Scientists have been studying for years an unusual cosmic object that “works” like a black hole, looks like
The problem is that this object —hypothetical. Scientists have not yet been able to observe them in space. Whether these mysterious objects really exist is a big question. However, in a recent study, a physicist from India may have discovered a new property of Buchdahl stars that may help answer this question.
How do black holes "work"?
In general, astronomers agree thatblack holes really exist. Scientists are observing evidence of their existence everywhere (High-Tech previously wrote about the main evidence of their existence).
An artist's idea of the neighborhood of a black hole. Illustration: ESO/L. Calcada
Astronomers also understand how blacks are formedholes: these are the remnants of the catastrophic gravitational collapse of massive stars. When they die, no force in nature can support their own weight. Therefore, these doomed objects continue to “press themselves” ad infinitum.
Dead stars
However, scientists do not yet understand howan object can shrink without turning into a black hole. Astronomers already know about the existence of white dwarfs, which “weigh” like the Sun, but are the size of the Earth. Physicists are also studying the nature of neutron stars, which further compress the star’s mass to the size of a city. But it is unknown whether there is an even smaller object that managed to avoid becoming a black hole.
Stars of Buchdal
In 1959, German-Australian physicist HansBuchdahl studied how an “ideal star” (which is an ideal spherical clump of matter) can behave if it is compressed as much as possible. As the clump of matter became smaller and smaller, the density of the object increased, which made the gravitational attraction more intense. Using calculations from Einstein's General Theory of Relativity, Buchdahl found an absolute lower limit on the size of a "star" that is as dense as possible without turning into a black hole. It is equal to 9/4 of the mass of the “star” multiplied by Newton’s gravitational constant (G) and divided by the speed of light (299 792 458 m/s) squared.
Thus, thanks to calculations, the scientist receivedthe densest object in space. But if you compress it even a little, then the Buchdahl limit will be overcome and the star will become a black hole. Below this value, an object should always become a black hole, at least according to General Relativity.
What did the scientist find out?
Search for exotic objects that are locatedat the edge of this limit, so-called Buchdahl stars, have become a popular pursuit for both theorists and observers, shared Paul M. Sutter, research professor of astrophysics at SUNY Stony Brook University and Flatiron Institute in New York. In a new study, Naresh Dadhich, a physicist at the Inter-University Center for Astronomy and Astrophysics in Pune, India, may have discovered a surprising property that such bodies have. He spoke about his discoveries in an article published on the preprint server arXiv.org, which has not yet been peer-reviewed.
Illustration: NASA
Dadhich, who names the stars of Buchdahl“black hole simulators,” studied what happens to the energy of a hypothetical star when it begins to collapse into “boundary objects.” After doing the calculations, he discovered something surprising: by the time the star reached the Buchdahl limit, the total kinetic energy was equal to half the potential energy.
This ratio applies to manysituations in astronomy when the force of gravity is in balance with others. This means that, theoretically, Buchdahl stars can exist as a stable object with already well-studied properties.
"The black hole's event horizon is blocking ouran idea of what is inside it. But we can study what Buchdahl stars are made of. This way we can understand what the inside of a black hole is like,” explains the author of the study to Live Science.
Last problem
Finding Buchdahl's star is another matter.To date, there is no known arrangement of matter that could create such an object. But Dadich's research suggests how it might work. More research will be needed to understand what other properties these exotic objects have and what they can tell scientists about black holes.
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