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One of the most interesting catalogues of celestial objects ever assembled is one called "The Atlas of Peculiar Galaxies" by an astronomer named Halton Alp in 1966. He collected images of 338 galaxies that exhibited unusual characteristics. Many of them were of mergers or interactions between galaxies.

Here is ARP 295. It is located in Aquarius (the "Water Bearer"). However, it is very far away, lying about 270 million light years from the earth.

Most of the images of galaxies that we have published in this column have been in the range of one to 100 million light years out. When you go out further you expand your sample size enormously at each additional increment of distance. This increases the total size of our galactic "zoo," and allows us to see more of the exotic "animals" in it.

ARP 295 surely qualifies as exotic. Here we can see 2 galaxies interacting with one another displaying a "bridge" of material between them, and a long tail coming out of the one at the bottom.

What is happening here?

Astronomers estimate that somewhere between a few hundreds of million years and a billion years ago the galaxies actually made contact with each other. Their gravitational fields drew them together in a sort of grazing collision. The relative speeds of the two galaxies drove them on past the hit and run scene. However, both galaxies spewed out material toward each other forming a "bridge" that now spans the enormous distance of 250,000 light years. The encounter was complex enough to also cause the galaxy on the bottom to spew out a "gravitational tail" of material.

The two galaxies are similar in that both are spirals. They look different because the upper one is seen "face on" while the lower one is seen "edge on". The difference in color is caused by the same thing. The bottom one lies like a coin on its side so the dust builds up in it along our line of vision, lengthening the wave length of the gas and stars in the galaxy into the red side of the spectra. (If we viewed the galaxy on the bottom from the top of it, instead of its edge, it would be a face on spiral like the one at the top).

The physics of a close encounter, bridge phenomena like the one shown here indicates that the gas, dust and stars making up the bridge come from the outer regions of the respective galaxies - not the cores. Careful examination of the origins of the bridge from both sides seems to verify this in the case of ARP 295.

What will happen to these galaxies?

It appears that initial collisions between galaxies are often hit and run events involving scrapes and celestial fender benders the first time. However, in most cases the speed of the offenders leaving the scene is not enough to escape the pull of the gravitational field between them. It’s like a dance where the participants separate a good distance from each other before coming back together.

For now the upper galaxy is continuing to pull away from the lower one. However, eventually they will head back toward each other for a "head on" collision which will result in a new, larger galaxy.

More: Looking Up: Rhapsody in blue

More: Looking Up: A ‘super bubble’ grows in another galaxy

Wolfe is a member of the Everglades Astronomical Society. Organized in 1981 it serves the Naples community providing information in all aspects of amateur astronomy. Its goals include educating the general public, school children, and other groups to the wonders of the universe. The Society meets at 7 p.m., every second Tuesday of the month at the Norris Center (public invited). Regular viewing visits to a special, dark sky site in the Everglades are held each month, allowing the general public to observe the night sky through telescopes, under pristine conditions. For more information visit the website at: http://naples.net/clubs/eas.

 

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