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Nebulas: The Birthplace of Stars
– A cloud of gas and dust in outer space
– Mostly consist of Hydrogen and Helium
When a nebula reaches a certain density,
gravitational forces begin to pull the gas
and dust particles close together causing a
lump to form inside the main cloud of the
• As more matter collects, more gravity
develops creating a protostar (baby star).
Crab Nebula
M16 Eagle Nebula
“Birth” of a Star
When the protostar reaches critical
density and temperature (~15x107°C),
the gravitational forces pulling matter
towards the center are so strong that it
causes nuclear fusion to begin.
 This event causes a chain reaction that
will continue for the star’s entire lifespan.
“Birth” of a Star
The star’s size
eventually stabilizes
when the
gravitational force
pulling matter inward
matches the outward
pressure of the
fusion reaction.
Not all Stars are Alike
A star’s mass determines
– Brightness
– Colour
– Size
– Lifespan
In the early 20th century, Ejnar
Hertzsprung and Henry Norris Russell
organized these variables into the
Hertzsprung-Russell diagram.
The Hertzsprung-Russell Diagram
(H-R Diagram)
Can be used to deduce the evolution of
stars (how they change over time)
 ~90% of all stars plotted onto the H-R
Diagram fall along a diagonal band
called the Main Sequence
 Our Sun is an example of a Main
Sequence Star
“Death” of a Star
Depending on its initial mass, a star may
endure 1 of 4 known fates.
Red Giant
After 10 billion years, a main sequence star (like
the Sun) has converted most of its hydrogen into
With less energy pushing outwards, the helium
center starts to contract.
This contraction causes the core to heat up.
Heat from the core causes any remaining
hydrogen in the outer layers to fuse and expand
outward (eventually cooling and becoming red)
White Dwarf
Small sized stars also convert most of their
hydrogen fuel to helium at some point in
their life.
• Since small stars don’t have as much
mass, they do not produce the conditions
to reignite nuclear fusion.
• The hot core remains and the outer layers
simply drift away
• When the white dwarf star cools, it looks
invisible and is called a black dwarf
Supermassive stars are rare compared
to main sequence stars
 They tend to burn significantly faster
than smaller stars
 Massive stars convert Hydrogen to
Helium, then Helium to Carbon, etc, until
Iron is formed through nuclear fusion. At
this point, fusion cannot continue
The growing force of gravity pulls matter
towards the iron core and the star
attempts to implode.
 The iron core prevents this and sends
the solar material (nebular gas and dust)
flying outwards into space in an
awesome explosion called a supernova
Neutron Star
Massive stars (larger than the Sun)
supernova and leave behind a neutron
star (an extremely dense star composed
of tightly packed neutrons)
 Neutron stars have immense
gravitational force and tend to spin
quickly. This spinning creates highfrequency radio waves, which have
been detected by astronomers on Earth.
Black Hole
When a supermassive star dies /
supernovas it leaves behind a core that
is so massive and so dense that the
gravitational force it produces does not
let light escape
 Black holes are surrounded by radiation
emitting celestial objects as they are
under the influence of the black hole’s
gravity (until they are absorbed)
The Solar Nebula Theory
The Solar system formed ~5 billion
years ago from a massive cloud of dust
and gas (nebula) that began to contract
The contraction caused a protostar to
As the protostar grew in mass it began
to spin faster and faster (like a spinning
skater pulling their arms and legs close
during a twirl) causing the surrounding
nebular dust to form a disc
The Solar Nebula Theory
When the protostar reached critical
mass, nuclear fusion began
 The lighter elements (H and He) were
thrown further from the Sun and became
the gas giants
 Heavier elements remained close to the
Sun and formed the terrestrial planets
Evidence for the Solar Nebula
 Explains
 All planets orbit in the same
 The planets all revolve around the
Sun on the same plane
 Terrestrial planets are closer to the
Sun while gas giants are further
from the Sun
Edwin Hubble and the Universe
Before 1920, it was established that the
Milky Way Galaxy was the Universe.
• In 1922-1923, Edwin Hubble observed what
was thought to be spiral nebulae (The
Andromeda and Triangulum galaxies)
• Concluded that these nebula existed
outside of the Milky Way and represented
other galaxies, implying that the Universe is
much larger than the Milky Way Galaxy.
Andromeda Galaxy
The Expanding Universe
Edwin Hubble also observed that each
galaxy seems to emit its own spectrum
of light.
 NOTE: Light shifts its wavelength depending
on whether it is moving toward an observer
or moving away from an observer
Hubble’s Law:
 The light from distant galaxies seems to be
redshifted = Moving away = The Universe is
Dark Matter
Upon further study and with the help of
technology, astronomers have found
celestial objects moving at a speed that
does not seem consistent with their
They have also concluded that there
isn’t enough visible mass in galaxies to
explain their tremendous gravity
This strange matter is unknown and
“dark” because we don’t know what it is
Dark Energy
In 1998, it was observed that the Universe
may be expanding at an accelerated rate (the
expansion is getting faster and faster)
 Astronomers acknowledge that there may be
an unknown force working against gravity.
 It is called “Dark” because we don’t know
what it is and if it exists.
The Big Bang Theory
Cosmologists (people who study the
physics and evolution of the Universe)
believe that all matter, energy, forces
and time expanded from a single
infinitely small point
 The Big Bang Theory places the
beginning of the Universe and beginning
of time ~13.8 billion years ago
Evidence for the Big Bang Theory
Arno Penzias and Robert Wilson, two
physicists, were conducting experiments
with a sensitive antenna in Crawford,
New Jersey (1965)
 They picked up radiation from all
 Through experimentation it was included
that the energy represented remnant
energy from the big bang
 Red Shift
The Future
The Big Freeze / Hear Death
 The Big Rip
 The Big Crunch
 The Big Bounce / Multiverse
The Future: Large Hadron Collider
The Large Hadron Collider (LHC) is a
gigantic scientific instrument near Geneva,
where it spans the border between
Switzerland and France about 100m
underground. It is a particle accelerator
used by physicists to study the smallest
known particles – the fundamental building
blocks of all things. It will revolutionise our
understanding, from the minuscule world
deep within atoms to the vastness of the
The Future: Large Hadron Collider
The precise circumference of the LHC
accelerator is 26 659 m, with a total of
9300 magnets inside. Not only is the LHC
the world’s largest particle accelerator, just
one-eighth of its cryogenic distribution
system would qualify as the world’s largest
• At full power, trillions of protons will race
around the LHC accelerator ring 11 245
times a second, travelling at 99.9999991%
the speed of light.
Space Test Review
You are responsible for the following text
 All of chapter 8 excluding 8.7
 All of the chapter 9 excluding 9.4, 9.5, and
 You DO NOT need to review anything from
chapter 10