Download Evolution of Stars and Galaxies

Chapter 25
Section 1: STARS
Patterns of stars: Constellations
Ancient cultures used mythology or
everyday items to name constellations.
 Constellations: Patterns of stars in the
night sky

Modern Astronomy Studies 88
Constellations (Most named long
ago)
Circumpolar Constellations

Stars in the northern sky that appear to


circle Polaris in 24 hours
are visible all year
Polaris or Northern Star located at end
Of Little Dipper in Constellation Ursa Minor
Some constellations
are not visible during
winter, only the summer
(and vise versa).

example – Orion
Can not see b/c daytime
side is facing it.
Absolute Magnitude

measure of the amount of light a star actually
gives off.
Apparent Magnitude

measure of the amount of a star’s light
received on Earth
Sirius
Fifth closest star
 Brightest star in
N. Hemisphere

Canis Major
Rigel

Absolute magnitude much higher than
Sirius but apparent magnitude is lower
because it is further away from Earth
- Characteristics of Stars
Parallax

Parallax is the apparent change in position
of an object when you look at it from
different places.
- Characteristics of Stars
Measuring Distances to Stars

Astronomers use parallax to measure
distances to nearby stars.
Space Measurement

Astronomers measure a star’s parallax

Need to know angle that the star’s position
changes and size of Earth’s orbit
Distance is measured in light-years
Light year: distance light travels in a year.
 300,000 km/s or 9.5 trillion kilometers/yr

Star Properties

Color indicates temperature
Hot stars are blue (hottest)-white
 Cool stars are orange – red (coolest)
 Average stars are yellow

Cool stars look orange or red
Medium Temp. Stars are Yellow
Like Our Sun!!!
Also known as Sol (Roman God)
The Sun’s official
symbol.
- Characteristics of Stars
Star Size

Stars vary greatly in size. Giant stars are
typically 10 to 100 times larger than the
sun and more than 1,000 times the size of
a white dwarf.
Sizes of Stars
Star Sizes
THE SUN
Closest star to the Earth
Sun’s Energy

Fusion reaction – when to atoms are fused
into one
Depend on Sun
Sun’s layers

energy created in the core moves outward
through the radiation zone and convection
zone into the Sun’s atmosphere.
How is energy
created in core?
Sun’s Atmosphere
Photosphere: lowest layer gives off light
and is about 6,000 K. (10,340.33 °F)
 “surface”

Sun’s Atmosphere

Chromosphere: above photosphere,
extends 2,000 km above photosphere
Sun’s Atmosphere
Corona – extends (millions of km) into
space, the 2 million K (3,599,540.33 °F)
 releases charged particles as solar wind.

Surface Features

sunspots: dark areas cooler than their surroundings.
 Temporary features which come and go over days,
weeks, or months
 Increase and decrease in a 10 to 11 year pattern
called solar activity cycle.
Sun’s rotation
Studying sunspots showed the Sun has
differential rotation
 faster at equator – 25 days
 Slower at poles – 35 days

Sun’s Surface Features

Prominences: huge, arching gas columns
possibly caused by magnetic fields

Solar flares: Violent eruptions near
sunspots

Coronal Mass Ejections (CMEs): When
large amounts of electrically – charged
particles are ejected form the corona
2-3 times a day
Highly charged solar wind particles
can disrupt radio signals, damage
satellites that orbit Earth.
Near Earth’s polar areas solar wind
material can create light called an
aurora.
Middle-aged / average star
 Typical absolute magnitude with yellow
light.
 Takes 8 min. to get here
 Unusual: Sun is not part of a multiple star
system or cluster (only 1 star near us!)

Star Systems

Binary System – two stars orbit each other

Triple Star System – when 3 stars orbit
each other

Star Cluster – many stars relatively close
to each other, gravity is strong
Evolution of Stars
Section 3
Hertzsprung – Russell Diagram
H-R diagram




higher temperatures =
brighter absolute
magnitude
Main sequence –
group of stars running
diagonally across
diagram; most stars fit
into this band (90%)
Hot, blue, bright in
upper left
Cool, red, dim stars in
the lower right

Yellow like our sun is
in between
Most stars are small, red stars found in the low right

White dwarfs – hot but not bright
Located in lower left corner of H-R diagram
 Same size as Earth


Giants or red giants – bright but not hot


Located in upper right corner of H-R diagram
Supergiants – bright but not hot

Located in upper right of H-R diagram
White dwarf
Giants and Red Giants
Red giant Mira
Red Giant Mira and its companion
When two stars orbit each other it is called?
Supergiant
How do stars shine?

