頁:
[1]
The deaths of stars(2)
Three major ways of death[*] Massive star →
supergiant →supernova
[*] Sun-like star → redgiant; Core →white dwarf
[*] Red dwarf → whitedwarf
Sun-like stars (類太陽恆星)
[*] 0.4 solar mass < mass of the star < 4 solar masses
[*] In the red giant phase, the star’s core is hot enough to fusehelium into carbon (triple- process) and then to oxygen
layers of heavy elements up to carbon and oxygen
[*] The core is not hot enough to fuse carbon, oxygen into heavier
elements
[*]Burning of hydrogen and helium in the shells releaseslarge amount of energy
the star expands further and loses a large amount of energy
The surface of a giant is held by gravity weakly
a lot of mass in the outer layers is pushed away by strong stellarwind (stream of high energy particles) and radiation pressure
Planetary nebulae are expelled outer layers ofgiant stars, pushed out by sudden bursts of energy when fuelsare ignited (e.g. helium burning)
A small, dense and hot core is revealed at the centre nuclear reactions extinguish, and luminosity drops
rapidly
Surface temperature is high but luminosity is low becauseof its small size
Resides on the lower-left side of the H-R diagram –becomes a white dwarf
Hot but small
Gas in the nebula is ionized by ultravioletradiation from the central hot star
Light is emitted when ions recapture electrons,forming an emission nebula
...<div class='locked'><em>瀏覽完整內容，請先 <a href='member.php?mod=register'>註冊</a> 或 <a href='javascript:;' onclick="lsSubmit()">登入會員</a></em></div><div></div>
頁:
[1]