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Virgo ClusterWhy Study the Virgo Cluster?To say that several questions involving X-ray astronomy are still unanswered would be an understatement. However, the study of the Virgo Cluster is leading astronomers to new revelations. Galaxy clusters are the largest organized structures in the universe, and give many clues to its origin and future. By measuring X-ray emissions, maps of Virgo's mass distribution can be made to help determine how it was formed. By figuring out how clusters and galaxies arose, the "Big Bang" theory of the origin of the universe can be refined.
New research shows that the X-ray emission from hot intracluster gas is between ten and twenty percent more than would be expected. This has lead some astronomers to believe that there is an area of cooler, condensed gas around M87. As this gas cools, its density rises, causing increased gravitational attraction. This "cooling flow" is not fully understood, and awaits further X-ray imaging for study. Astronomers have also found the most conclusive evidence to date of a black hole existing in the Virgo Cluster. Thanks to better imaging equipment and techniques, a rotating disk of gas was clocked at 1.2 million miles per hour in the center of M87. The calculated mass required to generate that speed was equivalent to the mass of three billion Suns in an area the size of our solar system. According to modern theory, an object with these characteristics could only be a black hole. Similar objects are being studied with X-ray imaging techniques elsewhere as well. Cepheids and the Hubble Constant Probably the most hotly debated topic in astronomy today is the value of the Hubble Constant, the speed at which the universe is expanding. This value gives us the age of the universe, which is a key factor in determining the validity of many accepted theories. The Virgo Cluster is an ideal galaxy cluster to more accurately study the hubble constant, thanks in part to its Cepheids. Cepheids are stars which are "variable," meaning they pulse. In 1907, Henrietta Leavitt discovered that a Cepheid's real brightness has a direct relationship to its pulse rate. The slower the pulse rate, the brighter the Cepheid. Using Cepheids, astronomers can more accurately gauge distance by comparing their calculated, actual brightness with their apparent brightness. The further away a Cepheid is, the dimmer it will appear. The Virgo Cluster contains many Cepheids in its spiral galaxies. The advantage of Virgo is that it is far enough from Earth to measure the universe's expansion as a whole, yet close enough that astronomers can locate its Cepheids. By better imaging Virgo's Cepheids, and finding more Cepheids in the cluster, the distance to Virgo can be more accurately measured. More accurate distance markers will enable better estimations of the Hubble Constant, and help settle the debate over the age of the universe. |
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Revised: August 29, 2006
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