Are there unsolved mysteries yet to be solved?
Despite our knowledge of galactic collisions there is still much we don’t understand due to the limitations of our observable views of the universe. By studying galaxy collisions we are able to develop better understanding of long standing issues in astronomy. Progress is being made on the study of black hole collisions and dark matter due to observations of colliding galaxies. But even here our knowledge falls short, as these topics are two of the greater mysteries especially in how they affect colliding galaxies.
Black holes are one of the biggest mysteries of our universe. What part they play in galaxy collisions and how they are affected are also questions that astronomers are attempting to answer. As the leading theory states that black holes are found at the center of every galaxy, it is important to address their role in collisions. Astronomers have found evidence of black holes at the center of galaxies orbiting each other, some in the same galaxy (Whitehouse) and others in separate colliding galaxies (O'Hanlon), and battling over cosmic matter to engulf as they come closer to collision with one another. In 2006 astronomers found a pair of supermassive black holes at the center of a cluster of galaxies named Abell 400 on a collision course that upon merging would form a super-supermassive black hole (Science Daily). However these collisions are many (possibly billion) years away in actually observing. This leaves our best hopes in gaining knowledge from these events in computer simulation that use the theory of relativity in their computations. From these simulations we can project the gravitational waves that occur in the event of black holes colliding. Gravitational waves are formed as the force of two black holes pull against each other causing a bend in both time and space. Knowing what to expect with these gravitational waves allows us to “listen” for when black hole collisions occur in the observable universe. By running different simulation types we can get the gravitational wave signal for a number of combinations of black hole collisions, from two (McKee) or possibly even three black holes (O'Neill). While much of our current understanding of the results of black hole collisions comes from mathematical and computational projections, the continued study of galaxy collisions allows us to come closer to observing the phenomenon.
Observation of galaxy collisions has also given scientists a helping hand in their research on dark matter. In 2006 astronomers observed the collision of galaxies in the “bullet” cluster, which allowed them to detect what they believe to be dark matter (NASA). Then again in 2008 they observed another collision in a new cluster (MACSJ0025), which confirmed the prior results (Bar-Asher). Through the force of the collision, dark matter and regular matter separate, giving astronomers a rare chance at seeing this otherwise invisible force. The separation comes through the event of ordinary matter slowing during the galaxy collision from drag forces and the dark matter did not slow due to it only being affected by gravity. If dark matter did not exist then the hot gasses would have been the most massive component in the clusters and a separation would have not been seen (NASA). One of the prime galactic collisions being studied for dark matter research is Abell 520 where it can easily be seen that something not yet understood has acted to split the galaxies away from dark matter after the collision (http://sciencenow.sciencemag.org/cgi/content/full/2007/817/1?ck=nck). However even despite these findings there is not enough data on dark matter to determine all of its properties. The continued observation of galaxy collisions is needed to aid the research on dark matter and it’s affects on galaxies.
“Two Supermassive Black Holes Spiraling Toward Collision.” sciencedaily.com. 2006. Science Daily. 11 Apr. 2006. <http://www.sciencedaily.com/releases/2006/04/060411080753.htm>
Whitehouse, Dr. David. “Black holes on collision course.” BBC News. 2002. 19 Nov. 2002. <http://news.bbc.co.uk/2/hi/science/nature/2493331.stm>
O'Hanlon, Larry. “Giant Black Holes Destined for Cosmic Collision.” Discovery Channel. 2008. 17 Oct. 2008. <http://dsc.discovery.com/news/2008/10/17/colliding-galaxies.html>
McKee, Maggie. “Black holes collide in the best simulation yet.” NewScientist.com. 2006. 18 Apr. 2006. <http://www.newscientist.com/article/dn9012>
“NASA Finds Direct Proof of Dark Matter.” nasa.gov. 2006. NASA. 21 Aug. 2006.
<http://www.nasa.gov/home/hqnews/2006/aug/HQ_06297_CHANDRA_Dark_Matter.html>
Bar-Asher, Shalhevet. “Galaxy Clusters Collision Captured.” thefutureofthings.com. 2008. The Future of Things. 6 Nov. 2008. <http://thefutureofthings.com/news/5708/galaxy-clusters-collision-captured.html>
Dark matter at work in the bullet cluster?
A composite image from optical and
x-ray telescopes shows visible matter
(pink) slowing down during the collision while most of the cluster's mass (blue) keeps up speed and passes right through the visible matter, creating two clumps that are moving away from the collision.
These clumps, astronomers think, are dark matter.
5.6 billion light-years from Earth, the new cluster is known as MACS J0025.4-1222
Photo courtesy of Hubble telescope
http://news.nationalgeographic.com/news/2008/08/080827-dark-cluster.html