Dark Matter Archives

June 24, 2008December 24, 2015 by Ian O'Neill

Primordial Stars Frozen Indefinitely by Dark Matter

Dark, cold stars from the young Universe could still be here today (University of Utah)

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…

This amazing theory comes from research carried out by Gianfranco Bertone and his team at the Paris Institute of Astrophysics in France. The thought that the first stars, born over 14 billion years ago, could possibly inhabit the Universe today is a very impressive idea. These primordial stars are thought to have been seeded inside dense clouds of dark matter, where gravity caused dark matter compression. As the matter became concentrated, non-baryonic particles may have begun annihilating, stopping natural hydrogen fusion (the mechanism commonly associated with star creation). “Normal” stellar evolution was therefore paused and the “dark star” phase began as dark matter annihilation heated the stellar cores.

It has long been the assumption that the “dark star” phase occurred for a short period of time in the early Universe where vast halos of dark matter may have dominated. Once the dark matter fuel ebbed away, primordial stars were left to self-destruct in a flurry of accelerated evolution. Now Bertone and his colleagues believe a few primordial specimens might be alive today, hidden inside particularly dense clouds of dark matter, in galactic centres, keeping some of the Universe’s first stars in a state of suspended animation.

“There could be conditions in the early universe where stars form in big enough reservoirs of dark matter to last until the present day.” – Gianfranco Bertone.

One of the most exciting implications to come from this research is the fact that these ancient relics may be observed, what’s more, we may have already seen some. “A frozen star would appear much bigger and colder than a normal star with the same mass and chemical composition,” says Marco Taoso, co-investigator in the French group. If stars matching the characteristics of these frozen stellar bodies are (or already have been) found, the discovery would have huge consequences for the quantum search for supersymmetry, indicating dark matter was indeed made up of massive “superpartners” to ordinary matter.

If dark matter influenced stars a few hundred thousand years after the Big Bang, can it still influence stellar evolution today? Researchers believe this could be the case. Present-day stars evolving in regions of dark matter clouds may be influenced by non-baryonic particles. White dwarfs are formed after the death of Sun-like stars and it is believed that should the dwarf star encounter a cloud of dark matter, it could be resurrected as a dark matter burner, shining like 30 Suns.

It will be interesting to see if there have already been any observations of these primordial stars, possibly providing more indirect evidence of dark matter in our Universe.

Source: New Scientist

May 21, 2008December 24, 2015 by Ian O'Neill

Could Dark Matter be the Root Cause of Flyby Anomalies?

The Galileo mission above Earth - the subsequent flybys caused an unexpected boost in velocity (credit: NASA)

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…

Dark matter is probably one of the most interesting, yet controversial, ideas in advanced cosmological studies. We have reported on many of the existing theories as to how we might be able to detect the Universe’s “missing matter” and it is thought that the bulk of universal mass may be held in a range of sub-atomic to massive stellar objects.

The flyby anomalies have been attributed to measurement error (spaceships using the Earth as a gravitational slingshot have their velocities measured by Doppler radar instruments on ground-based observatories), the Unruh effect, even variations in the speed of light, but so far, dark matter hasn’t really featured. So if there is dark matter out there in space, perhaps it will influence the spaceships we send out there. Now Stephen Adler at the Institute for Advanced Study in Princeton examines this possibility and imposes some limits that dark matter may influence flyby anomalies.

The biggest challenge facing any anomaly theory is that spacecraft have experienced increases and decreases in acceleration, what could be the chief suspect causing these sudden changes in acceleration? Alder points to the strange physics behind dark matter accumulating around the Earth, confined within a planetary ring, much like the visible rings around Saturn. What’s more, to explain flyby observations, the ring would have to contain at least two types of dark matter (non-baryonic particles). Interestingly, I recently wrote about the proposed LUX detector to be buried in a disused South Dakota goldmine. This detector will be the first of its kind to attempt to measure the elusive Weakly Interacting Massive Particles (WIMPS) that have been theorized to contain large quantities of matter, hence a large proportion of the dark matter in our universe. This leads to the possibility that the Earth may be passing through “clouds” of WIMPs, giving some credence to the idea that dark matter varieties may also be contained in the volume of space surrounding Earth. As spacecraft orbiting Earth passes through this dark matter ring, perhaps there will be some complex interaction causing this sudden change in acceleration.

