Black Holes – Formation

Black Hole

Black holes form after supermassive stars (> 10 solar masses) explode as Type II supernovae. The remaining cores of these stars range from 2- 103 solar masses. Nothing is strong enough to hold the remaining mass against the force of gravity and the dying supermassive stars collapse into black holes. Nothing escapes from black holes, not even light; thus, the escape velocity of black holes is the speed of light. Since nothing can travel faster than the speed of light, nothing can escape. Matter that disappears from black holes loses contact with the rest of the Universe. Black holes are a consequence of Einstein’s theory of gravity, or General Relativity.


More About the Sun

The Sun

The Sun: Basics

  • Radius: 696,000 km (109 times Earth’s radius)
  • Mass: 2×10³º kg (332,946 times Earth’s mass)
  • Temperature: 15,000,000 K – center; 5,780 K – photosphere; 2-5 million K – corona
  • Luminosity: 3.8×1026 watts
  • Rotation Period at Equator: 25.4 days
  • Photospheric Composition (by number of atoms): 92.1% hydrogen, 7.8% helium, 0.1% other elements
  • Photospheric Composition (by mass %): 73.5% hydrogen, 24.9% helium, 1.6% other elements

Energy Transport Mechanisms

  • Conduction: most important in solids (e.g. pot over open flame or stove)
  • Radiation: transport of energy by motion of photons; efficiency depends on how opaqueness of the matter (e.g. heater in a cold room)
  • Convection: bulk transport of packets of matter in a liquid or gas (e.g. boiling water — hot water rises, cold water sinks)

Layers of the Sun

  • Radiative Zone: the sun’s center is opaque, so energy takes hundreds of thousands of years to escape
  • Convective Zone: hot gases rise, cold gases sink

Solar Atmosphere (photosphere, corona, chromosphere)

  • Photosphere: 5,800 K; 500 km thick; granulation in solar atmosphere
  • Chromosphere: 10,000 K; 1,000 km thick; red color, Balmer series emission line of hydrogen
  • Corona: 2 million K; large region of high-density plasma

Solar Magnetic Activity

  • Sunspots: magnetic field prevents convective bubbles; lower temperature than rest of Sun’s surface; has magnetic storms; maximum number of sunspots at 11 years, which is half of a 22-year cycle; every 11 years, sunspots’ magnetic fields change
  • Solar Flares: powerful, energetic eruptions that releases magnetic energy, and up to 20 million K
  • Corona Mass Ejections: huge flows of hot gas at 1,500 km/sec

Detecting Solar Neutrinos

  • Neutrinos: matter that interact very weakly with normal matter; the interior of the Sun is transparent to neutrinos (discovered in 1956 by Clyde Cowan and Frederick Reines)
  • First neutrino “telescope” at Homestead gold mine, South Dakota: used 400,000 liters of dry-cleaning fluid (perchloroethylene -C2Cl4) because a neutrino can interact with a chlorine nucleus to form an argon nucleus
  • Only 1 out of 10²² passing neutrinos reacted, once every two days
  • 1/3 of expected neutrinos detected based on understanding of the proton-proton chain
  • Other experiments: Sudbury Neutrino Observatory (1,000 tons of heavy water) and Super-Kamiokande experiment in Japan (50,000 tons of water)