Dark Matter | Universe Today

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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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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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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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. Read more…

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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? This might be one cosmic phenomenon dark matter can't be blamed for…
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Being a very hands-on-type person, I have a hard time wrapping my brain around the concepts of dark energy and dark matter. These are invisible, hypothetical stuffs that cosmologists tell us make up a combined 96% of the universe. These ubiquitous substances are unlike anything we’re familiar with. They don’t emit or reflect enough electromagnetic radiation to be detected directly, but their presence is inferred by the gravitational effect they have on everything we can see. So, scientists are trying to determine if dark energy and dark matter are really there, and if so, what they’re made of. A couple of studies have come out recently dealing with dark energy and dark matter. One study released says that what we think might be dark energy may only be tiny whiskers of carbon materials, formed in the early days of the universe. And a new experiment tried to determine if dark matter is made of particles called axions.
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It is well documented that dark matter makes up the majority of the mass in our universe. The big problem comes when trying to prove dark matter really is out there. It is dark, and therefore cannot be seen. Dark matter may come in many shapes and sizes (from the massive black hole, to the tiny neutrino), but regardless of size, no light is emitted and therefore it cannot be observed directly. Astronomers have many tricks up their sleeves and are now able to indirectly observe massive black holes (by observing the gravitational, or lensing, effect on light passing by). Now, large-scale structures have been observed by analyzing how light from distant galaxies changes as it passes through the cosmic web of dark matter hundreds of millions of light years across…
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Astronomers have no idea what dark matter is, but they have a few guesses. Since they can't see the stuff directly, they're trying to chip away at what it can't be, peeling away theory after theory. Eventually, there should be a few theories that have withstood the most experiments, and best model what astronomers see out in the Universe. Physicists at Fermilab have made one of those steps forward, constraining the characteristics of dark matter, and overturning a recent discovery… by not seeing anything unusual.
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Early stars that began to form about 200 million years after the Big Bang were strange creatures. From observation, the earliest stars (formed from coalescing primordial gas clouds) were not dense enough to support fusion reactions in their cores. Something within the young suns was counteracting the collapsing gas clouds, preventing the core reactions from taking place. Yet, they still produced light, even in absence of nuclear processes. Could dark matter have had a part to play, fueling the stellar bodies and sparking early stars to life?
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I've said it many times, but it bears repeating: regular matter only accounts for 4% of the Universe. The other 96% - dark matter and dark energy - is a total mystery. Wouldn't it be convenient if we could find a single explanation for both? Astronomers from the University of St. Andrews are ready to decrease the mysteries down to one.
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Filed under: Cosmology, Dark Energy, Dark Matter | 51 Comments »

Understanding the mysterious dark matter in our universe is paramount to cosmologists. Dark matter and dark energy makes up the vast majority of mass in the observable universe. It influences galaxy rotation, galactic clusters and even holds the answer to our universe's fate. So, it is unsurprising to hear about some outlandish physics behind the possible structure of this concealed mass. A Harvard scientist has now stepped up the plate, publishing his understanding about dark matter, believing the answer may lie in a type of material that has a mass, but doesn't behave like a particle. "Unparticles" may also be detected by the high energy particle accelerator, the Large Hadron Detector (LHD) at CERN going online in a few weeks time. High energy physics is about to get stranger than it already is…
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Enough of this small stuff, let's look at the big picture. The really really big picture. In this case, one of the largest patches of the sky ever observed by the Hubble Space Telescope. A new detailed survey was released today that combines 80 separate Hubble images together. In addition to a framework of galaxy clusters, the images show the distribution of dark matter that holds the clusters together - and tears it all apart.
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This strange photograph is a composite image of Abell 520, a massive cluster of galaxies in the process of colliding with one another - it's one of the most massive structures in the Universe. Several different instruments and observatories came together to produce the image, and the final result gave astronomers a big mystery: its dark matter is behaving strangely.
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An international team of astronomers have conclusive new evidence that a recently discovered "dark galaxy" is, in fact, an object the size of a galaxy, made entirely of dark matter. Although the object, named VIRGOHI21, has been observed since 2000, astronomers have been slowly ruling out every alternative explanation.
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Most of the Universe is a complete and total mystery. And one of these mysteries is dark matter. It's out there, and astronomers are slowly teasing out its characteristics, but it's not giving up its secrets easily. The problem is, dark matter only interacts with regular matter through gravity (and maybe through the weak nuclear force). It doesn't shine, it doesn't give off heat or radio waves, and it passes through regular matter like it isn't there. But when dark matter is destroyed, it might give astronomers the clues they're looking for.
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Astronomers using the Hubble Space Telescope have turned up a ghostly ring of dark matter, surrounding the aftermath of a collision between two galaxy clusters. This is one of the strongest pieces of evidence ever found for the existence of dark matter; a shadowy substance that only interacts with regular matter through gravity.
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What role did dark matter play in the early Universe? Since it makes up the majority of matter, it must have some effect. A team of researchers is proposing that massive quantities of dark matter formed dark stars in the early Universe, preventing the first generations of stars from entering their main sequence stage. Instead of burning with hydrogen fusion, these "dark stars" were heated by the annihilation of dark matter.
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When we think of a galaxy, we think of our own Milky Way or perhaps Andromeda; a majestic spiral containing hundreds of billions of stars. Or maybe we think of an irregular galaxy, not so majestic-looking, but still made of regular stuff, like stars, planets… people.
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