Transcript Stars and The Universe

Can you
guess why I
am showing
you this
picture?
Electromagnetic Waves, Stars, and
The Universe
Contents:
• How we know what’s in a star (emission
spectra)
• Nuclear Fusion
• Star life cycles (our sun versus massive
stars)
• Supernovae and creation of heavy
elements
• Black Holes
• Big Bang Theory, with Evidence
Longer wavelengths (left side) have less energy. Think of these waves a
Which
of being shaken. Rapidly shaken (high energy) strings look like
strings type
that are
electromagnetic
radiation is
the ones on the right.
typically most dangerous?
What color are the hottest
Why?
stars that we can see?
The coolest stars?
Gamma rays. Shorter
wavelengths have more
energy.
Blue. Red.
Under the right conditions,
even visible light can be
dangerous. Can you
describe one such
condition?
Laser light. When visible
light is amplified and
brought “into phase,” it can
become intense enough to
burn things.
These shorter wavelengths have more
energy. That’s why they’re dangerous.
The Electromagnetic Spectrum
•Visible light is just a small segment of the continuum.
•The “red end” of the spectrum has longer wavelengths. The “blue
end” has shorter wavelengths.
•Shorter wavelengths have higher energy, so we know that a red
star is cooler and a blue star is hotter.
Blue stars –
40,000 degrees
These green stars are bogus! The stars in
the middle of the “rainbow” actually look
white, because they’re a mix of the colors on
either side. When you mix all the colors of
light, you get white.
Red stars –
3,000 degrees
Why are there no green
stars?
If a star’s radiation output
Why there are
is centered on green, that
no green
star produces all colors of
stars…
the spectrum. A star that
produces every color will
appear white.
•Stars emit many different wavelengths of “light.”
•Light refracts (turns) when it passes through
materials of different density (such as a glass prsim.
Which color refracts the
different
so a
most?amounts,
Least?
•Different wavelengths refract
prism can separate light into a color spectrum.
Violet. Red.
Correct
Refraction
Incorrect
Refraction,but it
shows light from a
star.
A spectroscope separates radiation into its
component wavelengths in an organized way that
can be easily analyzed.
•When elements are in gas state, they absorb or emit
specific wavelengths of radiation.
•The wavelengths of radiation an element emit or absorb
depend on their electron configurations.
•Those wavelengths can be used as a “fingerprint” to
identify elements in distant stars.
In the•When
diagram,gases
which part
Why
do differentorbit
elements
absorb light, their
electrons
faster,
shows emission of light?
absorb and emit different
causing them to jump out to more
distant energy levels
Which part shows
colors?
(orbiting
farther from the nucleus).
absorption
of light?
•When electrons release energy
(by giving off light), they
Each element has a
themdifferent
to fall arrangement
inward to of
an orbit
The bottom diagram, “deslow shows
down.
This causes
excitation,”
emission
(giving
off) of light.
closer
to the nucleus.
The top diagram,
“excitation,” shows
absorption of light.
electrons. Some electrons
fall farther, giving off light
with more energy (and a
different color).
“Fingerprints” of different elements
Are these absorption
spectra or emission
spectra?
Emission
Example
•The black lines are wavelengths of radiation that are
absorbed by Neon.
•If we see these black lines when we analyze
starlight with a spectroscope, we know that neon
is in the star.
Neon
Absorption
Spectra
In the sun, nuclei fuse. When they do this, the products
of fusion have less mass than the nuclei that fused. This
“lost” mass is actually converted to energy, according to
Einstein’s famous equation…
E = Energy
produced
by nuclear
fusion
C = Speed of light
M = Mass that’s “lost”
when nuclei fuse.
Most stars are
“Main Sequence”
stars. These
stars are
powered by
hydrogen fusion
proceeding at a
steady pace.
Luminosity
vs. Surface
Temperature
Luminosity =
energy
radiated each
second
In
an average
star,get
like
our
Why
will the sun
bigger
sun,
its energy
as itmost
gets of
older?
comes from the fusion of
Fusion produces
helium
Hydrogen.
Hydrogen
(heavier than
Hydrogen),
produces
helium
when it
which sinks to the sun’s
fuses.
core and displaces
This
heliumoutward.
is heavier, so it
hydrogen
sinks to the sun’s core and
Why willthe
the
sun turn
pushes
hydrogen
redder as it gets older?
outward.
As
ages,
this outward
Asour
thesun
fusing
hydrogen
movement
of fusing
moves outward,
it
Hydrogen
willless
cause
the sun
encounters
pressure,
to
soexpand.
fusion slows down.
Temperature
drops.
This
outward movement
also
causes the rate of hydrogen
fusion to diminish (due to
lower pressure away from the
core), thus cooling the sun.
Cooling will turn it red.
11. AfterAtour
sun point,
burns fusion
up all of
andsun’s core. The sun
some
willitsnousable
longerhydrogen
occur in the
helium (some
helium
also
fuse),will
why
will itit shrink?
will cool,
andwill
that
cooling
cause
to shrink. This shrinkage will
whichshrink
will, in
turn,they
cause
the sun to heat back
It will coolcreate
down.compression,
Things generally
when
cool
up (and turn from a cooler red to a hotter white). This stage is
down.
called a white dwarf.
12. Shrinking will cause the sun to turn white (becoming a
white dwarf). Why?
As the sun shrinks, it compresses itself. This causes it to
heat back up and turn from red to white.
13. Eventually, our sun will turn into a black dwarf. Why?
The energy it has as a white dwarf will slowly be lost to
space. There is no new energy source.
This stage is called a “planetary
nebula.” The super hot core creates a
“solar wind” that blasts away and
“lights up” the outer layer of gases.
