Dark Matter | Universe Today

380,000 years after the Big Bang, the Universe cooled from being a hot soup of plasma, to a temperature where protons and electrons could combine to form atoms. This calm period of neutral hydrogen in universal history didn't last for long however. The neutral hydrogen atoms were ripped apart once more, by a mechanism that would go on to reionize the entire Universe, a process that eventually ended a billion years after the Big Bang.

It is thought the first stars that formed prior to the reionisation epoch probably pumped out some fierce ultraviolet radiation, ionizing the neutral hydrogen, but a new (controversial) theory has been put forward. Did dark matter have a role to play in the reionisation the Universe?
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For all you dark matter and dark energy fans out there, now there's another new "dark" to add to the list. It's called "dark gulping," and it involves a process which may explain how supermassive black holes were able to form in the early universe. Astronomers from the University College of London (UCL) propose that dark gulping occurred when there were gravitational interactions between the invisible halo of dark matter in a cluster of galaxies and the gas embedded in the dark matter halo. This occurred when the Universe was less than a billion years old. They found that the interactions cause the dark matter to form a compact central mass, which can be gravitationally unstable, and collapse. The fast dynamical collapse is the dark gulping.
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An international collaboration of astronomers is reporting an unusual spike of atmospheric particles that could be a long-sought signature of dark matter.

The orbiting PAMELA satellite, an astrophysics mission operated by Italy, Russia, Germany and Sweden, has detected a  glut of positrons — antimatter counterparts to electrons — in the energy range theorized to be associated with the decay of dark matter. The results appear in this week's issue of the journal Nature.

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Astronomers think they've found a way to explain why Ultra Compact Dwarf Galaxies, oddball creations from the early universe, contain so much more mass than their luminosity would explain.

Pavel Kroupa, an astronomer at the University of Bonn in Germany, led a research team that's proposing the unexplained density may actually be a relic of stars that were once packed together a million times more closely than in the solar neighbourhood. The new paper appears in the Monthly Notices of the Royal Astronomical Society.

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Astronomy organizations in the United States, Australia and Korea have signed on to build the largest ground-based telescope in the world – unless another team gets there first. The Giant Magellan Telescope, or GMT, will have the resolving power of a single 24.5-meter (80-foot) primary mirror, which will make it three times more powerful than any of the Earth's existing ground-based optical telescopes. Its domestic partners include the Carnegie Institution for Science, Harvard University, the Smithsonian Institution, Texas A & M University, the University of Arizona, and the University of Texas at Austin. Although the telescope has been in the works since 2003, the formal collaboration was announced Friday.
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Two of the hottest and most engaging topics in space and astronomy these days are 1.) exoplanets – planets orbiting other stars – and 2.) dark matter—that unknown stuff that seemingly makes up a considerable portion of our universe. There's a spacecraft currently in development that could help answer our questions about whether there really are other Earth-like planets out there, as well as provide clues to the nature of dark matter. The spacecraft is called SIM – the Space Interferometry Mission. "We'll be looking for other Earths around other stars," said Stephen Edberg, System Scientist for the mission, "and by making accurate mass measurements of galaxies, we should be able to measure dark matter, as well."

Listen to the January 20, 2009 "365 Days of Astronomy" Podcast and my interview with Steve Edberg, and/or read more about the SIM Lite mission below!
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The first stars to light the early universe may have been powered by dark matter, according to a new study. Researchers from the University of Michigan, Ann Arbor call these very first stars "Dark Stars," and propose that dark matter heating provided the energy for these stars instead of fusion. The researchers propose that with a high concentration of dark matter in the early Universe, the theoretical particles called Weakly Interacting Massive Particles(WIMPs), collected inside the first stars and annihilated themselves to produce a heat source to power the stars. "We studied the behavior of WIMPs in the first stars," said Katherine Freese and her team in their paper, "and found that they can radically alter the stellar evolution. The annihilation products of the dark matter inside the star can be trapped and deposit enough energy to heat the star and prevent it from further collapse."
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Weakly Interacting Massive Particles (WIMPs) are thought to dominate dark matter and huge efforts are under way to detect them. By their definition, WIMPs are massive theoretical particles, and they are very weakly interacting with normal matter. WIMPs are therefore notoriously difficult to detect, if they exist that is.

