Download Stars and Galaxies

Stars and Galaxies
Chapter 1
A Trip through the Universe
• Light- years are used to measure distances
btwn. Celestial objects
• Celestial objects in descending order:
– Universe
– Galaxy
– Nebula
– Earth
Multiple-Star Systems
• Stars appears as smalls points of light
• Alpha Centauri is the closest star to the sun (triplestar system)
– 4.3 light-years from Earth
• Our sun is a single-star system
• Most stars are paired stars called Binaries
– Binary stars are double-stars systems
How to you think astronomers view stars?
Use Optical Telescopes (visible light)
Constellations: Star Groups that form
Patterns
• Sirius/Dog Star, 8 light-years from Earth
– Twice size of the sun, brightest star in sky
• Polaris/North Star, 700+ light-years
– Important in navigation
– End of Little Dipper which is part of:
– Ursa Minor/Little Bear – constellation of stars
• Group of stars which people can see at one time
• Imaginary figures
– Ursa Major/Big Bear – 7 stars of this make up the Big
Dipper
– 2 bright stars in the cup called Pointers → Polaris
• Orion, the Hunter – seen on clear winter
nights
– 2 bright stars in Orion:
• Betelgeuse
• Rigel
– Other close constellations are: Gemini, Canus
Major/Big Dog, Canis Minor/Little Dog
– Summer constellations:
• Scopius, Leo, Virgo
Novas
• Nova – stars that suddenly increase in
brightness up to 100x for a short time then
dims
– Almost all novas are binary systems
– Gases from companion stars strike the other
• Nuclear explosion occurs creating: heat, light, &
gases
Star Clusters
2 types of Star Clusters, appear as 1 star from
Earth
1. Open Clusters
•
•
•
Not well organized
Hundreds of stars
Pleiades
2. Globular Clusters
•
•
•
•
More common
Spherical, round shape
100,000+ stars
Hercules
Nebulae
• Huge clouds of dust that glow btwn stars
• Birthplace of new stars
Galaxies
• Galaxies – major features of the universe
– Contain various groups of stars
– Milky Way – we live in
– 100 billion + galaxies
• 3 Types of Galaxies:
– Spiral – shaped like a pinwheel
• Andromeda
• Milky Way
– Elliptical – spherical to flat in shape
• Very little dust & gas
• Older stars
– Irregular – no orderly shape, less common
• Large and Small Magellanic Clouds closest to the Milky Way
The Milky Way Galaxy
• Planet Earth is in the Milky Way
• Older stars found near the center/nucleus
– Dense in stars
– 20,000 light-years in diameter
• Milky Way 100,000 light-years across and 15,000
light-years thick
– 100,000 yrs to travel across @ speed of light
• Sun located in pinwheel arm abt. 30,000 lightyears from center
– One of the youngest stars in Milky Way
• Spins counter clockwise
– Takes 200 million yrs to rotate 1 time around center
Formation of the Universe
• Spectroscope – breaks up light into its
characteristic colors
– Light focused into a beam by a lens then it
passes through a prism then broken into a
band of colors
– Spectrum – band of colors formed when
white light passes through a prism
Stars on the Move
• All objects in the Universe are moving
• Spectroscopes help to determine if
galaxies or stars are moving toward or
away from Earth
The Red and Blue Shift
• As light strikes the prism of the spectroscope,
prism bends the light according to the
wavelength of each color
• Stars moving fast toward Earth, light waves are
compressed
– Blue end of spectrum known as Blue Shift
• Stars moving away from Earth, light waves are
expanded
– Red end of spectrum known as Red Shift
• Doppler Effect – apparent change in
wavelengths of light moving toward or away
from Earth
The Big Bang Theory
Big Bang Theory states that the universe began to
expand with the explosion of concentrated matter
and energy and has been expanding ever since.
• Evidence
– Expanding Universe
– Background Radiation
• Based on the assumptions that our present
universe is the result of expansion of matter from a
single point
• Astronomers believe that all galaxies are speeding
away from the center of the Universe
• Gravity is the force that holds all galaxies together
An Open Universe
•
•
•
•
Galaxies will continue to race outward
Universe will continue to expand
Stars will eventually die, no more energy
Future means everything may eventually
disappear in the universe
Closed Universe
• Gravity will eventually pull all galaxies back
toward each other
• Blue shift will begin to be see
• Matter & energy will again become packed
into a small area and another big bang will
occur
Quasars
• Quasars – most distance objects from center
of universe
– Abt 12 billion light-yrs from Earth
– Quasar stands for quasi-stellar radio sources
• Gives off radio waves
• Quasi = something like
• Stellar = star-like
• Quasars most mysterious objects in universe
because they give off more energy that 100+
galaxies
• Light from a quasar 6 billion light-years from
Earth has traveled more that 6 billion years to
reach Earth
Characteristics of Stars
• 200 billion billion stars in the
Universe
• Stars differ in many features:
– Size
– Mass
– Color
– Temperature
– Brightness
How Large are Stars?
