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