collapse, generally abruptly, and a crushing "rebound effect" will accelerate the heavy fusion, extracting MORE energy, leading to a core collapse supernova. The star explodes, leaving a black hole or pulsar at the center and blasting a lot of the stellar material back into space.

Which is where we got the iron for our blood, or the gold for our jewelry - blasted out of a supernova. Probably MANY of them.

Re:Star?

[MightyMartian]

Stellar fusion can occur with atomic elements up to iron. There are a number of metals that are lighter than iron. If I'm reading this right, stellar fusion could conceivably be triggered by heavier metallic elements if they were "selected for" by the properties of vortices during the formation process.

Using a different definition of "metal"

[jcochran]

What astronomers mean for the word "metal" isn't what the rest of us mean.

As mentioned in the link to Metallicity, the all metal stars could be composed of carbon, nitrogen, oxygen, etc. Basically anything other than hydrogen and helium.

Re:Star?

[Zcar]

Additionally, in astrophysics the term "metal" includes many elements which are not metals in any other field. Astrophysically, metals are any element other than hydrogen or helium, so in addition to ordinary metals like sodium and lithium non-metallic elements such as carbon and oxygen are counted as metals.

Not the Usual Definition of Metal

[kenwd0elq]

In astrophysics, the term "metal" normally applies to any element heavier than lithium. Carbon, silicon, even gasses like oxygen and nitrogen, are "metals". We're not talking about star remnants that are primarily iron or lead or uranium. Gold would be right out.