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Stars, Galaxies, and Cosmology

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Title: Stars, Galaxies, and Cosmology


1
Stars, Galaxies, and Cosmology
2
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!

3
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, _at_ 65 mph, it would take about
    10.3 million years driving non-stop to get there
    (and at these gas prices)

4
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.

5
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
6
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

7
Mass/Lifetime Line
Chandrasekhar Limit
0.085Msol
0.80Msol
1.4Msol
3Msol
Red Dwarf
Yellow Dwarf
Brown Dwarf
Giants
12 Tyr
20Gyr
5Gyr
10Myr
8
Stellar Types (simplified view)
  • Stars lt 8.5 the Suns mass (Ms) fail to start
    the fusion processcalled Brown dwarfs.
  • Stars gt 10 Ms but lt 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 gt300 Ms collapse completely out of the
    Universe and become Black Holes.

at the end of their fusion epoch
9
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.

10
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.

11
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?

12
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.

13
Supernova 1987A
  • Exploded in the Large Magellanic Cloud 167,000
    years ago
  • Light finally arrived in 1987
  • As much light billions of 1013 suns!

14
You Can Check In
  • But you can never check out of a Black Hole.
  • When a supermassive star (gt10 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.

15
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

16
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.

17
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

18
Globular and Open
19
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.

20
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 100-500 billion
    stars.
  • Our solar system is about 30,000LY from the core.
  • We orbit the core about once every 240 million
    years.

21
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 galaxys 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!

22
For Classification Purposes Only no evolution is
implied
23
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.

24
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.

25
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
26
(part of) Large Scale Structure
27
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.

28
And it continues..
29
How do we know this?
  • Edwin Hubble 1929 observed all distant galaxies
    moving away from us, indicating expansion
  • Einsteins 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.

30
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.

31
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.

32
WMAP Map of CMB
33
Where We Are Going Possible Fates of the Universe
1 2 3
4
34
Critical Mass
  • Einsteins 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)

35
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.

36
Plenty of Time to Study for the Final Exam!
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