Universe Today » Dark Matter

Did Dark Matter Annihilate Our Early Universe?

Ian O'Neill — Sun, 26 Apr 2009 11:46:50 +0000

A billion years after the big bang, hydrogen atoms were mysteriously torn apart into a soup of ions.

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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Dark Matter, Dark Energy; Now There's "Dark Gulping"

Nancy Atkinson — Thu, 23 Apr 2009 02:29:40 +0000

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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Astrophysics Satellite Detects Dark Matter Clue?

Anne Minard — Wed, 01 Apr 2009 18:26:56 +0000

The PAMELA satellite may have uncovered a new clue indicating dark matter annihilation.

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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Ultra Compact Dwarf Galaxies once crowded with stars

Anne Minard — Thu, 12 Feb 2009 17:57:55 +0000

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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Next-Generation Telescope Gets Team

Anne Minard — Sun, 08 Feb 2009 02:26:58 +0000

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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Space Telescope of the Future: SIM

Nancy Atkinson — Tue, 20 Jan 2009 14:52:57 +0000

Artist's concept of the current mission configuration. Credit: JPL

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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Did Dark Matter Power Early Stars?

Nancy Atkinson — Fri, 02 Jan 2009 23:41:48 +0000

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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Bringing WIMP Theory into Question: Is There Another Dark Matter Explanation?

Ian O'Neill — Sun, 14 Dec 2008 06:24:04 +0000

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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Are We Close to Finding Dark Matter?

Nancy Atkinson — Thu, 06 Nov 2008 15:59:54 +0000

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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PAMELA Results Mean Only One Thing: Please Trust the Scientific Process

Nancy Atkinson — Wed, 05 Nov 2008 22:49:50 +0000

The PAMELA Spacecraft

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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Forget the LHC, the Aging Tevatron May Have Uncovered Some New Physics

Ian O'Neill — Tue, 04 Nov 2008 05:01:09 +0000

The Collider Detector at Fermilab may have found some unexpected particles (Fermilab)

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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Companion Dwarf Galaxy Almost Invisible

Nancy Atkinson — Thu, 18 Sep 2008 17:46:56 +0000

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. â€œSegue 1 is the most extreme example of a galaxy that contains only a few hundred stars, yet has a relatively large mass,â€ said Marla Geha, an assistant professor of astronomy at Yale and lead author on a paper about Segue 1.
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Dark Matter Halos? How About Disks, Too

Nancy Atkinson — Tue, 16 Sep 2008 13:44:39 +0000

A composite image shows a dark matter disk in red. From images in the Two Micron All Sky Survey. Credit: Credit: J. Read & O. Agertz.

Scientists are trying to understand the invisible and hypothetical 'dark matter' â€“ 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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Pushing the Polite Boundaries of Science About Dark Matter

Nancy Atkinson — Tue, 02 Sep 2008 22:46:20 +0000

Hubble and Chandra composite image showing possible dark matter. Credit: X-ray(NASA/CXC/Stanford/S.Allen); Optical/Lensing(NASA/STScI/UC Santa Barbara/M.Bradac)

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 â€“ 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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Minimum Mass for Galaxies Provides Insight on Dark Matter

Nancy Atkinson — Fri, 29 Aug 2008 14:15:58 +0000

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 â€“ 10 million times the mass of the sun. This mass could be the smallest known â€œbuilding blockâ€ 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. â€œBy 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,â€ said Louis Strigari, lead author of this study from the University of California, Irvine.
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Dark Matter is Missing From Cosmic Voids

Nancy Atkinson — Sun, 17 Aug 2008 17:38:45 +0000

Cosmic voids really are devoid of matter. Astronomers have found that even the pervasive 'dark matter' which accounts for about 80% of the mass of the universe is not present in these voids, which are areas of vast emptiness in space that can be tens of millions of light-years across. "Astronomers have wondered for a quarter-century whether these voids were 'too big' or 'too empty' to be explained by gravity alone," said University of Chicago researcher Jeremy Tinker, who led the new study using data from the Sloan Digital Sky Survey II (SDSS-II). "Our analysis shows that the voids in these surveys are exactly as big and as empty as predicted by the 'standard' theory of the universe."
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Large Hadron Collider Could Generate Dark Matter

Ian O'Neill — Wed, 09 Jul 2008 23:46:26 +0000

One of the biggest questions that occupy particle physicists and cosmologists alike is: what is dark matter? We know that a tiny fraction of the mass of the universe is the visible stuff we can see, but 23% of the Universe is made from stuff that we cannot see. The remaining mass is held in something called dark energy. But going back to the dark matter question, cosmologists believe their observations indicate the presence of dark matter, and particle physicists believe the bulk of this matter could be held in quantum particles. This trail leads to the Large Hadron Collider (LHC) where the very small meets the very big, hopefully explaining what particles could be generated after harnessing the huge energies possible with the LHC…
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Dark Matter is Denser in the Solar System

