A newly developed solution to the equations at the heart of Albert Einstein‘s most revolutionary theory suggests that hypothetical stars called “nestars” could be made of stacked gravitational stars, or “gravastars,” like Russian tea dolls, also known as matryoshka dolls.
One of the most impressive things about Einstein’s 1915 theory of gravity, general relativity, is how many incredible cosmic objects its central equations predicted.
General relativity not only predicted that gravity arises from massive objects that curve the fabric of spacetime, but also generated theories about black holes and the ripples they create in that fabric, called gravitational waves. The existence of both things has been confirmed by observation; anti-black holes called white holes, and ‘wormholes’ possibly connecting them to black holes, are other ideas based on general relativity that have, however, remained purely theoretical. Only time will tell whether Einstein can be proven right again on that front.
To this end, another theoretical idea that emerged from general relativity in 2001 is the concept of ‘gravastars’, or compact bodies with dark energy nuclei. Dark energy is the force that appears to be accelerating the expansion of the universe. In gravastars, scientists believe that dark energy would exert negative pressure to protect the stars from their own inward gravitational forces.
And now a new solution to general relativity suggests another interesting aspect of such so-called gravastars. They can be stacked together to create a series of ‘nestars’.
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“The nestar is like a matryoshka doll; our solution to the field equations allows for a whole series of nested gravastars,” one of the solution developers, theoretical physicist Daniel Jampolski of Goethe University, said in a statement.
Meet gravastars like black holes, but different
Just a year after general relativity was released to the broader scientific community, and while serving on the front lines of World War I, German physicist Karl Schwarzschild developed the first solution to his field equations, surprising even Einstein, who believed that a solution would last. years to develop.
Within the Schwarzschild solution, there were two features that would ultimately give rise to the concept of a black hole. The German physicist predicted that, at a certain radius of a body with mass, the speed required to escape that body would have to increase to more than the speed of light.
For most bodies, this so-called Schwarzschild radius would be deep below their surface; for example, for the Sun it would be 3 kilometers from the heart of our star, which has a total radius of 700,000 kilometers. But if a star were allowed to collapse and its radius became smaller than the Schwarzschild radius, this would result in a body with a outer border from which not even light could escape. This led to the concept of the black hole event horizon.
Even more curiously, the Schwarzschild solution suggested that there might be a point at which matter is so dense that even the general equations of relativity themselves stop working. This became known as the central singularity of a black hole, where all known physical theories no longer make any sense.
These concepts were verified in 1971 when humanity discovered the first black hole, followed in the 2000s by the discovery that a strong radio source at the heart of the Milky Way is indeed a supermassive black hole with a mass 4.5 million times greater is like the sun. This enormous void in our Milky Way is called Sagittarius A* (Sgr A*.)
The visual shape of black holes, as painted by general relativity, was also incredibly confirmed in 2019 when an image of a glowing ring of material surrounding the supermassive black hole at the heart of the galaxy Messier 87 was revealed to the public by the Event Horizon. Cooperation in the field of telescope.
Gravastars, or “gravitational condensate stars,” were theorized by Pawel Mazur and Emil Mottola in 2001 as an alternative to black holes.
From the perspective of theoretical physicists, gravastars have several advantages over black holes. They are almost as compact as black holes and have a gravitational influence on their surface that is essentially as strong as that of a black hole, and thus show a strong similarity. But there are important differences. First, gravastars have no event horizon, so they block out no light, and therefore no information, behind a one-way screen. Second, there would be no singularity in the hearts of gravastars, which are instead believed to have hearts of dark energy.
This recipe for gravastars, prepared by Mazur and Mottola, contains an almost infinitely thin skin of ordinary matter that is difficult for scientists to explain. Nestars puts an end to this, suggesting that the “stacking” part would lead to a somewhat thicker shell of matter.
“It’s a little easier to imagine that something like this could exist,” Jampolski said.
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But of course, because field equations from general relativity allow an object to exist in the cosmos, that doesn’t mean the object must exist.
“Unfortunately, we still have no idea how such a gravastar could be created,” Luciano Rezzolla, co-developer of the nestar theory and theoretical physicist from Goethe University, said in the statement. “But even if nestars do not exist, investigating the mathematical properties of these solutions ultimately helps us better understand black holes.”
Research like this is also useful even if the primary theory is wrong, because it shows wonderful paths forward from a theory first considered more than a century ago.
“It’s great that even 100 years after Schwarzschild presented his first solution to Einstein’s field equations from general relativity, it is still possible to find new solutions,” Rezzolla concluded. “It’s a bit like finding a gold coin along a path that has been explored by many others before.”
This research was published on February 15 in the journal Classical and Quantum Gravity.