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.
Now, ASTRO 3D and UNSW Sydney astronomer Kim-Vy Tran and colleagues have evaluated 77 of the lenses using the Keck Observatory in Hawai’i and the Very Large Telescope in Chile. She and her international team have confirmed that 68 of the 77 are strong gravitational lenses spanning vast cosmic distances.
This 88% success rate suggests that the algorithm is reliable and that we could have thousands of new gravitational lenses. To date, gravitational lenses are hard to find and only about 100 are commonly used.
Kim-Vy Tran’s paper published today in the Astronomical Journal presents spectroscopic confirmation of previously identified strong gravitational lensing using convolutional neural networks, developed by ASTRO 3D data scientist Dr. Colin Jacobs 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 corresponding author Dr. Tran of the ARC Center of Excellence for Astrophysics of the Sky. in 3 dimensions (ASTRO3D) and the University of NSW (UNSW).
“Our goal with AGEL is to confirm by spectroscopy about 100 strong gravitational lenses that can be observed from 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.
“With this, we were able to identify several thousand lenses versus a few handfuls,” says Dr. Tran.
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 Dr. Tran.
While these lenses allow us to more clearly see objects millions of light-years away, 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 Dr. 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 study these more distant objects. Hopefully we can better measure the demography of very young galaxies,” says Dr Tran.
“Then somewhere between those very early first galaxies and us, 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. »
Dr. 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.
Professor Stuart Wyithe of the University of Melbourne and director of the ARC Center of Excellence for Astrophysics of the Sky in 3 Dimensions (Astro 3D) says that every gravitational lens is unique and teaches us something new.
“In addition to being beautiful objects, gravitational lenses provide a window to study how mass is distributed in very distant galaxies that are not observable via other techniques. By introducing ways to use these new large sky datasets to search for many new gravitational lenses, the team opens up the possibility of seeing how galaxies get their mass,” he says.
Professor Karl Glazebrook of Swinburne University and Dr Tran’s co-lead scientist on the paper paid tribute to the work that had gone before.
“This algorithm was developed by Dr Colin Jacobs at 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. »
UC Davis Associate Professor Tucker Jones, another co-scientist on the paper, described the new sample as “a giant leap in learning about the formation of galaxies throughout the history of space.” ‘Universe’.
“Normally, these early galaxies look like small fuzzy specks, but the magnification of the lens allows us to see their structure with much better resolution. They are ideal targets for our most powerful telescopes to give us the best possible view of the early universe,” he says. .
“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.
The ARC Center of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D) is a $40 million research center of excellence funded by the Australian Research Council (ARC) and six collaborating Australian universities – the National University Australia, University of Sydney, University of Melbourne, Swinburne University of Technology, University of Western Australia and Curtin University.