Hubble captures new gravitational lens

A new Hubble image shows a spiral galaxy at the center of the field and a striking gravitational lens in the lower‑right corner. The lens is made of a reddish elliptical foreground galaxy and blue arcs from a magnified background galaxy. The foreground galaxy sits about 4.5 billion light‑years away, while the background galaxy lies roughly 8 billion light‑years from us. The lens produces a classic arc‑counterarc pair, with a large arc to the upper left and a smaller, flipped arc to the lower right. The central spiral, similar in size to the Milky Way, also contains a tiny satellite galaxy nearby.

How the lens reveals mass

Gravitational lensing happens when the mass of a foreground object warps spacetime, causing light from a background source to bend, distort, and magnify. The stronger the lens, the larger the bending, and the more the background image is distorted. By measuring these distortions, astronomers can calculate how much mass the foreground galaxy contains, including the amount of invisible dark matter. Because visible matter alone cannot explain the observed bending, the excess mass points to dark matter making up the majority of the galaxy’s mass. The shapes of the arcs also reveal how that mass is distributed within the galaxy.

Hubble captures these lenses with high‑resolution visible and ultraviolet light, while the upcoming Nancy Grace Roman Space Telescope will scan the sky mostly in infrared and with a far larger field of view. The sharp Hubble images are used to build detailed models that help astronomers interpret the broader, lower‑resolution views that Roman will provide. In addition, Hubble will follow up on any interesting lenses that Roman discovers, giving them a closer look. By combining the two telescopes’ strengths, scientists hope to survey thousands of lenses across the sky. This collaboration will allow a more complete map of dark‑matter distribution.

The observations are part of a larger effort by NASA, ESA, and researchers such as X. Huang from the University of San Francisco. Processing was done by Gladys Kober at Catholic University of America. Together, the team is using the data to study dark‑matter–induced distortions and to lay the groundwork for future Roman observations. They are also building a computer model to analyze Roman’s large images more effectively. This work will deepen our understanding of the universe’s invisible mass.