Chapter 10: The Death of Stars ( part a ). The evolution of low-mass vs. that of high-mass stars. Planetary nebulae and the formation of white dwarf stars. Supernova explosions: two types Type I: due to “carbon detonation” of an accreting white dwarf in a binary.
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Chapter 10: The Death of Stars (part a) The evolution of low-mass vs. that of high-mass stars. Planetary nebulae and the formation of white dwarf stars. Supernova explosions: two types Type I: due to “carbon detonation” of an accreting white dwarf in a binary. Type II: due to “core collapse” in a high-mass star. Both types of supernovae leave behind remnants. Evidence from clusters confirms our theories of stellar evolution. Compact objects: neutron stars, pulsars, quark stars, and black holes.
In a young star on the main sequence, hydrogen shell burning occurs around an “ash” core, which is mostly helium. The core temperature is about T = 10 million K
Stars with Masses between 0.08 and 0.4 times the mass of the Sun have low core temperatures, live a long time, convect helium from the core, so it mixes uniformly, and will end up composed entirely of helium.
Stars with mass greater than 0.4 solar masses burn faster. During stage 7 hydrogen burning causes a build-up of helium in the star’s core.Eventually a core of helium “ash” accumulates in the core.On the next slide, we follow the evolution of a star like the Sun, with one solar mass.
Planetary Nebulae form when the core can’t reach 600 million K, the minimum needed for carbon burning.
A Planetary Nebula shaped like a sphere, about 1.5 pc across. The white dwarf is in the center.
A Planetary Nebula with the shape of a ring, 0.5 pc across, called the “Ring Nebula”.
Cat’s Eye Nebula, 0.1 pc across, may be from a pair of binary stars that both shed envelopes.
M2-9 has twin lobes leaving the central star at 300 km/sec, reaching 0.5 pc end-to-end.
(See the slide show of planetary nebulae.) Many more examples of planetary nebulae are known: • NOAO: • http://www.noao.edu/outreach/aop/observers/pn.html • http://www.noao.edu/image_gallery/planetary_nebulae.html • AAO: http://www.aao.gov.au/images/general/planetary_frames.html • ESO:http://www.eso.org/gallery/v/ESOPIA • And for a list of the Messier Catalog, see the SEDS Messier database: (using a chart of icons here) http://seds.lpl.arizona.edu/messier/ ?link
White Dwarfformation on the H–R DiagramSome heavier elements are formed in the last years of the burning in the shells surrounding the carbon core. H, He, C, O, and some Ne and Mg are expelled from the star as a “planetary nebula”
Sirius B has a high mass for a white dwarf, and probably came from a mass 4 Msolar star.
A Nova is an explosion on a white dwarf, but only a small amount of material on the surface of the white dwarf explodes. Nova Herculis 1934a) in March 1935b) in May 1935, after brightening by a factor of 60,000
Nova Persei - matter ejection seen 50 years after 1901 flash (brightened by factor of 40,000)