New star described in a model combining relativity and quantum mechanics

Credit: CC0 Public Domain

A new kind of star is reported in a study by SISSA
postdoctoral researcher Raúl Carballo-Rubio. In a paper
recently published in Physical Review Letters,
Carballo-Rubio describes a novel mathematical model
combining general relativity with the repulsive effect of
quantum vacuum polarization. The result is a description of
an ultra-compact configuration of stars that scientists
previously believed did not exist in equilibrium.

“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” says Carballo-Rubio. In neutron
stars, stellar is the result of
the balance between gravity, an attractive force, and a
quantum mechanical repulsive force called degeneracy
pressure. “But if the star’s mass becomes higher than a
certain threshold, about three times the solar mass, the
equilibrium would be broken and the star collapses due to the
overwhelming pull of the gravitational force.”

In the study, Carballo-Rubio investigated the possibility
that additional quantum mechanical forces expected to be
present in nature permit new equilibrium configurations for
stars above this threshold. The additional force is a
manifestation of the quantum vacuum polarization effect,
which is a robust consequence of mixing gravity and mechanics in a semiclassical framework.
“The novelty in this analysis is that, for the first time,
all these ingredients have been assembled 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.”

There are still several important issues that remain to be
studied, including the observational applications of these
results. “It is not clear yet whether these configurations
can be dynamically realized in astrophysical scenarios, or
how long would they last if this is the case.” From an
observational perspective, these “semiclassical relativistic
stars” would be very similar to . However, even minute differences
would be perceptible in the next generation of gravitational
wave observatories: “If there are very dense and ultracompact
in the Universe, similar to black holes
but with no horizons, it should be possible to detect them in
the next decades.”

Explore further:
better way to model stellar explosions

More information: Raúl Carballo-Rubio, Stellar
Equilibrium in Semiclassical Gravity, Physical Review
(2018). DOI: 10.1103/PhysRevLett.120.061102

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