Transcript The Sun, Stars, and Beyond

Stars, Galaxies, and Cosmology
Extra-Solar Planets
• Meaning planets around other stars.
• So far over 400 planets around over 300 stars
have been detected by Doppler shifts in starlight.
• As a planet orbits its sun, it tugs one way then the
other.
• The subsequent movement of the star causes the
Doppler shift in its light.
• So far, only large planets can be detected.
• But one has recently been spectrographed!
• When we find O2, BINGO!
A Lot of Nothing
• After the Sun, the nearest star is 4.3 light
years away.
• A light year (LY) is about 5.87 trillion
miles, or the distance light travels in a year
• Put another way, @ 65 mph, it would take
about 10.3 million years driving non-stop
to get there (and at these gas prices…)
Not Exactly Empty
• Giant Molecular Clouds exist between the
stars.
• Very thin dust, more like cigarette smoke,
and lots of hydrogen.
• Our cloud is called The Local Bubble.
• These clouds tend to redden the light from
stars, much like our air pollution reddens
the sunset.
Nursery
• These clouds are “thicker” in
certain parts of the galaxy,
providing a nursery for new
stars.
• When a pressure wave travels
through these clouds, the gas
(H) and dust compacts enough
so that gravity can slowly
compress the “clumps” into
protostars that eventually
become solar nebula that then
become_____________.
Bok Globule
One Quality to Rule Them All
• The single quality of a star that most
determines its existence and its fate is its
mass, both initially and at the end of its life
cycle
– A reminder: when we talk about the life and
death of a star, we are not talking Hollywood;
our stars have more character but are not alive
Mass/Lifetime Line
Chandrasekhar Limit
0.085Msol
Brown
Dwarf
12 Tyr
0.80Msol
Red
Dwarf
1.4Msol
Yellow
Dwarf
20Gyr
~3Msol
Giants
5Gyr
10Myr
Stellar Types (simplified view)
• Stars < 8.5% the Sun’s mass (Ms) fail to start the fusion
process—called Brown dwarfs.
• Stars > 10% Ms but < 80% Ms are called Red Dwarfs and
exist for up to 200 Billion years.
• Stars between 80% Ms and 140% Ms are like our sun, and
live about 10 billion years.
• Stars* between 140% Ms and 300% Ms live only about 10
million years and explode when they die.
• Stars* >300% Ms collapse completely out of the Universe
and become Black Holes.
*at the end of their fusion epoch
So….
• What conclusion can you draw about the mass of
a star predicting its lifespan?
• The more massive a star, the shorter it “lives”.
• This is because larger, more massive stars are
much hotter and burn (fuse) their nuclear fuel
much more quickly.
• Like a Corvette burning gas more quickly than a
Prius.
The Death of Sun-like Stars
• After about 5 billion more years, the H in
the core will run out.
• The core will collapse, and the outer layers
will be blown outward, engulfing the inner
planets.
• Eventually the core will collapse so much
that the temperature will rise to 100 million
K; then Helium will fuse into Carbon.
“Shine On You Crazy…”
• Eventually though, the helium will run out,
and the star, now only the size of a large
rocky planet, will be made of hot, highly
compressed carbon, cooling off for billions
of years as a White Dwarf, shining by its
heat alone.
• What do you get when you compress hot
carbon for a long time?
KaBoom Stars
•
•
•
The more massive stars that
explode fuse elements all the way
down to iron, and in their
explosion fuse elements even
heavier.
In fact, all elements, in your body,
your car, your pet cat Fluffy,
except for hydrogen and some
helium, were generated in this
stellar explosion, called a Super
Nova.
The remnants of these explosions
is a tiny dense object known as a
Neutron Star.
Supernova 1987A
• Exploded in the
Large
Magellanic
Cloud 167,000
years ago
– Light finally
arrived in 1987
• As much light
billions of 1013
suns!
You Can Check In…
• But you can never check out of
a Black Hole.
• When a supermassive star (>10
Msol) runs out of fuel and tries
to explode, gravity thwarts the
kaboom and squeezes the star
into zero volume.
• This has the effect of bending
the space around it, like taking
the floor and wrapping it up in
a ball around you.
• Called Black because no light
escapes, and Hole because it is
made out of nothing, like any
good hole.
