Dark Matter

Dark Matter should not to be confused with Dark Energy, Dark Fluid (is an alternative theory to both Dark Matter and Dark Energy and attempts to explain both phenomena in a single framework), or Dark Flow (astrophysical term describing a peculiar velocity of galaxy clusters).

In astronomy and cosmology, dark matter is matter that is inferred to exist from gravitational effects on visible matter and background radiation, but is undetectable by emitted or scattered electromagnetic radiation.

Its existence was hypothesized to account for discrepancies between measurements of the mass of galaxies, clusters of galaxies and the entire universe made through dynamical and general relativistic means, and measurements based on the mass of the visible "luminous" matter these objects contain: stars and the gas and dust of the interstellar and intergalactic medium. It is probably cold and if so, probably comprised of weakly interacting massive particles or many primordial intermediate mass black holes between 30 and 300,000 solar masses, or both.

According to observations of structures larger than galaxies, as well as Big Bang cosmology interpreted under the Friedmann equations and the FLRW metric, dark matter accounts for 23% of the mass-energy density of the observable universe. In comparison, ordinary matter accounts for only 4.6% of the mass-energy density of the observable universe, with the remainder being attributable to dark energy. From these figures, dark matter constitutes 83% of the matter in the universe, while ordinary matter makes up only 17%.

Dark matter was postulated by Fritz Zwicky in 1934 to account for evidence of "missing mass" in the orbital velocities of galaxies in clusters. Subsequently, other observations have indicated the presence of dark matter in the universe; these observations include the rotational speeds of galaxies, gravitational lensing of background objects by galaxy clusters such as the Bullet Cluster, and the temperature distribution of hot gas in galaxies and clusters of galaxies.

Dark matter plays a central role in state-of-the-art modeling of structure formation and galaxy evolution, and has measurable effects on the anisotropies observed in the cosmic microwave background. All these lines of evidence suggest that galaxies, clusters of galaxies, and the universe as a whole contain far more matter than that which interacts with electromagnetic radiation. The largest part of dark matter, which does not interact with electromagnetic radiation, is not only "dark" but also, by definition, utterly transparent.

As important as dark matter is believed to be in the cosmos, direct evidence of its existence and a concrete understanding of its nature have remained elusive. Though the theory of dark matter remains the most widely accepted theory to explain the anomalies in observed galactic rotation, some alternative theoretical approaches have been developed which broadly fall into the categories of modified gravitational laws, and quantum gravitational laws. Read more ...

In the News ...

Unexpected interaction between dark matter and ordinary matter in mini-spiral galaxies   PhysOrg - December 15, 2016

Statistical analysis of mini-spiral galaxies shows an unexpected interaction between dark matter and ordinary matter. According to the SISSA study where the relationship is obvious and cannot be explained in a trivial way within the context of the Standard Model, these objects may serve as "portals" to a completely new form of Physics which can explain phenomena like matter and dark energy. They resemble a spiral galaxy like ours, only ten thousand times smaller.

Solution To Dark Matter Proposes That Gravity Is An Illusion   Forbes - November 9, 2016

As dark matter continues to vex astronomers, new solutions to the dark matter question are proposed. Most focus on pinning down the form of dark matter, while others propose modifying gravity to account for the effect. But a third proposal is simply to remove gravity from the equation. What if the effects of gravity aren't due to some fundamental force, but are rather an emergent effect due to other fundamental interactions? A new paper proposes just that, and if correct it could also explain the effects of dark matter

Gravitational waves spotted for a second time: Scientists make 'spectacular' new detection of ripples in space-time   Daily Mail - June 15, 2016

The detection was made by the Ligo (Laser Interferometer Gravitational-Wave Observatory) Scientific Collaboration (LSC) and Virgo collaboration on 26 December last year, just three months after the first gravitational wave was detected by the same group. Known as the 'Boxing Day event', the newly detected gravitational wave came about from the merging of two black holes over a billion years ago. The gravitational waves of the Boxing Day signal were produced by a pair of black holes, of around 14 and 8 solar masses, that travelled for over a billion years before reaching Earth. 'Einstein gave us a Christmas present!' said a spokesman from the American Astronomical Society.

Did gravitational wave detector find dark matter?   Science Daily - June 15, 2016

When an astronomical observatory detected two black holes colliding in deep space, scientists celebrated confirmation of Einstein's prediction of gravitational waves. A team of astrophysicists wondered something else: Had the experiment found the "dark matter" that makes up most of the mass of the universe?

