Dozens of newly discovered gravitational lenses could reveal ancient galaxies and the nature of dark matter

Cambridge, MA – Earlier this year, a machine learning algorithm identified up to 5,000 potential gravitational lenses that could transform our ability to trace the evolution of galaxies since the Big Bang.

Today, astronomer Kim-Vy Tran and his colleagues evaluated 77 of the lenses using the Keck Observatory in Hawai’i and the Very Large Telescope in Chile. She and her international team, including Lisa Kewley from the Center for Astrophysics, confirmed that 68 of the 77 are strong gravitational lenses spanning vast cosmic distances.

The 88% success rate suggests the algorithm is reliable and there could be thousands of new gravitational lenses. To date, gravitational lenses are hard to find and only about 100 are commonly used.

Trans paperpublished today in the Astronomical Journal, presents spectroscopic confirmation of previously identified strong gravitational lenses using convolutional neural networks, developed by data scientist Colin Jacobs of ASTRO 3D and Swinburne University.

The work is part of the ASTRO 3D Galaxy Evolution with Lenses (AGEL) survey.

“Our spectroscopy allowed us to map a 3D image of the gravitational lenses to show that they are genuine and not just a chance overlay,” says Tran of the ARC Center of Excellence for Astrophysics of the Sky in 3 Dimensions (ASTRO3D) and from the University of NSW. (UNSW).

“Our goal with AGEL is to confirm by spectroscopy about 100 strong gravitational lenses that can be observed in both the northern and southern hemispheres throughout the year,” she says.

The article is the result of a worldwide collaboration with researchers from Australia, the United States, the United Kingdom and Chile.

The work was made possible by the development of the search algorithm for certain digital signatures.

“This research merges gravitational lensing, an effect predicted by Einstein, with modern machine learning techniques to dramatically increase our discoveries of galaxies in the distant universe,” says Kewley, study co-author and Center director. for Astrophysics | Harvard & Smithsonian. “This is the first glimpse of what will be an avalanche of lensed galaxy data to help us understand how galaxies like our Milky Way formed and evolved over 13 billion years of cosmic time. “

Gravitational lensing was first identified as a phenomenon by Einstein who predicted that light bends around massive objects in space the same way light bends when passing through a lens.

In doing so, it dramatically enlarges images of galaxies that we otherwise wouldn’t be able to see.

While it’s been used by astronomers to observe distant galaxies for a long time, finding these cosmic magnifying glasses in the first place has been hit and miss.

“These lenses are very small, so if you have blurry images, you won’t really be able to detect them,” says Tran.

While these lenses allow us to see objects millions of light-years away more clearly, they should also allow us to “see” the invisible dark matter that makes up most of the universe.

“We know that most of the mass is dark,” says Tran. “We know that mass makes light bend and so if we can measure how much light is bent, then we can infer how much mass must be there.” Having many more gravitational lenses at different distances will also give us a fuller picture of the timeline going back almost to the Big Bang.

“The more magnifying glasses you have, the more likely you are to try to monitor these more distant objects. Hopefully, we can better measure the demography of very young galaxies,” Tran says.

Then, somewhere between those very early first galaxies and Earth, there’s a lot of evolution happening, with tiny star-forming regions converting pristine gas into the first stars from the sun, the Milky Way.

“And so with these lenses at different distances, we can look at different points in the cosmic timeline to basically track how things change over time, between the very first galaxies and now.”

Tran’s team spanned the globe, with each group bringing different expertise.

“Being able to collaborate with people, in different universities, was so crucial, both to set up the project in the first place, and now to continue with all the follow-up observations,” she says.

Stuart Wyithe of the University of Melbourne and director of ASTRO 3D says each gravitational lens is unique and teaches us something new.

“In addition to being beautiful objects, gravitational lenses provide a window to study the distribution of mass in very distant galaxies that are not observable via other techniques. By introducing ways to use these new large ensembles data from the sky to search for many new gravitational lenses, the team opens up the possibility of seeing how galaxies get their mass,” he says.

Karl Glazebrook of Swinburne University and Tran’s co-lead scientist on the paper, paid tribute to the work that had come before.

“This algorithm was pioneered by Colin Jacobs in Swinburne. He sifted through tens of millions of images of galaxies to narrow down the sample to 5,000. We never imagined the success rate would be so high,” he says.

“Now we are getting images of these lenses with the Hubble Space Telescope, they range from breathtakingly beautiful to extremely eerie images that will take us considerable effort to understand.”

Tucker Jones of UC Davis, another co-scientist on the paper, described the new sample as “a giant leap in learning about galaxy formation throughout the history of the universe.”

“Through lensing, we can learn what these early galaxies look like, what they are made of, and how they interact with their environment.”

The study was conducted in collaboration with researchers from the University of New South Wales, Swinburne University of Technology, Australian National University, Curtin University and the University of Queensland in Australia, the University of California at Davis in the United States, the University of Portsmouth, United Kingdom, and the University of Chile.

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