The universe is filled with galaxies, and it is quite common that they collide. But collissions between two galaxies isn't similar to everyday objects colliding together: for one they consist of billions of stars. All these stars are bound together in one giant gravitational field. Two galaxies colliding are thus two gravitational fields interacting together. Stars are exchanged (but rarely collide themselves!), and the shape of one galaxy is being distorted by the other. It's a process that takes hundreds of millions of years, and we can observe several cases of colliding galaxies in different stadia of their collision.
In 1999 I atttended an astrophysics summer school at ASTRON in Dwingeloo, organized by the University of Leiden, where lectures were given by prof. dr. J. Jaffe and prof. dr. V. Icke. During the weeks we also made observations, and did computer modelling on the subject of colliding galaxies. I transfered this last subject to my highschool thesis.
For this thesis I made observations of the two colliding galaxies M51 and NGC 5195. After I obtained a visual impression of their composition, I set up their data in a simulation program. Starting with hypothetical values obtained from the images I made, I experimentally determined the ratio of stars, mass and radius between these galaxies, and their inclination and speed.
With the simulations I came to the following ratios:
The amount of stars from the spiral galaxy is 4 1/3 times as high as from the elliptical galaxy.
The mass of spiral galaxy is three times as high as that of elliptical galaxy.
The radius of the spiral galaxy is twice as large as that of the elliptical galaxy.
With respect to the axis of rotation the inclination of spiral galaxy is twenty degrees.
The elliptical galaxy has in the x direction a speed of -0.2 Mm/s, and in the y direction of 1.8 Mm/s.
The halo of the elliptical galaxy is as large as the core and has 4/5th times the mass.
This is one of the pictures I made of the colliding galaxies M51 and NGC 5195.
This is one image of the final simulation I ran.
During the summer school, we used a telescope made available by ASTRON, along with one of their computers and digital cameras. On the clearest observation night we calibrated the telescope, and prepared ourselves and the equipment to make observations. Then we discovered that the hard disk was full. We couldn't just clear it up to make space, since it wasn't our computer, and it contained data from ASTRON. After a while we discovered that the temporary images made to calibrate the telescope were stored instead of deleted immediately: we cleared those and were ready to finally make some observations. Then the full moon rose and overshone the night sky, making sensitive observations impossible.