Astronomers Discover Hundreds of New Strong Gravitational Lenses

Using data from the Dark Energy Camera Legacy Survey (DECaLS), astronomers have discovered 335 new candidate strong lensing systems.

These two columns show side-by-side comparisons of gravitational lens candidates imaged by the Dark Energy Camera Legacy Survey (color) and the NASA/ESA Hubble Space Telescope (black and white). Image credit: Dark Energy Camera Legacy Survey / NASA / ESA / Hubble / Huang et al.

Gravitational lensing was first theorized by Albert Einstein more than 100 years ago to describe how light bends when it travels past massive objects like galaxies and galaxy clusters.

These lensing effects are typically described as weak or strong, and the strength of a lens relates to an object’s position and mass and distance from the light source that is lensed.

Strong lenses can have a mass of 100 billion solar masses, causing light from more distant objects in the same path to magnify and split, for example, into multiple images, or to appear as dramatic arcs or rings.

“Finding these objects is like finding telescopes that are the size of a galaxy. They’re powerful probes of dark matter and dark energy,” said co-author Dr. David Schlegel, a senior scientist in the Physics Division at Lawrence Berkeley National Laboratory.

In the study, Dr. Schlegel and colleagues used Cori, a supercomputer at Berkeley Lab’s National Energy Research Scientific Computing Center, to analyze imaging data from the DECaLS project, one of three surveys conducted in preparation for the Dark Energy Spectroscopic Instrument (DESI) survey.

The lens candidates were identified with the assistance of a neural network, which is a form of artificial intelligence in which the computer program is trained to gradually improve its image-matching over time to provide an increasing success rate in identifying lenses.

“It takes hours to train the neural network. There is a very sophisticated fitting model of ‘What is a lens?’ and ‘What is not a lens?’,” said lead author Dr. Xiaosheng Huang, an astronomer in the Department of Physics and Astronomy at the University of San Francisco.

The newly-discovered strong lensing system candidates could provide specific markers for precisely measuring distances to galaxies in the early Universe if supernovae are observed and precisely tracked and measured via these lenses, for example.

Strong lenses also provide a powerful window into the unseen Universe of dark matter, which makes up about 85% of the matter in the Universe, as most of the mass responsible for lensing effects is thought to be dark matter.

Dark matter and the accelerating expansion of the Universe, driven by dark energy, are among the biggest mysteries that physicists are working to solve.

“We already succeeded in winning time on the NASA/ESA Hubble Space Telescope to confirm some of the most promising lensing candidates revealed in the study, with observing time on the Hubble that began in 2019,” Dr. Huang said.

“Hubble can see the fine details without the blurring effects of Earth’s atmosphere.”

paper on the findings was published in the Astrophysical Journal.