•
5 main groups of size
1. Super Giant (largest)
–
–
1000 times size of sun
Die quickly due to size
2. Giant
–
10 – 100 times size of sun
3. Sun-sized (medium)
–
Most abundant
4. White dwarf
–
–
Smaller than Earth
Smallest white dwarf Van Mannen’s star
5. Neutron (smallest)
–
Abt. 16 km
Composition of Stars
• Elements have “fingerprints”
– Creating certain color lines passed through the
spectroscope when burned
• Hydrogen is most common element in stars
– 60-80% of total mass
• Helium is 2nd most common element
• Both elements make up abt 96 -99 % of
star’s mass
Surface Temperature of Stars
• Star’s color help to determine surface
temperature of a star
– Color is related to surface temperature
• Surface temp. much lower that core temp.
– Ex. Sun
• Surface temperature abt 6000°C
• Core temperature abt. 15,000,000°C
– Hottest star abt. 50,000 °C
– Coolest star abt. 3,000°C
– Most stars somewhere in between
Brightest Stars
• Brightness depends on size of star, surface
temperature, distance from Earth
• Apparent Magnitude – brightness of a star
as it appears from Earth
• Absolute Magnitude – amount of light a star
actually gives off
• Most stars brightness is constant
• Variable stars brightness varies
– North Star/Polaris is a Pulsating Variable star
that changes size and brightness
Hertzsprung-Russell Diagram
• Ejnar Hertzsprung – Danish astronomer
• Henry Norris Russell – American astronomer
• Both found that as absolute magnitude of stars
increase the temperature of stars also increases
• Definite patterns formed called the HertzsprungRussell diagram
– Temperature plotted on horizontal axis
– Absolute magnitude on vertical axis
• Main-sequence stars are found in the upper left
corner to the lower right corner
Measuring Star Distance
• Parallax – used to measure distance to stars
– Refers to the apparent change in the position in
the sky, Earth’s position not movement of star
• Brightness of the star is also used to
measure distance
– Use apparent and absolute magnitude in a
complicated formula
Why Stars Shine
– Very strong gravitational forces in the core of
stars
– Gravity pulls together atoms of Hydrogen gas so
tightly they become fused
• Nuclear Fusion – hydrogen atoms are fused
to form helium atoms
– Hydrogen changed into Helium at a huge rate
but a large amt of Hydrogen is lost.
• Lost Hydrogen changed into energy in the form of
heat and light
– This is why stars shine
• Fusion within an aging red giant star
causes temperature in the core of the star
to rise
A Special Star: Our Sun
• Layers of the Sun
– Ball-shaped object made of extremely hot gases
– 4 main layers of sun
•
•
•
•
Corona – outermost layer of sun’s atmosphere
Chromosphere – 2nd layer of sun’s atmosphere
Photosphere – innermost layer of sun’s atmosphere
Core – center of the sun
The Active Sun
• Calm star
• Prominences – solar storm, seen as huge bright
arches/loops of gas
• Solar Flares – solar storm, bright bursts of light on
sun’s surface
– Lasts less than 1 hour
• Solar Winds – continuous stream of high-energy
particles released into space
• Sunspots – dark, cooler areas on sun’s surface
– Storms in the lower atmosphere of sun
• Sun rotates on an axis like the Earth
– Gases rotate once every 25 days
Evolution of Stars
• Life cycle of stars from “birth” to “death”
Protostars
• New stars form from gases in a nebula
– Hydrogen gets clumped together by gravity
– Begin spinning in a cloud formation
– Collision heat up and nuclear fusion occurs
• Protostar – great heat that is given off during
nuclear fusion causing a new star
Medium-Sized Stars
• Life cycle of star is now fixed
• Main factor that shapes the evolution of a star is how much
mass it began with.
• Stars shine with a red color when most of the hydrogen gas
has been converted into helium
• Star begins to grow and heats up becoming a giant red star
• As giant red continues to age the temperature of the Helium
core rises to abt 200,000,000°C
– Causing carbon atoms to form
– Star begins to die
– Gravity causes matter to collapse inward squeezing tightly becoming
White Dwarf
White Dwarfs
•
•
•
•
Matter extremely dense
Not a dead star, shines with hot white light
Stars will slowly die
Life span range:
– 10 billion – 100 billion yrs
Massive Stars
• Mass of massive stars 6x that of sun
• Take same path as medium-sized stars
except for after red giant stage they do not
become white dwarfs
• Carbon atoms continue to fuse creating
heavier elements like oxygen & nitrogen
• Core of massive star so hot that fusion
continues until the heavy element of iron is
formed
Supernovas
• Massive stars begin falling apart
• Supernova - tremendous explosion occurs
– Lights up sky for weeks
– Most famous supernova on record observed in
1054 by a Chinese astronomer
• lit the sky for 23 days and seen at night for more that
600 days
• Crab Nebula – remains of this supernova
Neutron Stars
• Neutron stars are the result of supernovas
– Very dense
– Spin rapidly, giving off radio waves as pulses
– Pulsars – neutron stars that give off bursts of
radio waves
Black Holes
• Black Hole – swallows matter and energy as
if a cosmic vacuum cleaner
– Result from death of super massive stars
– No light escapes but sometimes have a
companion star
• Helps astronomers to find black holes