Are Pulsars the Key to Finding Dark Matter?

A composite image of the Crab Nebula. Credit: X-ray: NASA/CXC/SAO; Optical: NASA/STScI; Infrared: NASA-JPL-Caltech

Ah, dark matter particles, what could you be? The answer still eludes us, and astronomers keep trying new ideas to find them. Such as a new paper in Physical Review Letters that suggests if dark matter is made of axions we might see their remnant glow near pulsars.

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Dark Matter Might Interact in a Totally Unexpected Way With the Universe

Image from Dark Universe, showing the distribution of dark matter in the universe. Credit: AMNH

According to Sir Isaac Newton’s theory of Universal Gravitation, gravity is an action at a distance, where one object feels the influence of another regardless of distance. This became a central feature of Classical Newtonian Physics that remained the accepted canon for over two hundred years. By the 20th century, Einstein began reconceptualizing gravity with his theory of General Relativity, where gravity alters the curvature of local spacetime. From this, we get the principle of locality, which states that an object is directly influenced by its surroundings, and distant objects cannot communicate instantaneously.

However, the birth of quantum mechanics has caused yet another conceptualization, as physicists discovered that non-local phenomena not only exist but are fundamental to reality as we know it. This includes quantum entanglement, where the properties of one particle can be transferred to another instantaneously and regardless of distance. In a new study by the International School for Advanced Studies (SISSA) in Trieste, Italy, a team of researchers suggests that Dark Matter might interact with gravity in a non-local way.

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Gravitational Lensing is Helping to Nail Down Dark Matter

Using the gravitational lensing technique, a team was able to examine how light from distant quasar was affected by intervening small clumps of dark matter. Credit: NASA/ESA/D. Player (STScI)

According to the most widely-accepted cosmological model, the majority of the mass in our Universe (roughly 85%) consists of “Dark Matter.” This elusive, invisible mass is theorized to interact with “normal” (or “visible”) matter through gravity alone and not electromagnetic fields, neither absorbing nor emitting light (hence the name “dark”). The search for this matter is ongoing, with candidate particles including Weakly-Interacting Massive Particles (WIMPs) or ultralight bosons (axions), which are at opposite extremes of the mass scale and behave very differently (in theory).

This matter’s existence is essential for our predominant theories of gravity (General Relativity) and particle physics (The Standard Model) to make sense. Otherwise, we may need to radically rethink our theories on how gravity behaves on the largest of scales (aka. Modified Gravity). However, according to new research led by the University of Hong Kong (HKU), the study of “Einstein Rings” could bring us a step closer to understanding Dark Matter. According to their paper, the way Dark Matter alters the curvature of spacetime leaves signatures that suggest it could be made up of axions!

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If Axions are Dark Matter, we've got new Hints About Where to Look for Them

Artist rendering of the dark matter halo surrounding our galaxy. For quasars, the dark matter halos are much more massive. Credit: ESO/L. Calçada
Artist rendering of the dark matter halo surrounding our galaxy. Credit: ESO/L. Calçada

If dark matter is out there, and it certainly seems to be, then what could it possibly be? That is perhaps the biggest mystery of dark matter. The only known particles that match the requirement of having mass and not interacting strongly with light are neutrinos. But neutrinos have low mass and zip through the cosmos at nearly the speed of light. They are a form of “hot” dark matter, so they don’t match the observed data that require dark matter to be “cold.” With neutrinos ruled out, cosmologists look toward various hypothetical particles we haven’t discovered, and perhaps the most popular of these are known as axions.

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Missing Mass? Not on our Watch—Dr. Paul Sutter Explains Dark Matter

Credit: ArsTechnica

Do you have a few minutes to spare and a thirst for knowledge about one of the greater mysteries of the Universe? Then head on over to ArsTechnica and check out the new series they’re releasing titled Edge of Knowledge, starring none other than Dr. Paul Sutter. In what promises to be an enlightening journey, Dr. Sutter will guide viewers through an eight-episode miniseries that explores the mysteries of the cosmos, such as black holes, the future of climate change, the origins of life, and (for their premiere episode) Dark Matter!

As far as astrophysicists and cosmologists are concerned, Dark Matter is one of the most enduring, frustrating, and confusing mysteries ever! Then, one must wonder why scientists are working so tirelessly to track it down? The short answer is: the most widely accepted theories of the Universe don’t make sense without out. The long answer is… it’s both complicated and long! Luckily, Dr. Sutter manages to sum it all up in less than 15 minutes. As an accomplished physicist, he also explains why it is so important that we track Dark Matter down!

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A Worldwide Search for Dark Matter Fails to Turn up a Signal for This Mysterious Particle

Simulation of dark matter and gas. Credit: Illustris Collaboration (CC BY-SA 4.0)

Axions are a popular candidate in the search for dark matter. There have been previous searches for these hypothetical particles, all of which have come up with nothing. But recently the results of a new search for dark matter axions have been published…and has also found nothing. Still, the study is interesting because of the nature and scale of the search.

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One Idea to Explain Dark Matter – Ultralight Bosons – Fails the Test

Some black holes rotate very quickly. Credit: Paramount Pictures/Warner Bros.

Dark matter continues to resist our best efforts to pin it down. While dark matter remains a dominant theory of cosmology, and there is lots of evidence to support a universe filled with cold dark matter, every search for dark matter particles yields nothing. A new study continues that tradition, ruling out a range of dark matter candidates.

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If Axions Explain Dark Matter, it Could be Possible to Detect Them Nearby Neutron Stars

The Robert C. Byrd Green Bank Telescope. Credit: Green Bank Observatory/NRAO

As we continue to search for dark matter particles, one thing is very clear: they cannot be any of the elementary particles we’ve discovered so far. The particles would need to have mass, but interact with light only weakly. Of the known particles, neutrinos fit that description, but neutrinos have a tiny mass, and aren’t nearly enough to explain dark matter. Some other kind of particle must make up the majority of dark matter.

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Japanese Dark Matter Detector is Seeing a “Surprising Excess of Events”

The top PMT array with all of the electric cables. Credit: XENON Dark Matter Project

Dark matter is notoriously difficult to detect. So difficult that we haven’t detected it yet. Evidence for dark matter can be seen in everything from the warping of light near galaxies to the way galaxies cluster together. We are pretty sure dark matter is real, but we also know it can’t be made of any type of particle we currently know. But a new study has found some interesting data that could be evidence of dark matter, or not.

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