For more technical information, have a read of the arXiv publication: “Can the flyby anomaly be attributed to earth-bound dark matter?” by Stephen L. Adler.

Source: arXiv blog

May 5, 2008December 24, 2015 by Ian O'Neill

Digging for Dark Matter: The Large Underground Xenon (LUX) Detector

The Hubble Space Telescope distribution of dark matter - indirect observations (HST)

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…

Galaxies observed from Earth have some strange qualities. The biggest problem for cosmologists has been to explain why galaxies (including the Milky Way) appear to have more mass than can be observed by counting stars and accounting for interstellar dust alone. In fact, 96% of the Universe’s mass cannot be observed. 22% of this missing mass is thought to be held in “dark matter” (74% is held as “dark energy”). Dark matter is theorized to take on many forms. Massive Astronomical Compact Halo Objects (astronomical bodies containing ordinary baryonic material that cannot be observed; like neutron stars or orphaned planets), neutrinos and WIMPS all are thought to contribute toward this missing mass. Many experiments are in progress to detect each contributor. Black holes can be indirectly detected by observing the interactions in the centre of galaxies (or gravitational lensing effects), neutrinos can be detected in huge tanks of fluid buried deep underground, but how can WIMPs be detected? It seems a WIMP detector needs to take a leaf out of the neutrino detector’s books – it needs to start digging.

To avoid interference from radiation such as cosmic rays, low energy detectors such as neutrino “telescopes” are buried well below the Earth’s surface. Old mine shafts make ideal candidates as the hole is already there for the instrumentation to be set up. Neutrino detectors are huge containers of water (or some other agent) with highly sensitive detectors positioned around the outside. One such example is the Super Kamiokande neutrino detector in Japan which contains a vast amount of ultra-purified water, weighing in at 50,000 tons (pictured left). As a weakly interacting neutrino hits a water molecule in the tank, a flash of Cherenkov radiation is emitted and a neutrino is detected. This is the basic principal behind the new Large Underground Xenon (LUX) detector that will use 600 pounds (272 kg) of liquid xenon suspended in a 25 foot high tank of pure water. If WIMPs exist beyond the realms of theory, it is hoped that these weakly interacting massive particles will collide head-on with a xenon atom, and like their light-weight cousins, emit a flash of light.

Robert Svoboda and Mani Tripathi, UC Davis professors, have secured $1.2 million in National Science Foundation (NSF) and U.S. Department of Energy funding for the project (this is 50% of the total required). When compared with the Large Hadron Collider (LHC) costing billions of Euros to build, LUX is a highly economic project considering the scope of what it might discover. Should there be experimental evidence of a WIMP interaction, the consequences will be enormous. We will be able to begin to understand the origins of WIMPs and their distribution as the Earth sweeps through the possible dark matter halo that is indirectly observed to exist in the Milky Way.

Detecting dark matter “would be the biggest deal since finding antimatter in the 1930s.” – Professor Mani Tripathi, LUX co-investigator, UC Davis.

The gold mine in South Dakota was closed in 2000 and in 2004 work began to develop the site into an underground laboratory. LUX will be the first large experiment to be housed there. It is hoped that the installation will start late summer, after water has been pumped out of the mine.

Original source: UC Davis News

April 16, 2008December 24, 2015 by Ian O'Neill

Galactic Ghosts Haunt Their Killers

Image of the stellar tidal stream surrounding the spiral galaxy NGC 5907 obtained with an amateur robotic telescope in the mountains of New Mexico. (R. Jay Gabany)

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…

So what happened to these ill-fated galaxies? Galactic cannibalism is what happened. In both examples, large spiral galaxies have overrun smaller dwarf galaxies, devouring most of their stars. All that is left are the huge fossilized remains in the form of a tenuous distribution of dim, old, metal-poor stars. Judging by the lack of galactic structure in these “ghosts”, the cannibalizing spiral galaxies have been very efficient at eating their smaller dwarf cousins.

