Hubble Discovery Suggests We May Need New Physics to Explain Dark Matter
In Brief
Scientists have observed galaxy clusters moving in a way that's inconsistent with what we know about dark matter. This might suggest that we need to rethink our current models, or that an entirely unknown phenomenon has been discovered.What’s the Matter?
It’s thought that dark matter makes up as much as a quarter of all matter in the universe, but we know very little about it because it has never been directly observed and it is exceedingly difficult to study. Now, new research might indicate that entirely new physics is required to properly understand its behavior.A team of Swiss, French, and British astronomers has used the Hubble Space Telescope to analyze galaxy clusters. The current cold dark matter model suggests that the brightest cluster galaxy (BCG) located in the center of one of these clusters will stay in place after a merging event, thanks to the gravitational influence of dark matter.
However, this study found that BCGs actually “wobble” long after the cluster has returned to a relaxed state. The visible area of each cluster and the center of its mass were observed to be offset by as much as 40,000 lightyears.
The researchers were able to determine this because the clusters serve as gravitational lenses, as their sheer scale means that they warp spacetime, which affects the light coming from objects beyond their location. This makes it possible to ascertain the exact position of the center of mass, and measure how far offset the BCG is.
A Shot in the Dark
The wobbling that was observed by this study is a fairly mysterious phenomenon, which offers up its own questions. However, if it is being caused by dark matter, then our current understanding of its properties is inaccurate.Dark matter particles, if they are indeed responsible, would have to be able to interact with one another to cause this motion, which contradicts current thinking on the nature and behavior of the particles. This would suggest that we need to establish entirely new physics to properly explain our many remaining questions about dark matter.
The next step for this investigation is to look at larger datasets that might reveal more about the observed activity. The ESA’s Euclid spacecraft could provide this information – but it’s set to launch in late 2020, so it will be a few years before this vein of study is used to advance our understanding of dark matter.
“We’re looking forward to larger surveys — such as the Euclid survey — that will extend our dataset,” commented co-author Frederic Courbin of the EPFL. “Then we can determine whether the wobbling of BGCs is the result of a novel astrophysical phenomenon or new fundamental physics. Both of which would be exciting!”
Breakthrough Treatment Restores Voluntary Movement to Paralyzed Man’s Legs
In Brief
A new type of implant helped a patient who became paralyzed after a spinal cord injury recover movement in his legs. The new method uses electric stimulation through an implant on the spine, combined with traditional rehabilitation techniques for patients with spinal cord injuries.Reversing the Irreversible
28 years ago, Andrew Meas broke his neck after a fall from a motorcycle — an accident that left him unable to move his limbs. Spinal cord injuries of this nature invariably lead to some form of paralysis (if not complete debilitation) that are usually deemed to be irreversible.Meas, however, can now stand and move his legs. He was one of several patients with varying degrees of spinal injury who were given a novel treatment as part of research at the University of Louisville’s Kentucky Spinal Cord Injury Research Center (KSCIRC). In the study, researchers paired standard rehabilitation techniques with a fairly invasive method called spinal cord epidural stimulation (scES).
A device was implanted over Meas’ spinal column to electrically stimulate the lumbosacral enlargement during his physical therapy sessions. After just 44 months of regular physical training and the scES, Meas was able to move his lower limbs without any help. “Activity-dependent plasticity can re-establish voluntary control of movement and standing after complete paralysis in humans even years after injury,” KSCIRC researcher Susan Harkema, senior author of the study that appears in the journal Scientific Reports, said in a press release.
Recovery-Based Rehabilitation
The conventional wisdom touted by experts has long been that, for patients who have suffered an injury like Meas’, recovery is highly unlikely. As lead researcher Enrico Rejc said in the press release, “It is commonly believed that one year from injury, you are classified as chronic and it’s likely that you will not improve any more. This data is proof of principle that the human nervous system has much greater recovery capabilities than expected.”It’s particularly worth noting how the treatment involved is not just electrical stimulation (a growing field in rehabilitation medicine) but rather, a combination of the new method with regular physical therapy. Meas went through both a period of assisted therapy and standard training at home, and the research team credited his recovery as much to the amount of effort he put in as they did to their implant.
Indeed, the new research surpasses the limits of current recovery treatments. As Harkema noted, “This should open up new opportunities for recovery-based rehabilitation as an agent for recovery, not just learning how to function with compensatory strategies, even for those with the most severe injuries.”
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