Searching the cosmic web: meet Dr Tessa Vernstrom

By  Rachel Rayner 30 January 2025 4 min read

“I’ve always wanted to work in a field where I’m constantly going, ‘wow’, which is why I’m in radio astronomy.”

Tessa started her student life studying political science and psychology, but a chance class in astronomy changed all that.

“I realised I wasn’t going to change the world, but I could change our understanding of space.”

Starry-eyed beginnings

At university in Canada, she met with different professors to figure out what projects were available to study in astronomy. The most interesting project to her was on studying unexplained radio emissions being detected by radio telescopes looking deep into space.

“I loved doing my PhD – it was a time when I was learning how to be a good researcher and doing awesome science. It was a really enjoyable experience for me.”

This project led Tessa to become a radio astronomer, an astronomer who specialises in using radio telescopes to observe very low energy light from space, called radio waves.

Radio astronomy is a field with many mysteries to solve. Was she successful in uncovering what these unexplained radio emissions were in Canada all those years ago?

“No! It turns out it wasn’t galaxies as I had suspected. Nearly a decade later, we still don’t know what causes these emissions. But I am currently supervising a Masters student who’s working on a new theory so we’re still exploring ideas!”

Tessa’s career has brought her to Australia, which is one of the world’s best locations for radio astronomy. Our Australia Telescope National Facility includes internationally-leading infrastructure like our ASKAP radio telescope on Wajarri Country, our Australia Telescope Compact Array on Gomeroi Country, and Murriyang, our Parkes radio telescope, on Wiradjuri Country. There’s also our huge archives of astronomy data spanning decades, which may contain intergalactic phenomena waiting to be discovered.

Australia can also boast one of the best views of our Milky Way, with the galactic centre being overhead for most of the year. This is something not seen often in the Northern Hemisphere.

From her base in Perth, Tessa is developing new methods for studying our Universe and figuring out ways to detect the things we think are there, even if we can’t see them.

“There’s no road map for the work we’re doing. We’re figuring it out as we go.”

How low can we go?

Frequency refers to a how often a light wave vibrates each second. High-frequency waves carry more energy, while low-frequency waves carry less.

In radio astronomy, telescopes can be catagorised by whether they detect low-, mid- or high-frequency radio waves. The telescopes within our Australian Telescope National Facility have an impressive range for any radio telescope. This is thanks to our innovative receiver technology, though it is mostly in the mid- to high-frequencies. Telescopes like the Curtin University-led Murchison Widefield Array (MWA) and the SKA Observatory’s incoming SKA-Low telescope operate at much lower frequencies.

Tessa focuses on low-frequency astronomy. Her first low-frequency project used MWA, which is located at Inyarrimanha Ilgari Bundara, our Murchison Radio-astronomy Observatory on Wajarri Country in Western Australia. She used the telescope to detect the radio signals from the cosmic web in a way that had never been done before.

The cosmic web refers to the structure of the Universe at the largest scale, which when zoomed out has a web like pattern.

She wasn’t reengineering the telescope for these new methods. Rather, she was working with the data from the telescope in new and experimental ways.

“It can be a little tricky as we’re not talking about data like an image of space you might expect from an optical telescope. What I want to see in space – the cosmic web – has an incredibly faint signal.”

Her process involved comparing sky surveys with the positions of millions of known galaxies. By removing the signals generated by these galaxies, she could enhance the visibility of these faint signals of the cosmic web.

“Astrostatistics is about thinking, ‘how can I use the properties of the signals in an image to tell me information about the things I can't see. How many galaxies are in there? And what’s in the space between galaxies?’”

“I reprocessed the data in many different ways to see which one might enhance this faint signal. We were developing new ways to see what we hadn’t before.”

Leading the next wave of discovery

Now, as a CSIRO Science Leader, she is building a low-frequency radio astronomy team to develop Australia’s capacity in this field. The SKA-Low telescope opens up even more opportunities to peer deep into space. This time, though, it is more than just working with data.

She’ll be working with a team of early career researchers and ATNF engineers to set up low-frequency stations across our observatory sites, and perhaps even connecting them into the SKA-Low telescope.

“Connected low-frequency stations are still something that doesn't exist in the Southern Hemisphere, so I'm excited to help that come to fruition.”

This could create a telescope with the diameter of Australia, capturing as many of these low-frequency wavelengths as possible. It would help build a more complete image of our Universe and the cosmic web within it.

“The data we’re getting now is showing us things we’ve never seen before, we don’t know what they are. With more telescopes, and bigger telescopes, we can put all the pieces of the puzzle together to understand these new and unexpected things. Then this will give us even more amazing things to research.”