Nicholos Wethington — Thu, 26 Jun 2008 15:24:27 +0000

Dark matter was theorized to exist relatively recently, and we've come a long way in understanding what makes up a whopping 23% of our Universe. Our own galaxy is surrounded by a halo of dark matter that adds to its mass. A recent paper on the dark matter closer to home â€“ right here in our own Solar System â€“ reveals that it is denser and more massive than in the galactic halo.(...)
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Primordial Stars Frozen Indefinitely by Dark Matter

Ian O'Neill — Tue, 24 Jun 2008 22:47:11 +0000

It is thought that primordial or "Population III" stars were born in dense clouds of dark matter, 100 million years after the Big Bang. During the period between birth and dark matter depletion, these first stars were effectively but into a "deep freeze" where normal star development was prevented. After this period when all the dark matter fuel had been consumed, these stars were allowed to commence normal stellar evolution, dying out within a few hundred thousand years. But say if a Population III star was born in an exceptionally dense cloud of dark matter? How long could "normal stellar evolution" be frozen for? According to new research, dark matter could theoretically freeze the star indefinitely, over timescales longer than the age of the Universe…
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Could Dark Matter be the Root Cause of Flyby Anomalies?

Ian O'Neill — Wed, 21 May 2008 13:42:51 +0000

When space probes Galileo, Rosetta, NEAR and Cassini carried out Earth flyby manoeuvre, scientists measured a bizarre and unpredictable jumps in orbital acceleration. To this day, the phenomenon remains unexplained, but there are many ideas as to how this flyby anomaly may be caused. As previously reported on the Universe Today, some of the scientific explanations can be pretty exotic (the Unruh Effect, after all, isn't that easy to understand), but this new theory is just as captivating. In a new study from the Institute for Advanced Study, Princeton, one researcher thinks dark matter might be messing around with our robotic explorers…
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Digging for Dark Matter: The Large Underground Xenon (LUX) Detector

Ian O'Neill — Tue, 06 May 2008 00:08:51 +0000

How do you catch a WIMP? No, I'm not talking about bullying the weakest kid in class, I'm talking about Weakly Interacting Massive Particles (those WIMPs). Well, it isn't easy. Although they are "massive" by definition, they do not interact with the electromagnetic force (via photons) so they cannot be "seen" and they do not interact with the strong nuclear force, so they cannot be "felt" by atomic nuclei. If we cannot detect WIMPs via these two forces, how can we possibly ever hope to detect them? After all, WIMPs are theorized to be flying through the Earth without hitting anything, they are that weakly interacting. But sometimes, they might collide with atomic nuclei but only if they collide head-on. This is a very rare occurrence, but the Large Underground Xenon (LUX) detector will be buried 4,800 feet (1,463 meters, or nearly a mile) underground in an old South Dakota goldmine and scientists are hopeful that when an unlucky WIMP bumps into a xenon atom, a flash of light will be captured, signifying the first ever experimental evidence of dark matter…
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Galactic Ghosts Haunt Their Killers

Ian O'Neill — Thu, 17 Apr 2008 01:54:51 +0000

The title may sound dramatic, but it is very descriptive. New observations of two galaxies have shown huge streams of stars, not belonging inside those galaxies, reaching out into space. These streams are all that are left of galaxies that are now dead, eaten by their cannibal neighbour, now sitting in their place. The streams form an eerie halo around their killers, looking like ghosts of their former selves…
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A Case of MOND Over Dark Matter

Nancy Atkinson — Tue, 08 Apr 2008 13:04:56 +0000

According to Newton's Second Law of Dynamics, objects on the farthest edges of galaxies should have lower velocities than objects near the center. But observations confirm that galaxies rotate with a uniform velocity. Some astronomers believe the orbital behavior of galaxies can be explained more accurately with Modified Newtonian Dynamics (MOND) — a modified version of Newton's Second Law — than by the rival, but more widely accepted, theory of dark matter. The dark matter theory assumes that a halo of dark matter surrounds each galaxy, providing enough matter (and gravity) that all the stars in a galaxy disc orbit with the same velocity. MOND, however uses a different explanation, and a recent study of eight dwarf galaxies that orbit the Milky Way seems to favor the MOND approach over the dark matter theory.
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Old Galaxies Stick Together In A Young Universe

Tammy Plotner — Tue, 01 Apr 2008 12:19:06 +0000

Can appearances be deceiving? According to the United Kingdom Infra-Red Telescope (UKIRT), galaxies that appear old in our Universe's early history are positioned in huge clouds of dark matter. Using the most sensitive images ever taken, UKIRT scientists believe these galaxies will evolve into the most massive yet known.(...)
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Greedy Supermassive Black Holes Dislike Dark Matter

Ian O'Neill — Sun, 09 Mar 2008 06:59:39 +0000

It is widely accepted that supermassive black holes (SMBHs) sit in the centre of elliptical galaxies or bulges of spiral galaxies. They suck in as much matter as possible, generating blasts of radiation. Stars, gas and everything else nearby forms a compact "halo" and then falls to a gravitationally enforced death spiral. The greedy nature and the sheer size of these black holes have led to the idea that dark matter may supply (or may have supplied) the SMBH with some mass during its evolution. But could it be that dark matter may not be significantly involved after all? ThisÂ might beÂ one cosmic phenomenon dark matter can't be blamed for…
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