Shedding light on dark matter

Perhaps one of the latest buzzwords in the news is the strange, potentially deadly material known as dark matter.

It is thought to comprise roughly 85 percent of the total matter throughout the cosmos and makes up about 27 percent of the Universe as we know it.

Now, for what may be the first time, this elusive quantity may have been spotted interacting alongside other particles of dark matter, in a star cluster approximately 1.4 billion light-years away from home.

Previous analysis done of colliding galaxy clusters have indicated that dark matter hardly interacts with anything at all. It is largely known by the gravity which it exerts, and the radiation that shines off of it.

The latest discovery, published this week in Monthly Notices of the Royal Astronomical Society, may suggest that exotic physics are at play – reaching well beyond the explanations offered by current theories.

The more widely accepted theories suggest that visible matter found in galaxies – a slim minority of the universe – exists within heaps of dark matter. If this dark matter did not contain the gravity necessary for their stability, galaxies including our Milky Way would gradually rip themselves apart while spinning.

As significant as it may be, the real nature of dark matter remains as mysterious as ever. So far, gravity seems to be the only known force with which it interacts.

Although many by and large believe that dark matter’s interactions are associated with one specific particle, the currently accepted theory of physics known as the Standard Model has yet to assign one.

In their study, a team of astronomers led by Dr. Richard Massey of Durham University studied a simultaneous collision between four different galaxies within the cluster Abell 3827.

Despite the fact that dark matter cannot be seen by the human eye, this team was capable of determining its location with the help of a technique known as gravitational lensing. Although dark matter can neither absorb nor give off light, it does contain gravity.

Much like when you place an object in a glass of water, dark matter distorts the pathway of any light passing nearby, altering our view of anything that may be the other side of the dark matter cluster. The dark matter within Abell 3827 twisted the path of the light rays emanated by a galaxy in the distant background, the one that just happened to be aligned perfectly for the team’s research. The Large Hadron Collider, which recently discovered the Higgs boson, or God particle, will also be making great strides in the hunt for dark matter. This month, after some initial delay, it commenced its second run. Kept at the French-Swiss border, this machine is currently firing up to strike protons with energies stronger and faster than ever before.

Dark matter is also thought to have influenced the Earth’s orbit on particular cycles within galaxies, and influencing dark matter already within our planet, meaning it may be suspect behind a number of extinction events. While there is still much to be found out, scientists are also deeper in their understanding of dark matter than ever before, and there is a large-scale effort currently under way to map out all dark matter found throughout the sky. The latest map suggests that dark matter outnumbers visible matter with a five to one ratio. Researchers hope to complete their map by the year 2018.

The researchers discovered that one particular clump of dark matter seemed to actually lag behind the galaxy which it surrounds. Such a lag between the dark matter and its associated galaxy would be expected if the mysterious stuff was interacting with itself – utilizing a force besides mere gravity. Although visible matter often interacts with other particles in normal ways, it is the dark matter that causes materials to lag behind, forming gravitational halos that cause a 5,000 light-year lag.

“We used to think that dark matter just sits around, minding its own business, except for its gravitational pull,” said Massey in an interview with Discovery News. “But if dark matter were being slowed down during this collision, it could be the first evidence for rich physics in the dark sector — the hidden Universe all around us.”

When Dr. Massey and colleagues had previously studied the collisions between enormous conglomerations of galaxies, such as the Bullet Cluster, infamous in dark matter studies for being one of the hottest clusters in the universe, they noticed that despite these violent collisions, the dark matter hardly slowed down at all.

“The Bullet Cluster collision took place at incredibly high speed,” Dr. Massey said in an interview with BBC News.

“But in this individual galaxy, the collision could have been going on for a long period of time.

“You would expect a small tiny force to build up over time, giving you a bigger offset to detect whether the dark matter interacts – just slightly. That’s why we looked at them.”

This slight interaction observed among the dark matter will probably need the more exotic theories of physics to evolve beyond what is already explained by the Standard Model.