An Extended Family of Stars
• The HR diagram
• Stellar output on
the vertical axis
• Temperature on
the horizontal
• O, B, A, F, G, K,
M are the Spectral
Classes
Clusters
• When an interstellar cloud is impacted by a
shock wave, many stars ultimately form,
depending on the size of the cloud.
• These masses of stars are known as
Clusters.
Types
• Globular Clusters can contain as many as a
million, older stars (red dwarfs), and most are
found in the halo outside the plane of the galaxy.
• Open clusters contain about 1-10 thousand
young, hot stars, and are mostly in the spiral arms
of the galaxy. The Pleides (7 sisters) is one such
example.
• Associations are very poor in stars, about 100 or
so young, hot stars, located in the plane of the
galaxy.
– Actually disassociating
Globular and Open
Altogether
• The stars and their
planets, the groups
of stars we call
clusters, the
interstellar dust and
gas clouds, all make
up a structure known
as a galaxy.
• Our galaxy is known
as the Milky Way.
Vitals
• Our galaxy has a spiral shape with two bright and
one faint arms.
• The core or nucleus of the Milky Way contains a
supermassive Black Hole.
• The galaxy is about 100,000LY across,
15,000LY at its thickest, and contains about 100500 billion stars.
• Our solar system is about 30,000LY from the
core.
• We orbit the core about once every 240 million
years.
Other Kinds of Galaxies
• The most common is the elliptical galaxy, shaped
sort of like a big egg.
• There are spiral and barred spiral galaxies,
• Irregularly shaped galaxies also exist, though
fewer in number.
• A galaxy’s shape is determined by its rate of
spin, and if it has been subject to any collisions or
mergers.
• These all contain 100 billion stars or more, and
there are 100 billion galaxies out there!
For Classification Purposes Only;
no evolution is implied
Grouping
• Galaxies also form groups
based on gravitational
attraction.
• The nearest galaxy to us
is Andromeda, about 1.5
million LY away.
• This and about 30 other
galaxies form the Local
Group, about 5-10
million LY across.
Bigger..
• In turn, our Local
Group is part of a
larger
conglomeration
known as a
galactic cluster.
• Our local cluster is
known as the,
well, the Local
Cluster.
And Bigger…
• Galactic clusters are arranged in huge filaments called
superclusters that stretch across vast regions of space, containing
millions of galaxies.
the Virgo Supercluster
(part of) Large Scale Structure
The Big Bang
• Neither big nor a bang.
• Based on the movement of galaxies observed
today, astrophysicists can “run the clock
backwards” and estimate that the Universe began
about 13.7 billion years ago.
• The event is now called the Big Bang; however,
it took place in an infinitesimally tiny space and
there was no sound.
And it continues..
How do we know this?
• Edwin Hubble ~1929 observed all distant
galaxies moving away from us, indicating
expansion
• Einstein’s General Theory of Relativity
mathematically predicts the curvature of space,
like in a Black Hole.
• This curvature is observed and measured
regularly because it changes as time passes and
the Universe “flattens”.
• Therefore, mathematics can predict when the
curvature was infinitely wrapped up.
Evidence?
• If the Universe was infinitely wrapped up, then
due to thermodynamics it would have been
infinitely hot.
• As it unwraps and flattens, it should cool to a
specific temperature, based on known cooling
processes.
• Also, high temperatures would have emitted
radiation, which would have changed frequency
as the Universe cooled.
Found in 1963
• Two scientists in NJ accidentally found this
cosmic microwave background radiation (CMB)
while experimenting with satellite
communication.
• Its frequency and the associated temperature
matched the predictions.
• Certain details need to be refined, but the idea of
a miniscule, impossibly hot start to our Universe
is widely accepted by Astrophysicists.
WMAP: Map of CMB
Where We Are Going: Possible
Fates of the Universe
1
2
3
4
Critical Mass
• Einstein’s theories say that mass curves
space.
• If enough mass exists, the Universe will
eventually curve back in on itself, causing
a “Big Crunch”. (1 on previous page)
• If too little mass exists, things will flatten
and expand forever, resulting in the “Heat
Death of the Universe”. (2 & 3)
Current Prediction
• Insufficient mass has been detected to ‘close’ the
Universe
• In addition, observations show the Universe is
not only expanding but accelerating (4)
• Current predictions are for the Universe to
expand for about 10,000 million, million, million,
million, million, million, million, million,
million, million, million, million years, at which
time it will be an empty, cold place.
Plenty of Time to Study for the
Final Exam!