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

Thousands more potential lenses await assessment.


To date, gravitational lenses have been hard to find, and only about a hundred are routinely used. Identified as a phenomenon by Einstein, gravitational lensing has been used by astronomers to observe far away galaxies for a long time, however, finding them in the first place has been hit and miss.

The new study presents spectroscopic confirmation of strong gravitational lenses previously identified using Convolutional Neural Networks, developed by data scientist Dr. Colin Jacobs at ASTRO 3D and Swinburne University.

A machine learning system discovered up to 5,000 potential gravitational lenses earlier this year, which could revolutionize our ability to trace the evolution of galaxies since the Big Bang.

Using the Keck Observatory in Hawaii and the Very Large Telescope in Chile, astronomer Kim-Vy Tran of ASTRO 3D and UNSW Sydney and colleagues have evaluated 77 of the lenses. She verified with the help of her multinational team that 68 of the 77 are powerful gravitational lenses spanning vast cosmological distances.

With an 88% success rate, the algorithm appears trustworthy, and thousands of new gravitational lenses may exist.

Corresponding author Dr. Tran from the ARC Centre of Excellence for All Sky Astrophysics in 3-Dimensions (ASTRO3D) said, “Our spectroscopy allowed us to map a 3D picture of the gravitational lenses to show they are genuine and not merely chance superposition. Our goal with AGEL is to spectroscopically confirm around 100 strong gravitational lenses observed from both the Northern and Southern hemispheres throughout the year.”

“The work was made possible by developing the algorithm to look for certain digital signatures. With that, we could identify thousands of lenses compared to just a few handfuls.”

“Gravitational lenses are very small, so if you have fuzzy images, you will not be able to detect them. While these lenses let us see objects that are millions of light years away more clearly, they should also let us ‘see’ invisible dark matter that makes up most of the Universe.”

“We know that most of the mass is dark. We know that mass is bending light, and so if we can measure how much light is bent, we can then infer how much mass must be there.”

“The more magnifying glasses you have, the better chance you can try to survey these more distant objects. Hopefully, we can better measure the demographics of very young galaxies.”

“Then somewhere between those early first galaxies and us, there’s a whole lot of evolution that’s happening, with tiny star-forming regions that convert pristine gas into the first stars to the sun, the Milky Way.”

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

Professor Stuart White of the University of Melbourne and Director of the ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (Astro 3D) says each gravitational lens is unique and tells us something new.

“Apart from being beautiful objects, gravitational lenses provide a window to studying how mass is distributed in distant galaxies that are not observable via other techniques. By introducing ways to use these new large data sets of the sky to search for many new gravitational lenses, the team opens up the opportunity to see how galaxies get their mass.”

Professor Karl Glazebrook of Swinburne University, and Dr. Tran’s Co-Science Lead on the paper, paid tribute to the work that had gone before.

“This algorithm was pioneered by Dr. Colin Jacobs at Swinburne. He sifted through tens of millions of galaxy images to prune the sample down to 5,000. Never did we dream that the success rate would be so high.”

“Now we are getting images of these lenses with the Hubble Space Telescope, they range from jaw-droppingly beautiful to extremely strange images that will take us considerable effort to figure out.”

Associate Professor Tucker Jones of UC Davis, another co-science lead on the paper, described the new sample as “a giant step forward in learning how galaxies form over the history of the Universe.”

“Normally, these early galaxies look like small fuzzy blobs, but the lensing magnification 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.”

“Thanks to the lensing effect, we can learn what these primitive galaxies look like, what they are made of, and how they interact with their surroundings.”

Journal Reference:

  1. Kim-Vy H. Tran et al. The AGEL Survey: Spectroscopic Confirmation of Strong Gravitational Lenses in the DES and DECaLS Fields Selected Using Convolutional Neural Networks. The Astronomical Journal. DOI: 10.3847/1538-3881/ac7da2
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