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One of the most amazing discoveries in the recent history of the field of astronomy, recognized with the 2011 Nobel Prize in Physics, is that not only is our universe expanding, but that this expansion is accelerating. Not only are galaxies becoming farther apart from each other, they are becoming farther apart faster and faster. What could be the cause of this "accelerating expansion"? The leading contender is a strange property of space dubbed “dark energy.” Another explanation, considered possible but less likely, is that at very large distances the force of gravity deviates from Einstein’s General Theory of Relativity and becomes repulsive. Whether the answer to the puzzle of the accelerating universe is dark energy or modified gravity, the first step to finding that answer and the answer to other questions is to measure accurate distances between as many galaxies as possible. From these measurements, astronomers can attempt to figure out the history of the universe’s expansion. The Baryon Oscillation Spectroscopic Survey (BOSS) is a part of the Sloan Digital Sky Survey (SDSS-III) and has produced the most detailed map of the universe ever made. This map measured the distances between galaxies with a new custom-designed spectrograph of the SDSS 2.5-meter telescope located at Apache Point Observatory in New Mexico. With this telescope and its new spectrograph, BOSS measured spectra of more than a million galaxies. The maps analyzed are based on data from the first year and a half of observations, and contain more than 250,000 galaxies. Some of these galaxies are so distant that their light has traveled more than six billion years to reach the Earth, which is nearly half the age of the universe. From this map the distances between galaxies can be judged and we can estimate how fast the universe is expanding.
What is amazing about the results of this survey is that they all come together to tell the same story, that ordinary matter is only a few percent of the universe. The largest component of the universe is dark energy, an energy associated with space itself that is thought to cause the expansion of the universe to accelerate.
I am a little over my head here, but this subject is simply fascinating. I do not understand it too well, but I am trying my best to learn more about it.
An image from NASA that shows the universe expanding, caused by dark energy
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A crystal clear air mass will bring splendid conditions for stargazers across the East Coast of the U.S. Look for the thin crescent moon near Venus this evening, then the Milky Way later at night.