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Space Science

New Class of Stars Are Totally Metal, Says Astrophysicist 119

Posted by samzenpus
from the hit-the-lights dept.
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.
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New Class of Stars Are Totally Metal, Says Astrophysicist

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  • by jcochran (309950) on Thursday July 03, 2014 @07:12PM (#47380471)

    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? (Score:5, Informative)

    by Zcar (756484) on Thursday July 03, 2014 @07:59PM (#47380697)

    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.

  • by dltaylor (7510) on Thursday July 03, 2014 @08:42PM (#47380863)

    Helium is not!

    If you read the article, however, it would point out that astronomers use a skewed definition of "metal", as any element heavier than lithium.

    At birth, stars contain little helium, but is is constantly generated by fusing hydrogen.

    If you start with metals like sodium and potassium, plus what we normally call non-metals, like carbon and oxygen, then you won't get around to generating helium until you fuze something radioactive that emits an alpha particle.

  • by kenwd0elq (985465) <kenwd0elq@gmail.com> on Thursday July 03, 2014 @08:44PM (#47380867)

    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.

  • by kenwd0elq (985465) <kenwd0elq@gmail.com> on Thursday July 03, 2014 @08:55PM (#47380913)

    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.

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