Changes in sizes and shapes of spherical galaxies in head-on collisions |
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| Authors: | Farooq Ahmed Saleh Mohammed Alladin |
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| Institution: | (1) Indian Institute of Astrophysics, 560034 Bangalore;(2) Centre of Advanced Study in Astronomy, Osmania University, 500007 Hyderabad;(3) Present address: Department of Physics, Kashmir University, 190006 Srinagar |
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| Abstract: | Head-on collisions of two identical spherical galaxies are studied for two initial velocities (1) nearly equal to and (2)
greater than the capture velocity. Orbits of about 500 representative stars are computed taking into account the effects of
dynamical friction in the motion of the galaxies. From the computer studies the changes in the structure of the galaxies are
deduced. The galaxies contract at closest approach and expand as they recede from each other. When the initial velocity is
nearly equal to the capture velocity, the mean radius expands to almost double its size and the galaxies have a prolate structure
until the closest approach with the longer axis in the direction of motion. The prolate structure is destroyed as the galaxies
recede. For larger collision velocity (V ∼ 1.5 Vcap), the mean radius expands by 50 per cent and the galaxies are prolate until the closest approach and distinctly oblate after
the collision. The fractional increase in the binding energy is 0.46 in the first case and 0.30 in the second case. |
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| Keywords: | stellar dynamics galaxy collisions tidal interaction |
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