With no fuel remaining, the star
will eventually radiate its heat
into space and turn to a cold,
dark “black dwarf.”
In the beginning, the massive star on the right was mostly
_________.
Hydrogen
In
a massive star, there is
enough
pressure
to layers
cause of a massive star come from?
Where do
the inner
more fusion.
Simply
the
elements
Fusion put,
of the
outer
layersin
the inner layers come from
fusion of the elements in the
Why does the “ash” that is created by fusion move to the
outer layers. It all starts with
center of the sun?
hydrogen fusion…
When atoms fuse, their product is a heavier, denser
The fusion process continues
material. Denser materials sink.
until iron is created. Even in
a massive star there is not
enough pressure for iron
nuclei to fuse.
Lifea massive
Cycle of
massive
star
(25 times
size of
thematerial
sun)
When
stararuns
out of fuel,
it collapses.
Thethe
collapsing
outer
Immediately after running out of fuel, a massive star’s
speeds toward the star’s center at an extremely high velocity. This outer material
temperature will ________.
then slams into the core and “bounces” back outward. This bounce is an explosion
Decrease
called
a supernova.
The temperature change of #16 will cause the volume of
the star to ________.
shrink
When a massive star runs out of fuel and collapses on
itself, its mass collides at its core and bounces back in an
explosion called a ____________. As a result of this
explosion, parts of the massive star fly away into space,
where they can form _____________. If the mass
remaining in the dead star’s core is 3 times our sun’s
mass, it will form a ____________. If it is less, a
__________ may form.
supernova
New nebulas that can turn into new solar systems like
ours
Black Hole
Neutron Star
Click mouse for
questions 16-18
Life Cycle
of a massive
star (25that
times
theeven
sizeheavier
of thethan
sun)
A supernova
produces
such high pressures
elements
iron
are
formed
by the
fusion.
Many(heavier
of thesethan
elements
are scattered
Where
were
heaviest
iron) elements
in into space and
“recycled.”
form new nebulas that create new stars.
our bodiesThey
created?
Supernova
explosions
Scientists
believe
that all of the earth’s heavy elements were created in a massive
star
that
exploded
long ago.
Why
does
the material
from dying stars sometimes form
“neutron stars?”
Our solar system formed
shrink
There
is so like
much
that the positive protons and
from
a nebula
thispressure
one,
the negative
electrons fuse to become neutrons.
but smaller.
Two characteristics of Neutron stars are:
Extreme density (3 suns compressed into the size of a city
--one spoonful would have the same mass as all of the
cars on the earth) and very rapid spinning.
Scientists believe the heavy
elements in our solar system
came from a supernova.
Lifeouter
Cycle
of aofmassive
The
portions
the star arestar
blasted outward and scattered
through space.
(25 times the size of the sun)
Ultimate Fate of A
Massive Star
(Greater than 25
Solar masses)
The core becomes so
compressed that
protons (+) and
electrons (-) fuse to
create neutrons…
If the material remaining in the
core is less than 3 solar
masses, a very dense
“neutron star” is created.
If the material
remaining in the core
is greater than 3
solar masses, its
gravitational force is
strong enough to
cause the collapse of
neutrons. The mass
compresses itself
into an infinitely
small point whose
gravity is so intense
that not even light
can escape from it.
Our Sun is an
average star like
this one.
What can this
graphic be used
to illustrate?
What do “main sequence” stars have in common?
Their energy is being produced by fusion of hydrogen into
helium
What percentage of stars are main sequence stars?
About 90%
The “Singularity”
The “Event Horizon”
The Big Bang Theory suggests that the universe
exploded outward from an infinitely small point, called
the “cosmic singularity” – and that the universe has
been expanding ever since.
As the universe expands, that
Today, the wavelength of that radiation
is so long that it corresponds to matter
at about 3 degrees Kelvin (degrees
above absolute zero).
This is the most distant light
that we can see. As space
has expanded, this radiation
has stretched along with
space.
radiation (emitted by the early
2000 degree universe) stretches
with the universe, so its
wavelength lengthens and energy
decreases.
Universe is now transparent
to light, so suddenly, light can
travel. Temperature of matter
filling the universe is 2000
degrees Kelvin.
Universe is a plasma,
which is opaque to light.
Radiation emitted just after the big bang
has stretched along with the expanding
universe.
13.7 billion years ago, the
background radiation was
consistent with radiation
from a 2000 K degree body.
Today, the background radiation has a
longer wavelength, consistent with
radiation from a 2.73 K degree body.
Evidence supporting the Big Bang Theory:
1) Cosmic Microwave Background Radiation: Space
is filled with low-energy microwave radiation of same temperature
that scientists predicted would be left over from the Big Bang.
More Big Bang Evidence: The Doppler Effect
•Waves emitted by a moving object are compressed in front of the object and
stretched out behind the object.
•When a star moves toward us, we see shortened wavelengths. This is called a
“blue shift,” because the blue end of the light spectrum has shorter wavelengths.
2) All distant galaxies, and most nearby galaxies, have redshifts (stretched waves), indicating that they are moving away
from us, and that, therefore, the universe is expanding.
Hubble’s Law
•The farther away a galaxy is, the faster it is moving away from us. We can tell this
by applying knowledge of the Doppler effect.
Is this diagram showing an emission spectrum or an
absorption spectrum?
Absorption – the dark areas show the wavelengths of light
that are being absorbed by the star.
http://periodictable.com/Properties/A/Unive
rseAbundance.ssp.log.html
Balloon Model of The Universe’s Expansion (coins = galaxies; balloon surface =
universe.)
•The universe is inflating like the surface of a balloon.
•Galaxies (pennies in diagram) are not moving through space, the space between
them is expanding.
•The space within galaxies is not expanding, because gravity is holding it together.