How a ring galaxy gets made?

--------- #1382 - Hoag’s Bull’s Eye Galaxy

- Attachments : picture of Hoag’s galaxy

- This is a picture of Hoag’s Bull’s Eye Galaxy. It is 600 million light years away. You will have to admit that it is a strange looking galaxy. This is not supposed to be how galaxies form. The Milky Way is a spiral galaxy about the same size, the outer ring is 120,000 lightyears in diameter.

- The Bull’s Eye is a giant yellow ball of stars. It is surrounded by emptiness until you reach the ring of stars. How could such a configuration of stars ever happen?

- Astronomers do the math and their conclusion is that this is actually the results of two galaxies in collision. A smaller galaxy shot through the center of a larger galaxy like a canon ball. The gravitational forces that result create a ring of density waves that in turn create star formations rippling out from the center. ( See review on the Cat’s Eye Nebula to learn how the math was done.)

- The Hoag’s Bull’s Eye Galaxy is what is known as a “ ring galaxy”. And, is not the only one. There are 127 galaxies classified as ring galaxies. Two other examples are the “Cartwheel Galaxy” and AM0644-741

- Ring galaxies are important events for astronomers to study because the star formations are linked to the radius of the ring. The density wave furthest out creates the newest stars where the wave hit’s the interstellar medium. The oldest stars lie towards the center where the density wave first began.

- The calculation for the propagation of the ring is 200 kilometers per second, or 465,400 miles per hour. This would mean the collision between the galaxies occurred around 180,000,000 years ago. There is not very close agreement here with the original astronomer’s estimate of a 2 to 3 billion year old collision based on how far away the second galaxy is today. But, it is in the math:

------------ Time = distance / velocity

------------ Time = 120,000 lightyears / 200 kilometers per second

-------------- One lightyear is 9.3 * 10^12 kilometers

------------- One year is 3.1 * 10^7 seconds

------------ Time = 120,000 lightyears / 200 kilometers per second * 9.3 * 10^12 kilometers / lightyear / 3.1 * 10^7 seconds / year

-------------- Time 180,000 000 years.

- Ring galaxies will be getting more study to learn more about star evolution in the galactic collisions. An announcement will be made shortly, stay tuned.
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(1) 2 learn more #1317 Cat’s Eye Nebula
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707-536-3272, Sunday, January 22, 2012