Download Chapter 28 Stars and Their Characteristics

Chapter 28
Stars
and
Their Characteristics
Spectral Analysis
• We can’t always get a sample of a piece of
the Universe.
• So we depend on light !
Spectral Analysis
• Light is a form of
Electromagnetic Radiation.
– Electromagnetic radiation = energy that travels in
waves (radiowaves, x-rays, etc)
– Length of the waves determine the characteristics of
the electromagnetic radiation.
– The types of electromagnetic radiation can be
arranged in a continuum called the Electromagnetic
Spectrum (longest wavelengths at one end and
shortest wavelengths at the other end)
Electromagnetic
Spectrum
• Visible white light is actually
made up of light of various
colors, each with a different wavelength.
(colors seen in rainbow or when light passes
through a triangular prism.)
– Red light has the longest wavelength, violet has the
shortest wavelength.
• Electromagnetic waves emitted by an object
provide information about elements within it or
its motion. (use this to learn about distant stars)
Spectroscope
• Spectroscope – tool astronomers use to
separate starlight into its colors (uses a
prism to split light, gathered by a
telescope, into a spectrum)
• Break light into 3 different types of
spectra:
– Continuous Spectrum
– Emission Spectrum
– Absorption Spectrum
Types of Visible Spectra
• Continuous Spectrum – unbroken band of
colors, which shows that its source is
emitting light of all visible wavelengths.
– Emitted by:
• Glowing solids, such as the hot filament of
an electric light
• Glowing liquids, such as molten iron
• The hot, compressed gases inside stars
Types of Visible Spectra
• Emission Spectrum – series of unevenly
spaced lines of different colors and
brightnesses. The bright lines show the
source is emitting light of only certain
wavelengths.
– Emitted by:
• Glowing thin gases (every element has its
own color signature)
Types of Visible Spectra
• Absorption Spectrum – a continuous spectrum
crossed by dark lines.
– Dark lines form when light from a glowing object
passes through a cooler gas, which absorbs some of
the wavelengths.
– Elements absorb the same wavelengths that they
would emit if they were in the form of glowing
gases.
– A stars absorption spectrum indicates the
composition of the star’s outer layer.
Spectral Analysis
• Each element has a unique spectral
signature:
• Determined by arrangement of electrons.
• Lines of emission or absorption arise from
re-arrangement of electrons into different
energy levels.
Hydrogen
(Developed by Shirley Burris, Nova Scotia)
Spread a rainbow of color across a piano keyboard
Then, “play” an element
Hydrogen
More Musical Elements
Now play another element
Helium
And Another
Carbon
Getting a Handle on Water
Oxygen
Hydrogen
All together now ...
Water
Doppler Effect
• If lines on the spectrum are
shifted toward the red side then
object is moving away = Red
Shift
• If lines on the spectrum are
shifted toward the blue side then
the object is moving toward you
= Blue Shift
Now that we can tell if a star is
moving toward or away from us lets
learn more about stars
… measuring their brightness,
their distances, their life cycles…
If we imagined that the distance
from the Earth to the Sun was
1 Centimeter…..
Sun
Earth
1 Centimeter
How far away do you think the
next nearest star would be???
?
How far away do you think the
next nearest star would be???
2.5 Kilometers
1.5 miles
In real distance, the next closest star
would be 300,000 times the distance
from the Earth to the Sun, or……
Earth
Sun
Proxima Centauri
39 Trillion miles (that’s 4.24 Light Years!)
What does 39 trillion miles
look like????
Objects in Space are so far
apart that units of
measurement used on Earth
are not useful.
The distance to the next nearest big galaxy, the
Andromeda Galaxy, is
21,000,000,000,000,000,000 km. This is a
number so large that it becomes hard to write
and hard to interpret. So astronomers use
other units of distance.
Andromeda Spiral Galaxy
Earth
21,000,000,000,
000,000,000 kms
The basic unit of measurement
of distance inside of our solar
system is the…
An Astronomic Unit is equal
to the distance from the Sun
to the Earth, which is about
93 million miles.
Sun
93 million miles
Earth
Planets inside Earth’s orbit
have distances from the Sun
of less than 1 AU.
(Mercury is .4 AU’s from the Sun.)
.4 AU’s
Sun
Mercury
Planets outside the orbit
of the Earth have
distances from the Sun of
greater than 1 AU.
(Mars is 1.5 AU’s and Pluto is 39
AU’s from the Sun.)
But, Astronomic Units are too
small for measuring distances
outside of our own Solar
System.
The closest star to the Sun,
Proxima Centauri, would be
more than 300,000 AU’s from
our star, and that’s the
closest!
Astronomers use
to measure distances
outside our Solar System.
