(ORDO NEWS) — In 1919, astronomers Arthur Eddington and Andrew Crommelin photographed a total solar eclipse.
The sun at that time was in the constellation of Taurus, and a small number of its stars could be seen in the photographs. But the stars were not quite in the expected places.
The enormous gravity of the Sun has distorted the light from these stars, thereby giving the impression that they are out of place.
This was the first demonstration that gravity could bend light, as Albert Einstein had suggested in 1915.
The bending of light by the mass of a star or galaxy is one of the main assumptions of general relativity.
Although Einstein was the first to predict that light would diverge from a single star, others such as Oliver Lodge have argued that a large mass can act like a gravitational lens, distorting light in the same way that a glass lens focuses it.
By 1935, Einstein had demonstrated how light from a distant galaxy could be distorted by the galaxy in front of it, creating a ring of light.
The so-called “Einstein’s ring” gives a distant galaxy an image of a ring or an arc of light around a nearby galaxy. Einstein thought that this effect could never be observed.
These arcs of light were too weak for optical telescopes. Einstein remained right until 1998, when the Hubble Space Telescope detected a ring around the galaxy B1938+666.
It was the first observed optical ring, but not Einstein’s first. The first ring was seen in radio light and was captured by a large array antenna (VLA).
In 1987, a group of students at the Massachusetts Institute of Technology’s Electronics Research Laboratory, led by student Jackie Hewitt, used the VLA to obtain detailed images of known radio-emitting objects.
One of them, known as MG1131+0456, had a distinct oval shape with two bright petals. Hewitt and her team looked at several models to explain the unusual shape, but only Einstein’s ring matched the data. Einstein’s galactic prediction has finally come true.
Radio astronomy is especially useful in observing such Einstein rings. They have become a powerful tool for radio astronomers.
Like a glass lens, a gravitational lens focuses light to make an object appear brighter and larger. By observing such phenomena, radio astronomers can study galaxies that would be too distant and faint to see.
Einstein rings can be used to measure the mass of a nearby galaxy or galaxy cluster, since the amount of gravitational lensing depends on the mass of the galaxy in front.
One of the most interesting aspects of gravitational lensing is that it can be used to measure the expansion rate of the universe. Light from a distant galaxy can take different paths as it passes by a nearby galaxy.
Each of these paths can have a different distance, which means that the light can reach us at different times.
We could see a flash of light from the galaxy several times, each time from a different trajectory. Astronomers can use this to calculate the galactic distance and therefore the scale of the cosmos.
Since the first discovery of Einstein’s ring, radio astronomers have discovered more such rings and recorded them in greater detail.
In 2015, for example, the Atakama Large Millimeter/Submillimeter Array (ALMA) captured a detailed image of lens arcs from the distant galaxy SDP.81.
The image was clear enough that astronomers could trace the arcs back to the source to study how stars formed in the galaxy.
Einstein’s rings are now often seen in astronomical images, especially in deep space images such as those from the James Webb Space Telescope. As radio astronomy has shown, they are not just beautiful. They give us a new perspective on space.
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