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Death from across the galaxy

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  • derhexer@aol.com
    URL to an article from World Science _http://www.world-science.net/exclusives/070226_grb-life.htm_
    Message 1 of 1 , Mar 3, 2007
      URL to an article from World Science

      Interesting. I wonder if this is a plausible explanation for why we haven't
      detected evidence of life on other planet? Either it is wiped out by these
      random gamma ray and UV bursts, or it never gets started.

      First few paragraphs
      "A type of co­los­sal cos­mic ex­plo­sion could beam
      le­thal ra­di­a­tion across a ga­laxy, fry­ing any life
      forms in its path, a new anal­y­sis has found.

      The blasts are thought to oc­cur rare­ly in our Milky Way
      gal­axy, but more of­ten in those where stars are born and die more
      fre­quent­ly. These in­clude ar­eas where as­tro­no­mers
      hope to find Earth-like plan­ets ripe for life.

      In a 1995 stu­dy, Steve Thor­sett of Prince­ton
      Uni­ver­si­ty in Prince­ton, N.J. cal­cu­lat­ed that such events,
      called gam­ma-ray bursts, might wreak hav­oc on an Earth-like
      plan­et if they oc­curred near it. But sci­en­tists don’t
      ful­ly un­der­stand the ex­tent of the pos­si­ble dam­age.
      Es­pe­cial­ly un­clear is how far a burst would have to
      oc­cur to af­fect life, ac­cord­ing to the au­thors of the
      new stu­dy.

      Gamma-ray bursts are flashes of high-en­er­gy
      ra­di­a­tion found to oc­cur ran­dom­ly in space. At least some are thought
      to be as­so­ci­at­ed with ex­treme­ly mas­sive
      stars that, hav­ing burnt out, col­lapse to form black holes.

      In the new re­search, Doug­las Galante and Jor­ge
      Er­nes­to Hor­vath of the Uni­ver­si­ty of São Pa­o­lo,
      Bra­zil, ar­gued that gam­ma-ray bursts could shine their
      le­thal ef­fects across a whole gal­axy, and dam­age life over
      great­er dis­tances still. The study is to ap­pear in a
      forth­com­ing is­sue of the In­ter­na­tion­al Jour­nal of

      The bursts could cause “global en­vi­ron­men­tal changes and
      bio­spheric dam­age” even at dis­tances five times the Milky Way’
      s width, they wrote. Our Milky Way is a rel­a­tively large,
      spir­al gal­axy, about 100,000 light-years wide (a light-year is the
      dis­tance light trav­els in a year).

      Gamma-ray bursts are thought to emerge main­ly from the poles of a
      col­laps­ing star. This cre­ates two,
      op­po­site­ly-shin­ing beams of ra­di­a­tion shaped like nar­row cones.
      Plan­ets not ly­ing in these cones would be
      com­par­a­tive­ly safe; the chief wor­ry is for those that do.

      Galante and Hor­vath iden­ti­fied three as­pects of
      gam­ma-ray bursts as par­t­i­cu­lar­ly deadly.

      The first is a flash of gam­ma rays, the high­est-en­er­gy
      form of light. The flash can im­pe­r­il even the most
      ra­di­a­tion-resistant or­gan­isms known, the
      bac­te­ri­um Deinococ­cus ra­dio­du­rans, the re­search­ers
      wrote. This mi­crobe can take 3,000 times the ra­di­a­tion that
      would kill a hu­man: the as­sault shreds its ge­nome to
      hun­dreds of bits, but the har­dy bug stitches them back to­geth­er.

      Galante and Hor­vath cal­cu­lat­ed that for a plan­et
      with a thin at­mos­phere, the gam­ma flash could kill 90
      per­cent of D. ra­dio­du­rans from dis­tances up to three times our
      gal­ax­y’s width. A thick at­mos­phere would pro­tect
      the mi­crobes from this, but not nec­es­sar­i­ly from a
      sec­ond com­po­nent of the beam, ul­t­ra­vio­let
      ra­di­a­tion. Ul­t­ra­vio­let is a type of light s
      light­ly low­er in en­er­gy than gam­ma rays, but
      le­thal, large­ly be­cause it pen­e­trates DNA very

      For thick-at­mos­phere plan­ets, a gam­ma-ray burst’s
      ul­t­ra­vio­let rays would kill 90 per­cent of D.
      ra­dio­du­rans at dis­tances rang­ing from 13,000 to 62,000 light
      years, about two-thirds the ga­lac­tic width, the re­search­ers

      Life sur­viv­ing that on­slaught would have to con­tend with
      a third ef­fect, de­ple­tion of the at­mos­phere’s
      pro­tective ozone lay­er by the burst. This would kill 90 per­cent of
      D. ra­dio­du­rans at up to 40 per­cent of the dis­tance
      across the Milky Way, Ga­lante and Hor­vath es­ti­mat­ed."


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