A Light-Year is a unit of Distance.
A Light Year is equal to the distance
that light can travel in one Earth year.
A Light Year is equal to 5.3 trillion
miles.
Use of Light Years makes the units
used in measuring distances in Space
smaller, but “small” is pushing it!
The Speed of Light is 186,000
miles per second.
Peeoooummmmmmm!!!
That is almost 8 times around the
Earth in 1 second!
The Crab supernova remnant is
about 4,000 light-years away.
The Milky Way Galaxy is about
150,000 light-years across.
The Andromeda Galaxy is 2.3
million light-years away.
The background radiation from
the big-bang is 14 billion lightyears away.
Types of Stars and Their
Organization in Space
How are Stars and Planets different?
• Stars emit light, due to nuclear fusion in
their center, while planets only reflect
light.
A Star is a “self-luminous” (it is giving off light
as opposed to reflecting it) sphere of gas that is
undergoing Nuclear Fusion in its center.
Not all stars are the same. In
fact, they vary in many ways.
Stars Vary in “Brightness”.
Magnitude-How bright an object in Space is, or appears to be.
Luminosity- Luminosity is the true brightness of an Individual
unit of a star. The Luminosity of a Star depends on a star’s
temperature.
5
5
5
5
A.
3
3
3
3
3
3
B.
3
3
Which star is hotter? Which is brighter?
Absolute Magnitude- Absolute
Magnitude is a measurement of the true
“brightness”of stars as if all stars were
viewed from the same distance. The
Absolute Magnitude of a star depends on
its Volume and Luminosity.
1
1
1
1
1
1
1
1
A.
1
1
1
1
3
3
3
3
1
3
3
3
B.
3
Which star is larger? Which is brighter?
Apparent Magnitude- Apparent Magnitude is a how
bright a star “appears” to be from Earth. The Apparent
Magnitude of a star is affected by Absolute- Magnitude
(Volume x Luminosity) and Distance from Observer.
Betelgeuse, one of
the brightest stars in
the Universe, does
not appear to be as
bright as our Sun,
because of its
distance from us
compared to the
Sun’s distance.
Stars also vary in their mass,
density and volume, interior
and surface temperature, rate
of fuel-consumption, color,
Main Sequence life-span, what
they do when they “die” and
what they become after they
“die”.
Stellar Mass
When comparing the masses of
different stars, we will use the
mass of our star, the Sun, as the
standard. A star that is
identical to ours would be a
star of 1 “Solar Mass”.
Stars vary in mass from a fraction of 1
solar mass, up to 50 times the mass of our
Sun, or “50 Solar Masses”.
Red Dwarf star
50 solar mass star
The Sun
Stars vary even more in their
volume/density
Number represents xSun volume
White Dwarf
Earth
Star Density
Stars vary in their Main Sequence
and Giant life-span
Stars vary in what they become when they
are no longer fusing Hydrogen.
Blue Supergiant
Red Supergiant
Betelgeuse
Orion’s Belt
Orion Nebula
Rigel
Supernova explosion
Stars vary in how they “die”
Supernova
Supernova
Planetary Nebula
White Dwarf in Binary System
Stars vary in
what they
become when
they “die” (Run
out of material
that can be fused
to create outward
pressure).
White Dwarfs
Neutron Stars
Neutron Star
Pulsars
Pulsar Cone
Black Holes
Volume
Life-Span
Temperature
Density
A star’s mass determines every
other characteristic of the star that
we mentioned earlier.
Rate of “Fuel” consumption
How it “dies”
Luminosity
HR Diagram
Main Sequence
Main Sequence
Line;
Core Fusion of H at
constant rate;
Volume directly
related to mass
..
25-50 M
sun
Masses/Luminosity of Main Sequence Stars
Giants
Core fusion of
He
Supergiants
.. .
Supergiants
White Dwarfs
White Dwarfs
“Dead” Star; High temps. Due to compression
Black Holes, Pulsars and NeutronStars are not identified on the HR
Diagram because they are either
very dim or do not give off energy
in the visible wavelengths.
Star Life Cycles
As we have discussed, stars are not
all the same.
All of the characteristics of a star
are determined by their mass.
Stars with different masses have
different life cycles.
Based upon their masses, stars can
follow three main “pathways” and
fit into three “candidate” groups
during the course of their “lives”.
These groups include:
White Dwarf Candidates (less than one
“solar mass” to 15 solar masses)
Neutron Star and Pulsar Candidates (16 to
30 solar masses)
Black Hole Candidates (Greater than 30
Solar Masses)
White Dwarf Candidates
Pulsar and Neutron Star Candidates
Supergiant
Pulsar
Black Hole Candidates
Supergiant
Black Holes