Milky Way & Hubble Law - Los Angeles Mission College F2015 MW... · Astronomy 1 — Elementary Astronomy LA Mission College Spring F2015 Milky Way & Hubble Law

Astronomy 1 — Elementary Astronomy LA Mission College

Spring F2015

Milky Way & Hubble Law

Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015

Quotes & Cartoon of the Day

“Two things are infinite: the universe and human stupidity; and I'm not sure about the universe.”

― Albert Einstein

Once you can accept the universe as being something expanding into an infinite nothing which is something, wearing stripes with plaid is easy.”

-- Albert Einstein

http://www.goodreads.com/author/show/9810.Albert_Einstein


Announcements

• 3rd midterm Thursday

• Review notes posted on the Lecture notes page

• I will drop the lowest midterm grade

• I will post HW key later today — study

• Final 12/15 at 10-12 AM!

• Comprehensive


Last Class

• Stellar Evolution wrapup.

• Black holes

• Binaries & Clusters

• Galaxies

• What’s a Galaxy?

• Galaxy types

• LT Galaxy Classification

• Our Galaxy, the Milky Way


This Class

• Our Galaxy, the Milky Way

• Hubble’s Law (LT Expansion)

• Cosmology (time permitting)


Spring F2015

We live in a Galaxy: The Milky Way


The Milky Way

• Our home galaxy

• A barred spiral galaxy

• From our solar system, we see this...


Milky Way over the VLT

Image Credit: ESO (Yuri Beletsky)


Structure of the Milky Way

• Looking through the disk from inside and combining the 2-D data with distance information allows us to construct a model of what the Milky Way looks like from outside...


Edge-on Model

http://woodahl.physics.iupui.edu/Astro105/


Face-on Model

Image Credit NASA/JPL-Caltech/R. Hurt



Structure of the Milky Way

• Bulge: spherioidal

• about 6000 ly diameter

• Densely packed old red stars

• Bar

• Disk: flat

• about 90,000 ly x 900 ly

• Stars and interstellar gas and dust, including young stars

• Sun about 24,000 ly from center

• Halo: Spheroidal

• about 300,000 ly diameter

• old stars, globular clusters, dark matter, hot gas

Image Credit: R.J. Hall


3D Model

WHAT’S IN THE MW?


Milky Way Recipe

300 ± 100 billion stars

at least 1983 planets

Interstellar Medium (ISM) ~ 1010 M⊙◉☉

Supermassive Black Hole ~ 4-4.5 x 106 M⊙◉☉

Dark Matter

to account for a total mass of 1-1.5 x 1012 M⊙◉☉


Where is the Interstellar Medium?

• Interstellar Medium = ISM

• Everywhere between stars

• not uniformly distributed, denser in bar and arms


Milky Way Galaxy

THE GALACTIC CENTER


The Galactic Center

Images about 8° across. GC in upper left

• Entirely obscured in visible light

• First explored using radio astronomy

• later further explored with IR astronomy


The Galactic Center

• The GC is very wierd place

• This image about 3° (1400 ly) across

• Sgr A* location of black hole


The Galactic Center

• stellar orbits in the central 3 ly

• evidence for a supermassive black hole, with mass 4 million solar masses.

DARK MATTER


Actual rotation of Milky Way

Predicted Keplerian orbit based on cataloged content

http://www.astro.ufl.edu/~guzman/ast1002/class_notes/Ch15/gal_rotation.gif

•The data (blue curve) indicate the stars in the outer Galaxy have higher orbital speeds than can be explained by the known mass.

•Dark matter that extends to great distances from the galactic center provides the gravitational force needed to give the outer stars these higher speeds.


What is Dark Matter?

• Rotation curve provides evidence for mass (gravity)

• We call it dark matter because we haven’t directly detected it through observing light

• We don’t really know what it is made out of, we just know where it is and how much of it there is!

