The Virtual Telescope Project captures the famous LRG 3-757 Einstein Ring, an extraordinary gravitational lensing phenomenon also known as Cosmic Horseshoe.
We are very excited and pleased to share with you this unique image, bringing you very far away, back in space and time, with the “Cosmic Horseshoe”.
The LRG 3+757 “Cosmic Horseshoe” gravitational lens. 14 Feb. 2024.
There are events happening in the universe that require our most vivid imagination for comprehension.
Many of you may recall the stunning images released by the James Webb Space Telescope almost two years ago. Among them, one stood out, revealed first for good reason. Dubbed Webb’s First Deep Field, it captured a distant galaxy cluster (SMACS0723) situated 4.6 billion light-years away. However, the most intriguing aspect was the presence of arc-shaped structures in that sea of galaxies What are they?
To understand, let’s go back to 1915 when Albert Einstein introduced the theory of general relativity. It describes gravitational interaction not as an attractive force between mass-bearing bodies (Newton) but as the consequence of the curvature of spacetime caused by mass or energy.
In short, bodies with mass can curve spacetime.
Planets in the Solar System, for instance, have elliptical orbits not because of the direct attraction force from the Sun, but because the Sun’s mass bends spacetime.
This spacetime curvature by celestial bodies also alters the trajectory of a light beam crossing the cosmic depths.
For example, if a light beam from a distant galaxy is aimed at a massive object, it will follow the curvature induced by that massive body on spacetime. This incredible phenomenon, hypothesized by Einstein and subsequently confirmed by direct observations, is known as gravitational lensing.
But it doesn’t end there. Sometimes, this lensing phenomenon may amplify the brightness of distant galaxies, enabling us to go deeper. Occasionally, if objects are aligned from the observer’s perspective, we can see objects that would otherwise be hidden, literally overcoming the obstacle between us and them.
In the image we present, coming from ninety minutes of exposure, we see this spectacular occurrence, a cosmic alignment, an unexpected leap into the past. The complex is known as LRG 3-757 or “Cosmic Horseshoe” and represents an extraordinary example of an “Einstein Ring.”
The nearest galaxy acting as a gravitational lens, a Luminous Red Galaxy, has a mass about ten times that of our Milky Way and a redshift z=0.44, corresponding to a distance of approximately 5 billion light-years.
The almost complete ring surrounding it is extraordinary because it is the light from an extremely remote galaxy. Its light is deviated and stretched by the LRG on the foreground, in a way “focused”, allowing us to observe it.
Our image clearly shows that the brightness of this Einstein ring is not uniform, an horseshoe indeed, displaying nodules and appearing incomplete towards the west. This is particularly evident in the false-color crop.
With a redshift z=2.4, its light has traveled for about 11 billion years before reaching us! This means its light belongs to a relatively young universe, when it was only 3.3 billion years old.
This observation was possible thanks to the exceptional quality of the Manciano sky, the most starry in the Italian peninsula: in the image, a limiting magnitude of 22.0 was achieved, probably the deepest ever obtained to date with our instruments.
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