Download Outline 8: History of the Universe and Solar System

Outline 8:
History of the Universe
and Solar System
The Andromeda Galaxy – One of
hundreds of billions of galaxies, each
with hundreds of billions of stars
A warped spiral galaxy, 150 MLY away and
100,000 LY across.
Galaxies in deep space viewed by the
Hubble space telescope: Looking
back in time
The Hubble eXtreme Deep Field,
made up of some 2,000 images taken
over a decade, provides a stunning
"time tunnel" capturing light from
dim proto galaxies within 500 million
years of the big bang. (NASA)
2012: Hubble looks back 13.2
billion years in deepest view yet
http://www.cbsnews.com/8301-205_162-57520513/hubble-looks-back13.2-billion-years-in-deepest-view-yet/?tag=cbsContent;cbsCarousel
Galaxy clusters viewed from Hubble
space telescope
Colliding Galaxies
Our home galaxy - the Milky Way
The Age of the Universe
• Many published estimates give an age
of 14-18 BY old.
• How are these ages determined?
The Age of the Universe
• The study of light from
galaxies indicates that the
universe is expanding.
This is the basis of the Big
Bang Theory.
• The velocity of expansion
is measured by the amount
of Red Shift in the light
from other galaxies.
Analogy for an expanding universe
where each galaxy moves away from
every other galaxy. No matter where the
observer sits, the universe is expanding.
Map of temperature variation in the Cosmic
Background Radiation (microwaves). The
average temperature is 3 degrees Kelvin. This is
the radiation left over from shortly after the Big
Bang. The lumpiness produced galaxies.
Red Shift of Light Waves
• Light waves are stretched as the galaxies
race away from the earth.
• The spectral lines of the visible spectrum
are shifted towards the red, or longer,
light waves.
• This is an example of the Doppler Effect.
The electromagnetic
spectrum
High energy
Low energy
Examples of spectral lines produced by absorption
of light by gases in a star’s atmosphere. Each line
represents a chemical element.
Red-shift of light indicates that all galaxies are
moving away from us, indicating that the
universe is expanding.
near
far
Calculating Expansion Velocity
• A spectral line for hydrogen from the sun
has a wavelength of  = 6562.85A.
(1 angstrom = 1 x 10-10m)
• Light from a nearby star in our galaxy
shows the same spectral line at
1 = 6563.15A.
• Wavelength shift  = 0.30A
Calculating Expansion Velocity
• Velocity = (x C
• Velocity = (0.30/6562.85) x C
C = speed of light: 300,000 km/sec
• Velocity = 13.7 km/sec
• So this nearby star is receding from us
at 13.7 km/sec.
Calculating Age
• Time = distance/velocity
• e.g., car trip:
5hrs = 300miles/60 miles/hr.
• The Hydra Galaxy is receding from the
earth at 61 x 103 km/sec.
• Its distance is 3.96 x1022 km
(4 billion light years, based on luminosity
of stars; farther stars are dimmer)
Calculating Age
• Amount of time the Hydra Galaxy has
been traveling?
• Time = distance/velocity
• T = 3.96 x 1022 km/61 x 103 km/sec
• T = 6.5 x 1017 sec (1 year=3.15 x 107 sec)
• T = 2.06 x 1010 years = 20 BY
20 BY??
• Is the Universe 20 BY old?
• No, gravitational forces have slowed
down the galaxies since the Big Bang.
• (Note: Recent observations suggest this was the case for the
first 2/3 of the Universe’s history. The expansion rate now
seems to have increased for the last 1/3 of the Universe’s
history. This is explained by “dark phantom energy”, which
is hypothesized to be forming between galaxies and pushing
them apart by repulsive gravitational force. Dark energy is
calculated to be ¾ of the mass-energy of the universe!)
20 BY??
• The present velocities give the
appearance that the galaxies have been
traveling longer than they actually have.
• Thus the estimates of 14-18 BY.
Why the apparent older age?
Consider the following example:
Travel at 100 mph for 2 hours = 200 miles
Travel at 60 mph for 3 hours = 180 miles
Total time is 5 hours. Total distance is 380 miles.
If you were observed traveling at 60 mph and had
covered 380 miles, the assumption would be made
that you had traveled for 6 hours and 20 minutes
(380miles/60mph) rather than 5 hours.
Origin of our Solar System
• The matter in our solar system is
recycled from older stars that exploded
as supernovas.
• Early in the history of our galaxy there
were large stars that ignited, burned
their fuel, and then exploded sending
new elements into space.
Life Cycle of a Star
• Small stars (e.g, the Sun): main sequence,
red giant, white dwarf. (10 BY years)
• Big stars: main sequence, red giant,
supernova. (1 BY years)
• Massive stars: main sequence, red giant,
supernova, black hole. (100 MY years)
Red Giants
Sun
White Dwarfs (circled)
in our galaxy
Life Cycle of a Star
• Main sequence: hydrogen burns
(nuclear fusion) to form helium
• Red Giant: helium burns (nuclear
fusion) to form carbon, carbon burns to
form oxygen, oxygen burns to form
iron. All elements lighter than and
including iron (56) formed this way.
Hydrogen through Iron form in Red
Giants. The rest in Supernovae.
Life Cycle of a Star
• When a red giant has exhausted its fuel, it
collapses inward by gravity.
• This collapse releases so much energy
through fusion that the star explodes as a
supernova.
• Explosive nucleosynthesis produces all the
elements heavier than iron (57-262) plus all
radioactive elements (except C14).
The Crab Nebula, remnant of a
supernova explosion
Ring nebula formed as a Red Giant
became a White Dwarf
Supernovas and the Origin of
our Solar System
Was the collapse of the nebular dust
cloud that formed our solar system
triggered by the shock wave from a
nearby supernova explosion? The
answer seems to be yes.
Supernovas and the Origin of
our Solar System
Evidence: Aluminum-rich inclusions in
meteorites contain the rare isotope Mg26,
which forms by radioactive decay of Al26
(most aluminum is Al27). The 1 MY half
life of Al26 indicates it became part of the
meteorite within a few million years (or
less) of a supernova explosion.
Supernovas and the Origin of our
Solar System
• If the meteorite had formed later than the
supernova explosion (>10 MY), then the
Mg26 would not be in the aluminum-rich
inclusion. Instead, it would be with other
atoms of magnesium (Mg24).
Al27 and
rare Al26
Half life of
1 M.Y.
Al27 and
rare Mg26
Origin of the Solar System
• Stage 1 – slowly rotating
nebula
• Stage 2 – contraction to
disc as rotation increases
• Stage 3 – material
separated into discrete
rings distinct from protosun
• Stage 4 - Planets form by
accretion of material from
the discs
A nebular dust cloud similar to the cloud
our solar system formed from.
The birth of
new stars
from giant
gas pillars
The Horsehead Nebula in the
Andromeda Galaxy
The Witch Head
Nebula, about
1000 light years
away in the
constellation
Orion.
Oldest Galaxy,
13.1 BY old