History of Galaxy Collisions

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History of Galaxy Collisions

IRAS launch of 1983

Alar Toomre

First picture of colliding galaxies

History of Galaxy Collisionsby Claire Berdel

Erik Holmberg

In the 1950's, a Swiss astrophysicist named Fritz Zwicky was the first to actually photograph interacting galaxies. He noticed certain features of these galaxies, like the whispy tails they both had, were similar to the ones Holmberg discovered in his simulations. He concluded that they must form from the gravitational interaction between the two, and they must be made of stars.

In the 1940's, a Swedish astronomer named Erik Holmberg constructed an analog computer to simulate what would happen if two galaxies collided. He conclued that some galaxies would collide. When they did there would be tides or distortions that would drain them of energy, causing them to slow down and form into just one galaxy. Most of the astronomical community ignored Holmbergs discovery.

Most astronomers believed that galaxies were orderly and symmetrical. In 1961, Allan Sandage wrote about these galaxies in a book titles "The Hubble Atlas of Galaxies." He said that blobby elipticals were formed before disk-shaped spirals. Halton Arp disagreed. In 1966, he published a catalogue of 338 interest systems titles "Atlas of Peculiar Galaxies." He was the firat person to say that galaxies could form from starbursts.

In 1972 themost-developed theory of galaxy collisions was written by Alar and Juri Toomre. They put the Antennae, M15, and two other galaxies into their computer to test if their information would match up to the observational evidence. Their models showed the strong gravitational interactions between the galaxies, producing features that look like the tails of dust and stars found in Arp's book. In his paper in1977, Alar Toomre said that about 10% of all galaxies are remains of galaxies that collided. That is also around the same number of ellipticals observed in the universe. The Toomres were two of the first astronomers to come up with the hypothesis that debris from galaxy interactions could help form black holes. They were the first to use the phrases "stroking the furnace" and "feeding the monster", which are now used in referrence to black holes and quasars.

Juri Toomre

In 1983, the Infrared Astronomical Satalite (IRAS) was launched. It's job was to take an infrared survey of the sky. It showed that the most luminous galaxies were always colliding galaxies that were illuminated by the dust surrounding them. The interacting galaxies were shown to have unusually vigorous star formaation, agreeing with Zxwicky's and Arp's theories.

In the 1960's, astronomers began to believe the discoveries made by Holmberg, Zwicky, and Arp, and the research of colliding galaxies sky-rocketted. There were faster and more powerful computers to make better and more accurate simulations of the interactions of galaxies.

In 1982, Francois Schweizer, an astronomer who had teamed up with Alar Toomre, studied the interacting galaxy NGC 7252. He observed six bluish knots of light near the nucleus of the galaxy through ground based telescopes, and interpreted them as young star clusters that formed when the galaxy began to merge. He, Keith Ashman, Steve Zepf, and others suggested that the formation of young globular clusters by colliding spirals may explain the reason why ellipticals have so many global clusters.

Jon Holtzman found 50 young clusters less than several hundred million years old using the Hubble Twelescope in 1992. He concluded they were formed by a merger. One year later, Brad Whitmore led Schweizer and a team of astronomers. They were able to provide evidencde for the theory that mergers produce new star clusters. They used the Hubble Telescope and 40 young clusters near the center of the same galaxy that Schweizer was studying. The young clusters were between 50 and 500 million years old. Since then, astronomers have continued to probe the colliding galaxies. The cameras have been able to see 10 time farther into the colliding galaxies and have revealed more clusters.


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