More gravitational waves detected   BBC - June 15, 2016
Scientists have collected a second burst of gravitational waves sweeping through the Earth. The warping of space-time was sensed on Christmas Day in the US at the Advanced LIGO laboratories - the same facilities that made the historic first detection in September last year. Back then, the waves came from two huge coalescing black holes. This new set of waves, likewise, is ascribed to a black hole merger - but a smaller one.

LIGO Has Detected Gravitational Waves for the Second Time   Wired - June 15, 2016

About 1.4 billion years ago, the universe gave scientists a Christmas present. Two black holes spiraled toward one another, approaching closer and closer until they finally collided. Ripples in spacetime spread from the collision at the speed of light until, for about a second on December 25, 2015 (if you were in the United States), the space holding the atoms that make you up buckled and then relaxed.

How We Plan to Bring Dark Matter to Light   Epoch Times - September 17, 2015

Long before we had the atomic theory of matter, scientists knew the air was real, even though it was invisible. This was because we could see its action as the wind caressed the leaves in trees. Likewise we see the influence of another invisible force in the wider cosmos in the movement of stars within galaxies. But we don't yet know what this mysterious dark matter is made of. Now a new generation of detectors - including one we're building in a gold mine in Victoria - is giving us hope that we might finally shed some light on dark matter. Some models predict that whatever particle makes up dark matter is also its own antiparticle. This leads to the fascinating prediction that if two dark matter particles interact they annihilate into a shower of either exotic particles or radiation.

New theory: If we want to detect dark matter we might need a different approach   Science Daily - August 20, 2015
Physicists suggest a new way to look for dark matter: They believe that dark matter particles annihilate into so-called dark radiation when they collide. If true, then we should be able to detect the signals from this radiation. The majority of the mass in the Universe remains unknown. Despite knowing very little about this dark matter, its overall abundance is precisely measured. In other words: Physicists know it is out there, but they have not yet detected it.

Experiment attempts to snare a dark energy 'chameleon'   Science Daily - August 20, 2015
Is dark energy hard to detect because it's hiding from us? According to a recent theory, hypothetical particles called chameleons vary in mass depending on nearby matter: in the vacuum of space, they have a small mass and large reach, pushing space apart. In the lab, surrounded by matter, they have a large mass and small reach, making them difficult to detect. A new experiment seeks to find chameleons by lessening the screening.

Dark matter becomes less 'ghostly'   BBC - April 15, 2015

The mysterious stuff known as dark matter just became less ghostly. It makes up 85% of the total matter in the cosmos and comprises some 27% of the known Universe. For the first time, the enigmatic quantity may have been caught interacting with other dark matter in a cluster 1.4 billion light-years away. Previous studies of colliding galaxy clusters have shown that dark matter barely interacts with anything.

Potential signs of 'interacting' dark matter suggest it is not completely dark after all   PhysOrg - April 14, 2015

Astronomers believe they might have observed the first potential signs of dark matter interacting with a force other than gravity. An international team of scientists, led by researchers at Durham University, UK, made the discovery using the Hubble Space Telescope and the European Southern Observatory's Very Large Telescope to view the simultaneous collision of four distant galaxies at the centre of a galaxy cluster 1.3 billion light years away from Earth.

Dark matter 'ghosts' through galactic smash-ups   BBC - March 26, 2015

By observing multiple collisions between huge clusters of galaxies, scientists have witnessed dark matter coasting straight through the turmoil. Dark matter is the mysterious, invisible stuff that makes up 85% of the matter in the cosmos - and these results rule out several theoretical models put forward to explain it. This is because it barely interacts with anything at all, including the dark matter in the oncoming galaxies. Dark matter is more difficult to "see" - but not impossible. Although it does not emit or absorb light, it does have gravity, and so it bends the path of light passing nearby. This warps our view of anything on the other side of it, in an effect called "gravitational lensing".

Dark matter even darker than once thought   Science Daily - March 26, 2015

Astronomers have studied how dark matter in clusters of galaxies behaves when the clusters collide. The results show that dark matter interacts with itself even less than previously thought, and narrows down the options for what this mysterious substance might be.

A possible signal from dark matter?   PhysOrg - August 12, 2014

Galaxies are often found in groups or clusters, the largest known aggregations of matter and dark matter. The Milky Way, for example, is a member of the "Local Group" of about three dozen galaxies, including the Andromeda Galaxy located about 2 million light-years away. Very large clusters can contain thousands of galaxies, all bound together by gravity. The closest large cluster of galaxies to us, the Virgo Cluster with about 2000 members, is about 50 million light-years away.

