Stars off the Main Sequence - ScienceEducationatNewPaltz
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Transcript Stars off the Main Sequence - ScienceEducationatNewPaltz
Stars on and off the Main
Sequence
Just a history of a star’s birth, life
and death
Main Sequence Stars
Where are they on
the H-R Diagram?
How long is their
life compared to
other stars?
What is their dying
process?
What do they
ultimately become?
Why?
A Look at the Non-Main Sequence
Stars: Birth and Death of Stars
Protostars
T-Tauri stars
Brown Dwarfs
Red dwarfs
Neutron stars
White dwarfs
Red Giants
Super Giants
Protostars
A protostar is what
you have before a
star forms
If it has enough
mass and begins to
fuse, it becomes a
T-Tauri star
If it does not have
enough mass it
becomes a Brown
Dwarf (not red)
T-Tauri Stars
Star's formation and
evolution right before
it becomes a main
sequence star
Occurs at the end of
the protostar phase
Gravitational pressure
holding the star
together is the source
of all its energy
T-Tauri Stars Continued
Don't have enough
pressure and
temperature at
their cores to
generate nuclear
fusion
Same temperature
as MS stars but
brighter because
they're a larger
T-Tauri Stars
Have large areas of
sunspot coverage
Have intense X-ray
flares
Extremely powerful
stellar winds
Remain in the T
Tauri stage for
about 100 million
years
Main Sequence Stars, Again
The majority of all stars
are main sequence
stars
Our nearest neighbors,
Proxima Centauri, Sirius
and Alpha Centauri are
main sequence stars
Stars can vary in size,
mass and brightness
Main Sequence Continued
All doing the same
thing
Converting
hydrogen into
helium in their
cores
Releasing a
tremendous
amount of energy
Main Sequence Continued
In a state of
hydrostatic
equilibrium
Gravity is pulling
the star inward
Pressure from all
the fusion
reactions in the
star are pushing
outward
Main Sequence Continued
Lower mass limit
for a main
sequence star is
about 0.08 times
the mass of the
Sun (ex: Red
Dwarf)
To more than 100
times the mass of
the Sun
Red Giant Star
When an average star
like our Sun consumes
all hydrogen in its’
core, fusion stops
No longer generates
outward pressure to
counteract inward
pressure
Outer shell of H around
core ignites, prolonging
life of star
Red Giants Continued
But the shell of
ignited H causes it
to increase in size
dramatically
Can be 100 times
larger than it was
in its main
sequence phase
Red Giants Continued
When hydrogen fuel is
used up, further shells
of helium and heavier
elements can be
consumed in fusion
reactions
Will only last a few
hundred million years
before it runs out of
fuel completely and
becomes a white
dwarf.
White Dwarf Stars
An average star
has completely run
out of hydrogen
fuel in its core
It lacks the mass
to force higher
elements into
fusion reaction
It becomes a white
dwarf star
White Dwarf Stars Continued
Outward light pressure
from the fusion
reaction stops
Star collapses inward
under its own gravity
No fusion reactions
happening and cools
down
Process takes hundreds
of billions of years
Red Dwarf Stars
Most common kind of
MS stars
Low mass
Much cooler than stars
like our Sun
Able to keep the
hydrogen fuel mixing
into their core for a
longer time
Red Dwarf Stars Continued
Can conserve their fuel
for much longer than
other stars
Some red dwarf stars
will burn for up to 10
trillion years
The smallest red dwarfs
are 0.075 times the
mass of the Sun and
largest up to ½ our Sun
Neutron Stars
If a stars has between
1.35 and 2.1 times the
mass of the Sun the
star dies in a
catastrophic
supernova explosion
The remaining core
becomes a neutron
star
Neutron Stars Continued
It is an exotic type of
star that is composed
entirely of neutrons
How? The intense
gravity of the neutron
star crushes protons
and electrons
together to form
neutrons
Neutron Stars Continued
More massive stars do
not become neutron
stars
What do they become?
What do we know about
these structures created
by the death of super
massive stars?
Supergiant Stars
The largest stars in
the Universe are
supergiant stars
Dozens of times
the mass of the
Sun
Consuming
hydrogen fuel at an
enormous rate
Supergiant Stars Continued
Will consume all the fuel in their
cores within just a few million
years
Live fast and die young
Detonating as supernovae
Disintegrating themselves in the
process
Betelgeuse is a prominent
example of a red supergiant star.
It is located at the shoulder of
Orion
Nova and Other Things to Consider
Nova means "new
star"
They are actually
"newly visible"
stars
One model of
novae suggests
that they occur in
binary systems
Nova Continued
One is a white
dwarf
The other is on its
way to becoming a
red giant
The red giant can
lose mass which
would trigger
hydrogen fusion as
it falls on the white
dwarf
Nova Continued
This would blow
the gas off and
the process
could repeat
itself. A notable
nova example
is Nova Cygni
1975.
Pulsars
Evidence: precisely
repeated radio
pulses
Attributed to
rotating neutron
stars which emit
lighthouse type
sweeping beams as
they rotate
Pulsars Continued
Variations in the
normal periodic rate
are interpreted as
energy loss
mechanisms or, in one
case, taken as
evidence of planets
around the pulsar
Quasars
These objects were
named Quasistellar
Radio Sources
Quasars are closely
related to the active
galaxies
The quasars have
very large redshifts
Quasars Continued
Quasars are extremely
luminous at all
wavelengths and
exhibit variability on
timescales as little as
hours, indicating that
their enormous energy
output originates in a
very compact source
Black Holes
What are they?
How do they form?
What do we know
about them?
What don’t we
know?
How does time
operate at a black
hole? How does
time operate inside
the black hole?
Black Holes Continued
What is singularity?
What is the event
horizon?
Do black holes
rotate?
What are the only
emissions from a
black hole?
We will add more to the
Hertzsprung-Russell Diagram
As
As
As
As
we
we
we
we
look
look
look
look
at
at
at
at
more information
mass
cycles
nebulae