Transcript Cosmic Collisions ( 12 MB)

Cosmic collisions
or
how most of the structure forms
in the Universe
Galaxy NCG 1365
Credit: AAO
Pleiades open cluster of
stars
Credit: Nasa
Hercules Cluster
Credit: V. Andersen (U. of
Alabama, KPNO)
Gravity, the main force in the Universe
It is all a matter of attraction:
every object in the Universe attracts every object in the
Universe
Simulation
of galaxy
collision
Credit:
Observations
of galaxy
collisions
The Mice
Credit: HST, NASA
Seyfert Sextet
Credits: Nasa, HST
Antennae Galaxy
Credits: HST, Nasa
100,000 light years
less than the Milky Way !
Come to the Public Talk of 24th of March for more
peculiar galaxies
Galaxy NCG 1365
Credit: AAO
Pleiades open cluster of
stars
Credit: Nasa
Hercules Cluster
Credit: V. Andersen (U. of
Alabama, KPNO)
Clusters of Galaxies, what do we observe ?
3% of mass
17% of mass
80% of mass
1.5 million light years
Optical light: stars,
galaxies
Hot 10 million degrees
plasma fills the space
between the galaxies
Dark Matter
?
Potential wells of Dark Matter are filled with hot gas
3 Million degrees
100 million degrees
Temperature of the gas
• What is the composition of the Universe?
Overview
4.5% Baryons: the matter we know
22.4% Dark Matter: governs gravity
73% Dark Energy
<0.1% Neutrinos, Radiation
How do galaxy clusters form?
(or how do we believe they do!)
http://www.mpa-garching.mpg.de/galform/data_vis/lcdm_color2_highres_divx.avi
Galaxy clusters
… form at the 3D intersections of the Cosmic Web filaments
Dark Matter
Theory !!!
Hot Baryons
What about reality?
9 million
light years
2.5 million light
years
Multiple galaxy cluster observed in visible light
Credits:
NASA, HST
Galaxy cluster collisions
What are the main differences between an experiment
in a Lab on Earth and an experiment (observation) in
space?
1)
2D NOT 3D
What are the main differences between an experiment
in a Lab on Earth and an experiment (observation) in
space?
2)
TIME: in the Universe everything
happens very slowly!
The blob is going to
merge in billions of
years!
Galaxy Clusters observed in X-rays
The evolution of a ….. person
4
1
2
3
What happens to clusters when they form?
Theory !!!
http://www.mpa-garching.mpg.de/galform/data_vis/S2_960x640.avi
What happens to clusters when they form?
Reality !!!
Bullet Cluster
Bullet from a revolver
Bullet cluster
F/A-18 Hornet
SHOCKS
Animation of cluster collision
(Credit: NASA/CXC/M.Weiss)
Hot gas between the
galaxies, X-ray
observation
Shocks are hot!
The Bullet cluster
Shocked gas,
HOTTER
What remains
of the small
cluster (the
bullet)
COOLER
Credits: Andersson,
Peterson & Madejski
Abell 3921 cluster observed in visible light (near infrared)
Credits: Ferrari et al.
Abell 3921 cluster observed in visible light (near infrared)
Credits: Ferrari et al.
Abell 3921 cluster observed in X-ray: hot gas
Credits: Belsole et al.
Abell 3921 cluster: X-ray + visible
Credits: Belsole et al.,
Ferrari et al.
Abell 3921 cluster: X-ray temperature map
From the temperature difference and the
shape and distribution of galaxies and gas
we can draw conclusions on the possible
scenario that formed this cluster
Undisturbed
gas 40
million
degree
Hot
shocked
gas
100 million
degrees
Density of the gas
Temperature of the gas
Solving the TIME PROBLEM with observations
Evolution of gas density structure
Compact
merger, close
to core
passage
Pre-merger
Post-merger
HOT >8 keV
Gas
Temperature
evolution
COLD <2 keV
Conclusions
The Universe is pretty violent place, shocks and collisions
happen at all scales
… but be ware! Everything happens sooooo slowly
There is a natural hierarchy in the Universe and
collisions appear to be the way the initially small structures
become big, out to the largest structures in the Universe
theory and observations mostly agree on that!
Observations in the visible, X-ray + other frequencies and
also simulations are necessary to understand how structure
forms in the Universe
one of these methods alone is not enough
Conclusions
There are plenty of open questions:
What happens to the galaxies in the cluster?
Do collisions generate more stars?
Where there more collisions in the past?
How much of each cluster survive the collision and how
can we measure this efficiently?
