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Quiz #5
• There are two stars, star A and star B.
Star A is approaching the Earth at 100
km/s and Star B is moving away from the
Earth at 200 km/s.
• Compare the Doppler shift for these two
stars by explaining how the spectra will be
shifted and by how much. (I am not
looking for a number here, just a
qualitative comparison)
• BUT, what happens when atoms, with
electrons attached, are packed really close
together?
• The electrons from the neighboring atoms
can have a small effect on the standing
wave of each of the atom’s electrons.
• In a supergiant star (luminosity class I) the
star has a huge volume. That means the
atoms are not close to each other near the
surface. They have virtually no effect on
the given energy levels.
• In a giant star (luminosity class III) the star
has a large radius but not as large as the
supergiant. The atoms near the surface
interact more with each other.
• In a main-sequence star (luminosity class
V) the radius is much smaller and atoms
are packed closely together near the
surface.
Luminosity classes in stars.
• The amount of pressure broadening is related
to the radius of the star. When the pressure
is high, (luminosity class V) the pressure
broadening is large and the radius of the star
is small.
• When the pressure is low (luminosity class I)
the broadening is small and the radius of the
star is big.
• We can calculate the radius of the star in this
fashion.
How do we now find the
distance?
• We can calculate it from
• B = σT4(R2)/d2
• Here is a visual example of how it works.
• We know the properties of the H-R
diagram for the near by stars.
NGC 3370 Spiral Galaxy
Galaxies currently produce stars
• In order for stars to form, gas and dust has
to be compressed to densities greater than
10 times the normal density in a gas cloud.
• This happens in the spiral arms of galaxies
where the density is higher.
• Once the density is high enough, gravity
can begin to collapse the cloud.
M 51 The Whirlpool Galaxy
The interstellar medium (ISM)
• The ISM contains both gas and dust.
• Dust are small grains, about the size of cigarette
smoke particles.
• The gas is mostly hydrogen. When hydrogen
atoms are close together they usually form a
diatomic molecule, H2
• Density of atoms in ISM ~ 1 atom/cm3
• In molecular clouds density ~ 10 atoms/cm3
• In the air around us density ~ 1 x 1021 atoms/cm3
NGC 6357 D = 8000 light years
Sharpless 171 D=3000 light years
Center of M8 – Lagoon Nebula
Eagle Nebula (M 16)
Already formed star
cluster
Star formation
Molecular
cloud
Infrared
Observations
show dust
which is warm
and glowing.
Large area is
the Orion
molecular cloud
Proto-stars with tails. The tails point away
from Trapezium.
Debris disk around young star
Stellar Wind and Radiation
pressure
• Stellar wind is comprised of charged particles
which are shot out of a star and move with very
high speeds out into space
• When stellar wind particles hit gas outside the
star, it causes the gas move rapidly away from
the star.
• Radiation (light) being emitted by stars can also
effect material outside of a star. When dust
absorbs the light, dust particles respond by
moving away from the star.
Proto-planetary Survivors
New star in the vicinity of a high mass O-star.
The same effect occurs with comets and our
Sun
Gas tail
Dust tail
When the comet leaves the
Sun, will it look like this….
• 1)
Or this?
• 2)
Please make your selection...
30
30
1. Choice One
2. Choice Two
50%
01
2
3
4
5
6
7
8
9
10
21
22
23
24
25
26
27
28
29
30
11
12
13
1
14
50%
15
16
17
18
2
19
20
It’s this one
• 2)
• In the vacuum of space the only thing
pushing on the tail is the solar wind and
the light coming from the Sun. The tail
has to always point away from the Sun,
regardless of how the comet moving.
Star pushing back with
its own, weaker wind
Direction of
intense light
and stellar
wind from
high mass
stars
Eagle Nebula (M 16)
Self-sustained star formation
• Very massive O-type stars and drive away all
the gas and dust near them. When the material
collides with other gas and dust in the molecular
cloud, the gas and dust becomes compressed
and new star formation begins.
• This is why most star forming regions have stars
forming, and nearby a cluster of stars with hot Ostars that are driving the new formation.
Perseus Double Cluster
• This is also why, not all of the star forming
regions in a galaxy are found in the spiral
arms. Some are in between the spiral
arms. Because of self-sustained star
formation.
M 51 The Whirlpool Galaxy