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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
– 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
• Bad news: when one shows
signs of blowing, it is time to
Gamma Ray Bursts
30 year mystery
Brightest flashes seen
Usually billions of light
years away.
Jets from
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
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
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….