The debris surrounding NGC 5907 (approximately 40 million light-years from Earth) extends 150,000 light-years across (pictured top). NGC 5907 destroyed one of its dwarf satellite galaxies at least 4,000 million years ago, consuming the stars, star clusters and dark matter, leaving only a small number of old stars behind to form a complicated criss-cross pattern of galactic fossils.

“Our results provide a fresh insight into this spectacular phenomenon surrounding spiral galaxies and show that haloes contain fossil dwarf galaxies, thus providing us with a unique opportunity to study the final stages in the assembly of galaxies like ours.” – David MartÃnez, from the Instituto de AstrofÃsica de Canarias (IAC) leading the team that carried out these observations.

In the second spiral galaxy, NGC 4013 (50 million light-years from Earth in the constellation of Ursa Major), the ghost of another dead dwarf galaxy stretches 80,000 light-years across and is made up of old stars. Its 3D geometry is unknown, but it has similar characteristics to the Monoceros tidal stream which surrounds the Milky Way. The Monoceros tidal stream is a ring of stars, originating from a local dwarf galaxy that was eaten by our galaxy over 3,000 million years ago.

These images have a huge amount of science to offer researchers. Primarily, the detection of these galactic fossils confirms the predictions of the cold dark matter model of cosmology, which describes how the large spiral galaxies were formed from merging stellar systems.

“…fitting theoretical models to these star streams enables us to reconstruct their history and describe one of the most mysterious and controversial components of galaxies: dark matter.” – Jorge PeÃ±arrubia, theoretical astrophysicist at the University of Victoria (Canada) who is working on this project.

Source: IAC

April 8, 2008December 24, 2015 by Nancy Atkinson

A Case of MOND Over Dark Matter

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.

“MOND was first suggested to account for things that we see in the distant universe,â€ said Garry Angus, of the University of St Andrews. â€œThis is the first detailed study in which we’ve been able to test out the theory on something close to home. The MOND calculations and the observations appear to agree amazingly well.”

Usually the equation F=ma (force = mass X acceleration) solves your basic acceleration problems. But it doesn’t explain the observed rotation of galaxies. MOND suggests that at low values of acceleration, the acceleration of a particle is not linearly proportional to the force. According to Angus, MOND adds a new constant of nature (a0) to physics, besides the speed of light and Planck’s constant. Above the constant, accelerations are exactly as predicted by Newton’s second law (F=ma). Below it, gravity decays with distance from a mass, rather than distance squared. This constant is so small that it goes unnoticed with the large accelerations that we experience in everyday life. For instance, when we drop a ball the gravity is 100 billion times stronger than a0 and the accelerated motion of the Earth round the Sun is 50 million times stronger. However, when objects are accelerating extremely slowly, as we observe in galaxies or clusters of galaxies, then the constant makes a significant difference to the resulting gravitational forces.

When MOND is applied to nearby dwarf galaxies, one effect is that tidal forces from the Milky Way, which have a negligible effect in classical Newtonian Mechanics, can actually make a big difference. This is particularly significant for the dwarfs orbiting close to our Galaxy.

“In these dwarf galaxies, the internal gravity is very weak compared to the gravity of the Milky Way,” said Angus. “MOND suggests that the Milky Way is a bit like a bank that loans out gravity to nearby dwarf galaxies to make them more stable. However, there are conditions on the loan: if the dwarf galaxies start to approach the bank, the loan is gradually reduced or even cancelled and the dwarfs must pay it back. In two galaxies, we’ve seen what could be signs that they’ve come too close too quickly and are unable to repay the loan fast enough. This appears to have caused disruption to their equilibrium.”

Angus used MOND to calculate the ratio of mass to amount of light emitted by the stars in the dwarf galaxies from the observed random velocities of the stars collected independently. He also calculated the orbital paths of the stars in the dwarf galaxies. In all eight cases, the MOND calculations for the orbits were within predictions. For six of the eight galaxies, the calculations were also a good match to expected values for mass-to-light ratios; however for two galaxies, Sextans and Draco, the ratios were very high, which could well suggest tidal effects. The value for Sextans could also be due to poor quality measurements of the galaxy’s luminosity, which Angus said are improving all the time for these ultra dim objects.

