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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Last Class
• Stellar Evolution wrapup.
• Black holes
• Binaries & Clusters
• Galaxies
• What’s a Galaxy?
• Galaxy types
• LT Galaxy Classification
• Our Galaxy, the Milky Way
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
This Class
• Our Galaxy, the Milky Way
• Hubble’s Law (LT Expansion)
• Cosmology (time permitting)
Astronomy 1 — Elementary Astronomy LA Mission College
Spring F2015
We live in a Galaxy: The Milky Way
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
The Milky Way
• Our home galaxy
• A barred spiral galaxy
• From our solar system, we see this...
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Milky Way over the VLT
Image Credit: ESO (Yuri Beletsky)
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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...
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Edge-on Model
http://woodahl.physics.iupui.edu/Astro105/
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Face-on Model
Image Credit NASA/JPL-Caltech/R. Hurt
Image Credit NASA/JPL-Caltech/R. Hurt
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
3D Model
WHAT’S IN THE MW?
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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⊙◉☉
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Where is the Interstellar Medium?
• Interstellar Medium = ISM
• Everywhere between stars
• not uniformly distributed, denser in bar and arms
Image Credit NASA/JPL-Caltech/R. Hurt
Milky Way Galaxy
THE GALACTIC CENTER
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
The Galactic Center
• The GC is very wierd place
• This image about 3° (1400 ly) across
• Sgr A* location of black hole
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
The Galactic Center
• stellar orbits in the central 3 ly
• evidence for a supermassive black hole, with mass 4 million solar masses.
DARK MATTER
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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.
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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⊙◉☉
Astronomy 1 — Elementary Astronomy LA Mission College
Spring F2015
Cosmology
the origin fate and history of the universe in no time at all
HUBBLE’S LAW
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Hubble’s Observations
• Hubble obtained distances and velocities for galaxies beyond our local group
• Velocity from Doppler shift
• Distance from standard candles
• Cephied variables
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Doppler Effect
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
THE HUBBLE LAW
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Hubble’s Law
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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?
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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/
THE EXPANDING UNIVERSE
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
THE OBSERVABLE UNIVERSE
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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.
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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.
Astronomy 1 — Elementary Astronomy LA Mission College
Spring F2015
LT -- “Making Sense of the Universe and Expansion”
Lecture Tutorial pp 151-154
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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…
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Expanding Universe + General Relativity + The Cosmological Principle implies....
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
It all started with a Big Bang
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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.
Astronomy 1 — Elementary Astronomy LA Mission College
Spring F2015
The Big Bang
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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...
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
From “the History of Everything” by the Barenaked Ladies
“Our whole universe was in a hot dense state...”
Accurate
Let’s Practice
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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.
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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)
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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!
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Discovery of CMB
• What would you do?
• Check the equipment for errors?
• remove the pigeons nesting in your radio antenna?
• ????
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
When was the Big Bang?
• 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!
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
When was the Big Bang?
• 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!
THE HISTORY OF THE UNIVERSE
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
The whole universe was in a hot, dense state...
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
From “the History of Everything” by the Barenaked Ladies
“...Then nearly fourteen billion years ago expansion started
Wait!”
Accurate
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
From “the History of Everything” by the Barenaked Ladies
“...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”
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
From “the History of Everything” by the Barenaked Ladies
“... 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.
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
From “the History of Everything” by the Barenaked Ladies
“... 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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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)
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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)
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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”
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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.
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Big Crunch, Big Freeze, Big Rip?
• Mass (or mass and energy) determine the scenario.
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
From “the History of Everything” by the Barenaked Ladies
“... 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!
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
From “the History of Everything” by the Barenaked Ladies
“... 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...”
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
From “the History of Everything” by the Barenaked Ladies
“... It all started with the big bang
It all started with the big
Bang!”
Yep
Let’s Practice
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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.
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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.
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
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
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Topic for Next Class
• The Big Bang & the fate of the universe
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Reading Assignment
• Astro: 11
• Astropedia:17
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Homework
• None at this time
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