Transcript Stars & Cosmology

Starry Night
Vincent Van Gogh
The Stars
Ch 14 The Sciences
• Astronomy, the study of objects in the
heavens, was probably the first “science”.
• Astronomy is the scientific study of cosmic
objects and celestial happenings.
• Please do not call it astrology.
Great Idea:
The Sun and other stars use nuclear fusion
reactions to convert mass into energy.
Eventually, when a star’s nuclear fuel is
depleted, it must burn out.
The stars that we see
throughout the year vary.
Common constellations
• Big dipper
• Southern cross
…distinguish between
a star and a planet.
At most, we see 3000 stars
“light year”
• A unit of distance
• One light year equals about ten trillion
kilometers (9.5 x 1012 km)
• or about 6 trillion miles,
• the distance light travels in a year.
• (speed of light = 300,000 km/sec)
Optical Telescopes:
Reflecting
Refracting
Large Reflecting Telescopes
• Keck telescopes,
Mauna Kea, Hawaii
• European Southern
Observatory, Chile
Radio Telescopes
Figure 14-4
Schematic diagrams of telescopes. In an optical telescope (a), light
strikes a curved mirror and is focused on a light-sensitive detector
such as the eye or a piece of film. In a radio telescope (b), radio
waves from space strike a curved metal dish that focuses the waves
onto an antenna. Signals are amplified and processed by computer.
Hubble Space Telescope
• launched in 1990 by
the space shuttle
Discovery
• Oops! Mis-shaped
mirror; repaired in
’93, ’97, ’98.
• Now it’s taking great
pictures of far away
galaxies
• Latest images!
Next Generation Space Telescope
• NGST and NASA’s
Origins Project
• Evolution of galaxies
• Production of
elements by stars
• Process of star and
planet formation
The Sun Gives Off Energy
• Nuclear fusion
reactions
• hydrogen atoms
merge to form
helium
The Sun: a nuclear furnace
• Sun produces energy at an enormous
rate, equivalent to the explosion of 92
billion nuclear bombs every second
• 700 million tons of hydrogen turn into
helium every second near the center of
the Sun, with 5 million tons vanishing,
turned into pure energy
Why is the Sun the size it is?
The size of the sun…
• Gravity pulls in,
pressure pushes
out, and the Sun
is the size it is:
1.4 million km in
diameter or over
100X the diameter
of the Earth.
The Parts of the Sun
Inside the Sun
• Core
• Convection Zone
Outer Region of Sun
• Photosphere
• Chromosphere
• Corona
The Parts of the Sun
Figure 14-2
The magnetic field of the Earth is swept out into a long tail by the
solar wind.
aurora borealis or
“northern lights”
Stars “live” and “die”.
“life cycle” of a Sun-like star
1) The star is created when gas and dust
condense, forming a “young stellar
object”
All stars have a beginning and
an ending
Young stellar objects (YSOs)
• Newborn stars
that are still
surrounded by
their birth
clouds.
• Example:
Orion Nebula
Orion Nebula
“life cycle” of a Sun-like star
2) Shrinking, the star dispels its birth cloud,
and its hydrogen fire ignites and nuclear
fusion is underway.
3) As the hydrogen burns steadily, the star
joins the main sequence stage of stellar
life.
Figure 14-6
A Hertzsprung-Russell diagram plots a star’s temperature versus
its energy output.Stars in the hydrogen-burning stage, including
the Sun, lie along the main sequence, while red giants and white
dwarfs represent subsequent stages of stellar life.
“life cycle” of a Sun-like star
4) When the star uses up all the hydrogen in
its core, the hydrogen in the shell (a larger
region surrounding the core) ignites.
“life cycle” of a Sun-like star
5) The energy released by the burning of the
hydrogen shell makes the star brighter and
expands it, making its surface larger,
cooler, and redder so it becomes a socalled red giant star
Figure 14-6
A Hertzsprung-Russell diagram plots a star’s temperature versus
its energy output.Stars in the hydrogen-burning stage, including
the Sun, lie along the main sequence, while red giants and white
dwarfs represent subsequent stages of stellar life.
