- 2745 - PLANCK - satellite measures an expanding universe? Astronomers using X-ray data from these orbiting observatories studied hundreds of galaxy clusters, the largest structures in the universe held together by gravity, and how their apparent properties differ across the sky. This new discovery flies in the face of one of the pillars of cosmology, the study of the history and fate of the entire universe. Cosmology up to now maintained that the universe is ‘isotropic,’ meaning the same in all directions.
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---------------- 2745 - PLANCK - satellite measures an expanding universe?
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- Most of us that are the least bit interested in science have learned that we live in an expanding Universe . It started as a Big Bang some 13,700,000,000 years ago. Our Planet as been on this ride some 4,500,000,000 years.
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- The Milky Way Galaxy that we are riding in is just one among billions and billions of galaxies out there in the cosmos. Once beyond the reach of gravity they are racing away from each other at an ever increasing acceleration.
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- The Universe is expanding, but, it may not be expanding at the same rate in all directions? One of the fundamental ideas of cosmology is that everything looks the same in all directions if you look over large enough distances. A new study using data from NASA’s Chandra X-ray Observatory and ESA’s XMM-Newton is challenging that basic notion.
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- Astronomers using X-ray data from these orbiting observatories studied hundreds of galaxy clusters, the largest structures in the universe held together by gravity, and how their apparent properties differ across the sky.
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- This new discovery flies in the face of one of the pillars of cosmology, the study of the history and fate of the entire universe. Cosmology up to now maintained that the universe is ‘isotropic,’ meaning the same in all directions.
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- Astronomers generally agree that after the Big Bang, the cosmos has continuously expanded. A commonly analogy is that this expansion is like a baking loaf of raisin bread. As the bread bakes, the raisins (which represent cosmic objects like galaxies and galaxy clusters) all move away from one another as the entire loaf (representing space) expands. With an even mix the expansion should be uniform in all directions, as it should be with an isotropic universe.
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- Scientists have previously conducted many tests of whether the universe is the same in all directions. These included using optical observations of exploded stars and infrared studies of galaxies. Some of these previous efforts have produced possible evidence that the universe is not isotropic, and some have not. The data to date was inclusive.
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- This latest data comes from test using a powerful, novel and independent technique. It capitalizes on the relationship between the temperature of the hot gas pervading a galaxy cluster and the amount of X-rays it produces, known as the cluster's X-ray luminosity.
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- The higher the temperature of the gas in a cluster, the higher the X-ray luminosity is. Once the temperature of the cluster gas is measured, the X-ray luminosity can be estimated. This method is independent of cosmological quantities, including the expansion speed of the universe.
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- Once they estimated the X-ray luminosities of their clusters using this technique, scientists then calculated luminosities using a different method that does depend on cosmological quantities, including the universe’s expansion speed. The results gave the researchers apparent expansion speeds across the whole sky. This result is revealing that the universe appears to be moving away from us faster in some directions than others.
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- This new study came up with two possible explanations for their results that involve cosmology. One of these explanations is that large groups of galaxy clusters might be moving together, but not because of cosmic expansion.
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- For example, it is possible some nearby clusters are being pulled in the same direction by the gravity of groups of other galaxy clusters. If the motion is rapid enough it could lead to errors in estimating the luminosities of the clusters.
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- These sorts of correlated motions would give the appearance of different expansion rates in different directions. Astronomers have seen similar effects with relatively nearby galaxies, at distances typically less than 850 million light years, where mutual gravitational attraction is known to control the motion of objects.
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- However, scientists expected the expansion of the universe to dominate the motion of clusters across larger distances, up to the 5 billion light years probed in this new study.
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- A second possible explanation is that the universe is not actually the same in all directions. One intriguing reason could be that dark energy, the mysterious force that seems to be driving acceleration of the expansion of the universe, is itself not uniform. In other words, the X-rays may reveal that dark energy is stronger in some parts of the universe than others, causing different expansion rates.
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- This conclusion would be like if the yeast in the bread isn’t evenly mixed, causing it to expand faster in some places than in others. It would be remarkable if dark energy were found to have different strengths in different parts of the universe.
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- Either of these two cosmological explanations would have significant consequences. Many studies in cosmology, including X-ray studies of galaxy clusters, assume that the universe is isotropic and that correlated motions are negligible compared to the cosmic expansion at the distances probed here.
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- This team used a sample of 313 galaxy clusters for their analysis, containing 237 clusters observed by Chandra with a total of 191 days of exposure, and 76 observed by XMM-Newton, with a total of 35 days of exposure.
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- They also combined their sample of galaxy clusters with two other large X-ray samples, using data from XMM-Newton and the Japan-US Advanced Satellite for Cosmology and Astrophysics (ASCA), giving a total of 842 different galaxy clusters. They found a similar result using the same technique.
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- So mysteries remain: Is the expansion rate really the same everywhere? What are we expanding into? Is there something beyond “space” out there? We have to leave something for new students to work on. The more we learn it seems to uncover still more to be learned.
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------------------------------------ Other Reviews available:
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- 2167 - PLANCK - measures the Cosmic Microwave Background. We have a Universe with 5% normal matter, 27% dark matter, and 68% dark energy. At last, we can state, with extraordinary confidence, what the Universe is made of. The curvature of the Universe is no greater than 1-part-in-1000, indicating that the Universe is indistinguishable from perfectly flat. Where have I heard that before? Christopher Columbus did not believe it either.
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- 1653 - Discoveries of Planck Telescope on Universe Evolution. The data collected tells astronomers how old the Universe is and its composition today. 95% of this composition is “ dark” , unknown to science. With these parameters they can still simulate the expansion of the Universe to what we see today.
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- 1586 - Measuring the Cosmic Microwave Background . The density waves in the radiation tell us much about the structure and composition of the Universe. If your eyes were sensitive to microwave frequencies and you were above the atmosphere the sky would have a similar background color over the entire sphere. If we translate this microwave frequency to a visible light frequency we could make it a cold light blue color that would be homogeneous in all directions. The color of this background would be 2.735 degrees Kelvin.
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- 1305 - “Cosmic Harmonics” The temperature of the background is 2.735 Kelvin which is nearly Absolute Zero and nearly homogeneous, but, not quite perfectly smooth at the very high resolution. At the highest resolution the temperature variations existed at 0.0005 Kelvin. Those “ hot spots” that started out due to quantum fluctuations have evolved into the stars and galaxies we see today.
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- 1108 - How Far Does the Astronomical Ladder Reach? The astronomical ladder is the method the astronomers learned to estimate the distance to the stars. The foundation of the ladder started 300 years before the birth of Christ.
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- 823 - Sound Waves and the Cosmic Microwave Background. The Big Bang blast created sound waves that can be heard even today. The sound waves of alternately compressed and rarefied regions of plasma were transmitted through the plasma must like sound waves travel through air. Plasma is a soup of ionized particles and photons that first emerged after the Big Bang. Ionized particles are atomic nuclei that have lost their electrons and therefore become electrically charged. Charged particles scattered the photons and made the plasma opaque.
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- 757 - Cosmic Background Radiation. Astronomers believe it is compelling evidence for the Big Bang. The radiation has been studied for 3 decades. The radiation left the Big Bang as Gamma Rays and has stretched with the expansion of the Universe to where the wavelengths are in the millimeter to centimeter wavelength, which is the microwave frequency range.
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- May 25, 2020 2745
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