• In the Milky Way, most is in the halo, and possibly an extended disk

• 6 x1011 to 3 x 1012 M⊙◉☉


Spring F2015

Cosmology

the origin fate and history of the universe in no time at all

HUBBLE’S LAW


Hubble’s Observations

• Hubble obtained distances and velocities for galaxies beyond our local group

• Velocity from Doppler shift

• Distance from standard candles

• Cephied variables


Doppler Effect


Detecting Doppler Shift

• In astronomy, we detect red (and blue) shift using spectral lines

http://mail.colonial.net/~hkaiter/aa_newest_images/dopp-shifts-spectra.jpg

http://mail.colonial.net/~hkaiter/aa_newest_images/dopp-shifts-spectra.jpg

THE HUBBLE LAW


Hubble’s Law


Hubble’s Law

• A straight line!

• The galaxies are all receding...

• ... and the speed with which they are doing so increases as the distance increases

WHAT IS COSMOLOGY?


What is Cosmology

“Cosmology is the scientific study of the large scale properties of the universe as a whole. It endeavors to use the scientific method to understand the origin, evolution and ultimate fate of the entire Universe.”

WMAP Science Team, "Cosmology: The Study of the Universe," NASA's Wilkinson Microwave Anisotropy Probe,last modified June 6, 2011,

http://map.gsfc.nasa.gov/universe/WMAP_Universe.pdfor http://map.gsfc.nasa.gov/universe/

http://map.gsfc.nasa.gov/universe/WMAP_Universe.pdf

http://map.gsfc.nasa.gov/universe/

THE EXPANDING UNIVERSE


Hubble’s Law

• Hubble’s Law: galaxies are redshifted & the further away they are, the more they are redshifted

• not traveling THROUGH space...

• ... space itself is getting bigger


The Raisin Bread Analogy

• every raisin travels away from every other raisin

• obeys Hubble’s Law

http://www.absoluteastronomy.com/topics/Metric_expansion_of_space

http://www.absoluteastronomy.com/topics/Metric_expansion_of_space

THE OBSERVABLE UNIVERSE


Telescopes are Time Machines

• Light takes time to travel

• We see things as they were

objectWe see they as they

were _____ agoWhat they would see looking at

earth

Proxima Centauri 4.3 years August 2009

Sirius ~ 28 years Apartheid dismantled

HD156668b(a 2 earth-mass planet) ~80 years Hitler’s rise to power

Rigel ~860 yearsHenry II marries Eleanor of

Aquitane

Center of MW ~24, 000 yearsThe traces of the very last

Neanderthals

Andromeda Galaxy 2.5 million years Homo erectus learns to use tools

Center of Virgo Cluster 65 million years Extinction of the Dinosaurs

Galaxy Cluster MCS J0416.1–2403 4.5 billion years Formation of the Solar System


The Observable Universe

• we can only see the portion of the Universe which is within the distance light could travel in the time since the beginning of the universe.

• Even though the Universe is infinite, we see only a portion of it.

• That portion is called the observable universe.


The Cosmological Principle

• We only see part of the infinite universe.

• Theorists want to apply theory to the whole universe

• the Cosmological Principle (an assumption)

• Universe is homogeneous and isotropic when averaged over very large scales.

• i.e. our location in the Universe is not special, it’s the same everywhere

WARMUP QUESTION


Which of the following statements about the observable universe is correct?

A. It includes all galaxies in the universe.

B. It is the same size for all possible vantage points.

C. It extends to the edge of the universe.

D. It includes the same region of space for all possible vantage points.

E. More than one of the above choices is correct.


Spring F2015

LT -- “Making Sense of the Universe and Expansion”

Lecture Tutorial pp 151-154


Which of the following statements about the observable universe is correct?

A. It includes all galaxies in the universe.

B. It is the same size for all possible vantage points.

C. It extends to the edge of the universe.

D. It includes the same region of space for all possible vantage points.

E. More than one of the above choices is correct.

Let’s Practice


In the “balloon analogy,” what aspect of the real universe does the inside of the balloon represent?

A. space and time

B. the center of the universe

C. nothing

D. where the universe used to exist


In the “raisin-bread analogy,” what aspect of the real universe does the surface of the loaf represent?

A. the size of the universe

B. the edge of the universe

C. nothing

IT ALL STARTED WITH…


Expanding Universe + General Relativity + The Cosmological Principle implies....


It all started with a Big Bang


Editorial Note

• The Bearnaked Ladies got a lot right except for making all the elements...

• But very smart people had the same wrong idea for a long time

• Only H and He (a little Li) are made by Big Bang nucelosynthesis.


