Interacting galaxies NGC6745

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NGC6745 in the constellation of Lyra is a striking example of a galaxy-galaxy collision. A large spiral galaxy, with its nucleus still intact, has interacted with a smaller passing galaxy (nearly out of the field of view at lower right), where bright blue and bright whitish-blue features show the distinct path taken during the smaller galaxy's journey. 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.

This image was created by the Hubble Heritage Team using NASA Hubble Space Telescope archive data taken with the Wide Field Planetary Camera 2 in March 1996. Members of the science team, which include Roger Lynds (KPNO/NOAO) and Earl J. O'Neil, Jr. (Steward Obs.), used infrared, red, visual and ultraviolet filters to image this galaxy system. Lynds and O'Neil are currently using the Hubble data along with ground-based radio observations to further study the interactions within NGC6745.

Image Credit: NASA and The Hubble Heritage Team (STScI/AURA) Acknowledgement: Roger Lynds (KPNO/NOAO)

Minimum credit line: Roger Lynds (NOAO), NASA and The Hubble Heritage Team, STScI/AURA (for details see Conditions of Use)