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Fwd: Article: Circumstellar space - Where chemistry happens for the very first

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  • Roger L. Bagula
    ... wrote: Circumstellar space: Where chemistry happens for the very first time The nebula RCW49 is a nursery for newborn stars and exists in
    Message 1 of 1 , Aug 1, 2007
      --- In physical_sciences@yahoogroups.com, "Robert Karl Stonjek"
      <stonjek@...> wrote:

      Circumstellar space: Where chemistry happens for the very first time

      The nebula RCW49 is a nursery for newborn stars and exists in
      circumstellar space, where chemistry is done for the very first time.
      Credit: NASA/JPL-Caltech/E.Churchwell U. of Wisconsin

      Picture a cool place, teeming with a multitude of hot bodies twirling
      about in rapidly changing formations of singles and couples, partners
      and groups, constantly dissolving and reforming. If you were thinking
      of the dance floor in a modern nightclub, think again.

      It's a description of the shells around dying stars, the place where
      newly formed elements make compounds and life takes off, said
      Katharina Lodders, Ph.D., research associate professor of earth and
      planetary sciences in Arts & Sciences at Washington University in St.

      Chemistry for the very first time

      "The circumstellar environment is where chemistry happens for the very
      first time," said Lodders. "It's the first place a newly synthesized
      element can do chemistry. It's a supermarket of things from dust to
      gas and dust grains to molecules and atoms. The circumstellar shells
      enable a chemistry that produced grains older than our sun itself.
      It's generated some popular interest, and this year marks the 20th
      anniversary of the presolar grain discoveries."

      After the discovery of presolar diamonds in a meteorite in 1987 - the
      first stardust found in a meteorite - researchers at Washington
      University in St. Louis have been prominent in finding and analyzing
      pre-solar grains made of silicon carbide, diamonds, corundum, spinel,
      and silicates. The latest discovery - a silicate grain that formed
      around a foreign star and became incorporated into a comet in our
      solar system - was captured and returned by the STARDUST space mission
      in 2006.

      Lodders said that nucleosynthesis - the creation of atoms - takes
      place in a star's interior, made of a plasma far too hot for any
      molecular chemistry to take place. The event that enables chemistry is
      the death of a star, when elements are spewed out of the core,
      creating a shell around the star. As this circumstellar shell cools,
      the elements react to form gas molecules and solid compounds.

      A star comes of age

      Our sun and other dwarf stars of less than about ten solar masses burn
      hydrogen into helium in their cores. As they come of age, they become
      Red Giant stars and burn the helium to carbon and oxygen. But many
      heavy elements such as strontium and barium, even heavier than iron,
      are also produced, albeit in much smaller quantities than carbon. At
      the same time, the star begins to eject its outer layers into the
      interstellar medium by stellar winds, building up a circumstellar
      shell. So eventually, most of a star's mass, including the newly
      produced elements, is ejected into the interstellar medium through the
      circumstellar shell. Most interstellar grains come from such stars.

      Heavyweight stars go out more spectacularly, in violent supernovae
      such as SN2006gy, first observed late last year, which has turned out
      to be the most massive supernova ever witnessed. But no matter what,
      all stars like the sun and heavier ones like SN2006gy empty their
      elements into their circumstellar environments, where gaseous
      compounds and grains can form. From there, the gas and grains enter
      the interstellar medium and provide the material for new stars and
      solar systems to be born.

      Lodders presented a paper on circumstellar chemistry and presolar
      grains at the 233rd American Chemical Society National Meeting, held
      March 25-29 in Chicago, where a special symposium was held to track
      the evolution of the elements across space and time. A book of
      proceedings is being prepared for publication.

      Lodders said that just one percent of all known presolar grains come
      from supernovas. She said that several million stars have been
      catalogued and several thousand individual presolar grains have now
      been analyzed. "Back in the 1960s, astronomers didn't know that
      presolar grains existed in meteorites," Lodders said. "They were
      discovered when researchers were looking at meteorite samples and
      studying noble gases. They asked what is the mineral carrier of the
      noble gases."

      By separating minerals from samples of meteorites, they eventually
      found the carriers of the noble gases - presolar diamonds, graphite
      and silicon carbide -, and thus started the study of presolar grains
      20 years ago. "So the genuine, micron-size star dust survived despite
      the potential chemical and physical processing in the interstellar
      medium, during solar system formation, and in the meteorite's parent
      asteroid," she said. "Since the star dust preserved in meteorites must
      have been already present before the solar system and the meteorites
      formed, researchers call this star dust presolar grains".

      "Laboratory astronomy of stardust has revealed much about stellar
      element and isotope production, and about gas and dust formation
      conditions in giant stars and supernovae."

      Source: Washington University in St. Louis

      Posted by
      Robert Karl Stonjek

      --- End forwarded message ---
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