Spring F2015

The Big Bang


What Was the Big Bang

• NOT an explosion

• NOT something that happened in a single place (despite the cartoon)

• “It is better thought of as the simultaneous appearance of space everywhere in the universe. That region of space that is within our present horizon was indeed no bigger than a point in the past. Nevertheless, if all of space both inside and outside our horizon is infinite now, it was born infinite.”*

* WMAP Cosmology 101 Website


The Father of the Big Bang

• Belgian physicist & Catholic priest Georges Lemaitre

• Also predicted theoretically Hubble’s Law

• “Rather than expanding into pre-existing space, The Big Bang created space. It has been expanding ever since.”

• Einstein had a hard time accepting the expanding universe: "Vos calculs sont corrects, mais votre physique est abominable"

• (Your math is correct, but your physics is abominable.)

http://exlaodicea.files.wordpress.com/2008/01/lemaitre-einstein.jpg

http://exlaodicea.files.wordpress.com/2008/01/lemaitre-einstein.jpg


Energy and Mass are Interchangeable

• Einstein realized that matter and energy are really the same thing

• E=mc2

• Mass can be converted to energy

• Energy can also be converted to mass

• In the hot, compact early universe, matter could not exist, only energy

• Energy later became matter...


From “the History of Everything” by the Barenaked Ladies

“Our whole universe was in a hot dense state...”

Accurate

Let’s Practice


If you watched the history of the universe like a movie playing backward, what would you see?

A. Objects getting farther apart.

B. The universe becoming denser.

C. The temperature of the universe decreasing.

D. Regions of space becoming smaller.

E. More than one of the above.


Compared to now, how would you best describe the early universe?

A. hotter and less dense

B. colder and less dense

C. hotter and more dense

D. colder and more dense

EVIDENCE FOR THE BIG BANG


3 Main Observations Support the Big Bang

• The Expansion of the Universe

• The abundance of H, He & Li in the early universe

• The Cosmic Microwave Background Radiation


What is the CMB?

• The Big Bang theory predicts that the early universe was very hot

• Implies that the early universe should be filled with radiation from the heat left over from the Big Bang

• This is the CMB (Cosmic Microwave Background)

http://map.gsfc.nasa.gov/universe/bb_theory.html

http://www.amazon.com/The-Big-Bang-Theory-Complete/dp/B0053O89WY/ref=sr_1_3?ie=UTF8&qid=1351195713&sr=8-3&keywords=the+big+bang


Discovery of CMB

• Imagine you built a spiffy new piece of equipment to measure radio emission from communications satellites...

• ...and you kept getting this irritating noise with wavelength 7.35 cm from every direction!


Discovery of CMB

• What would you do?

• Check the equipment for errors?

• remove the pigeons nesting in your radio antenna?

• ????


Discovery of CMB

• Arno Penzias and Robert Woodrow Wilson, at Bell Labs in 1964

• They eventually concluded the faint signal was real and came from outside the galaxy

• At that same time, Robert H. Dicke, Jim Peebles, and David Wilkinson, astrophysicists at Princeton University, were preparing to search for microwave radiation in this region of the spectrum.

• A friend told Penzias about Peebles’ paper on the subject

• They realized what they had discovered

• Penzias and Wilson were awarded the Nobel Prize in Physics in 1978

http://en.wikipedia.org/wiki/Robert_H._Dicke

http://en.wikipedia.org/wiki/P._J._E._Peebles

http://en.wikipedia.org/wiki/David_Todd_Wilkinson

http://en.wikipedia.org/wiki/Astrophysicist

http://en.wikipedia.org/wiki/Princeton_University

http://en.wikipedia.org/wiki/Microwave_radiation


The CMB today

• Very cold

• ~2.725 K (2.725° above absolute zero)

• can be detected everywhere we look.

• astonishingly uniform in every direction

• tiny fluctuations are of extreme interest to cosmologists

http://www.astro.ubc.ca/people/scott/cmb_intro.html

http://www.astro.ubc.ca/people/scott/cmb_intro.html


The Blackbody Spectrum that got a Standing Ovation

• John Mather presented this the January 1990 meeting of the American Astronomical Society Meeting.

