Stellar Evolution

Fig. Chapter cover

Planetary nebula NGC 3132

In 5 billion years, our Sun will be similar

Stability in Stars

Pressure = Force/area

Outward pressure (thermal and radiation)

Inward force is gravity

Fig. 20.1

Evolution of the Sun

Sun evolves from main sequence

Describe the various stages of the Sun's evolution

Fig. 20.12

Properties of Stellar Evolution of the Sun

Table 20.1

Properties of Stellar Evolution of the Sun

Evolution of stars on Main Sequence

Fig. 20.17

Properties of H-R Diagram Evolution

Once a star reaches the main sequence (M.S.), it spends most of its life on the M.S.

Which stars evolve first off main sequence? (Which property of a star most affects the first answer?) What is the Zero Age M.S.?

What is the Horizontal Branch?

What is the Asymptotic Branch?

How does the track of high mass stars evolving off the M.S. Compared to low mass stars?

Can a high mass star have a helium flash?

Fusion in Stars

End product depends on mass

Fig. 20.3 (Sun) and 21.5 (high mass star)

Planetary Nebula

Planetary nebula have nothing to do with planets

Ring like structure is due to the effect of seeing a sphere enhanced where the emission arises from the longest path length

Fig 20.10

Planetary Nebula Gallery

Fig 20.10c, 20.11b, Discovery 20-1

White Dwarf

Star is supported from gravitational collapse due to electron degeneracy pressure

Pauli exclusion principle (Quantum)

Electrons cannot be forced closer than a distance defined by quantum mechanics

Age I and the H-R Diagram

The Hyades Cluster

Young

Distance=46 pc

Turnoff at spectral class A 600 Myr

Fig. 20.19

Age II and the H-R Diagram

Globular Cluster 47 Tucanae

Old

Turnoff at spectral class G 12-14 billion yrs

Fig. 20.20

Comparisons between Turnoffs on H-R Diagram

Side-by-side comparison of old (left Fig 20.20b) and young (right Fig. 20.19b) H-R diagrams

Binary Stars

Lagragian point= balance point

Roche Lobe= sphere in which all the material gravitationally belongs to a star

As star evolves to red giant, the radius exceeds the Roche lobe

Binary Systems

Detached, semidetached, and contact binary

When extent of star exceeds Roche Lobe, mass transfer can occur

Blue Stragglers

Mass transfer in binary system creates a massive blue giant from an original Solar mass star