KU research team probes new way to detect cosmic strings
Dr. Davide Batic, Associate Professor of Mathematics, Maha Alrais Alawadi, and Dr. Marek Nowakowski, Associate Professor from the Universidad de los Andes, Colombia, published their work last month
A team of researchers from Khalifa University has used the theory of General Relativity to figure out a new way to detect cosmic strings across the universe. The team applied the concept of ‘gravitational lensing’ to a family of pairs of black holes connected by a cosmic string in what is known as a C-metric, and computed the first ever lensing formula that can be coupled with existing technologies to chart our universe.
Dr. Davide Batic, Associate Professor of Mathematics, Maha Alrais Alawadi, student from the Department of Mathematics, and Dr. Marek Nowakowski, Associate Professor from the Universidad de los Andes, Colombia, published their work last month in the journal Classical and Quantum Gravity.
What is gravitational lensing? According to Einstein, the presence of a mass deforms the space-time geometry in such a way that light rays passing nearby get deflected. This is the idea behind gravitational lensing, where rays of light bend near sources of gravitation, such as stars.
The greater the mass, the greater the gravity and the closer to the source of gravity, the greater the bending.
This effect was observed for the first time in 1919, when English physicist Arthur Eddington measured the position of stars near the Sun before a total eclipse of the Sun and during the eclipse.
By doing this, Eddington could discern if the Sun’s gravity bent the rays of light from these nearby stars.
The stars did appear to be displaced, but only by a small amount. However, this was compatible with what was predicted by Einstein’s theory of General Relativity. The mass of the Sun had caused the light to bend only at the plasma limb, or the very edge of the Sun.
“What Eddington observed was the least striking aspect of this gravitational distortion,” explained Dr. Batic. “However, scientists soon realised that this phenomenon could be used to probe the cosmic depths with an accuracy never imaged before, opening the door to modern cosmology. Gravitational lensing became and still is an extremely active research field.”
Modern technology in astronomy can measure the relative position of the stars, using this technique.
Imagine two stars and the Earth in a line: the effect of gravitational lensing would bend the light from the furthest star around the nearest star, creating a a displaced faint image of the star, which otherwise would be impossible to observe.
If we replace the gravitational source between the Earth and the distant star with a black hole, light rays emanating from the distant star may get caught by the black hole.
These rays may move around a circular orbit in the exterior of the black hole and we would observe a ring of light around the black hole. In this way, we could infer the existence of the distant and apparently hidden bright gravitational object.
This hypothetical effect is what scientists call an “Einstein ring.” Since the prediction of the light bending rule of general relativity, which suggests a direct interaction between gravitation and electromagnetism, several distorted images of distant galaxies, stars, star clusters and Einstein rings have been detected by extremely sensitive telescopes. The strong evidence of gravitational lensing in the universe suggests that this technique could be used to infer the existence of black holes scattered across the universe.
USING GRAVITATIONAL LENSING TO SPOT BLACK HOLES: Light rays passing very close to a black hole may experience very strong deviations allowing us to ‘see’ black holes whether the light source is behind the black hole (standard gravitational lensing) or in front of the black hole (retrolensing).
“Light bending and possible bound states of light are genuine effects of general relativity,” explained Dr. Batic. “Whereas light bending has been studied and even observed in a variety of situations, bound orbits of massless particles are an interesting phenomenon and they deserve special attention.”