Colliding galaxy Ngc 6745 in Lyra - Colliding galaxy NGC 6745 in Lyra - The...

Colliding galaxy Ngc 6745 in Lyra - Colliding galaxy NGC 6745 in Lyra - The spiral galaxy NGC 6745 is located about 206 million years away - light from Earth. This galaxy is double; a second galaxy at the bottom right of the image collides with it, causing star formation. Image obtained by the Hubble Space Telescope in 1996. A large spiral galaxy, with its nucleus still intact, peers at the smaller passing galaxy (almost out of the field of view at lower right). These galaxies did not merely interact gravitationally as they passed one another, they actually collided. When galaxies collide, the stars that normally comprise the major portion of the luminous mass of each of the two galaxies will almost never collide with each other but will pass rather freely between each other with little damage. This occurs because the physical size of individual stars is tiny compared to their typical separations, making the chance of physical encounter relatively small. In our own Milky Way galaxy, the space between our Sun and our nearest stellar neighbor, Proxima Centauri (part of the Alpha Centauri triple system), is a vast 4.3 light - years. However, the situation is quite different for the interstellar media in the above two galaxies - material consisting largely of clouds of atomic and molecular gases and of tiny particles of matter and dust, strongly coupled to the gas. Wherever the interstellar clouds of the two galaxies collide, they do not freely move past each other without interruption but, rather, suffer a damaging collision. High relative velocities cause ram pressures at the surface of contact between the interacting interstellar clouds. This pressure, in turn, produces material densities sufficiently extreme as to trigger star formation through gravitational collapse. The hot blue stars in this image are evidence of this star formation