The DangerDanger of Deadly Cosmic ExplosionsSupernovae and Gamma Ray Bursts

John LearnedUH 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 Sanduleak 69 69 202202

Large Magellanic Cloud Large Magellanic Cloud Distance 50 kpcDistance 50 kpc (160.000 light years)(160.000 light years)

Tarantula NebulaTarantula Nebula

Supernova 1987ASupernova 1987A 23 February 198723 February 1987

Georg Raffelt, Max-Planck-Institut für Physik, München, Germany

A Nearby Supernova Can Ruin Your Existence

• DeadlyDeadly from neutrinos within 30 light years.

• Atmosphere, weather, ruined.• Major extinctionMajor extinction.• Not much harm if furtherNot much harm if further.• SN material in sediments.• 1 SN/100 years in our galaxy • Close 1 per 100million years.• Good newsGood news: our neighbors are

peaceful.• Bad newsBad 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 reachacross 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 / 1 kiloton TNT / kmkm22 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 areare galactic hazards to life on earth.

• We probably experienced some in the past.

• Explain lack of evident lack of evident life in galaxylife in galaxy?

• Cosmic disasters WILL WILL happenhappen eventually, within ~100Million years.

• We shall have to leave leave earthearth to survive.

• But for now, everything everything is fineis fine, is fine, is fine….