However, some physicists aren't so confident that WIMPs are key to the hunt for dark matter. In a new study, two US researchers have re-opened the debate about dark matter, suggesting the bulk of it could be composed of heavier, strongly interacting particles, or possibly smaller, even more weakly interacting particles than WIMP theory. The physicists also go as far as suggesting that the Universe would be an even more interesting place where WIMP-less dark matter dominates…
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Scientists say he search for the mysterious substance which makes up most of the Universe could soon be at an end. A massive computer simulation was used to show the evolution of a galaxy like the Milky Way, and analysts were able to "see" gamma-rays given off by dark matter. Dark matter is believed to account for 85 per cent of the Universe's mass but has remained invisible to telescopes since scientists inferred its existence from its gravitational effects more than 75 years ago. If the computations are correct, the findings could help NASA's Fermi Telescope to search for the dark matter and open a new chapter in our understanding of the Universe.
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Scientists from the PAMELA (Payload for Antimatter/Matter Exploration and Light-nuclei Astrophysics) orbiting spacecraft have published preliminary results, putting an end to months of speculation about the first direct detection of dark matter. The science team was, in essence, "forced" to publish before they had conclusive results because other scientists "pirated" data from the team. “We wanted to make our final results available to the scientific community once the data analysis was finalised,” PAMELA member Mirko Boezio said in an article in Physicsworld.com. “Given that our preliminary conference data are starting to be used by people, we felt this was a necessary step — not least because it provides a proper reference that correctly acknowledges the whole PAMELA collaboration and is available to the scientific community at large.” This is not the way the PAMELA team wanted to present their results, but really, they had no choice.
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If you thought any quantum discoveries would have to wait until the Large Hadron Collider (LHC) is switched back on in 2009, you'd be wrong. Just because the LHC represents the next stage in particle accelerator evolution does not mean the world's established and long-running accelerator facilities have already closed shop and left town. It would appear that the Tevatron particle accelerator at Fermilab in Batavia, Illinois, has discovered…

…something.

Scientists at the Tevatron are reluctant to hail new results from the Collider Detector at Fermilab (CDF) as a "new discovery" as they simply do not know what their results suggest. During collisions between protons and anti-protons, the CDF was monitoring the decay of bottom quarks and bottom anti-quarks into muons. However, CDF scientists uncovered something strange. Too many muons were being generated by the collisions, and muons were popping into existence outside the beam pipe…
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A team of astronomers has discovered the least luminous, most dark matter-filled galaxy known to exist. The Segue 1 galaxy is one of about two dozen small satellite galaxies orbiting our own Milky Way. This is a very faint galaxy, a billion times less bright than the Milky Way. But despite its small number of visible stars, Segue 1 is nearly a thousand times more massive than it appears, meaning most of its mass must come from dark matter. “Segue 1 is the most extreme example of a galaxy that contains only a few hundred stars, yet has a relatively large mass,” said Marla Geha, an assistant professor of astronomy at Yale and lead author on a paper about Segue 1.
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Scientists are trying to understand the invisible and hypothetical 'dark matter' – the stuff that we know exists by inference of its gravitational influence on the matter we can see. The most common held notion of dark matter is that it exists in 'halos' or clumps that surround galaxies. But a new study predicts that galaxies like our own Milky Way, also contain a disk of dark matter. Using the results of a supercomputer simulation, scientists from the University of Zurich and the University of Central Lancashire say that if dark matter in fact resides as a disk within a galaxy, it could allow physicists to directly detect and identify the nature of dark matter for the first time.
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Rumors are spinning faster than a neutron star about the possibility that a European satellite mission called PAMELA may have made a direct detection of dark matter, the mysterious particles thought to make up as much of 85% of all matter in the Universe. Word got out in August at a conference about dark matter in Stockholm, Sweden where the PAMELA (Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics) team presented their preliminary findings to a few selected physicists. What information has leaked out says the satellite has detected more positrons than can be explained by known physics and that this excess exactly matches what dark matter particles would produce if they were annihilating each other at the center of the galaxy. But the PAMELA team is not allowing any more information to be made public, until they re-analyze their data and allow other scientists to evaluate and verify the findings. This is good, if not wonderful, in all respects – making sure their findings are peer reviewed before publishing their work and going public. (Does anyone remember the cold fusion debacle?) But in what seems to cross the line of good science — as well pushing the boundaries of what is just plain polite, two other scientists have published an abstract based on what was revealed to them at the conference.
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More news on dark matter this week: By analyzing light from dwarf galaxies that orbit the Milky Way, scientists believe they have discovered the minimum mass for galaxies in the universe – 10 million times the mass of the sun. This mass could be the smallest known “building block” of the mysterious, invisible substance called dark matter. Stars that form within these building blocks clump together and turn into galaxies. Scientists know very little about the microscopic properties of dark matter, even though it accounts for approximately five-sixths of all matter in the universe. “By knowing this minimum galaxy mass, we can better understand how dark matter behaves, which is essential to one day learning how our universe and life as we know it came to be,” said Louis Strigari, lead author of this study from the University of California, Irvine.
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