“life cycle” of a Sun-like star
6) Stellar winds blowing off the star
gradually expel its outer layers, which
form a planetary nebula around the
remaining hot stellar core
“life cycle” of a Sun-like star
7) The old star dissipates into space, leaving
just the hot little core.
This white dwarf star, cools and fades
forever.
StarStuff
• Elements heavier than H and He
are made in star cores
• All atoms on the earth heavier than
helium were once part of another
star
Figure 14-6
A Hertzsprung-Russell diagram plots a star’s temperature versus
its energy output.Stars in the hydrogen-burning stage, including
the Sun, lie along the main sequence, while red giants and white
dwarfs represent subsequent stages of stellar life.
Life of Stars
• The life span of a star depends on the rate
at which it burns its fuel
• High mass stars burn fast, bright, and are
shorter lived
• Low mass stars burn slow, dim, and live
longer
Death of Stars
• star expands to become a red giant
• Eventually cools
and contracts to
become a white dwarf
What happens to the stellar remnant?
• may continue to radiate energy as it cools,
but ultimately, it fades to a cold black lump
of matter (black dwarf)
• white dwarf might (by its own gravity) pull
H from its companion star and ignites to
embroil the white dwarf in a thermonuclear
holocaust that we see as a nova
Figure 14-7
The life cycle of the Sun on a Hertzsprung-Russell diagram. The
Sun started hydrogen burning in its core more than 4.5 billion
years ago on the main sequence (at point 1), and it will remain
near that point on the diagram for several billion years more. As
the hydrogen in the core is consumed, however, a short period of
helium burning (point 2) will move the Sun’s position on the
diagram rapidly upward toward the red giant stage (point 3).
Once the helium is consumed, the nuclear fusion reactions will
cease and gravitational collapse will cause the Sun to heat up
(point 4). Eventually the Sun will cool to a white dwarf (point 5).
White Dwarf Supergiants
Figure 14-6
A Hertzsprung-Russell diagram plots a star’s temperature versus
its energy output.Stars in the hydrogen-burning stage, including
the Sun, lie along the main sequence, while red giants and white
dwarfs represent subsequent stages of stellar life.
nova
• Possible fate for white
dwarf
• In binary stars,
• white dwarf may pull
H from companion
star and re-ignite.
Supernova
• More massive stars
• Nuclear fusion forms
higher elements
• Fe and higher at #s
• Core eventually
collapses and
rebounds in an
explosion
Black Holes
• Collapsed stars that
attract their own light
• By far, the most dense
stellar remnant
• So much mass packed
in a small space that
not even light can get
out!
For review…
• try discussion questions 1-7, 9-11, 14, 15
on page 296
• Please consider the Whitman poem
given in Investigations # 5, and
• by all means, when the night sky is clear,
go out and stare at the stars! ;o)
Cosmology
SCI 2201
Ch 15
Great Idea:
The universe began billions of years ago
in the big bang,
and it has been expanding ever since.
Milky Way Galaxy
Milky Way Galaxy
Cosmology
• 1924, Edwin Hubble established the fact
that the Milky Way is just one of countless
galaxies
• cosmology – study of the structure and
history of the entire universe
Kinds of galaxies
• –2 major types, see top p325
• Spiral
• Elliptical
• Dwarf
“redshift”
• Hubble was first to notice that colors
emitted by different elements seemed to be
shifted toward the red (long-wavelength)
end of the spectrum.
• --pitch drops as moving source of sound
travels away from you
• --light shifts to red as it moves away from
you
Hubble’s observation meant
that distant galaxies are
moving away from Earth!
Hubble’s Law
• The farther
away a galaxy
is, the faster it
recedes.
Hubble’s Law tell us:
• the universe is expanding.
• The whole cosmos is blowing up like a
balloon
• The universe began at a specific point in
the past, and it has been expanding ever
since.
Evidence for Big Bang
•
•
•
•
explained pp 306-308
Universal Expansion
Cosmic Microwave Background
Abundance of Light Elements