“These tidal effects can be tested by updating the 13 year old luminosity of Sextans and making accurate observations of the orbits of Draco and Sextans around the Milky Way. We also need to carry out some detailed simulations to understand the exact mechanisms of the tidal heating,” said Angus.

If Newton’s gravity holds true, the dark matter needed in the dwarf galaxies has constant density in the center which is contrary to theoretical predictions, which suggest density should rise to the center.

“Even without direct detection, the dark matter theory is difficult to prove or refute and although we may not be able to prove whether MOND is correct, by carrying out these kind of tests we can see if it continues to hold up or if it is definitely ruled out,” said Angus.

Original News Source: Royal Astronomy Society’s National Astronomy Meeting

April 1, 2008December 24, 2015 by Tammy Plotner

Old Galaxies Stick Together In A Young Universe

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.

Today University of Nottingham PhD student Will Hartley is speaking to the Royal Astronomical Society’s National Astronomy Meeting in Belfast. As the leader of the study, Hartley proposes the distant galaxies identified in the UKIRT images are considered elderly from their content of old, red stars. Because these systems are nearly 10 billion light years distant, the images are as the galaxies appeared about 4 billion years after the Big Bang. Fully evolved galaxies at that point in time are hard to explain and the answer has been puzzling astronomers who study galactic formation and evolution.

Hartley and his team used the deep UKIRT images to estimate the mass of the dark matter formed in a halo surrounding the old galaxies – a halo which collapses under its own gravity to form a even distribution of matter. By measuring their ability to form galactic clusters, astronomers can get a better sense of what causes older galaxies to stick together.

Hartley explains “Luckily, even if we don’t know what dark matter is, we can understand how gravity will affect it and make it clump together. We can see that the old, red galaxies clump together far more strongly than the young, blue galaxies, so we know that their invisible dark matter halos must be more massive.

The halos of dark matter surrounding the old galaxies in the early Universe are found to be extremely massive, containing material which is one hundred thousand billion times the mass of our Sun. In the nearby Universe, halos of this size are known to contain giant elliptical galaxies, the largest galaxies known.

“This provides a direct link to the present day Universe,” says Hartley, “and tell us that these distant old galaxies must evolve into the most massive but more familiar elliptical-shaped galaxies we see around us today. Understanding how these enormous elliptical galaxies formed is one of the biggest open questions in modern astronomy and this is an important step in comprehending their history.”

March 8, 2008December 26, 2015 by Ian O'Neill

Greedy Supermassive Black Holes Dislike Dark Matter

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…

Black hole accretion disks are compact halos created as dust, gas and other debrisÂ are pulled toward a black hole event horizon. Accretion disks radiate electromagnetic radiation, and the frequency of which depends on the mass of the black hole. The more massive it is, the higher the energy of radiation emitted into space. In the case of a SMBH, the huge mass causes very bright emission as the matter from the accretion disk falls into the event horizon (the point at which gravity becomes so strong that even light cannot escape). As accretion disk matter falls toward the event horizon, approximately 10% of the mass is converted into energy and ejected as X-rays. This is a far more efficient energy conversion rate than the most efficient nuclear fusion reaction (approximately 0.5%). This X-ray emission can then be observed, creating a quasar, signifying a SMBH is driving the active galaxy.

Interestingly, an SMBH is not thought to be formed from single dead massive star. They are thought to have been created from a “seed” and then grown over billions of years. The source of the mass feeding the growing SMBH comes from its accretion disk, but it is uncertain what form the matter comes in and at what rate it “feeds” the black hole. There are several possibilities as to how the largest black holes were seeded, but two are the most widely accepted:

Intermediate black holes (with masses of several thousand Suns) are created by vast clouds which collapse to a single point. Black holes form and accretion disks grow.
Massive primordial stars (the first stars, formed only 200 million years after the Big Bang) of a few hundred Sun masses may have collapsed to create smaller black holes, again forming accretion disks and growing over billions of years.

