To date, there is no known arrangement of matter that can create a Buchdahl star. But we can interact with a Buchdahl star and study what it's made of, which may give us clues as to what black hole interiors are like."įinding a Buchdahl star is another matter. "The event horizon of a black hole blocks our view of what's inside it. "There has always been attempts to define objects that are as close as possible to black holes," Dadhich said in an email to Live Science. This finding suggests that theoretical Buchdahl stars may really be out there, and could lead to insights about the inner workings of black holes. This means that a Buchdahl star could theoretically exist as a stable object with known, well-understood properties. This relationship is known as the virial theorem, and it applies to numerous situations in astronomy where the force of gravity is in balance with other forces. At the same time, the interior of the star gains kinetic energy as all the particles are forced to jostle against each other in a smaller volume.īy the time the star reaches the Buchdahl limit, Dadhich found a surprising yet familiar relationship: The total kinetic energy was equal to half the potential energy. "As the star collapses, it picks up gravitational potential energy, which is negative because gravity is attractive," Dadhich explained. 11 to the preprint server .ĭadhich, who calls Buchdahl stars "black hole mimics" because their observable properties would be nearly identical, studied what happens to the energy of a hypothetical star as it begins collapsing into a Buchdahl star. Dadhich discusses this property in a new paper submitted Dec. Now, Naresh Dadhich, a physicist at the Inter-University Centre for Astronomy and Astrophysics in Pune, India, may have discovered a surprising property held by Buchdahl stars.
Living on the edgeįinding exotic objects that come right to the edge of that limit - so-called Buchdahl stars - has become a popular pastime of theorists and observationalists alike. Below that, the blob of material must always become a black hole, at least in the theory of relativity. The Buchdahl limit is important because it defines the densest possible object that can still avoid becoming a black hole. That special radius is equal to 9/4 times the mass of the blob, multiplied byNewton's gravitational constant, all divided by the speed of light squared. Using the tools of Einstein's general theory of relativity, Buchdahl found an absolute lower limit to the size of that blob. As the blob got smaller and smaller, its density rose, making its own gravitational pull even more intense. In 1959, German-Australian physicist Hans Adolf Buchdahl explored how a highly idealized "star" - represented as a perfectly spherical blob of material - might behave as it was compressed as much as possible. (Image credit: NASA Goddard Space Flight Center/Chris Smith (USRA)) Buchdahl stars An artist's concept of an ultra-dense neutron star, flashing with bursts of X-ray energy.
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