Cosmic collisions

or

how most of the structure forms in the Universe

Pleiades open cluster of starsCredit: Nasa

Galaxy NCG 1365 Credit: AAO

Hercules ClusterCredit: 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 collisionCredit:

The MiceCredit: HST, NASA

Observations of galaxy collisions

Antennae GalaxyCredits: HST, Nasa

Come to the Public Talk of 24th of March for more peculiar galaxies

Seyfert Sextet

Credits: Nasa, HST

100,000 light years

less than the Milky Way !

Hercules ClusterCredit: V. Andersen (U. of Alabama, KPNO)

Pleiades open cluster of starsCredit: Nasa

Galaxy NCG 1365 Credit: AAO

Clusters of Galaxies, what do we observe ?

1.5 million light years

Optical light: stars, galaxies

Hot 10 million degrees plasma fills the space between the galaxies

Dark Matter

?

3% of mass 17% of mass 80% of mass

Potential wells of Dark Matter are filled with hot gas

Temperature of the gas 3 Million degrees 100 million degrees

Overview• What is the composition of the Universe?

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

Dark Matter Hot Baryons

… form at the 3D intersections of the Cosmic Web filaments

Theory !!!

What about reality?

2.5 million light years

9 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

1

23

4

http://www.mpa-garching.mpg.de/galform/data_vis/S2_960x640.avi

What happens to clusters when they form?

Theory !!!

What happens to clusters when they form?

Reality !!!

Bullet Cluster

Bullet from a revolver Bullet cluster

F/A-18 Hornet

SHOCKS

(Credit: NASA/CXC/M.Weiss)

Animation of cluster collision

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

Hot shocked gas

100 million degrees

Undisturbed gas 40 million degree

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

Temperature of the gas

Density of the gas

Solving the TIME PROBLEM with observations

Evolution of gas density structure

Pre-merger

Compact merger, close to core passage

Post-merger

HOT >8 keV

COLD <2 keV

Gas Temperature

evolution

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 CollisionThis 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 SoundNavy 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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