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Intro presentation on Galaxies, Big Bang and Dark Matter. (Presented at Thammasat University on November 17, 2014)
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Galaxies, The Big Bang
& Dark Matter
Stephen Perrenod, Ph.D.
Interstellar Intergalactic!
What is a Galaxy?
Gravitationally bound system of:
StarsPlanets
GasDust
"Dark Matter" (mostly!)
3 Major Types of Galaxies
Elliptical - M87
Spiral - M101
Irregular - NGC1427A
Image credit: X-ray: NASA/CXC/SAO; Optical: Detlef Hartmann; Infrared: NASA/
JPL-Caltech
Our Galaxy: The Milky Way200 to 400 Billion Stars
A Spiral Shape
Size 100,000+ light-year Diameter
(Only 1000 thickness)
Sun distance to center, 27,000 light-years
Sun orbits around center once in 240 million years
Portion of Milky Way
NGC 6744
Milky Way: Latest Star Map
Density map of stars in a portion of the Milky Way disk
New catalog from the Isaac Newton Telescope
219 million stars mapped
10 years of data!
Credit: Hywel Farnhill, University of Hertfordshire
Milky WaySchematic
Top Down View:
Bar, Spiral Arms &You are Here!
Milky WaySchematic
Side View:
Disk, Bulge, Halo &You are Here!
Disk: ~100 billion solar massesBulge: ~10 billion solar massesHalo: ~1 trillion solar masses
Our Neighbor: Andromeda Galaxy
Distance - 2.5 Million light-years
Size - 220,000 light-years
Will collide with us in ~4 Billion years!
M31
Andromeda Attacks!
Lots of time to prepare..
The Magellanic Clouds
Southern Hemisphere objects, visible to the naked eye
About 200,000 light-years away
Large Magellanic Cloud is 14,000 light-years in size
Small Magellanic Cloud size is 7,000 light-years
The Local Group
Our neighborhood!
10 million light-years across
Will coalesce eventually into one Supergalaxy
Rich Cluster of Galaxies~ 1000 galaxies bound together
Along with dark matter and gas
High gravitational potential heats gas to 100 million degrees
X-ray emission
Abell 2218
Why Galaxies?
Galaxies exist so that multiple generations of stars
can be created
Stars exist to create elements for, and provide heat and
light to, planets
Planets exist as friendly abodes for life:Including You!
Stellar Factories
Galaxies are Huge
They are old ~ up to 13 billion years
They are factories for star formation and planet
formation Orion Nebula
Life Cycle of Stars
Main Sequence—-
White DwarfNeutron StarBlack Hole
Ages of Earth, Universe
Age of Earth = 4.6 billion years
Age of Universe = 13.8 billion years
Age of Universe ~ 3 * Age of Earth
Cosmology: Study of Universe as a Whole
Big Bang:
Homogenous, expanding universe
Finite age
Same laws of physics everywhere
Key Dates: Big Bang theory
1912: Galaxy redshifts (V. Slipher)
1915: General Relativity (A. Einstein)
1922: Friedmann equations (A. Friedmann)
1927: Expanding Universe (G. Lemaitre)
1929: Hubble Diagram, Law (E. Hubble)
1964/5: Cosmic Microwave Background Radiation (A. Penzias & R. Wilson)
RedshiftLight is shifted toward the red, if the distant galaxy is moving away
from our galaxy(Almost all are!)
V = c * z (Small z)
c = 300,000 km/s
Distant galaxy
e.g. a few percent of c
Hubble Diagram: 1929
Plot of velocity (recession speed) vs. distance
Hubble's estimate: 500 kilometers/sec/Megaparsec
Megaparsec ~ 3.26 million light-years
Nearest star 4.2 light years
Sun 8 light-minutes
~ Millions of light-years
Hubble's Law
V = H * D
Speed of recession is proportional to distance
H = Hubble's constant
H = 68 km/sec/Mpc (units are inverse time)
Age of Universe
T (now) = 1 / H(now) = 13.8 billion years
Dark Matter
Our galaxy is mostly made of mysterious "Dark Matter"
Not stars or light-emitting gas, but gravitational effects
seen
All galaxies and clusters of galaxies are like this!
Harvard computer simulation
What does "Dark Matter" mean?
Simply, matter that is hard to detect because
it doesn't emit light
But it has mass, so has gravitational effects
Thought to be some kind of new, unknown
particle (or more than one)
Abell 1689
Ways to Detect Dark Matter's Gravitational Effects
Galaxy rotation curves
Clusters of galaxies, X-ray emission
Gravitational lensing
How Much Dark Matter is there?
5 times as much as all ordinary matter!
Dark
Ordinary
What is it composed of?We don't know!
NOT candidates: faint stars, black holes, dust, planets, lumps of coal
Candidates are all hypothetical new particles!Weakly Interacting Massive Particles:
NeutralinosAxions
Sterile neutrinoss-quark matter
CDMS-IISi wafers
3 particles?
Thank you!
Cosmology blog:darkmatterdarkenergy.com
e-book on Amazon, iBooks