Mr. Sherlock
http://aspire.cosmic-ray.org/Labs/StarLife/starlife_proto.html
http://www.enchantedlearning.com/subjects/astronomy/stars/startypes.sh
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Carina nebula
Pillars of Creation
Nebula
• nebula is an interstellar cloud of dust,
hydrogen, helium and other ionized
gases.
• Originally, nebula was a name for any
diffuse astronomical object, including
galaxies beyond the Milky Way.
•97% Hydrogen 3% Helium
•Baby Star factories!
Accretion begins
•Accretion-Within a nebula, there are varying regions
when gravity causes this dust and gas to “clump”
together.
• As the lumps get larger they start to pull in more and
more material the material in the center get compressed
closer together and begins to heat up due to friction.
• The star must eventually meet equilibrium- the pressure
of gravity pulling the material together must eventually
be offset by the pressure of the gasses pushing heat and
light out of the core.
• When equilibrium is met it becomes a protostar
• What happens to make all this happen? Outside forces?
Supernovas?
What is a star?
•A star is a really hot ball of gas, with hydrogen fusing into
helium at its core. Stars spend the majority of their lives
fusing hydrogen, and when the hydrogen fuel is gone,
stars fuse helium into carbon.
•The more massive stars can fuse carbon into even
heavier elements, which is where most of the heavy
elements in the universe are made.
•Throughout this whole process is that battle between
gravity and gas pressure, known as equilibrium.
Equilibrium
Equilibrium is a battle between gravity and gas pressure. It works like this:
1. Gravity pulls gas and dust inward toward the core.
2. Inside the core, temperature increases as gas atom collisions increase.
3. Density of the core increases as more atoms try to share the same space.
4. Gas pressure increases as atomic collisions and density (atoms/space)
increase.
5. The protostar’s gas pressure RESISTS the collapse of the nebula.
6. When gas pressure = gravity, the protostar has reached equilibrium and
accretion stops
Protostar Formation
Protostar options
• Option 1: If a critical temperature in the core of a
protostar is not reached, it ends up a brown
dwarf. This mass never makes “star status.”
• Option 2: If a critical temperature in the core of a
protostar is reached, then nuclear fusion begins.
We identify the birth of a star as the moment that
it begins fusing hydrogen in the core into helium.
Thus, it becomes a main sequence star.
Hertzsprung-Russell Diagram
I digress
•Apparent Magnitude- Astronomers use the term apparent magnitude to
describe how bright an object appears in the sky from Earth.
•Absolute Magnitude- Absolute magnitude is the measure of a celestial
object's intrinsic brightness. It is the hypothetical apparent magnitude of an
object at a standard luminosity distance of exactly 10.0 parsecs or
about 32.6 light years from the observer, assuming no astronomical
extinction of starlight.
•Parsec is a combination of 2 words, parallax (par) and arc second (sec). A
parsec is equivalent to 3.26 light years. And since a light year is the distance
light travels in 1 year 9.4 trillion km, 1 parsec equals 30.8 trillion km.
What is a parsec?
Parsec is a combination of 2 words, parallax (par) and arc second (sec). A
parsec is equivalent to 3.26 light years. And since a light year is the distance
light travels in 1 year 9.4 trillion km, 1 parsec equals 30.8 trillion km.
Brown Dwarf- low mass protostar
Low Mass Stars
•Becomes A main sequence star
•Burns out its fuel and becomes a Red Giant.
•After burning all its fuel it blows off the outer layers and
forms a planetary nebula.
•What is left over compresses even more and burns as a
white dwarf.
•When all the fuel burns out it becomes a black dwarf star.
A cold chunk of burn out Carbon. (theoretical)
High Mass Stars
•Becomes A main sequence star
•Burns out its fuel and becomes a Red Super Giant.
•After burning all its fuel it blows up in a super nova.
•What is left over compresses even more and becomes
either a neutron star or a black hole.
The stars life
•Stars live out the majority of their lives in a phase termed as the
Main Sequence.
•Once achieving nuclear fusion, stars radiate (shine) energy into
space.
• The star slowly contracts over billions of years to compensate for
the heat and light energy lost. As this slow contraction continues, the
star’s temperature, density, and pressure at the core continue to
increase.
•The temperature at the center of the star slowly rises over time
because the star radiates away energy, but it is also slowly
contracting.
• This battle between gravity pulling in and gas pressure pushing out
will go on over the entire life span of the star.
Hydrogen  Helium  Carbon
For the most part, hydrogen in the core is gone. If the star wants to maintain
equilibrium between gravity and gas pressure, it needs increased temperatures
in the core to re-ignite fusion. The star is forced to burn helium in an effort to
maintain stability. It takes a temperature of 10×107 °K to initiate helium burning,
whereas it only takes a temperature of 2×107 °K to initiate hydrogen burning.
Remember, to remain stable the star must balance the gas pressure pushing out
and the gravitational force pulling in. Gravity will cause the core to contract.
Helium burns inside the core, but a rapid hydrogen reaction occurs faster in the
shell of the star. As the temperature in the shell of the star increases, the outer
layers of the star expand.
Helium in the core of the star is still burning hot. Gravity keeps contracting the
core to maintain equilibrium, and as the core contracts the atoms are packed
together even tighter than before. The outer shell has expanded in an effort to
help heat from the core escape into space. At this point, the star is often termed
a red giant. The red giant is the first step in old age.
