Death from across the galaxy
- 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
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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