A star resembling a Matryoshka doll: Fresh theory on gravastars

The scientific community continues to grapple with the mysteries of the interior of black holes. In 1916, Karl Schwarzschild, a German physicist, presented a solution to Albert Einstein’s general relativity equations, proposing that the center of a black hole contains a singularity—a point where space and time cease to exist. According to this theory, all known physical laws, including Einstein’s general theory of relativity, become invalid, and the principle of causality is suspended.

This poses a significant challenge for scientists, as it implies that no information can escape from a black hole beyond its event horizon. Consequently, Schwarzschild’s solution initially received limited attention outside the realm of theory. However, the discovery of the first black hole candidate in 1971, followed by the identification of the black hole at the center of our Milky Way in the 2000s, and the groundbreaking image of a black hole captured by the Event Horizon Telescope Collaboration in 2019, brought renewed interest to the subject.

In 2001, Pawel Mazur and Emil Mottola proposed an alternative solution to Einstein’s field equations, leading to the concept of gravitational condensate stars, also known as gravastars. Unlike black holes, gravastars offer several advantages from a theoretical astrophysics standpoint.

On one hand, they possess a comparable level of compactness to black holes and exhibit a surface gravity that is essentially as strong as that of a black hole, making them practically indistinguishable. On the other hand, gravastars lack an event horizon—a boundary that prevents the transmission of information—and their core does not contain a singularity.

On the other hand, the core of a gravastar consists of an exotic form of energy, known as dark energy, which counteracts the immense gravitational force that compresses the star by exerting a negative pressure. The outer surface of a gravastar, on the other hand, is composed of an extremely thin layer of ordinary matter, with a thickness that approaches zero.

A recent study conducted by theoretical physicists Daniel Jampolski and Prof. Luciano Rezzolla from Goethe University Frankfurt has introduced a new concept in the field of general relativity. They have proposed the existence of a gravastar within another gravastar and have named this hypothetical celestial object a “nestar” due to its nested nature. The findings of their research have been published in the journal Classical and Quantum Gravity.

Daniel Jampolski, who made this discovery during his Bachelor’s thesis under the guidance of Luciano Rezzolla, compares the nestar to a matryoshka doll, as their solution to the field equations allows for a series of nested gravastars. While previous theories suggested that the gravastar’s outer layer is infinitely thin and composed of normal matter, the nestar’s shell is slightly thicker, making it easier to conceptualize its existence.

Luciano Rezzolla, a Professor of Theoretical Astrophysics at Goethe University, expresses his excitement about the discovery, stating that even a century after Schwarzschild’s initial solution to Einstein’s field equations, new solutions are still being found. He likens it to stumbling upon a gold coin on a path that has been explored by many others before. However, the process of creating a gravastar, including the nestar, remains unknown. Nevertheless, studying the mathematical properties of these solutions contributes to a deeper understanding of black holes, even if nestars do not actually exist.

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