Transcript The Big Bang, Galaxies, & Stars Big Bang theory – Origin of the Universe  Big Bang marks the inception of the universe • • Occurred about 13.7

The Big Bang,
Galaxies, & Stars
Big Bang theory – Origin of the
Universe
 Big
Bang marks the inception of the
universe
•
•
Occurred about 13.7 billion years ago
All matter and space was created
 Not
a huge explosion that hurled matter
in all directions. Technically, there was
no “bang”
 Technically, matter is not moving outward
in all directions. Reality: space expands
Big Bang Evidence

Distant galaxies are moving away from
each other – Doppler Red Shift. Hubble
(1929) – the farther away the galaxy is the
faster it is moving away.

Cosmic Microwave Background Radiation
– Penzias & Wilson (1965). Left over
radiation from the “explosion”
Raisin bread analogy of an
expanding universe
Expansion Evidence for Big Bang

Electromagnetic Energy - Type of energy
given off in the form of transverse waves

Different types of electromagnetic energy
are distinguished by their different
wavelengths
Page 14 of the ESRT
Electromagnetic Spectrum –
humans can only see one part of
spectrum – visible light
Expansion Evidence
 Most
stars are made of Hydrogen &
Helium gas.
 Elements
that emit specific wavelengths
within the electromagnetic spectrum.
 The
spectral line pattern can be used to
identify the star rather like a fingerprint or
bar code.
Red Shift – Blue Shift
 In
1929, Edwin Hubble observed that
spectral lines emitted by stars in distant
galaxies were considerably Red shifted.
 If
a galaxy or star were moving toward the
earth, the spectral lines would show a
blue shift.
Shifting of Wavelengths is called
the Doppler Effect
•
Change in the wavelength
of light emitted by an object
due to its motion
•
Movement toward “squeezes”
the wavelength
•
•
•
Shorter wavelength
Light shifted toward the blue
end of the spectrum
Movement away stretches the
wavelength
•
•
Longer wavelength
Light shifted toward the red
end of spectrum
RED SHIFT – BLUE SHIFT

The greater the degree of shift of the spectral
lines, the faster the object is moving away

The star light DOES NOT appear red or blue (it
still appears as white light from the star)

The “bar code” for each element either shifts to
the shorter wavelength blue end of the spectrum
or to the longer wavelength red end of the
spectrum
What is the best
inference that can be
made concerning the
movements of
Galaxies A, B, and
C?
Structure of the Universe
Hubble Telescope allowed scientists to
infer the structure of the universe
 A GALAXY is a collection of billions of
stars held together by gravity
 Over l00 billion galaxies
spiral – elliptical - irregular

Our solar system is part of the
spiral Milky Way Galaxy
Edge-on view of the
Milk Way Galaxy
Elliptical Galaxy
Spiral galaxy in the constellation
Andromeda
Barred Spiral
Understanding Stars
Grouping of stars and the
classification system has changed
over time with more advanced
tools
STELLAR SPECTRAL
CLASS
Grouping the stars based
on their temperatures
Each class of star has a unique pattern of lines
(“bar code”) to identify it.
Hydrogen
“Hottest”
“Coldest”
Hydrogen
Sodium
Hydrogen
Hertzsprung-Russell
Diagram
Comparing temperature and
brightness for various stars
Hertzsprung-Russell Diagram
aka Luminosity and Temperature of
Stars Diagram – NOT A MAP
 DIAGRAM
IS A USEFUL WAY TO
FOLLOW CHANGES THAT TAKE PLACE
AS THE STARS LIVE OUT THEIR LIVES
 Diagram
is made by plotting (graphing)
each star's LUMINOSITY (brightness) and
TEMPERATURE (as reflected by color)
COMPARED TO THE SUN
Which groups of stars are the BRIGHTEST?
Which group of stars is the HOTTEST?
Which groups of stars are the SMALLEST
and DIMMEST?
Schematically, stars fall into regions
shown below with respect to the sun.
Most stars are on the Main Sequence
because that is where they spend most
of their lives
Our sun is an
average main
sequence star
Luminosity of 1
Temperature
5500°C – yellow
in color
What
color
stars are
hottest?
Coldest?
Red Super
Giants
Red
Giants
White
Dwarfs
COLOR
AND
TEMPERATURE
ARE
RELATED!
Star Formation
 A star
is born when nuclear fusion starts.
 Gravity
pulls hydrogen atoms together. As
trillions of hydrogen atoms are
compressed the temperature increases.
 Once
the temperature reaches ~15 million
ºC, nuclear fusion begins and a star is
born.
Stellar Nursery
filled
Space Space
is filledis with
with the stuff to
the stuff
to stars.
make
make
stars – mostly
hydrogen gas.
Image of the pillars
of creation inside the
crab nebula
At 15 million degrees Celsius in the
center of the star - nuclear fusion
begins
Stars start from clouds
Clouds
provide the
gas and dust
from which
stars form.
But not this kind of dust
Rather: Irregular Grains
Of Carbon or Silicon
A Balancing Act
Energy released from nuclear fusion counteracts inward force of gravity.
Throughout its life, these
two forces determine the
stages of a star’s life.
As long as the forces of gravity and
thermal pressure are balanced, the
star exists on the main sequence.
Life Cycle of Stars – Depends upon
their original mass
After they spend their life as main
sequence star ….
 Sun size > expand to red giant in about 5
billion years > white dwarf > black dwarf
 Super giant > supernova >
very high mass – black hole
high mass – neutron star

Star Life Cycle: Stars are like humans.
They are born, live and then die.
Nebula – cloud
of gas and dust

Protostar – new, just
forming star
Main Sequence
(like the sun)
Red Giant
– once the
star runs out of
hydrogen and the
balance of forces is
upset.
(Betleguise)
DEPENDING ON THE ORIGINAL MASS
White Dwarf: Smaller stars
shrink and cool and
eventually become cold
black dwarves.
Supernova: Star that
has died an explosive
death.
Star Dies – Star casts off shell . It creates
nebula that can take a variety of shapes – Ant
Nebula
JUST FOR FUN
Validity of the following slides is unknown?
But it is still cool to imagine the sizes of
things in space …
Terrestrial Planets – Earth largest
solid, smaller, denser
Earth compared to Jovian Planets
gaseous, large, low density
All planets compared to Our Sun
No longer
considered
a planet