How the SKA will use fast radio bursts to decode the universe

There are parts of the universe that are extremely hard to see, even for our most advanced telescopes. Gas and dust don’t emit light and are visible only by the light they block from stars and galaxies. Magnetic fields are even harder to detect because ordinary light typically passes right through them. However, according to a new paper available on the arXiv preprint server by Manisha Caleb of the University of Sydney and their co-authors, a potentially game-changing new tool being commissioned could use a particularly violent astronomical phenomenon to provide new insight into these hard-to-see places.

That tool is the Square Kilometer Array (SKA), which we’ve reported on numerous times during its development and commissioning process. This continent-spanning telescope will be the most powerful radio telescope ever built once it is officially brought online. But that hasn’t stopped astronomers from dreaming of ways they can potentially use it already.

One way they plan to use it is to watch fast radio bursts (FRBs). These temporary, high-energy bursts from the cosmos can act as the perfect cosmic flashlight if we happen to be looking at them with a radio telescope.

To be clear, SKA won’t be busy finding as many FRBs as possible. That crown will likely go to a wide-field array like the DSA-2000 array in Nevada or CHIME (Canadian Hydrogen Intensity Mapping Experiment) in Canada, which are expected to catch up to 10,000 FRBs a year. But what the SKA lacks in scope, it makes up for in sensitivity. It will be able to find the faintest FRBs we’ve ever seen, and its SKA-low array in Western Australia will be looking at incredibly low frequencies at which we’ve never seen an FRB before.

There are several aspects of an FRB signal that the paper showcases as important “fingerprints.” The first is known as the “dispersion measure”—as an FRB travels through normal matter, low-frequency signals are delayed, allowing cosmologists to measure the amount of normal matter the signal passed through. If, on the other hand, it passes through a magnetic field, the polarization of a radio wave will twist, which the SKA can then detect. Traveling through plasma gives the data a third distinct twist, or, more specifically, scattering, allowing astronomers to estimate how much plasma lies between the FRB and the SKA.

The paper also lays out three important scientific tests researchers plan to conduct with these high-power cosmic flashlights. The first is to weigh the photon. Yes, you read that correctly. We’ve been taught in introductory physics classes for decades that the fundamental particle of light has no mass. But that is an assumption, and FRBs offer a way to test it at a level of precision impossible with anything we can do on Earth. Since FRBs travel billions of light-years, if photons possess even a minuscule amount of mass, low-energy radio waves will travel slightly slower than high-energy ones, and the SKA will be able to detect that speed difference given the distances those waves will have to travel.

A second seems to be a favorite pastime of physicists everywhere—testing Einstein. Measuring how the gravity of massive galaxy clusters affects different frequencies of an FRB will allow researchers to test the equivalence principle, a core component of the general theory of relativity. The SKA will be capable of detecting those minute differences at a sensitivity well beyond anything available today.

The third is a search for dark matter. If ultralight dark matter exists, it should form dense objects called “solitonic cores” inside galaxies. The SKA should be able to pick up a dispersion pattern that can reveal the telltale density signatures of these cores if an FRB happens to pass through one of them.

It will be a few years before the SKA is fully operational. But as more use cases are defined, the astronomical and cosmological communities are likely to grow more excited about the new capabilities the system offers. This is surely not the last paper brimming with ideas for how to use it.

Who’s behind this story?

Lisa Lock

BA art history, MA material culture. Former museum editor, paramedic, and transplant coordinator. Editing for Science X since 2021.

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Andrew Zinin

Master’s in physics with research experience. Long-time science news enthusiast. Plays key role in Science X’s editorial success.

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