Chapter 12: Stellar Evolution Stars more massive than the Sun The evolution of all stars is...
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Chapter 12: Stellar Evolution Stars more massive than the Sun The evolution of all stars is basically the same in the beginning. Hydrogen burning leads to Helium in the core and then to the red giant stage. Thereafter things are different.
Chapter 12: Stellar Evolution Stars more massive than the Sun The evolution of all stars is basically the same in the beginning. Hydrogen burning leads
Chapter 12: Stellar Evolution Stars more massive than the Sun
The evolution of all stars is basically the same in the beginning.
Hydrogen burning leads to Helium in the core and then to the red
giant stage. Thereafter things are different.
Slide 2
Chapter 12: Stellar Evolution A strong distinction exists
between stars with more than 8 solar masses and stars with less.
Lower mass stars never become hot enough to burn carbon and end up
as carbon white dwarfs. As fusion of each element stops in the
core, the core contracts until it begins to burn the next element
and layers of different burning elements develop. A high mass star
can fuse not only hydrogen, helium, and carbon but also oxygen and
more.
Slide 3
Chapter 12: Stellar Evolution The burning of each new element
requires higher temperatures, produces less energy, and lasts
shorter period of time. A 20 solar mass star burns hydrogen for 10
million years, helium for 1 million, oxygen for 1 year, silicon for
one week, and iron for one day. Once we reach iron we can no longer
get energy from the fusion process. The massive stars begin to die.
Since the star is so massive, when the core turns to iron the force
of gravity is so strong the outer layers come crashing down on
themselves and the star implodes. The energy of the collapse is
used to undo all that nuclear fusion has done for the last 10
million years, in one second!
Slide 4
Chapter 12: Stellar Evolution All that is left in the core now
is electrons, protons, neutrons and photons. As the core continues
to collapse the intense pressure forces the electrons and protons
together to form neutrons. As the collapse continues the neutron
will ultimately be pressed together and will then become a
degenerate mass behaving much like the electrons do in a white
dwarf. This sudden stop in the collapse of the core causes a shock
wave to propagate out through the outer atmosphere casting it off
into space. We call this a supernovae.
Slide 5
Chapter 12: Stellar Evolution Supernovae SN1987A
Slide 6
Chapter 12: Stellar Evolution A supernovae will radiate as much
energy in a few months as our Sun will in its entire life. While
novae explosions can take place time and again, a supernovae can
only occur once. Supernovae come in two types I and II. Type I
supernovae occur when the white dwarf in a recurrent novae system
gets too much mass and implodes just like the type II
supernovae.
Slide 7
Chapter 12: Stellar Evolution
Slide 8
Supernovae Remnants The most famous supernovae remnant is the
crab nebula. This was observed by Chinese astronomers in 1054 A.D.
We should see an observable supernovae in our galaxy every 100
years or so. Crab Nebulae.
Slide 9
Chapter 12: Stellar Evolution Most of the hydrogen and helium
in the universe is primordial. All other elements (virtually
everything we see around us) formed later through stellar
evolution. We are made of star dust. There is a cycle of life for
stars.
Slide 10
Chapter 12: Stellar Evolution Star Clusters Star clusters are
important because all the stars were formed at the same time,
distance, and out of the same material. The only difference are due
to their masses and thus were they are in their evolutionary path.
We can tell the age of a cluster by noting where the stars enter
the main sequence or leave the main sequence.
Slide 11
Chapter 12: Stellar Evolution The Hayades Cluster. A young
cluster.
Slide 12
Chapter 12: Stellar Evolution A Globular Cluster. A old
cluster.
