Gravitational compact objects like neutron stars and black holes have puzzled scientists and the general public for decades with their extreme gravity and sometimes counterintuitive nature. And now they might be joined by an even weirder sibling.
In a paper published in Physical Review Letters, researcher Raúl Carballo-Rubio has proposed the theoretical existence of an ultra-compact star, where the gravitational collapse is balanced out by several different quantum mechanical effects. Something similar already happens in neutron stars, where gravity is balanced out by a repulsive force known as degeneracy pressure. But in these new stars, the repulsive force is also produced by the quantum vacuum polarization.
“As a consequence of the attractive and repulsive forces at play, a massive star can either become a neutron star or turn into a black hole,” explained Carballo-Rubio, from SISSA, in a statement. “But if the star’s mass becomes higher than a certain threshold, about 3 times the solar mass, the equilibrium would be broken and the star collapses due to the overwhelming pull of the gravitational force.”
The question that Carballo-Rubio wanted to answer was a challenging one. Could other quantum mechanics effects come into play beyond that mass threshold? Here enters the quantum vacuum polarization. In this phenomenon, electromagnetic fields create electron-positron pairs, which being matter and antimatter would annihilate back into photons, acting as a repulsive force.
The vacuum polarization would provide an additional force to balance out the gravitational collapse and could create an incredibly dense star that behaves similarly to a black hole but without an event horizon. Similar objects have in the past been called black stars or gravastars.
“The novelty in this analysis is that, for the first time, all these ingredients have been assembled together in a fully consistent model. Moreover, it has been shown that there exist new stellar configurations, and that these can be described in a surprisingly simple manner,” Carballo-Rubio added.
While the theoretical solution appears sound, it is unclear if such an object could exist in our own universe. Several gravastar scenarios have been disproven because they are not stable, and this solution might end up being similar to those.
But if they do exist, they won’t stay hidden for long. Carballo-Rubio believes that by using gravitational observatories like LIGO and VIRGO, we could possibly detect them within the next decade.
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