Transcript Ch 20 Notes Starsx

The Universe
Chapter 20
“Recognize that the very molecules that make
up your body, the atoms that construct the molecules,
are traceable to the crucibles that were once the
centers of high mass stars that exploded their
chemically rich guts into the galaxy, enriching pristine
gas clouds with the chemistry of life. So that we are all
connected to each other biologically, to the earth
chemically and to the rest of the universe
atomically…It’s not that we are better than the
universe, we are part of the universe. We are in the
universe and the universe is in us.”
- Neil deGrasse Tyson
HUNTING THE EDGE OF SPACE
What are Stars?
3
What are Stars?
• The warthog was right…
• Stars: huge sphere of very
hot gas that emits light and
other radiation
• Formed from clouds of
dust and gas, or nebulas,
and go through different
stages as they age
4
Light Years
• Stars are located at various distances from the
Earth
• We measure this distance in light-years (ly)
• Distance light travels in one year - 9.5 × 1012 km
• UNIT OF DISTANCE, it would take us 10 million years to
“drive” 1 light year
5
Life Cycle of Stars
• Like all things, stars have a natural progression from
birth, through development, and then death
• About 90% of the stars in our galaxy, including the
sun, are around midlife
• They are converting hydrogen into helium in their
interiors (with nuclear fusion!).
6
Life Cycle of Stars
• Nebula: thin cloud of gas and
dust
• Gravity causes nebula to
collapse inward and begin
spinning – creating a protostar
• Hydrogen atoms begin fusing
into Helium
7
Life Cycle of Stars
• The onset of this fusion marks the
birth of a star
• Hydrostatic Equilibrium: The fusion
reactions in the core of the sun
produce energy and outward
pressure, this balances the inward
pressure from gravity
• This creates the round shape of the
sun
8
Life Cycle of Stars
• A star that is stable, like our sun, is
called a Main Sequence Star
• When the sun’s supply of hydrogen runs
out, it begins to fuse heavier elements,
all the way up to iron
• The outer layers of dust and gas expand,
and the star swells to a Red Giant – a
large reddish star in its late life cycle
9
Life Cycle of Stars
• The outer layers eject themselves as a planetary
nebula
• In the sun’s case, these layers will engulf Mercury,
Venus, and possibly Earth and Mars
• The remaining core will shrink to an Earth-size ball
– called a White Dwarf
10
Life Cycle of Stars
• Stars larger than the sun will
become supernovas
• Supernova: a stellar explosion
• The collapse of the core
rebounds with a shock wave that
violently blows the star’s outer
layers away from the core.
• A supernova can become a black
hole or a neutron star
11
Life Cycle of Stars
• A black hole consists of matter
so massive and compressed that
nothing can escape its
gravitational pull, not even light.
• The only way to detect one is by
observing the radiation of light
and X rays from the objects that
revolve rapidly around them
12
Life Cycle of Stars
• Neutron stars are only a
few dozen kilometers in
diameter, but they are very
dense.
• Just a teaspoon of matter
from a neutron star would
weigh more than 100 million
tons on Earth.
13
Energy of a Star
• Stars have various layers that
differ in number and depth
• Energy moves slowly through
the layers by a combination of
radiation and convection.
14
Energy of a Star
• Convection: hot gas moves away from the star’s
core
• Radiation: energy is transferred to individual
atoms; the atoms absorb the energy and transfer
it to other atoms in random directions; atoms
near the surface give off the energy into space as
electromagnetic radiation
15
Studying Stars
• Ancient Greeks classified
stars by their color and
brightness
 Telescopes allowed
astronomers to study
stars in more detail for the
first time
16
Traits of Stars
• Brightness of a star depends on the star’s temperature,
size, and distance from the Earth.
• Stars produce energy in different wavelengths of
electromagnetic radiation, such as high energy X rays
and low energy radio waves
17
Traits of Stars
• A star’s color is related to its
temperature
• Hotter Objects: colors that are more
intense, shorter wavelengths,
toward the blue end
• Cooler Objects: have longer
wavelengths, closer to red
• The wavelength at which a hot
object emits the most light will
determine the color we see when
looking at it
18
Traits of Stars
• Spectral lines reveal the composition of stars
• When you pass light through a spectrograph, it
makes a unique pattern
• The pattern is determined by what types of elements
make up the gas emitted from the light
• Each element has its own unique “fingerprint”
when passed through this fancy prism and
comparing these will give the make up of a star
19
H-R Diagram
• Diagram that shows how stars evolve
• This diagram doesn’t show where stars are literally,
only their progression as they age
• Y-axis: luminosity, or the brightness of stars.
