Illusion gravitational

In astrophysics, an illusion that astronomers are familiar with is the gravitational lensing or gravitational mirage.
A massive object, a cluster of galaxies, for example, which is between an observer and a distant light source, prints a strong curvature in spacetime.
This has the effect of deflecting all light rays passing near the object, thereby distorting the images received by the observer.
This amplification of the brightness of a distant celestial object, by a massive star in front, was predicted by the theory of general relativity in 1917.
Massive objects are changing the geometry of space and time in their neighborhood.
Light on it always takes the shortest route, but in a curved space modified by the presence of a huge mass, the shortest path is not straight.
The light path is curved in the vicinity of massive stars. Most images of galaxies that lie in this photograph are multiple images of a single ring galaxy.
A giant cluster of galaxies located in front, acts as a huge gravitational lens. In the foreground galaxies of this cluster are shown in yellow and behind the observed galaxy appears blue. A gravitational lens can create multiple images of background galaxies.

The singular form of the galaxy blue background (small blue spot in the center of the image), enabled us to deduce that this is the same as we see in 4 hours, 10 hours, 11 hours and 12 hours.
The analysis showed that at least 33 images of 11 different background galaxies are discernible in this image.
This spectacular photo of the galaxy cluster CL0024 1654 was taken by the Hubble Space Telescope in November 2004. Predicted by general relativity by Albert Einstein, gravitational lensing several have since been observed by Hubble.
Sometimes, when the alignment between two objects is perfect, the image of the distant object can take the form of a ring of light surrounding the subject at hand. In case of perfect alignment between the observed source (eg a star), and another stellar object (a black hole for example), the black hole in front will act as a gravitational lens or deflector.
The observer will not see the star as such but rather as a ring, this ring is appointed, the Einstein ring.
A star, although having a mass much lower than that of a galaxy, can also act as a gravitational lens.
The effect is obviously much less powerful, it is called, micro gravitational lens.