Lecture 11 - Module 11 Star Lives-How Stars Evolve and Die.pptx

Module 11
Star Lives:
How Stars Evolve and Die
Chandra X-ray image of Kepler’s
supernova remnant. Analysis of the X-
ray data has correctly identified Kepler
SN 1604 as the result of a Type 1a
supernova. Kepler is about 13,000 l-y
(4.0 kpc) distant in the constellation
Ophiuchus. (NASA/CXC/NCSU/S.
Kepler’s supernova remnant
imaged in visible, X-ray, and
infrared light. (NASA, ESA, R.
Sankrit and W. Blair/Johns
Hopkins University)

Stellar Mass and Fusion

The mass of a main sequence star determines its
core pressure and temperature.

All main-sequence stars are in gravitational
equilibrium.

Stars of higher mass have higher core temperature
and more rapid fusion, making those stars both
more luminous and shorter-lived.

Stars of lower mass have cooler cores and slower
fusion rates, giving them smaller luminosities and
much longer lifetimes.
Fig. 11–1:
Gravitational
equilibrium.

Three Basic Groups of Stars

Low-mass stars: born with < 2 solar masses
(Some astronomers classify low-mass stars as those having 1 solar mass or
less.)

Intermediate-mass stars: born with 2–8 solar masses

High-mass stars: born with > 8 solar masses
Fig. 11–2: Main sequence stars in scale with mass
increasing from right to left.

Future of Stars
Fig. 11–3: The
gas/star/gas cycle and
the production of heavy

Low-mass and intermediate-mass stars swell into red giants near the ends of
their lives and ultimately become white dwarfs.
 For small stars less than 1 M

, there has not yet been enough time for these stars
to move off the main sequence, become a red giant, eject a planetary nebula, and
shrink to a white dwarf.

High-mass stars will also become red and large in their late stages, but their
lives will end more violently.

Stars are born of interstellar
gas and return much of that
gas to interstellar space when
when they die.
Watch this video (2
m
24
s
) “How Do
Stars Live and Die”:
?
v=ASSkPvXo2mo&feature=player_
detailpage
.

Fig. 11–4: The entire cycle
of the birth and death of
stars promotes chemical
reactions. Nuclear fusion
in stars produces the
elements—H, C, O, N—
necessary to make life as
we know it. (NASA/JPL)
Stellar Life Cycle Chemistry

Star Mass and H-R Diagram
Fig. 11–5: Along
the main
sequence, star
mass increases
from lower right

Star Clusters and Stellar Lives

Our knowledge of the life stories of stars comes from comparing mathematical
models of stars with observations.

Star clusters are particularly useful because they contain stars of different
mass that were born about the same time.
Fig. 11–6: The Quintuplet Cluster is a
4-million-year-old cluster that has
stars on the verge of blowing up as
supernovae. It is the home of the
brightest star seen in the Milky Way
Galaxy, called the Pistol Star. The
cluster is a dense grouping of massive
young stars about 100 l-y from the
galactic center, which is 26,000 l-y
(8.0 kpc) from Earth. Its name comes
from the fact it has five prominent
infrared sources residing in it. Along
with the Arches cluster, it is one of two
in the region near the galactic center.