Matías S. Zavia
WriterAerospace and energy industries journalist at Xataka.
The European Space Agency’s (ESA) Euclid telescope has discovered its first Einstein ring. This observation is a remarkable example of gravitational lensing, a phenomenon predicted by Albert Einstein. It also provides astronomers with a valuable opportunity to study the distribution of dark matter in distant galaxies more accurately.
A unique gravitational lensing. The galaxy identified as NGC 6505 is located around 590 million light-years from Earth. Although this distance is relatively short in cosmic terms, the ring-shaped light that surrounds it originates from a galaxy 4.4 billion light-years away.
The perfect alignment between galaxy NGC 6505 and the background light source has resulted in a complete Einstein ring. These gravitational lenses are extremely rare. ESA estimates that the Euclid space telescope will discover no more than 20 of them during its mission. This first discovery may be named the Altieri ring in honor of the researcher who identified it, Bruno Altieri.
What is an Einstein ring? In his 1915 theory of general relativity, Einstein predicted a concept that continues to confound scientists even 110 years later. Gravity can bend spacetime, causing light to curve as it passes near extremely massive objects.
When a galaxy aligns almost perfectly between ours and a more distant galaxy, the light from that distant galaxy bends symmetrically. Instead of seeing a single image, you can then observe a luminous circle. This phenomenon, known formally as strong gravitational lensing, is referred to as an Einstein ring.
A powerful tool. Einstein rings enable scientists to “weigh” the galaxy NGC 6505 and examine its mass distribution, including the portion of dark matter that would otherwise remain invisible.
By modeling how light bends, astronomers have found that dark matter constitutes about 11% of the total mass in the center of this galaxy. Interestingly, while dark matter makes up about 85% of all matter in the universe, the influence of visible matter (such as stars) is much more pronounced in the central regions of galaxies.
A map of the universe. The Euclid space telescope isn’t limited to detecting gravitational lenses. Launched by ESA in July 2023, its mission is to create the most accurate 3D map of the universe ever constructed.
The map is expected to eventually cover 14,000 square degrees of the sky and include more than 100,000 gravitational lenses. This will enhance the scientific community’s understanding of visible and dark matter distribution throughout cosmic history.
Image | ESA/Euclid/Euclid Consortium/NASA
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