Analyzing signals from across the universe

Coming from across the cosmos, the signals reaching Canadian radio telescopes are mysterious and intriguing.  

Perimeter is part of two cross-country and international collaborations that are deciphering those signals. During a recent visit to Montréal, the Perimeter team heard from researchers at the Trottier Space Institute at McGill University, which plays a big part in those collaborations.  

There, Professor Matt Dobbs is leading the effort to pioneer and test the techniques that the Canadian Hydrogen Observatory and Radio-transient Detector (CHORD), now under construction in British Columbia, will use to map the universe when it was only about a fifth of its current age.

The new telescope builds on earlier successes of the Canadian Hydrogen Intensity Mapping Experiment (CHIME), an award-winning telescope collaboration that has so far discovered and analyzed thousands of mysterious fast radio bursts.  

Perimeter faculty member and Daniel Family James Peebles Chair in Theoretical Physics Kendrick Smith, is a “data-oriented cosmologist” who led the development of new mathematical algorithms and software for CHIME, and is doing the same for CHORD.  

During the lab tour at McGill, the Perimeter team also heard from Seth Siegel, a postdoctoral researcher who is cross-appointed between Perimeter and McGill. He described the building and the subsequent achievements of the CHIME telescope which has been recognized through numerous prizes including the Governor General’s Innovation Award, the NSERC Brockhouse Prize, and most recently the Buchalter Cosmology Prize. CHIME’s observations of the radio sky have given us an incredible new vista into the nature of fast radio bursts and other cosmological puzzles.

The novel radio telescope is designed to map the universe’s most abundant element – hydrogen – across a significant portion of the observable cosmos.  

“I spend half of my time here at McGill, and I act as an interface between the hardware and instrumentation work going on here at McGill, and the theory and some of the software development happening at Perimeter,” Siegel said.  

The researchers at McGill developed what is known as a “correlator,” the electronic workhorse of the telescope and its Field-Programmable Gate Array (FPGA) motherboards. It performs mathematical operations on the signals.  

“We designed the FPGA motherboards here in the lab. We assembled them, tested them, deployed them at the site, commissioned the telescope, and we continue to analyze the data and drive these science results,” Siegel said.

The CHIME team released its first catalogue of 500 fast radio bursts (FRBs) in 2021. It was one of the top-cited papers in astronomy and astrophysics. Now, it is ready to publish a second catalogue that contains some 5,000 FRBs.

“We have learned a lot about what might be causing these FRBs. We have identified key clues that point to young neutron stars that form in the core collapse of supernovas as a source of a large fraction of them. But the exact emission mechanism is still poorly understood and there are pieces of evidence that don’t fit, suggesting that there might be multiple ways of forming these sources that we are still trying to understand,” Siegel said.

The next step is to use these detections to understand how baryons (particles such as protons and neutrons) are distributed relative to galaxies.

Next to CHIME in British Columbia, the foundations for CHORD are now going into the ground, and various institutions across Canada, including Perimeter and McGill, are involved in that as well.  

Dallas Wulf, academic associate and project manager for CHORD at McGill University, says CHORD will use individual six-metre dishes instead of the half-pipe U-shaped cylinders that CHIME uses.  

CHORD is an ultra-wideband telescope that combines a large number of these dishes in order to get much more extreme sensitivity with a much larger field-of-view.

Ian Hendricksen, a PhD student at McGill University who is working on commissioning the CHORD correlator, said in traditional radio astronomy, one normally has to have bigger and bigger and bigger dishes in order to get high sensitivity from the telescopes. But the digital hardware and technology of the past few decades has led to the ability to combine signals from many smaller dishes to get a similar level of sensitivity. This is what CHORD can accomplish.  

Dobbs spoke of the important interplay between theory and experiment, something that connects Perimeter to this important work of better understanding what is happening in our cosmos.

“It has to be a marriage from the start, in order to understand exactly what the big questions are, what the big uncertainties are and exactly what the challenges are,” Dobbs said.

“What we've managed to do so far in our collaboration with Perimeter is to really bring together people on both sides in order to draw the expertise in instrumentation into the theory analysis and the expertise from the theorist into some of the instruments,” Dobbs said.