Same as Sun NUCLEAR FUSION
Energy given off as visible, infrared, and UV
light
 Only small amounts make it to Earth

E=MC²

Albert Einstein

Mass can be converted into energy
E = energy
 M = mass
 C = speed of light


Small amounts of mass “lost” during fusion
can be converted into large amounts of
energy
Fusion in core
2 H nuclei collide
 1 proton decays to neutron
energy
 1 more proton fuses to He
energy
 Another He isotope combines with the
other and fuse
 Helium nucleus forms 2 protons break
away
energy

Evolution of a star

Mass of the star determines the path of
the life cycle
Star size video clip
Nebula
Always starts as a nebula
 gravity causes cloud to contract
 Tighter the dust the hotter the core at 10
million K fusion begins
 STAR IS BORN

Main sequence (Low Mass)
Fusion pressure and gravity balance out –
stable for millions/billions of years
 Hydrogen is fusing into Helium
 Star runs out of Hydrogen to fuse causing
an imbalance in the core, core heats

Giant
Core temperature inc to 100 million K
allowing for Helium to fuse into Carbon
 Outer layer expands/cools

White dwarf
After core uses up He, contracts more
 Outer layer escapes into space
 Leaves behind a hot, dense core (about
the size of Earth)
 Eventually will cool and stop giving off light

Main Sequence (High mass stars)
Core heats to higher temperatures than
low mass stars
 Hotter temperature form heavier elements
– Hydrogen fuses to Helium at a much
faster rate

Super Giant

Star expands fusing Carbon to iron in the
core
Supernova
The iron in the core can not release
energy through fusion
 Core collapses causing an explosion

Neutron Stars

If star was 1.4 to 3 times as massive as
the sun the supernova will contract until so
tight only neutrons can exist in the core

Teaspoon would weigh 600 million metric
tons (1 ton = 2,000 lbs.)
Black hole
If supernova core is 3 or more times as
massive as Sun core will collapse
 Not even light can escape
 An event horizon anything crossing this
will go (region nothing can escape)
 Other stars orbit around it as usual

- Lives of Stars

A star’s life history depends on its mass.
After a star runs out of fuel, it becomes a
white dwarf, a neutron star, or a black hole.
Chapter 25
Section 4
Galaxies and the Universe
The Milky Way
Contains over 400 billion stars
Galaxy

when gravity holds together a large
collection of stars, gas, and dust
Grouped into
clusters
Milky Way

our galaxy exists in a galaxy cluster
named the Local Group, 45 galaxies in
cluster
26,000 light years from center
26,000 light years from center
Spiral Galaxies
spiral arms wind out from inner section;
some have barred spirals with stars and
gas in a central bar
 Normal spiral

Elliptical Galaxies
large, three-dimensional ellipses
 football – shaped


Irregular Galaxies
small, less common galaxies, with various
shapes
Irregular Galaxies

Ex. Clouds of Magellan

Orbit the Milky Way
The Milky Way
classified as a NORMAL SPIRAL GALAXY
 may contain one trillion stars
 100,000 light years wide
 We are 26,000 light years from center
 sun orbits core every 225 million years
 Center is a super massive black hole 2.5
million times as massive as Sun

Evidence

Chandra X-Ray Observatory


X-rays produced as matter spirals into hole
Observing stars orbiting a black hole
Origin of the Universe
Steady State Theory – universe has
always existed as it does now
 Oscillating Model – universe expands and
contracts repeatedly over time
 Big Bang Theory – the universe is
expanding

Doppler Shift
Starlight moving toward the Earth shifts to
blue-violet end of spectrum
 . . . . . . . . . . . . . away from the Earth
shifts to red end of spectrum
 All galaxies that we can see have a red
shift (moving away from earth)

Red Shift
Discovered by Edwin P. Hubble
 Objects moving toward – compressed
wavelengths – blue/violet
 Objects moving away – stretched
wavelengths - red

Big Bang Theory

universe began 13.7 billion years ago with
a huge explosion that caused expansion
everywhere at the same time.
Great website

http://sunshine.chpc.utah.edu/labs/star_life
/hr_interactive.html
movie

Far away galaxies (10 billion light years
away) give us information about the young
universe

it took that long for the light to reach us

Whether the universe may eventually stop
expanding and begin contracting is
UNKNOWN.