• Based on the first 9 minutes of data from COBE (COsmic Background Explorer)

• John Mather and George Smoot were awarded the Nobel Prize in Physics in 2006.

Photo: P. Izzo


Structure in the Early Universe

• COBE map showing fluctuations

• extremely faint, only one part in 100,000 compared to the 2.73 K average temperature

Let’s Practice


The Cosmic Microwave Background Radiation looks like radiation from a perfect blackbody at a temperature _____.

A. a few K above absolute zero

B. similar to water ice

C. billions of K

D. about the temperature of burning wood


The temperature of the cosmic microwave background is very uniform except _____.

A. it is hottest in the direction of the Big Bang

B. it is coolest in the direction of the Big Bang

C. for small fluctuations randomly distributed

TIMING OF THE BIG BANG & INFLATION


When was the Big Bang?

• Until recently, astronomers estimated that the Big Bang occurred between 12 and 14 billion years ago.

• Solar System ~ 4.5 billion years old

• Humans ~ few million years.

• Astronomers estimate the age of the universe in two ways:

• by looking for the oldest stars

• by measuring the rate of expansion of the universe and extrapolating back to the Big Bang

http://www.amazon.com/The-Big-Bang-Theory-Complete/dp/B0053O89WY/ref=sr_1_3?ie=UTF8&qid=1351195713&sr=8-3&keywords=the+big+bang

http://map.gsfc.nasa.gov/universe/uni_expansion.html



• Oldest Stars

• Oldest globular clusters contain only stars less than 0.7 solar masses.

• suggests that the oldest globular clusters are between 11 and 18 billion years old.

• Working backward

• WMAP measured detailed structure of the CMB

• deduce the density, composition and expansion rate

• gives age 13.7 ± 0.13 billion years!

http://map.gsfc.nasa.gov/news/facts.html



• Working backward

• WMAP satellite measured the detailed structure of the cosmic microwave background fluctuations

• more about this in a moment

• This allows astronomers to deduce the current density of the universe, the composition of the universe and its expansion rate

• able to estimate the age of the universe to about 1%:

• 13.7 ± 0.13 billion years!

http://map.gsfc.nasa.gov/news/facts.html

http://map.gsfc.nasa.gov/universe/bb_cosmo_fluct.html

http://map.gsfc.nasa.gov/universe/uni_matter.html

http://map.gsfc.nasa.gov/universe/uni_expansion.html

THE HISTORY OF THE UNIVERSE


The whole universe was in a hot, dense state...



“...Then nearly fourteen billion years ago expansion started

Wait!”

Accurate



“...The earth began to cool

The autotrophs began to drool

Neanderthals developed tools

We built a wall

We built the pyramids

Math, science, history

Unraveling the mystery

That all started with the Big Bang

Bang!”

FORMATION OF “STRUCTURE”


Formation of Structure

• The universe starts out uniform (homogenous and isotropic) and somehow it becomes “stringy” and “clumpy”.

• First stars and galaxies at about 2 million years

• Process not yet well understood



“... Since the dawn of man is really not that long

As every galaxy was formed in less time than it takes to sing this song”

Partially accurate. The seeds of structure... dark matter organizing the universe… occurred at about 100s. The actual galaxies appeared much later.

“A fraction of a second and the elements were made”

Inaccurate. H & He (a little Li) very quickly at few second. Everything else as massive stars fused elements up to iron in their core and then went supernova.



“... The bipeds stood up straight

The dinosaurs all met their fate

They tried to leap but they were late

And they all died

They froze their asses off

The oceans and Pangea

See ya, wouldn't wanna be ya

Set in motion by the same Big Bang

It all started with the big Bang!”

THE ROLE OF DARK MATTER AND DARK ENERGY


What is the Universe Made of?

• Current theory suggests that 95% of the universe is Dark

• 70% Dark Energy

• 25% Dark Matter

Credit: NASA / WMAP Science Team


What is Matter Anyway?

• Ancient Greeks thought the atom was the smallest particle

• Late 19th, early 20th century realized atoms were made of protons, neutrons & electrons

• But that’s not the end of the story!

