Hypernovae at the edge of the universe

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Hypernovae at the edge of the universe

• A Lecture in Understanding Science
• Simon JefferyArmagh Observatory

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• This talk needs updating for 1999
• most energetic GRB ever
• nearby GRB identified with SN

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GRBs and PUS

• Hottest new results in astronomy
• ? papers during 1998
• Concepts
• Gamma rays, energies, distances
• Importance of communicating science
• PUS Public Understanding of Science
• Armagh is a centre of excellence for science,
  culture and commerce

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gamma rays

• What are gamma rays ?
• Form of light all light travels in waves
  classified according to wavelength or energy
• Very energetic if a white light particle is a
  ping pong ball, a gamma ray is an ocean liner
• How are they made ?
• subatomic particles such as electrons are
  destroyed in nuclear reactions
• How are they detected ?
• techniques developed in High Energy Nuclear
  Physics

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gamma rays
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The cold war and GRBs

• 1967 Vela satellites launched to monitor secret
  tests of nuclear bombs by looking for bursts of
  x-rays or gamma rays
• Discovery of gamma ray bursts from outer space -
  ORIGIN UNKNOWN!
• first discovery, July 2, 1967
• What are GRBs ?
• unanswered for thirty years, until .

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locating GRBs

• gamma ray sources are hard to locate quickly
• Compton Observatory (launch 1991)
• eight special detectors one at each corner
• monitors whole sky continuosly
• one GRB each day from random direction
• BeppoSAX
• rapid and accurate location of GRB positions
• Ground-based Telescopes
• optical identifications - GRB970228

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Compton Gamma Ray Observatory
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BeppoSAX
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The GRB Coordinates Network
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GRB971214

• Finding the smoking gun
• Compton detects GRB on 14 Dec 1997
• Optical pictures show faint object fading quickly
• Keck, Hawaii, 2days after outburst
• Two months later - only a very faint galaxy
  remains
• More observations show galaxy near edge of
  universe
• 12 billion light years (if universe is 14 billion
  years old)
• Four months on, HST shows host galaxy in finer
  detail

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So what are GRBS ?

• Biggest explosions in nature
• 1051 - 3.1053 ergs in gamma rays alone
• equivalent to 100 - 10000 supernovae
  (SN I 1049 ergs)
• 50 x Suns radiation in 10 billion years - in a
  few seconds
• "For about one or two seconds, this burst was as
  luminous as all the rest of the entire universe."
  George Djorgovski (Caltech)
• Most likely cause
• Collision of two neutron stars causes explosion
• A fraction of the mass is converted to energy
  Emc2 (0.2Msun)
• Remainder forms a black hole
• NOT PROVEN

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Understanding Science

• Astronomy is exciting
• everyone can benefit
• the sky belongs to everyone
• Astronomy makes a contribution to the economy
• extraterrestrial effects on climate
• solar interference radio and power
• space debris and impact hazards
• Anyone can make discoveries
• meteorites in gardens
• nuclear surveillance