The End
http://galaxydynamics.org/galacticencounters.html
"We find them smaller and fainter, in constantly increasing numbers, and we
know that we are reaching into space, farther and farther, until, with the
faintest nebulae that can be detected with the greatest telescopes, we arrive
at the frontier of the known universe."
-Edwin Hubble, Realm of the Nebulae 1936
2. Galactic Encounters (3:11)
The dark matter provides the framework for the universe but what we see are the galaxies - vast
islands of stars and gas that form at the centre of the dark halos. The galaxies themselves can
gather into enormous clusters with hundreds and even thousands of members. There is little
breathing room for a galaxy in a cluster and soon strong interactions and collisions ensue as the
galaxies fall together. Galaxies are diaphanous objects - puffs of smoke easily torn apart by the
forces of gravity and many merge together into an amorphous central blob of stars while others are
left severely damaged.
Here we watch a hundred galaxies fall together into a forming cluster. Our perspective is from a
starship flying into the cluster starting several million light years away and cruising to within a
hundred thousand light years of the giant elliptical galaxy forming at the cluster centre. As we fly
through, we observe the merging and tidal disruption of many spiral galaxies as they orbit within the
cluster. Ten billion years elapses within about 3 minutes so time passes at a rate of 50 million years
per second!
Cosmological Structure Formation: All of the structure in the universe
originates in the gravitational collapse of tiny density perturbations that are
imprinted on the universe early in its history. As the universe expands,
these perturbations grow denser and collapse upon themselves to form
galaxies and clusters of galaxies. Cosmologists use N-body simulations
to study this process. Particles represent the dark matter distribution and
fall into clumps that are commonly known as dark halos. We can't
observe these halos directly but we know of their presence through their
gravitational influence on galaxies' rotational motions.
Click on this image to fly through the dark matter universe and watch the
evolution of structure from the Big Bang to the present . The small clumps
are galaxy sized dark halos while the larger ones are clusters of galaxies.
Look closely and you can see small halos orbiting within the larger ones.
Time in years before the present ticks up on the left while the
cosmological redshift ticks down on the right. (You may need DVD drivers
to see this movie on a Windows/Apple machine - use xine or mplayer with
Linux).
Animation of Cluster Collision
This animation shows an artist's representation of the huge collision in the bullet cluster. Hot gas,
containing most of the normal matter in the cluster, is shown in red and dark matter is in blue.
During the collision the hot gas in each cluster is slowed and distorted by a drag force, similar to air
resistance. A bullet-shaped cloud of gas forms in one of the clusters. In contrast, the dark matter is
not slowed by the impact, because it does not interact directly with itself or the gas except through
gravity, and separates from the normal matter. The animation ends by dissolving into an image
showing the hot gas seen with Chandra (pink) and the cluster mass as inferred by gravitational
lensing (blue), which is mostly dark matter.
View Stills
[Runtime: 0:15]
(Credit: NASA/CXC/M.Weiss)
This composite image
shows the galaxy
cluster 1E 0657-56,
also known as the
"bullet cluster." This
cluster was formed
after the collision of two
large clusters of
galaxies, the most
energetic event known
in the universe since
the Big Bang.
Hot gas detected by Chandra in X-rays is seen as two pink clumps in the image and contains most of the
"normal," or baryonic, matter in the two clusters. The bullet-shaped clump on the right is the hot gas from
one cluster, which passed through the hot gas from the other larger cluster during the collision. An optical
image from Magellan and the Hubble Space Telescope shows the galaxies in orange and white. The blue
areas in this image show where astronomers find most of the mass in the clusters. The concentration of
mass is determined using the effect of so-called gravitational lensing, where light from the distant objects
is distorted by intervening matter. Most of the matter in the clusters (blue) is clearly separate from the
normal matter (pink), giving direct evidence that nearly all of the matter in the clusters is dark.
http://www.npaci.edu/enVision/v15.2/ricker.html
http://www.public.iastate.edu/~curt/cg/section9.html
http://universe.nasa.gov/press/2005/050408b.html
The Sight of Sound
Navy Lt. Ron Candiloro's F/A-18 Hornet creates a shock wave as he
breaks the sound barrier July 7. The shock wave is visible as a large
cloud of condensation formed by the cooling of the air. A smaller shock
wave can be seen forming on top of the canopy.
It is possible for a skilled pilot to work the plane's throttle to move the
shock wave forward or aft.
Candiloro is assigned to Fighter Squadron 151, currently deployed with
the USS Constellation battle group. (U.S. Navy photo by Ensign John
Gay)
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