Backward Shockwaves From Deep Space Are Puzzling Scientists

Caroline Delbert - Yesterday 


A faraway galaxy cluster boasts an unusual backward shockwave phenomenon.
Galaxy clusters contain up to thousands of galaxies and tons of plasma in motion.
The backward shockwave may be from overlapping collisions among subclusters.

Scientists from the University of Western Australia and Italy’s Università di Bologna have been studying an extremely faraway galaxy cluster, Abell 3266, where they’ve identified three phenomena that are unheard of elsewhere—at least so far. And all three emit radio waves that have allowed us to observe them across a distance so far it almost defies units of measure altogether.

Abell 3266 is a galaxy cluster that’s 809 million light years away from Earth in an area known as the Horologium-Reticulum Supercluster. (As you zoom out further and further into space, you see that we, in the Milky Way, are part of a supercluster as well. Some supercluster-like structures we believe to exist are so large they potentially unmake our existing theory of the universe itself!)

In a piece for the Conversation, a website that publishes content from academics, the scientists explain that the term “galaxy cluster” is a little bit misleading. Yes, a cluster may contain “hundreds, or even thousands” of galaxies, they say, but the overwhelming majority of mass in these clusters is dark matter, with “hot plasma ‘soup’” making up the rest. The Milky Way is made up of an estimated 85 percent dark matter, for example. Galaxies, themselves, make up a measly “few percent.”

On Earth, we primarily understand plasma as the makeup of stars, including our sun. But plasma physics is a huge field, since plasma itself is just another state of matter. The more we can examine it in different contexts, the more we can understand—knowledge that may also eventually help people on Earth who work on projects like nuclear fusion energy.

Abell 3266 is “a particularly dynamic” cluster, named for prolific astronomer and public scientist George O. Abell, who surveyed both the northern and southern skies for galaxy clusters during his lifetime. (Abell 3266 is in the southern sky.) While observing the cluster with the Australian Square Kilometre Array Pathfinder and Australia Telescope Compact Array radio telescopes, the researchers observed three different unusual phenomena: radio relics, radio haloes, and fossil radio sources.

All three of these phenomena are created by energy slamming into abundant plasma. With radio relics, this reaction sends out shockwaves like the sonic booms we experience on Earth. They themselves aren’t unusual in galaxy clusters, but the one these researchers found is backward. The brightness in this area of the cluster suggests that a shockwave should travel from north to south, but instead it goes from south to north. The researchers dubbed this a “wrong-way” radio relic.


© Risely et. alRadio-on-optical overlay of the ‘wrong-way’ relic to the SE of Abell 3266.

The researchers say other scientists have begun to observe other backward radio relics in similar work, showing that this is an uncommon, but not nonexistent, phenomenon. And they theorize that the wrong-way radio relics result from not just energy striking plasma, but multiple subclusters striking each other simultaneously. Think about biting down on a crunchy potato chip versus biting down on a crunchy potato chip that was folded over during manufacturing.

In their paper, published August 1 in Monthly Notices of the Royal Astronomical Society, the researchers present all three radio anomalies with the follow-up note that they all require a lot more study; this paper is kind of an announcement, rather than a conclusion.“[F]urther work is required to fully unpack the history of Abell 3266 and its constituent radio galaxies, and the answers to a number of questions remain elusive,” they conclude.

Astrophysicists observe one of the most powerful short gamma-ray bursts ever


An artist's rendering shows the collision between a neutron star and another star (seen as a disk at the lower left), which caused an explosion resulting in the short-duration gamma-ray burst, GRB 211106A (white jet, middle). 

Aug. 5 (UPI) -- The collision of two distant neutron stars released one of the most powerful short gamma-ray bursts ever recorded, scientists say.

The collision marked the first time scientists have recorded millimeter-wavelength light from a fiery explosion to be caused by the merger of a neutron star with another star. It was observed on Nov. 6, 2021.

The observation was made with the Atacama Large Millimeter/submillimeter Array, or ALMA, in Chile. ALMA is an international observatory operated by the National Science Foundation's National Radio Astronomy Observatory.

"Afterglows for short bursts are very difficult to come by, so it was spectacular to catch this event shining so brightly," ALMA principal investigator Wen-fai Fong said in a statement.

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"After many years observing these bursts, this surprising discovery opens up a new area of study, as it motivates us to observe many more of these with ALMA and other telescope arrays in the future."

Research into the collision will be published in an upcoming issue of the Astrophysical Journal Letters.

Photo courtesy Atacama Large Millimeter/submillimeter Array Observatory


A short-duration gamma-ray burst usually lasts only a few tenths of a second and researchers look for an afterglow when it fades. Only a half dozen short-duration bursts have been detected at radio wavelengths and only in millimeters.

Gramma-ray bursts, though, are incredibly powerful. They are capable of emitting more energy in a matter of seconds than the sun will emit during its entire lifetime. There are three types -- short, long and ultra-long.

Gamma-ray bursts, in fact, are considered to be one of the most catastrophic space threats to the Earth, although scientists agree that the likelihood of the Earth being affected by a gamma-ray burst is extremely low. The destructive energy from gamma-ray bursts can travel for thousands of light years.

"Millimeter wavelengths can tell us about the density of the environment around the GRB," Northwestern scientist Genevieve Schroeder, a co-author of the research, said in a statement. "And, when combined with the X-rays, they can tell us about the true energy of the explosion.

"Because emission at millimeter wavelengths can be detected for a longer time than in X-rays, the millimeter emission also can be used to determine the width of the GRB jet."