Download Phys 214. Planets and Life

Phys 214. Planets and Life
Dr. Cristina Buzea
Department of Physics
Room 259
E-mail: [email protected]
(Please use PHYS214 in e-mail subject)
Quiz +Lecture 7. Big Bang evidence and stellar lives
+ Hubble Movies
(Page 58-63)
January 21
Contents
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QUIZ no. 1 (10 minutes)
Contents
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Textbook pages 58-63
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The Big Bang Evidence
Looking back in time
Stellar lives and galactic recycling + movie
We are star stuff
Implications for the life in the Universe
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Movie: Hubble 15 years of discovery
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Acknowledgments: NASA/ESA images
The Expanding Universe
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The Universe has continued to expand ever since the Big Bang.
For at least the past few billion years, the rate of expansion of the
universe has been speeding up.
The Expanding Universe
The Big Bang evidence 1
According to current astronomical data, the Universe is approximately 14 billion years old.
The expansion implies the universe was smaller, denser and hotter in the past.
When the visible universe was only one hundred millionth its present size, its temperature
was much hotter (273 million K) and denser - the hydrogen was completely ionized into
free protons and electrons.
WMAP Science Team, NASA
The Big Bang evidence 1
The strongest evidence that supports the Big Bang theory is the detection of the
remnant heat (cosmic microwave background radiation) from the Big Bang.
The heat is only 2.725° above absolute zero and is detected as microwaves.
The Cosmic Microwave Background radiation was emitted only a few hundred
thousand years after the Big Bang, long before stars or galaxies ever existed.
It fills the universe and can be detected everywhere we look.
WMAP
Science
Team,
NASA
WMAP Science Team, NASA
Looking back in time
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When we look far into space and back time we cannot see beyond the time the first
stars were formed.
WMAP Science Team, NASA
The Big Bang Evidence 2
A second evidence that supports the Big Bang theory is the overall
chemical composition of the Universe.
Calculations predict that the composition of the Universe should be
about three fourths hydrogen and one fourth helium by mass, being
a closed match to the overall chemical composition of the universe.
This prediction implies that the universe was born only with light
elements, such as hydrogen and helium, and traces of lithium.
Consequently, the universe was born without the elements necessary
for life, such as C, N, O, with the exception of H.
The Expanding Universe
Despite the fact that the Universe is expanding since the Big Bang, on
smaller scale the force of gravity has drawn matter together.
While the universe as a whole expands, individual galaxies and their
content do not expand, only the space between them.
Stellar Lives and Galactic Recycling
Gravity drives the collapse of clouds of
gas and dust to form stars.
Stars go through life cycles.
Stellar Lives and Galactic Recycling
V838 Monocerotis star burst.
The star brightened to about a million times solar
luminosity ensuring that at the time of
maximum, the star was one of the most
luminous stars in the Milky Way galaxy. The
brightening was caused by a rapid expansion of
the outer layers of the star.
Stellar Lives and Galactic Recycling
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SN 1006 was a
supernova, widely seen
on Earth beginning in
the year 1006 AD;
Earth was about 7200
light-years away.
Egyptian astrologer left us a historical
description of the
supernova - the object
was 2-1/2 to three
times as large as the
disc of Venus, and
about one-quarter the
brightness of the Moon.
Stellar Lives and Galactic Recycling
A star is born when gravity compresses
the material in the cloud that the
center becomes dense enough and
hot enough to generate energy by
nuclear fusion.
Nuclear fusion - two or more nuclei
fuse or stick together to form a
heavier nucleus whose combined
mass is slightly less than the
original nucleus.
He nucleus has slightly less mass than
4 H nuclei.
Star formation. The young star is
surrounded by a disc of gas and dust.
The matter a) finds its way onto the star
through magnetic funnels, b) stays in
the disc to form planets, c) or is thrown
out of the system by the magnetic field.
(ESA)
E = mc 2
Stellar Lives and Galactic Recycling
NASA/ESA
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Once a star is born, it shines with energy released by the nuclear fusion in its core. A star
lives until it exhausts its usable fuel for fusion.
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Massive stars, with denser and hotter cores, burn faster their fuel than smaller stars, living
shorter (only a few million years).
