Focus lens spectroscopy and machine learning at the distant universe scales | Research and technology | October 2022

MELBOURNE, Australia, October 11, 2022 – Researchers from the ARC Center of Excellence for All Astrophysics in Three Dimensions (ASTRO 3D) and the University of New South Wales (UNSW) in Sydney have confirmed through spectroscopy a number of powerful gravitational lenses that were in Initially it was determined using Convolutional Neural Networks (CNNs).

“Our spectroscopy allowed us to 3D map gravitational lenses to show that they are real and not just a chance superposition,” said Professor Kim-Vy Tran.

A machine learning algorithm that searched for specific digital signatures made Tran and the team’s work possible. The algorithm was developed by researcher Colin Jacobs at Swinburne University of Technology, who scanned tens of millions of images of galaxies to shrink the sample down to 5,000.

Gravitational lens images from an AGEL survey.  The images are centered on the foreground galaxy and include the name of the object.  Each panel includes the confirmed distance to the foreground galaxy (zdef) and the far background galaxy (zsrc).  Courtesy of Kim-Vy H. Tran, et al., The ASTROnomical Journal (2022).


Gravitational lens images from an AGEL survey. The images are centered on the foreground galaxy and include the name of the object. Each panel includes the confirmed distance to the foreground galaxy (zdef) and the distant background galaxy (zsrc). Courtesy of Kim-Vy H. Tran et al./Astronomical Journal (2022).


Using the Keck Observatory in Hawaii and the Very Large Telescope in Chile, the researchers evaluated 77 of about 5,000 potential gravitational lenses identified using a machine learning algorithm. The team confirmed that 68 of the 77 lenses, or 88% of the lenses, are strong gravitational lenses covering vast cosmic distances. This high ratio indicates that the algorithm used to detect the lenses is reliable – and that thousands of new gravitational lenses, discovered by the algorithm, have yet to be confirmed.

Gravitational lenses are cosmic magnifying lenses used to explore a range of astrophysical phenomena. A powerful gravitational lens extends scientists’ observational range to objects extremely faint even for the most powerful telescopes.

In addition to giving scientists a clearer view of objects millions of light years away, the newly validated powerful gravitational lensing could help scientists identify the invisible dark matter that makes up most of the universe. “We know that most of the block is dark,” Tran said. “We know that mass bends light, so if we can measure how much light bends, then we can infer how much mass there should be.”

“Aside from being beautiful objects, gravitational lenses provide a window into how mass is distributed in galaxies too far away to be observed by other techniques,” said Professor Stuart Wyeth, Director of ASTRO 3D. “By offering ways to use these new large data sets in the sky to search for many new gravitational lenses, the team opens up the opportunity to learn how galaxies get their mass.”

Access to the many gravitational lenses located at different distances from Earth will also give scientists a more complete overview of the timeline of the universe, going back roughly to the Big Bang.

“The more magnifying lenses you have, the better you can try to scan these distant objects,” Tran said. “Hopefully we can better measure the demographics of very young galaxies. Somewhere between those first early galaxies and us, there’s a lot of evolution going on, with young star-forming regions turning pristine gas into the sun’s first stars, the Milky Way.” Using these lenses at different distances, we can look at different points in the cosmic timeline to essentially track how things change over time, between the first galaxies and now.”

Professor Tucker Jones of the University of California, Davis described the new sample as “a giant step forward in learning how galaxies have formed over the course of the history of the universe.” To date, gravitational lenses have been difficult to identify, and about 100 lenses are used routinely.

This work is part of the ASTRO 3D Galaxy Evolution with Lenses (AGEL) survey. The goal of the AGEL international research team is to confirm a statistically robust sample by spectroscopy of about 100 strong gravitational lenses that can be observed with adaptive optics using telescopes in both hemispheres throughout the year.

To more accurately model lens mass distribution, resolve subkiloparsec structure spatially in sources, and search for dark matter infrastructure at aberrations and along line of sight, the team is acquiring high-resolution imaging using the Hubble Space Telescope for a subset of AGEL systems.

The search was published in Astronomical Journal (www.iopscience.iop.org/article/10.3847/1538-3881/ac7da2).

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