The mechanisms affecting the rate of accretion disk growth are not so clear-cut. Some theories suggest that huge quantities (most of the black hole mass) comes from dark matter.Â However, as dark matter is “non-baryonic” (i.e. the opposite to baryonic matter – the matter we know, love and observe in our universe) it will emit very little radiation as it falls into the black hole event horizon.Â IfÂ thisÂ is the case, SMBHs would grow disproportionately when compared with radiation emitted from galactic centres (only baryonic particles will emit X-rays).

New research headed by Sebastien Peirani (at the Institut dâ€™Astrophysique de Paris, France) suggests only a very small fraction of a SMBH is composed from dark matter as itÂ evolved. Dark matter is predicted to be collisionless and will be scattered very easily by baryonic gas clouds and stars. It seems unlikely that dark matter will be able to stay inside the black hole’s accretion disk for very long before it is repelled by all the “normal” matter being pulled toward the event horizon.

By modelling a “typical” accretion disk and comparing the results with observations of quasar luminosity, the French group found that most of the matter fuelling the SMBHs is relativistic baryonic matter. At a critical distance, outside the black hole, baryonic matter from the accretion disk is accelerated to a significant fraction of the speed of light, emitting radiation. Comparing this with simulations of a collisionless disk (i.e.Â the characteristics of dark matter), the baryonic model fits observations the best.

“Application of our results to black hole seeds hosted by halos issued from cosmological simulations indicate that dark matter contributes to no more than [approx.] 10% of the total accreted mass, confirming that the bolometric quasar luminosity is related to the baryonic accretion history of the black hole.” â€“ Abstract from “Dark Matter Accretion into Supermassive Black Holes“

Source: arXiv

March 5, 2008December 26, 2015 by Nancy Atkinson

That Dark Stuff, Matter and Energy

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 weâ€™re familiar with. They donâ€™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 theyâ€™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.

Andrew Steele and Marc Fries from the Carnegie Institution say that what we thought was dark energy may just be a haze of tiny whiskers of carbon, strewn across the universe and perhaps those whiskers — and not dark energy — would dim faraway objects such as supernovae. Scientists proposed the dark energy hypothesis a decade ago in part to explain the unexpected dimness of certain stellar explosions.

The researchers report discovering an unusual new form of carbon in minerals within meteorites dating from the formation of the solar system. They believe the â€œgraphite whiskersâ€? were likely produced from hot, carbon-rich gases that formed near stars and were blown into interstellar space by solar winds or supernovae. A thin haze of the whiskers in space would affect how light of different wave-lengths pass through space. The researchers postulated that light of near-infrared wavelengths would be particularly affectedâ€”the same wavelengths whose dimming first led to the dark energy model.

Things like these graphite whiskers have been proposed previously to possibly explain observations where dimming appeared, but the presence of any types of materials in space has never been confirmed previously, said Steele and Fries. With their discovery in the meteorite, the pair added, researchers can test the whiskersâ€™ properties against theories and observations.

Dark matter: To make hypothetical matter, you might just need a little dash of hypothetical particles. How about axions? Axions are theoretical particles that have a small mass, about 500 million times lighter than an electron. Additionally, according to theory, an axion should have no spin. A group from the Fermi National Accelerator Laboratory (Fermilab) in Batavia, Illinois designed an experiment to try to find axions.

They set up a magnetic field and shot a lazer into it. A â€œwallâ€? was placed in the middle of the magnetic field as well. It was thought that the magnetic field would possibly change some of the photons from the laser into axions. The wall would stop the photons, but the axions would emerge on the other side.

They tried four different configurations of their system, unfortunately, the experiment found no evidence of new particles. But, they were able to exclude some constraints or regions where this type of particle could or could not exist.

And the data from the Fermilab experiment is still being examined. Scientist William Wester is optimistic about the role he and his colleagues are playing. â€œWe did a serious measurement and excluded a region,â€? he says. â€œIf our small experiment helps heighten awareness and leads to more experimental efforts, even using other techniques as well, it will be a huge benefit that we have done this.â€?

The group believes that maybe with a stronger magnetic field, it might be worth trying their experiement again.

