Largest 2D Map of Universe Helps Discover New Gravitational Lenses

There is a particular power in mapping the sky—a power that comes not from a single observation but from the accumulation of millions, from the patient assembly of a picture so large that it reveals patterns invisible to any individual telescope. The Dark Energy Spectroscopic Instrument, or DESI, has been doing exactly that. Now, the largest two-dimensional map of the universe ever created has helped scientists discover new gravitational lenses—cosmic magnifying glasses that offer a rare window into the most distant galaxies and the mysterious dark matter that surrounds them.

The map, assembled from data collected by DESI at the Kitt Peak National Observatory in Arizona, covers more than 14,000 square degrees of the sky—roughly a third of the total sky visible from Earth. It contains hundreds of millions of galaxies, each a beacon of light that has traveled for billions of years. From this vast dataset, researchers have identified 1,350 new candidate gravitational lenses—objects where the gravity of a foreground galaxy is so strong that it bends and magnifies the light from a more distant galaxy behind it .

Gravitational lensing was predicted by Einstein's theory of general relativity, and it has become one of the most powerful tools in astronomy. When a massive object lies between Earth and a distant galaxy, its gravity warps the fabric of space-time, causing light from the background galaxy to follow a curved path. The result is a distorted, magnified image—sometimes a ring, sometimes an arc, sometimes multiple images of the same object. By studying these lenses, astronomers can measure the mass of the foreground galaxy, including the dark matter it contains, and can see distant galaxies that would otherwise be too faint to detect.

The discovery was made possible by a new technique that uses machine learning to identify lens candidates from the DESI imaging data. The algorithm was trained on known lenses and then applied to the full dataset, flagging potential candidates for follow-up observation. The researchers then confirmed the candidates using higher-resolution imaging from other telescopes. The result is the largest sample of gravitational lenses ever assembled, and it is already being used to study the distribution of dark matter and the expansion history of the universe.

The implications extend beyond the lenses themselves. Gravitational lensing is one of the most sensitive probes of dark energy—the mysterious force that is accelerating the expansion of the universe. By measuring how the lenses distort the light from background galaxies, scientists can test different models of dark energy and refine their understanding of how the universe evolves. The DESI map is a tool, and the lenses it has found are the first of many discoveries it will enable. The universe is vast, and the map is large, but the questions it can answer are larger still.

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Sources: Dark Energy Spectroscopic Instrument (DESI), Lawrence Berkeley National Laboratory, Phys.org