Life on the
Main Sequence

(Section Not Complete)

Timescales for Stellar Evolution
Mass (Solar Units) Formation (years) Main Sequence (years) Giant Phase (years)
1 1x108 9x109 1x109
5 5x106 6x107 1x107
10 6x105 1x107 1x106

Main Sequence Spectral Class Properties
Spectral Class Mass (Solar Units) Luminosity (Solar Units) Temperature (K) Radius (Solar Units) Time on Main Sequence (Million Years)
O5 40 400,000 40,000 13 1.0
B0 15 13,000 28,000 4.9 11
A0 3.5 80 10,000 3.0 440
F0 1.7 6.4 7,500 1.5 3,000
G0 1.1 1.4 6,000 1.1 8,000
K0 0.8 0.46 5,000 0.9 17,000
M0 0.5 0.08 3,500 0.8 56,000

Wolf-Rayet Stars (where should this go?)

Very massive stars may go through a stage in their lives where they expel large portions of their envelopes into space at velocities as large as 1000 km/s. About 200 such stars are known in our galaxy; they are called Wolf-Rayet stars. They are thought to be stars that were very massive when they were young and have since blown off their outer layers of gas, exposing the hot helium core. As a result, they are usually very strong UV emitters.

The adjacent image shows the nebula N2359. This is a wind-blown shell that has been expelled from the Wolf-Rayet star HD56925, which is marked with the arrow (Ref). The star lies on the edge of a thick molecular cloud and the nebula contains shocks associated with the interaction of the wind with the interstellar medium, and also excitation of previously expelled material.

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