Download Pistol Star - University of Dayton

Earth is only one planet orbiting one star among roughly a
hundred billion stars in our Milky Way Galaxy. The Milky Way is
only one galaxy of billions in the universe. Looking beyond the
solar system into galactic and intergalactic space, we must stretch
our minds to nearly unimaginable distances to look backward in
time to events that occurred billions of years before the Earth
formed, and attempt to fathom energy sources powerful enough to
create an entire Universe.
In this presentation we will look at the basics of how stars
come to be? We will take a look at how they were born? We will
talk about and explain the largest star in the universe, the sun. We
will understand, how stars maintain their sequence. We will also
take a look at the life and death of a star. In conclusion, we will
look at other stars in the Universe.
• The Big Bang Theory
states that the
universe began with a
cataclysmic explosion
that
instantly created
space and time.
The BIG BANG Theory
• The Big Bang Theory is the dominant
scientific theory about the origin of the
universe.
• According to the big bang, the universe was
created sometime between 10 billion and 20
billion years ago from a cosmic explosion
that hurled matter in all directions.
Edwin Hubble observed all galaxies are moving away
from each other
• Hubble reasoned that they must have started moving outward
from a common center at the same time.
• Hubble began the Big Bang Theory when he stated that in the
beginning, the entire universe was compressed into a single
infinitely dense point. The point exploded, and our universe
was instantly created.
 Matter, energy and space came into existence with this single
event.
 The Big Bang was the start of space and time.
• The big bang was initially suggested because
it explains why distant galaxies are traveling
away from us at great speeds. The theory also
predicts the existence of cosmic background
radiation (the glow left over from the explosion
itself).
• The Big Bang Theory received its strongest
confirmation when this radiation was
discovered in 1964 by Arno Penzias and
Robert Wilson, who later won the Nobel Prize
for this discovery.
The Birth of a Star
•
•
•
•
•
•
Over time, dense regions of the
Universe draw matter inward by
gravity to form huge clouds of
hydrogen and helium, called nebulae.
Within each cloud, matter further
agglomerates into billions of smaller
bodies.
As the atoms in the nebula accelerate
inward under the force of gravity, they
collide rapidly with one another.
The center of each cloud becomes
very dense and hot; under this intense
heat, electrons are stripped away from
their atoms, leaving a plasma of
positively charged nuclei and
negatively charged electrons.
If this cloud is large enough, the
gravitational attraction will accelerate
the nuclei until they collide, with
enough energy to fuse.
Once Fusion is started, the collapsing
portion of the original nebula becomes
a Star.
•Nobody has ever traveled to the sun, the current thought
is nobody ever will.
•Mass is 2x10^30kg. Although this number seems huge,
the sun is only a star with average mass.
•Diameter is 1.4 million kilometers (109 earth diameters)
•Our Sun is a star that holds about 99.9 percent of all the
matter in the solar system. Its hot atmosphere expands
supersonically outward, creating a flow of electrically
charged ions called the solar wind that sweeps outward
past all the planets at nearly one million miles per hour.
•After Einstein discovered the theory of
relativity scientists began to look at nuclear
reactions.
•From these studies we found that the sun is
powered by hydrogen fusion. Our
knowledge of the core is derived from
calculations of hydrogen fusion reactions
and gravitational forces.
•Sun is more than 15 million K and has
enough hydrogen to fuel the fusion reaction
for another 5 billion years.
•Called the solar atmosphere because its cool
and diffuse compared to the core, even though
the sun is actually gaseous.
•The temperature is 5,700 K and fusion doesn’t
occur at this temperature, therefore the core
heats the photosphere and the light we see
comes from the atmosphere of hydrogen and
helium.
•
•Chromosphere (turbulent, diffuse, gaseous) is above
the photosphere and can been seen by the eye during a
solar eclipse
•Spicules (jets of gas) shoot up from the
chromosphere and look like flames
•They are about 700 km across and 7000 km high
and last for 5-15 minutes
•Corona is above the chromosphere, more diffuse, and
about 2,000,000K
•Appears as a halo around the sun during a solar
eclipse
•One hypothesis about how the photosphere (5700K)
heats the corona is the twisting magnetic fields that
accelerate the particles in the corona
•Made from granules caused by convection
currents that carry energy to the surface
•These dark spots are the cooler areas of
descending gas, which may be small and last a
few days, or they can be 150,000km and last for
months
•Sunspots are 1000 degrees cooler than
surrounding area and put off half the amount of
energy
•Remember from SCI190 that heat travels from
hot to cold objects? The sunspots are heated
from the surrounding area and then disappear
•Apparent Luminosity of a star is its luminosity as seen from Earth. It
appears luminous either because its intrinsically bright or because it’s
close.
