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Transcript
The Danger of Deadly Cosmic Explosions
Supernovae and Gamma Ray Bursts
John Learned
UH Physics & Astronomy, 4 May 2005
Stars Get Old
• Run out of fuel.
• Smaller stars
– Long (billions of years) boring
lives,
– Flash before senescence (like
the sun).
• Big stars (10-100 sun mass),
– Live fast (millions of years)
– Die young, glorious display…
a supernova
– Brighter than a galaxy for a
few days
– More radiation than during
whole life of star
Sanduleak -69 202
Supernova 1987A
23 February 1987
Tarantula Nebula
Large Magellanic Cloud
Distance 50 kpc
(160.000 light years)
Georg Raffelt, Max-Planck-Institut für Physik, München, Germany
A Nearby Supernova
Can Ruin Your Existence
• Deadly from neutrinos within
30 light years.
• Atmosphere, weather, ruined.
• Major extinction.
• Not much harm if further.
• SN material in sediments.
• 1 SN/100 years in our galaxy
• Close 1 per 100million years.
• Good news: our neighbors are
peaceful.
• Bad news: when one shows
signs of blowing, it is time to
migrate.
Gamma Ray Bursts
30 year mystery
Brightest flashes seen
Usually billions of light
years away.
Jets from
Supernovae?
Beaming factor:
340? 10,000?
Beams may reach
across galaxy.
Can happen here!
Eta Carinae
Ready to Blow?
• Brightest star in galaxy
– 4 million x sun
• Maybe still dangerous
at 7000 light years
• Fortunately not pointed
at us, we think.
• Other stars old too…
Recent “Soft GR Repeater” in Our
Galaxy – SGR 1806-20, 12/27/04
• Brightest X-Ray burst
– damaged satellites
– affected radio.
• Across galaxy, maybe
50,000 light years away.
• Rotating neutron star,
fantastic magnetic field.
• Spectacular, but not
lethally dangerous
– well, except for astronauts
maybe.
GRBs Can Zap Us
from Across the Galaxy
• Narrow beam, confined over
galactic distances.
• We see GRB in distant
galaxies that have most
radiation at high energies….
penetrates even underground
and underseas.
• Equivalent to 1 kiloton TNT /
km2 over earth surface, and
clearly kills everything
immediately exposed.
• Longer term destroys
atmosphere, brings on nuclear
winter.
Dar & DeRujula Astro-ph/0110162
The End May be in Sight!
• There are galactic
hazards to life on earth.
• We probably experienced
some in the past.
• Explain lack of evident
life in galaxy?
• Cosmic disasters WILL
happen eventually, within
~100Million years.
• We shall have to leave
earth to survive.
• But for now, everything
is fine, is fine, is fine….