This brings to mind something that I heard cosmologist Michael Turner say: “If I succeed in confusing you about dark matter and dark energy, then I will have brought you up to where the experts are.â€?

Original News Sources:
World Science
Physorg.com release

February 25, 2008April 26, 2016 by Ian O'Neill

Record Breaking “Dark Matter Web” Structures Observed Spanning 270 Million Light Years Across

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…

Dark matter is believed to hold over 80% of the Universe’s total mass, leaving the remaining 20% for “normal” matter we know, understand and observe. Although we can observe billions of stars throughout space, this is only the tip of the iceberg for the total cosmic mass.

Using the influence of gravity on space-time as a tool, astronomers have observed halos of distant stars and galaxies, as their light is bent around invisible, but massive objects (such as black holes) between us and the distant light sources. Gravitational lensing has most famously been observed in the Hubble Space Telescope (HST) images where arcs of light from young and distant galaxies are warped around older galaxies in the foreground. This technique now has a use when indirectly observing the large-scale structure of dark matter intertwining its way between galaxies and clusters.

Astronomers from the University of British Columbia (UBC) in Canada have observed the largest structures ever seen of a web of dark matter stretching 270 million light years across, or 2000 times the size of the Milky Way. If we could see the web in the night sky, it would be eight times the area of the Moons disk.

This impressive observation was made possible by using dark matter gravity to signal its presence. Like the HST gravitational lensing, a similar method is employed. Called “weak gravitational lensing”, the method takes a portion of the sky and plots the distortion of the observed light from each distant galaxy. The results are then mapped to build a picture of the dark matter structure between us and the galaxies.

The team uses the Canada-France-Hawaii-Telescope (CFHT) for the observations and their technique has been developed over the last few years. The CFHT is a non-profit project that runs a 3.6 meter telescope on top of Mauna Kia in Hawaii.

Understanding the structure of dark matter as it stretches across the cosmos is essential for us to understand how the Universe was formed, how dark matter influences stars and galaxies, and will help us determine how the Universe will develop in the future.

“This new knowledge is crucial for us to understand the history and evolution of the cosmos […] Such a tool will also enable us to glimpse a little more of the nature of dark matter.” – Ludovic Van Waerbeke, Assistant Professor, Department of Physics and Astronomy, UBC

Source: UBC Press Release

February 19, 2008December 26, 2015 by Fraser Cain

Bubble Experiment Fails to Find Dark Matter

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.

We can’t see dark matter, but we know it’s out there. Galaxies should spin themselves apart but they don’t thanks to being inside a halo of dark matter. Amazing images from the Hubble Space Telescope show dark matter’s gravitational distortion on the light from distant galaxies. Oh, it’s out there all right.

So what is it?

Astronomers have two theories. One is that their ideas about gravity are wrong. By modifying our understanding of how gravity works over large distances, you can remove the need for dark matter entirely.

The other possibility are “weakly interacting massive particles”. These are actual particles, made of “something”, but we can’t see them or detect them in any way except through their pull of gravity.

Particle physicists have been searching for dark matter particles using powerful atom smashers, just like they discovered all the sub-atomic particles they’ve found so far.

A new experiment at the US Department of Energy’s Fermi National Accelerator Laboratory announced this week that they’ve made some headway in this search. According to theories, when dark matter particles interact with regular matter, it’s different from the way regular matter interacts. The Fermilab experiment has ruled out one of the last possible ways that the theories have predicted this should happen.

Their experiment, called COUPP, uses a glass jar filled with a litre of iodotrifluoromethane (a fire-extinguishing liquid known as CF₃I. As particles strike the CF₃I, it causes tiny bubbles to form in the liquid. The scientists can detect these bubbles as they reach a millimetre in size. By watching the interactions, researchers should be able to know if they’re coming from regular matter or dark matter.

So far, their results contradict another search called the Dark Matter experiment (DAMA) in Italy, who claimed to see dark matter interactions. The results for the DAMA experiment predicted that COUPP should have found hundreds of dark matter interactions, but they didn’t see any.

This research appears in the February 15th issue of the journal Science.

Original Source: Fermilab News Release