Smaller stars, like our Sun, live much longer, 10 billions years. Very small star can live up
to hundreds of billions of years.
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Stellar Lives and Galactic Recycling
When the fusion fuel is exhausted,
the star blows much of its
content back out into space.
Massive stars die in huge
explosions - supernovae.
The matter spreads out in clouds
dust and gas, from which new
generations of stars are born.
Galaxies are recycling plants,
reusing material expelled from
dying stars to make new
generations of stars and
planets.
Crab Nebula – remnant of a
supernova witnessed on Earth
in 1054 AD.
Stellar Lives and Galactic Recycling
• Movie7a (4 min)
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Hubble news Full heic0312 Video News Release
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http://www.spacetelescope.org/videos/html/mov/180px/heic0312p.html
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Movie 7b. (13min)
Hubble DVD 15 Years of Discovery, Chapter 4, THE LIVES OF STARS
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http://www.spacetelescope.org/videos/html/hst15_chapter04.html
• Movie 7c. (3 min)
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Hubble news
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http://www.spacetelescope.org/videos/html/heic0306a.html
Full heic0306 Video News Release
Supernovae
Supernovae role in:
- stellar evolution
- Mutations (gamma rays)
- Extinctions
Gamma rays induce a chemical reaction in the
upper atmosphere, converting molecular
nitrogen into nitrogen oxides, depleting
the ozone layer enough to expose the
surface to harmful solar and cosmic
radiation.
The gamma ray burst from a nearby
supernova explosion - the cause of
the end Ordovician extinction, which
resulted in the death of nearly 60%
of the oceanic life on Earth.
A composite image of the Crab Nebula
showing the X-ray (blue), and optical
(red) images superimposed. NASA/ESA.
We are star dust!
The Big Bang theory predicts the Universe
was born containing only the simplest
elements, H and He, and a trace of Li.
Living things and the Earth are made
primarily of C, N, O, Fe.
The main chemical building blocks of life –
C, O, N, and heavier elements were
formed in the nuclear burning cores of
stars and then ejected into space when
they died.
Stars spend most of their lives generating
energy by fusing H into He. Towards
the ends of their lives, stars like our Sun
can fuse He into C.
More massive stars can continue to create
heavier elements, fusing C into O and
Si, O into Ne and S, and Fe.
We are star dust!
Evidence 1: Stars of different ages show the expected pattern in the proportions of
elements heavier than helium.
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Older stars are mostly made up of H and He.
Younger stars, like our Sun, contain higher proportions (up to 2%) of their
mass in the form of heavier elements.
This suggests that younger stars were born from gas clouds that contained the
elements manufactured and released by earlier generations of stars!
We are star dust!
Evidence 2: Studies of overall
abundances of chemical elements
in the universe today.
The theory of nuclear fusion
predicts relative abundances of
elements in good agreement
with the observed abundances.
e.g. Carbon and Oxygen are more
abundant than Nitrogen.
Neon is more abundant than Fluorine.
The observed relative abundance of
elements in the galaxy.
We are star dust!
Evidence 3: Studies of gas
from exploding stars.
Models of massive stars
and their deaths allow
astronomers to
calculate the
composition of the
clouds from recently
dead stars.
The observations are in
good prediction with
the models.
Hubble Space Telescope-Image of Supernova 1994D
(SN1994D) in galaxy NGC 4526 (SN 1994D is the bright spot
on the lower left)
We are star dust!
Carl Sagan (1934-1996)
“We are star stuff.”
The recycling of matter and production of heavier elements has been taking
place in the Milky Way galaxy for billions of years before the Solar
System was born.
The clouds that gave birth to our Solar System was made of about 98% H &
He, and 2% of heavier elements (by mass), enough to make the small
rocky planets, including Earth.
On Earth some of these elements became the raw ingredients for life.
The materials we are made were created inside stars that died before the birth
of our Sun.
Implications for Life in the Universe
The process of stellar and galactic recycling operate everywhere in the Universe.
The chemical composition of many stars systems is similar to our own.
Many (perhaps most) other star systems have the necessary raw ingredients to
build Earth-like planets and LIFE!
Next lecture
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The scale of time
The observable Universe
The nature of worlds
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Movies