Gamma-Ray Hints of Dark Matter Seen at Galaxy's Center   NBC - April 8, 2014

Astronomers have perhaps their best lead to date about the nature of dark matter, the strange and invisible stuff that dominates the material universe.

  Dark matter hunt: LUX experiment reaches critical phase   BBC - April 8, 2014

The quest to find the most mysterious particles in the Universe is entering a critical phase, scientists say. An experiment located in the bottom of a gold mine in South Dakota, US, could offer the best chance yet of detecting dark matter. Scientists believe this substance makes up more than a quarter of the cosmos, yet no-one has ever seen it directly. Early results from this detector, which is called LUX, confirmed it was the most powerful experiment of its kind.

Tracking the transition of early-universe quark soup to matter-as-we-know-it   Science Daily - April 7, 2014

Ever wonder how the hot soup of subatomic particles that filled the early universe transformed into the ordinary matter of today's world? Nuclear physicists exploring this question can't exactly travel back 13.8 billion years to watch what really happened, but they can recreate matter at the extreme temperatures and densities that existed just after the Big Bang by smashing together ordinary atomic nuclei at the Relativistic Heavy Ion Collider (RHIC).

Fermi data tantalize with new clues to dark matter: Gamma rays from center of Milky Way galaxy   Science Daily - April 4, 2014
A new study of gamma-ray light from the center of our galaxy makes the strongest case to date that some of this emission may arise from dark matter, an unknown substance making up most of the material universe. Using publicly available data from NASA's Fermi Gamma-ray Space Telescope, independent scientists at the Fermi National Accelerator Laboratory (Fermilab), the Harvard-Smithsonian Center for Astrophysics (CfA), the Massachusetts Institute of Technology (MIT) and the University of Chicago have developed new maps showing that the galactic center produces more high-energy gamma rays than can be explained by known sources and that this excess emission is consistent with some forms of dark matter.

Dark Matter Near Earth Peaks Every March, New Study Suggests   Scientific American - January 6, 2014

Billions of particles of invisible "dark matter" are probably flying through your body right now, passing through the spaces between your atoms without a trace. According to conventional thinking, these particles should be somewhat less abundant during the winter and should peak around June 1. But a new study suggests this calculation is way off; the real peak is actually at the beginning of March.

Dark Matter Search Considers Exotic Possibilities   Scientific American - January 3, 2014

Ever since astronomers realized that most of the matter in the universe is invisible, they have tried to sort out what that obscure stuff might be. But three decades of increasingly sophisticated searches have found no sign of dark matter, causing scientists to question some of their basic ideas about this elusive substance. Physicists still have no proof that dark matter exists at all, but the evidence for it is substantial. The movements of stars and galaxies can apparently be explained only if there is much more gravitating matter in the universe than the visible stuff of atoms and molecules. Attempts to correct the discrepancy by rewriting the rules of gravity in Einstein's general theory of relativity have repeatedly failed.

Telecommunications expert suggests Earth may have dark matter disc   PhysOrg - January 3, 2014

Dark matter is of course the mysterious stuff that physicists have come to believe exists all throughout the universe. We can't see it, but researchers have managed to sense its presence in a variety of ways (such as measuring its gravitational impact on stars, other planets, etc.). In so doing, most in the field have come to believe that it makes up approximately 80 percent of all matter. Unfortunately (mainly because it doesn't appear to absorb or emit light or electromagnetic radiation) none of the studies done so far have been able to prove that dark matter truly exists thus, the search goes on for some new kind of method to prove that dark matter isn't just a theory, or alternatively, for some other explanation of what has been observed.

Giant Dark Matter Bridge Between Galaxy Clusters Discovered   Live Science - July 5, 2012
darkmatter114.jpg A giant string of invisible dark matter has been discovered across the universe between a pair of galaxy clusters. The filament forms a bridge between two huge clusters called Abell 222 and Abell 223, which lie 2.7 billion light-years away. The universe is thought to be filled with such strings of dark matter, a mysterious substance that cannot be seen, only sensed through its gravitational pull. Scientists have made previous attempts to find dark matter filaments, which are predicted by theories that suggest galaxy clusters form at the intersections of filaments. Dark matter is thought to make up 98 percent of all matter in the universe.

