Download Galaxy interactions - collisions Many stars are thrown out into space

The Lives of Galaxies
These deep field images provide our observational evidence of galaxy evolution
These deep field images provide our observational evidence of galaxy evolution
The most distant
galaxies we can
see have
lookback times
over 13 billion
years
These deep field images provide our observational evidence of galaxy evolution
The most distant
galaxies we can
see have
lookback times
over 13 billion
years
Since it’s
starlight we are
seeing, we know
there were stars
already in these
early galaxies
These deep field images provide our observational evidence of galaxy evolution
The most distant
galaxies we can
see have
lookback times
over 13 billion
years
Since it’s
starlight we are
seeing, we know
there were stars
already in these
early galaxies
The oldest stars in our
galaxy are about the same
age, so it’s safe to assume
that many galaxies started
to form around this time.
Knowing that many galaxies started forming about the same time allows us to compare
galaxies of different ages – by simply looking at different distances
Galaxy “family albums” – grouped by galaxy type
We suspect that there are stars and galaxies even older than we can see with HST
These will be very faint and very red-shifted…
The James Webb Space
telescope will be much
larger than HST, and it
will specialize in IR
observations.
Planned launch = 2018
To observe galaxies immediately after they formed, we’ll have to look in what
wavelength?
A. Radio
B. Infrared
C. Visible
D. Ultraviolet
E. X-ray
To learn about the births of stars and galaxies in the early universe, we have to use
theoretical models and computer simulations.
These are based on two key assumptions:
1.
Hydrogen and helium gas filled space almost uniformly when the universe was
very young.
2.
The distribution of matter was not perfectly uniform: certain areas started out
slightly denser than others, and those areas served as seeds for the formation of
galaxies.
Computer simulations using only those assumptions and the known laws of physics lead
to galaxy distributions very similar to what we see in the universe today.
(1) Expansion was slowed and
then reversed by gravity in the
densest regions
(2) Those regions collapsed
and cooled to form
protogalactic clouds
(3) In those clouds, the first
generations of stars formed in
the coolest, densest parts.
(4) These were very large,
exploding as supernovae within
a few million years, seeding
the galaxy with its first heavy
elements
(5) These early supernovae also warmed the protogalactic cloud, slowing the collapse and the formation of
stars for a while, allowing more time for gas and dust to collect and settle into a disk
This process explains the basic features of a spiral galaxy
The spheroidal population formed
before the galaxy’s rotation became
organized – hence the randomly
oriented orbits
The disk population is made up of stars that
formed after the galaxy’s dust and gas settled
into a rotating disk – hence the uniform
orbits of those stars
This is a nice model, but all galaxies are not the same.
Why the differences?
This is a nice model, but all galaxies are not the same.
Why the differences?
Two possible reasons:
1) Slightly different “birth conditions”
2) After starting similarly, a galaxy may change through interactions with other
galaxies
Different conditions upon formation
One possible difference in the formation process is – a difference in total angular momentum
Different conditions upon formation
Another possible difference in the formation process is – a difference in density
Different conditions upon formation
Evidence for the effect of differing conditions upon formation is found in the Hubble photos
we’ve talked about
This elliptical galaxy is
VERY young, and it
contains about 8 times
more stars than the Milky
Way.
Its color indicates that it
has very little new star
formation going on.
What property of a protogalactic cloud determines if it ends up as a spiral or elliptical
galaxy?
A. its composition
B. its angular momentum
C. its density
D. A or C
E. B or C
Galaxy interactions - collisions
Galaxy collisions are not uncommon
Galaxy interactions - collisions
And they were even more common in the early universe
Galaxy interactions - collisions
Computer simulations allow us to study galaxy collisions in the laboratory
Galaxy interactions - collisions
Computer simulations on youtube:
1.5 minutes – comparison to observations
https://www.youtube.com/watch?v=C0XNyTp5brM
1 minute:
https://www.youtube.com/watch?v=QcDtJ_-jdMw
4 minutes:
https://www.youtube.com/watch?v=PrIk6dKcdoU
Galaxy interactions - collisions
Many stars are thrown out into space, but also the dust clouds get slammed together, sparking a
wave of new star formation
After a few billion years, when all has settled down, the result is an elliptical galaxy:
Stars in random orbits, and little gas and dust left for new star formation.
Computer simulations of galaxy
collisions suggest that clues of the
past collision may remain in the
elliptical galaxy.
For example, a shell structure, which
represents the end points of very
elliptical orbits of a group of stars.
This is very difficult to explain if all
stars formed together, but it’s a natural
consequence of a collision.
Computer simulations of galaxy
collisions suggest that clues of the
past collision may remain in the
elliptical galaxy.
Even more telling are the central
dominant galaxies found at the
center of many dense galaxy
clusters.
They often contain tight clumps that
were probably once the centers of
smaller galaxies.
They can be 10 times the mass of our
Milky Way or more.
Another mechanism for interactions
that can alter a galaxy is due to the hot
gas that fills the interior regions of
dense galaxy clusters
If a spiral galaxy passes through this
hot gas, the gas can strip away the cool
dust and gas from the spiral, leaving it
dustless.
If the spiral has not yet formed many
stars in its disk, it will be left looking
like an elliptical galaxy.
If it already has a large disk
population, it will be left looking like a
lenticular galaxy.
Galaxy evolution in color and
luminosity
This is NOT an HR diagram – we
are not plotting individual stars, but
whole galaxies
Galaxies can go from “blue cloud”
to “red sequence” by undergoing
collisions, or through “gas
stripping”
Starburst galaxies
Some galaxies are undergoing very high rates of star formation
The Milky Way produces roughly
one new star each year
These galaxies may produce more
than 100 new stars per year – a
rate that will use up all the gas
and dust in a few hundred million
years
Star formation would then cease
until more gas and dust can
accumulate
Star burst can be triggered by
collisions, as in this photo
Starburst galaxies
Some galaxies are undergoing very high rates of star formation
Star burst galaxies often hide their
young stars in dust clouds
This means they will look like
normal galaxies in visible and
ultraviolet light, but they will be
very bright in infrared
(Why?)
Starburst galaxies
Some galaxies are undergoing very high rates of star formation
These galaxies can blow very hot gas out in all directions:
Supernovae bubbles creating giant galactic fountains all over
X-ray
visible
The gas and dust lost in this way is lost forever!
This is another way that a galaxy may end up in the “red sequence”
What is likely to happen if two galaxies collide?
A. Their stars will crash into each other.
B. Their mutual gravitational pull will greatly distort each galaxy.
C. Starbursts—greatly enhanced star formation—may occur.
D. All of the above
E. B and C
Astro-Cash Cab!
Lucas
Isaiah
Zach
Patrick
1) True or False? Starburst galaxies have been forming stars at the same furious pace
since the universe was about a billion years old.
True, starburst galaxies are the most prolific regions of star formation in the universe.
False, after too many stars form, a black hole results and a galaxy stops forming stars.
False, the bursts of star formation would use up all the gas in a galaxy in a much
shorter period of time than the age of the universe.
False, starburst galaxies are only found nearby, and are all very young.
2) Starburst galaxies have a lot of gas and dust that hides their star formation. For
this reason,
A. we're not really sure how much star formation is occurring.
B. we use infrared observations to penetrate the dust.
C. we look for X rays from very hot gas powered by many supernovae.
D. all of the above
E. B and C
3) What type of galaxy can result from collisions between galaxies?
A. spiral
B. elliptical
C. irregular
D. A or C
E. B or C
4) In what part of the spectrum are starburst galaxies brightest?
A. X-ray
B. ultraviolet
C. visible
D. infrared
E. radio