• Contemporary physics uses the “standard model” to describe matter (& forces)


Standard Model

• “Baryons are made of quarks & account for the mass of normal matter

• electrons have little mass

• Gauge bosons mediate forces

• Super-symmetry (SUSY) proposes a partner for each of these


WIMPS

• SUSY theories predict the lightest supersymmetric particle to be stable and electrically neutral and to interact weakly with the particles of the Standard Model.

• Just what is needed for dark matter

• (adapted from CERN http://home.web.cern.ch/about/physics/supersymmetry)

http://home.web.cern.ch/about/physics/supersymmetry


Dark Matter

• Dark matter is typically detected by its gravitational effects on matter we can “see”

• Baryonic dark matter is “normal” matter we just haven’t detected (too cold/faint)

• Brown Dwarfs

• MACHOs (MAssive Compact Halo Objects)

• Supermassive Black Holes

• Not likely to account for all the “missing matter”


Dark Matter

• Nonbaryonic dark matter is the exotic stuff

• One of the primary motivations for building “supercolliders"

• may be made of particles produced shortly after the Big Bang.

• very different from ordinary "baryonic matter".

• WIMPs are the main contender

• Other possibilities include massive neutrinos, cosmic strings, modified gravity


Dark Energy

• In 1998 we discovered that the Universe is actually speeding up its expansion

• total shock to astronomers.

• Discovered by observing Type Ia supernovae

• Surveys determined they were fainter than their redshift-distance indicated


Dark Energy

• "dark energy" refers to the fact that something must be causing space to accelerate in its expansion.

• We don’t know what it is. At all.

• Some astronomers identify dark energy with Einstein's Cosmological Constant.

http://imagine.gsfc.nasa.gov/docs/dict_ei.html#einstein

http://imagine.gsfc.nasa.gov/docs/dict_ad.html#cosmological_constant


Here we are

• Just when you started to think you knew what was in the Universe....

• We think 70% of it is made out of something that we have no idea what it is!

• The ultimate fate of the Universe depends on this unknown stuff

THE FATE OF THE UNIVERSE


Big Crunch, Big Freeze, Big Rip?

• Mass (or mass and energy) determine the scenario.


Fate of the Universe

• The most current relevant results, support the “Big Chill” scenario

• from WMAP (Wilkinson Microwave Anisotropy Probe)

• Other scenarios, however, are not conclusively ruled out.

• Stay Tuned



“... It's expanding ever outward, but one day

It will cause the stars to go the other way

Collapsing ever inward,

We won't be here,

It won't be heard

Our best and brightest figure that it'll make an even bigger Bang!”

Not ruled out! However, not what the best current data suggests. It all depends on dark energy & dark matter. Know how to defend it!



“... Austrelopithicus would really have been sick of us

Debating how we're here

They're catching deer

We're catching viruses

Religion or astronomy

Descartes, Deuteronomy

It all started with the Big Bang

Music and mythology

Einstein and astrology...”



“... It all started with the big bang

It all started with the big

Bang!”

Yep

Let’s Practice


What is the ultimate fate of the Universe?

A. To expand forever and grow colder and colder.

B. To remain exactly as it is today.

C. To stop expanding, turn around, and eventually become a point again in the “Big Crunch”.

D. We don’t really know.


What do observations of the structure and content of the universe suggest will be the ultimate fate of the Universe?

A. To expand forever and grow colder and colder.

B. To remain exactly as it is today.

C. To stop expanding, turn around, and eventually become a point again in the “Big Crunch”.

D. We don’t really know.


Most of the Universe is made up of which of the following?

A. Visible matter

B. Energy

C. Baryonic dark matter

D. Non-baryonic dark matter

E. Dark energy


Dark energy is _______.

A. what keeps the Cosmic Microwave Background warm

B. a name for the unknown cause of the Universe’s present increase in its rate of expansion

C. what you get when you plug dark matter into E=mc2

D. the cosmological equivalent of dragons

WRAP-UP


Topic for Next Class

• The Big Bang & the fate of the universe


Reading Assignment

• Astro: 11

• Astropedia:17


Homework

• None at this time

Documents

Milky Way & Hubble Law - Los Angeles Mission College F2015 MW... · Astronomy 1 — Elementary Astronomy LA Mission College Spring F2015 Milky Way & Hubble Law