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yesterday

Rare Einstein Cross With Fifth Image Points to Massive Dark-Matter Halo

Lens models now set specific signals for upcoming checks using ALMA, VLA, Hubble.

A rare cosmic configuration: An Einstein Cross with five points of light, instead of the usual four, has been discovered by scientists. (Credit: Nicolás Lira Turpaud (ALMA Observatory) & adapted from Cox et al. 2025)
Image

Overview

  • Observations of the dusty galaxy HerS-3 reveal five lensed images, including a central spot that is unusual for Einstein Crosses.
  • Pierre Cox first noticed the anomaly in NOEMA data, and ALMA follow-ups confirmed the feature as real rather than an instrumental artifact.
  • Gravitational-lens modeling by Charles Keeton and Lana Eid showed the four visible foreground galaxies cannot reproduce the configuration without additional unseen mass.
  • The analysis, published September 16 in The Astrophysical Journal, infers a large dark-matter halo associated with the lensing group.
  • The team issued falsifiable predictions, including possible signatures of outflowing gas, with targeted observations planned using ALMA, the VLA, and the Hubble Space Telescope.