•Absolute Luminosity is how bright a star would appear if it were a fixed
distance away.
•We use the standard distance of 32.6 light years to calculate luminosities.
•We use a scale in which the absolute luminosity of a star is divided by the
absolute luminosity of the sun.
•Therefore bright objects have a luminosity of over 1 and faint objects are
less than one.
•The color of a star is a measure of its temperature.
•Main Sequence stars are mainly hydrogen and
helium and are fueled by hydrogen fusion
•Major reason for difference in temperature and
luminosity is that some are more massive than
others
•Gravity is stronger in more massive stars and the
hydrogen nuclei are packed more tightly and
move faster, thus the fusion is faster which makes
the stars hotter and more luminous (upper left of
H-R diagram)
•Between 1911 and 1913 the Hertzsprung- Russel
Diagram (H-R diagram) was discovered, which plots
luminosity (y) and temperature (x).
•Observation: 90% of stars fall along a sinuous band
from upper left (bright and hot) to lower right, called
the main sequence.
•Therefore, luminosity increases with temperature in
main sequence stars.
•To explain the stars that do not lie on the main
sequence, we must consider the life and death of a
star.
•The energy in a star the size of our Sun ins derived from
Hydrogen fusion in the core.
•When most of the hydrogen in the core is consumed, the
star first contracts then expands as hydrogen fusion starts
in the outer shell.
•In the red giant phase, gravitational coalescence in the
core and hydrogen fusion in the outer shell produce
hundreds of times as much energy as was produced when
the star was mature.
•The star contracts again when helium fusion
initiates in the core.
•As our Sun hydrogen nuclei fuse to form helium but the helium nuclei
do not fuse to form heavier element.
•For fusion to occur, two nuclei must collide so energetically that they
over come their nuclear repulsion.
•the original nebula condenses
•The star glows with the intense heat of the
gravitational coalesces.
•The star enters the main sequence when
hydrogen fusion starts in the core.
•After hydrogen fusion ends in the core, the star
leaves the main sequence and passes through
the red giant stage.
•Finally, it explodes to produce a planetary nebula
and then,
•The remaining core glows as a white dwarf.
•If a star is larger than 1.44 solar masses, a white dwarf
does not form.
•In this case, helium fusion ends, gravitational
contraction produces enough heat to fuse carbon.
Renewed fusion produces increasingly heavier
elements.
•When hydrogen or helium fuse, energy is released. In
contrast, iron fusion absorbs the energy and cools a
star. When this happens the thermal pressure that
forced the stellar gases outward diminishes , and the
star collapses under the influence of gravity.
•Due to this strange phenomena supernovas occur.
•Supernova- An exploding star that releases massive amounts of
energy.
•The star’s temperature reaches trillions of degrees and the star
explodes. A supernova shines as brightly as hundreds of billions of
normal stars and may even emit as much energy as an entire
galaxy.
•Observers from earth appears that a new brilliant star suddenly
materialized in the sky, only to become dim and disappear to the
naked eye within a few months.
•Violent enough to send shock waves through the atmosphere of
the star fragmenting atomic nuclei and shooting particles in all
different directions.
•On February 24, 1987, an astronomer named Ian Shelton was carrying
out research unrelated to Supernova’s. He walked and looked into the sky
and saw a star with his naked eye. He looked up into the sky and saw a
bright star where previously there was a dim one.
•This was the first supernova explosion visible to the naked eye since
1604, five years before the invention of the telescope.
•Hydrogen and helium were the first elements to form when our Universe
was 300,000 years old.
•All the stars in the universe were composed entirely of these two elements.
•These old, first generation stars are called population II stars.
•Within the cores hydrogen fused to helium changing the ratio of these
two element in the Universe.
•Elements heavier than iron formed during supernova explosions of
massive population II stars.
•When a star dies, it blasts gas and dust into space to form a new nebula.
•The nebulae condenses once again into new, second generation stars
called population I stars. Example: The sun
•Stars begin life with primordial hydrogen and helium mixed with small
concentration of heavy elements that we inherited from population II
stars and from supernova explosions.
•Pistol Star- The largest star in the Universe
•We discovered that the largest known star, in terms
of mass and brightness, is the dramatically dubbed
Pistol Star.
•The Pistol Star is closer to the center of the Milky
Way than we are, and isn't visible to the naked eye
on account of galactic dust. It's about 100 times the
size of our sun, and burns 10,000,000 times as
bright.