The Euclid Telescope of the European Space Agency has discovered its first Einstein ring. Not only is it one of the most impressive examples of gravitational lenses predicted by Albert Einstein, but a window through which astronomers can study more precisely the distribution of dark matter in distant galaxies.
A unique gravitational lens. The NGC 6505 galaxy is located about 590 million light years from Earth. Although in cosmic terms this distance is relatively short, the ring -shaped light that surrounds the galaxy that is 4.4 billion light years.
The perfect alignment between the NGC 6505 galaxy and the background light source formed a complete Einstein ring, a type of gravitational lens so rare that that does not expect the Euclid space telescope to find more than 20 throughout its useful life . This first could be baptized as Altieri’s ring in tribute to the researcher who has discovered it: Bruno Altieri.
What is an Einstein ring. Albert Einstein predicted with his theory of general relativity of 1915 something that even today, 110 years later, it is hard for us to understand: gravity can curve the space-time, causing the light to deviate when passing near very massive objects.
When a galaxy aligns almost perfectly between us and another galaxy that is more at the bottom, the light of the distant galaxy is curved so symmetrically that, instead of seeing a unique image, we observe a light circle. This phenomenon, formally known as strong gravitational lens, is what is called an Einstein ring.
A powerful tool. Thanks to Einstein’s ring, scientists can “weigh” the NGC 6505 galaxy and study how its mass is distributed, including the portion of dark matter that would otherwise be invisible.
Modeling how light folds, astronomers have discovered that in the center of this galaxy, dark matter represents approximately 11% of the total mass. It is interesting because, although dark matter constitutes about 85% of the total matter of the universe, in the central regions of the galaxies, the influence of visible matter (the stars) is much greater.
A map of the universe. The Euclid space telescope is not limited to looking for gravitational lenses. Released by ESA in July 2023, it has the mission of creating the most precise 3D map of the universe ever performed.
It is expected to end up covering 14,000 square degrees of the sky and contains more than 100,000 gravitational lenses, which will help to better understand the distribution of visible and dark matter throughout cosmic history.
Image | ESA/EUCLID/EUCLID CONSORTIUM/NASA
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