Fusion is releasing more energy during helium burning than at the main
sequence stage, so the star is bigger, but less stable. Eventually, the core will run
out of helium fuel, and in order to maintain equilibrium, the core will contract
again to initiate the last type of fusion – carbon burning
Yellow Dwarf and Red Giant
Star Comparison
Star Comparison
Star Comparison
Low mass main sequence star-our sun
Sun Phases
Red Giant Blowing off outer layersNova –Planetary nebula
White Dwarf
Red Supergiant
Supernova
•A supernova is a stellar explosion that briefly outshines
an entire galaxy, radiating as much energy as the Sun or
any ordinary star is expected to emit over its entire life
span, before fading from view over several weeks or
months.
•Can form either a Neutron star or a black hole depending
on the mass of the star.
Supernova
Option 1 super massive stars
- Neutron Stars
Neutron Stars- When the core of a massive star undergoes
gravitational collapse at the end of its life, protons and electrons
are literally scrunched together, leaving behind one of nature's
most wondrous creations: a neutron star. Neutron stars cram
roughly 1.3 to 2.5 solar masses into a city-sized sphere perhaps
20 kilometers (12 miles) across. Matter is packed so tightly that a
sugar-cube-sized amount of material would weigh more than 1
billion tons, about the same as Mount Everest!
Pulsars- Most known neutron stars belong to a subclass known
as pulsars. These relatively young objects rotate extremely
rapidly, with some spinning faster than a kitchen blender. They
beam radio waves in narrow cones, which periodically sweep
across Earth like lighthouse beacons.
Neutron star / Pulsar
Option 2 super massive starsBlack holes
•A black hole is a region of spacetime from which gravity
prevents anything, including light, from escaping.
•The theory of general relativity predicts that a
sufficiently compact mass will deform spacetime to form
a black hole.
•The boundary of the region from which no escape is
possible is called the event horizon.
Black Holes
Quasars
Quasars are the brightest and most distant objects in the known universe. In
the early 1960's, quasars were referred to as radio stars because they were
discovered to be a strong source of radio waves. In fact, the term quasar
comes from the words, "quasi-stellar radio source".
We still do not know exactly what a quasar is. But the most educated guess
points to the possibility that quasars are produced by super massive black
holes consuming matter in an acceleration disk. As the matter spins faster
and faster, it heats up. The friction between all of the particles would give off
enormous amounts of light other forms of radiation such as x-rays. The black
hole would be devouring the equivalent mass of one Sun per year. As this
matter is crushed out of existence by the black hole, enormous amounts of
energy would be ejected along the black hole's north and south poles.
Lifetime of Stars
•It can be counter intuitive, but Larger stars burn out
faster than smaller ones
•Larger stars have more fuel, but they have to burn (fuse)
it faster in order to maintain equilibrium. Because
thermonuclear fusion occurs at a faster rate in massive
stars, large stars use all of their fuel in a shorter length of
time.
•This means that bigger is not better with respect to how
long a star will live. A smaller star has less fuel, but its rate
of fusion is not as fast. Therefore, smaller stars live longer
than larger stars because their rate of fuel consumption is
not as rapid
Definitions
Brown Dwarf- A failed protostar roughly 1/100 the size of the sun. Probably the size of
Jupiter but 15-75 times more massive.
Main Sequence Stars-Main sequence stars are the central band of stars on the HertzsprungRussell Diagram. These stars' energy comes from nuclear fusion, as they convert Hydrogen
to Helium. Most stars (about 90%) are Main Sequence Stars. For these stars, the hotter
they are, the brighter they are. The sun is a typical Main Sequence star.
Red Giant- A red giant is a relatively old star whose diameter is about 100 times bigger than
it was originally, and had become cooler (the surface temperature is under 6,500 K). They
are frequently orange in color. Betelgeuse is a red giant.
Planetary Nebula-A planetary nebula is a nebula formed from by a shell of gas which was
ejected from a certain kind of extremely hot star (a red giant or supergiant). As the giant
star explodes, the core of the star is exposed. Planetary nebulae have nothing to do with
planets.
White Dwarf-A white dwarf is a small, very dense, hot star that is made mostly of carbon.
These faint stars are what remains after a Red Giant Star loses its outer layers. Their
nuclear cores are depleted. They are about the size of the Earth (but tremendously
heavier)! They will eventually lose their heat and become a cold, dark black dwarf.
Definitions Continued
Black Dwarf- A black dwarf is a white dwarf that has cooled down to the
temperature of the cosmic microwave background, and so is invisible. They are
entirely hypothetical.
Red Supergiant-A supergiant is the largest known type of star; some are almost
as large as our entire solar system. Betelgeuse and Rigel are supergiants. These
stars are rare. When supergiants die they supernova and become black holes.
Supernova-A supernova is a stellar explosion that briefly outshines an entire
galaxy, radiating as much energy as the Sun or any ordinary star is expected to
emit over its entire life span, before fading from view over several weeks or
months.
Neutron Star- The compressed matter of a super nova or binary star system that
is made of mostly neutrons- about the size of a medium sized city.
Black Hole-A black hole is a region of spacetime from which gravity prevents
anything, including light, from escaping. The theory of general relativity predicts
that a sufficiently compact mass will deform spacetime to form a black hole. The
boundary of the region from which no escape is possible is called the event
horizon.