Dark Matter Hits the Average Human Once a Minute?   National Geographic - April 24, 2012
The average human body gets hit by a particle of dark matter about once a minute, according to new calculations based on several dark matter detection efforts. Dark matter is an invisible form of material that's thought to exist because scientists have observed its apparent gravitational effects on galaxies and galaxy clusters. Scientists estimate that the mysterious substance makes up almost 80 percent of the matter in the universe. So far no one's been able to pinpoint the particles that make up dark matter. But a leading candidate is a theoretical group known as Weakly Interacting Massive Particles, or WIMPs.

Dark Matter Is Missing in Sun's Neighborhood?   National Geographic - April 19, 2012
Dark matter is mysteriously missing from the sun's neighborhood, according to a new study that could provide ammunition for skeptics who argue that the invisible substance is just an illusion. Even though dark matter particles can't be detected with current instruments, astronomers think the substance must make up about a quarter of the universe, based on the gravitational effect it has on visible matter such as galaxies and galaxy clusters. Since its discovery in the 1930s, the material has become crucial for galaxy-formation theories, which say that dark matter functions as a kind of invisible scaffold around which normal matter gravitationally coalesces to form stars and larger objects.

Dark matter images reveal widest view of dark mystery   BBC - January 10, 2012

Researchers have released the biggest images yet detailing dark matter, the mysterious substance that makes up 85% of the Universe's mass. Each image, a billion light-years across, shows vast dark matter clumps and voids scattered through the cosmos.

Astronomers create largest map yet of dark matter's web   MSNBC - January 9, 2012
Astronomers have created a vast cosmic map revealing an intricate web of dark matter and galaxies spanning a distance of 1 billion light-years. This unprecedented task was achieved not by observing dark matter directly, but by observing its gravitational effects on ancient light traveling from galaxies that existed when the universe was half the age it is now.

Could dark matter not matter?   PhysOrg - December 5, 2011

You probably want to put on your skeptical goggles and set them to maximum for this one. An Italian mathematician has come up with some complex formulae that can, with remarkable similarity, mimic the rotation curves of spiral galaxies without the need for dark matter.

Dark-Matter Galaxy Detected: Hidden Dwarf Lurks Nearby?   National Geographic - January 15, 2011

Signs point to an invisible "Galaxy X" just outside our own. An entire galaxy may be lurking, unseen, just outside our own. The invisibility of "Galaxy X"- as the purported body has been dubbed - may be due less to its apparent status as a dwarf galaxy than to its murky location and its overwhelming amount of dark matter, astronomer Sukanya Chakrabarti speculates. Detectable only by the effects of its gravitational pull, dark matter is an invisible material that scientists think makes up more than 80 percent of the mass in the universe.

Dark matter 'beach ball' unveiled   BBC - January 6, 2010

Milky Way's halo more squished than spherical   MSNBC - January 6, 2010
Dark matter's flattened appearance around galaxy surprises scientists.

The first glimpse of dark matter?   BBC - December 18, 2009

US scientists have reported the detection of signals that could indicate the presence of dark matter. A team announced on Thursday detecting two events with characteristics "consistent with" what physicists believe make up the elusive matter. The main announcement came from the Department of Energy's Fermi National Accelerator Laboratory near Chicago. The scientists were keen to stress that they could not confirm that what they had seen was definitely dark matter.

Dark Matter And Dark Energy Make Up 95 Percent Of Universe, Detailed Measurements Reveal   Science Daily - November 4, 2009
A detailed picture of the seeds of structures in the universe has been unveiled by an international team co-led by Sarah Church of the Kavli Institute for Particle Astrophysics and Cosmology, jointly located at the Department of Energy's SLAC National Accelerator Laboratory and Stanford University, and by Walter Gear, of Cardiff University in the United Kingdom. These measurements of the cosmic microwave background -- a faintly glowing relic of the hot, dense, young universe -- put limits on proposed alternatives to the standard model of cosmology and provide further support for the standard cosmological model, confirming that dark matter and dark energy make up 95% of everything in existence, while ordinary matter makes up just 5%.

Cluster Smashup Is Dark Matter Proof   National Geographic - August 27, 2008
If the latest image from the Hubble Space Telescope looks familiar, that's because this candy-hued galaxy cluster could be a twin of the so-called bullet cluster, a formation hailed in 2006 as the first direct proof for the existence of dark matter. At 5.6 billion light-years from Earth, the new cluster known as MACS J0025.4-1222 - is much farther away, and thus older, than its famous relative. But the formation shows the same separation of dark and ordinary matter occurring as its two parent galaxy clusters collide at high speed.