“You just need the special conditions to enable this to be seen,” explained Dr. Massey.

Research that was published by this same team back in March placed an upper limit over the interaction between dark matter and its surroundings. Their newer research will focus on the lower limit.

“We are finally homing in on dark matter from above and below – squeezing our knowledge from two directions,” said Richard Massey.

James Sullivan
James Sullivan is the assistant editor of Brain World Magazine and a contributor to Truth Is Cool and OMNI Reboot. He can usually be found on TVTropes or RationalWiki when not exploiting life and science stories for another blog article.

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Astronomers are still further than they’d like to be to solving the mystery that is dark matter, concentrations of mysterious, invisible energy throughout the universe that may have impacted our own planet more than we think. While they were once thought to be part of a “dark sector,” a hidden quantum field out of the standard model of the universe that just reflects the matter around it. Instead, it may be something more interesting: its particles interact the way that galaxy clusters collide.

When this type of event takes place, hot gases filling the gaps between stars within these galaxies begin colliding and splattering in every direction, a movement similar to water hitting and splashing off a flat surface. About 90 percent of the matter in these clusters is actually dark matter – so does dark matter also splatter like water?

New research, however, has eliminated this colorful possibility – therefore limiting what types of particles constitute dark matter, and reducing the possibility that they hide away mirrors of our visible universe.

How does this work? Our own galaxy has billions of stars – just a miniscule fraction of the hundreds of billions scattered throughout the visible universe – a countless array of stars, planets, galaxies, and then even the debris – the dust and gas that’s responsible for producing all of it – but even this is totals up to just 15 percent of the universe at best. The rest is dark matter – which is detected by its extreme gravitational pull that it exerts on the matter it surrounds. It is impervious to light, neither radiating nor reflecting it. However, they are able to spot the patches of dark matter due to light bending around it.

David Harvey, who is a postdoctoral researcher at the Swiss Federal Institute of Technology Lausanne, is among the ranks of scientists actively trying to solve the mystery of dark matter, which led him to study galactic collisions – events where 90 percent of what collides is actually dark matter.

“[Galaxy cluster mergers] are incredibly messy,” said Harvey. “You’ve got [the stars], the highest densities of dark matter and hot gas all swirling together.”

While this has been the epicenter of dark matter studies for decades, interest has renewed due to changes in technology. “We wanted to have a big statistical sample that tries to average over all these different merging scenarios, and try to get a statistical idea of what dark matter is doing during these cosmological crashes.”

What they have learned about these collisions, which feel more like mergers, is that they aren’t as violent as one might think. The stars are often so far apart when they take place that they tend to neatly fold together in place.

Between the galaxies, however, lies a heavy blanket of gas crackling with charged particles. Once the galaxy clusters come together, this gas spews in every direction.

“If we measure the dark matter [after the collision], and should it lie where the galaxies are, we know the dark matter is completely collisionless, and doesn’t interact with itself at all,” Harvey said. “And if it should lie where the gas is, we’d say that the dark matter is actually interacting with itself a lot, like a liquid.”

So far, the researchers compared data from 30 different galaxy-cluster collisions with the help of NASA’s Hubble Space Telescope and the Chandra X-ray Observatory. What they found was equally striking: dark matter appears to behave similar to stars, remaining largely unaffected in the collision. Perhaps these observations suggest that dark matter is made of similar components to stars?

So what about the splattering gas? This is due to the gas behaving like a solid, in the same way that liquids bubble and cling together in a microgravity environment. Atomic protons interact in such a way as well.

By comparison, dark matter doesn’t behave like a gas, interacting less with its own particles than the protons of atoms interact with each other. This has led many to suspect that dark matter is made up of dark protons or electrons, sort of a mirror version of the atom.

“Chances are that dark matter is not made up of dark protons interacting with dark protons, and chances are, there is not a mirror universe out there with these dark particles,” said Harvey. “The caveat is that theorists could change some of their parameters, so the field is still open to what [dark matter] could be, but we’re narrowing it down.”

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