• X-axis: surface temperature of the stars, with hotter
temperatures on the left side
20
21
The Milky Way and
Other Galaxies
Section 2
22
Galaxies
• Galaxy: a collection of millions to
billions of stars
• Grouped in clusters
• The Milky Way and the Adromeda
galaxy are two of the largest, with
a cluster of more than 30 galaxies
• Superclusters contain thousands of
galaxies
• They are the largest known
structures in the universe
23
Galaxies
• Gravity holds galaxies
together, and the solar
system revolves
around the center of
the galaxy because of
this gravity
• It takes our solar
system about 226
million years to
complete one orbit of
our galaxy
24
Galaxies
• Can be divided into three
main types:
• Spiral, Elliptical, and
Irregular
• Each has many stars, but
differs in structure
25
Spiral Galaxies
• Spiral arms made of gas,
dust, and stars
• Milky Way
• Has a lot of interstellar
matter –
• the medium needed to
create new stars, mostly
gas and dust
26
Elliptical Galaxies
• Little gas or dust, no
spiral arms
• Spherical or egg
shaped
• Often reddish in
color
27
Irregular Galaxies
• Lack regular shapes and well
defined structures
• Some have little interstellar
matter while others have a
lot
28
Galaxies Over Time
• When a scientist observes a galaxy that is 1 billion years
away, they are observing light that left the galaxy 1
billion years ago
• Scientists don’t know what the galaxy looks like now,
but can study similar closer galaxies to piece together
the evolution of galaxies
• The gas, dust and stars that make up galaxies is in
constant motion, as they consume their gas/dust they
can no longer make stars
• The gas/dust from nearby galaxies can collide and set
off rapid burst of new star formation
29
Origin of the Universe
Section 3
30
The Universe
• Universe: consists of all space, matter and energy
that exists- now, in the past or in the future
• We see the universe now as it was in the past
• The farther an object is, the older the light that we
get from that object is
• The sun is 8 light minutes away, that means we are seeing
what the sun looked like 8 minutes ago
31
The Universe
• Most of the universe is
empty space
• Space is a vacuum with
no air and no air
pressure
32
Edwin Hubble
• 1929: Announced the universe is expanding based on
observations of spectral lines in the light from other
galaxies
• He found these lines were almost always shifted
toward the red end of the spectrum
33
Edwin Hubble
• The red shift can be
explained by the Doppler
Effect
• Light waves from an object
moving away would be
stretched out
• The faster the object
moves, the longer the
wavelength
34
Cosmic Background Radiation
• 1965: Arno Penzias and Robert Wilson were making
adjustments to a radio antenna they built
• There was a steady but dim signal they kept
intercepting
• They realized it was cosmic background radiation
• The detected microwaves are remnants of radiation
produced by the Big Bang
35
The Big Bang
• Scientists use telescopes to study the ancient light
emitted by stars
• Scientists have theorized that the universe formed
during a cataclysmic event known as the big bang
• The Big Bang Theory: States that the world began
with a giant explosion 13 billion to 15 billion years ago
(universe is believed to be about 13.7 billion years
ago)
36
The Big Bang
• According to this theory, before the big bang
there was:
• Nothing
• No time
• No space
• But out of this big nothing came the vast system
of space, time, matter, and energy that now
makes up the universe
37
The Big Bang
• According to the Big Bang Theory:
• Immediately after, the universe was extremely hot and
made up of pure energy
• There was a period of rapid expansion that caused the
energy to cool, and allowed electrons, neutrons and
protons to form
• Hydrogen nuclei started to form but it was still too hot to
form stable atoms
• About 380,000 years after the big bang is when electrons
could combine with atomic nuclei to form atoms
• The first stars were born about 400 million years after the
big bang
38
39
The Big Bang
• There are several theories being tested, and as
new information is found, we might revise what
we believe
• The Big Bang is the most supported by current
evidence
• cosmic background radiation and observation of the
movement of distant galaxies
40
Future of the Universe
• The future of the universe is uncertain
• The universe is still expanding but it will not do this
forever
• The combined gravity of all the mass in the universe is
also pulling the universe inward
41
Future of the Universe
• Possible outcomes:
• 1. the universe will keep
expanding forever
• 2. the expansion of the
universe will gradually slow
down and the universe will
approach a limit in size
• 3. The universe will stop
expanding and start to fall
back on itself
42
Future of the Universe
• If there isn’t enough mass – gravity will not be strong
enough to stop the expansion
• Just right amount of mass – the expansion will slow
down but not end completely
• Too much mass – gravity will overcome the
expansion and the universe will start to contract (the
big crunch), becoming very hot and small, at this
point the universe could end, or they cycle would
start again
43