Bulk of Missing "Normal" Matter Found in Cosmic Web   National Geographic - May 21, 2008

Much of the missing "normal" matter in the cosmos has been found clustered around wispy ropes of invisible matter spanning the space between galaxies. The filaments form part of the vast weblike superstructure of the universe, within which galaxies are embedded like sparkling sequins.

Astronomers discover largest-ever dark matter structures spanning 270M light-years   PhysOrg - February 21, 2008
A University of British Columbia astronomer with an international team has discovered the largest structures of dark matter ever seen. Measuring 270 million light-years across, these dark matter structures criss-cross the night sky, each spanning an area that is eight times larger than the full moon. The results are a major leap forward since the presence of a cosmic dark matter web that extends over such large distances has never been observed before.

Violent Lives Of Galaxies: Dark Matter Found Tugging At Galaxies In Supercluster   Space Daily - January 15, 2008
Mapping dark matter Guardian - January 11, 2008

Dark Matter May Have Powered Universe's First Stars   National Geographic - December 6, 2007
According to a new theory, disintegrating fragments of the mysterious substance could have created "dark stars" hundreds of thousands of times wider than the sun around 13 billion years ago, just after the big bang.

Hubble spots ring of dark matter   BBC - May 16, 2007

Astronomers have found one of the best pieces of evidence for the existence of dark matter, a mysterious quantity that pervades our Universe. They have identified what appears to be a ghostly ring in the sky which is made up of this enigmatic substance. Using the Hubble Space Telescope, the scientists have established that the ring formed long ago after a colossal smash-up between two galaxy clusters.

Mapping The Invisible: Dark Matter Charted Out To Five Billion Light Years   Science Daily - April 23, 2007
Most of the matter in the Universe is not the ordinary kind made up of protons, neutrons, and electrons, but an elusive "dark matter" detectable only from its gravity. Like a tenuous gas, dark matter is all around us - it goes through us all the time without us noticing - but tends to collect in large quantities around galaxies and clusters of galaxies and makes up about one-sixth of the mass of the Universe.

Hubble makes 3D dark matter map   BBC - January 8, 2007

Astronomers have mapped the cosmic "scaffold" of dark matter upon which stars and galaxies are assembled. Dark matter does not reflect or emit detectable light, yet it accounts for most of the mass in the Universe. The study provides the best evidence yet that the distribution of galaxies follows the distribution of dark matter. This is because dark matter attracts "ordinary" matter through its gravitational pull.

Dark Matter: Mysterious has always existed   BBC - November 16, 2006

Dark energy - the mysterious force that is speeding up the expansion of the Universe - has been a part of space for at least nine billion years. Dark energy makes up about 70% of the Universe; the rest is dark matter (25%) and normal matter (5%). "It appears this dark energy was already boosting the expansion of the Universe as much as nine billion years ago," said co-investigator Adam Riess from the Space Telescope Science Institute in Baltimore, US. "That's out of a Universe which we think is about 13.7 billion years old - most of the way back."

The findings are consistent with the idea of dark energy behaving like Albert Einstein's cosmological constant. The cosmological constant describes the idea that there is a density and pressure associated with "empty" space. In this scenario, dark energy never changes; it has the same properties across the age of the Universe. Einstein first conceived of the notion of a repulsive force in space in his attempt to balance the Universe against the inward pull of its own gravity, which he thought would ultimately cause the Universe to implode. His cosmological constant remained a curious hypothesis until 1998, when astronomers used observations of supernovae from ground-based telescopes and Hubble to show that the expansion of space was accelerating. These findings suggested there really was a repulsive form of gravity in space, a force that was shortly dubbed "dark energy". There have been many attempts to explain the nature of dark energy.

Team finds 'proof' of dark matter   BBC - August 21, 2006

US astronomers say they have found the first direct evidence for the mysterious stuff called dark matter. Dark matter - which does not emit or reflect enough light to be "seen" - is thought to make up 25% of the Universe. By contrast, the ordinary matter we can see is believed to make up no more than about 5% of our Universe. Until now, astronomers have only been able to infer the existence of this dark material through the gravitational effects it has on ordinary matter. What the researchers have done is, in effect, to identify the gravitational "signature" of dark matter. This signature was created by dark matter and ordinary matter being wrenched apart by the immense collision of two large galaxy clusters.

Dark matter comes out of the cold   BBC - February 5, 2006
Astronomers have for the first time put some real numbers on the physical characteristics of dark matter. This strange material that dominates the Universe but which is invisible to current telescope technology is one of the great enigmas of modern science. That it exists is one of the few things on which researchers have been certain.