Neutron Stars Are Doomed if Vacuum Energy Goes Wild
Artist's illustration of an "isolated neutron star"--a neutron star that does not have an associated supernova remnant, binary companion or radio pulsations.
Credit: Casey Reed/Penn State University

A mind-bogglingly huge buildup of "vacuum energy," which would occur in just milliseconds, could lead the stellar remnants known as neutron stars to instantly collapse or explode, scientists now suggest.

What is often thought of as the empty vacuum of space is actually filled with ghostly energy and virtual particles wavering in and out of existence, a bizarre prediction of quantum theory that numerous experiments have proven true.

This "vacuum energy," as scientists call it, is usually thought of as extremely weak at best. But theoretical physicists in Brazil suggest that the immensely powerful gravitational fields of neutron stars could "awaken the vacuum," causing its energy to build up exponentially very quickly.

Neutron stars are the remnants of stars left over from supernovas ? huge star explosions that crush protons together with electrons to form neutrons. [The Strangest Things in Space]

They are extremely dense but are usually only about 12 miles (20 km) in diameter and 1? to three times the mass of the sun. A sugar cube-size piece of neutron star matter can weigh as much as a mountain ? about 100 million tons.

Vacuum energy explosions?

To learn more about how gravity might affect empty space, theoretical physicist Daniel Vanzella of the University of S?o Paulo in S?o Carlos and his colleagues modeled the gravitational fields of neutron stars.

The extraordinary density of neutron stars means they possess incredibly strong gravitational pulls that warp the fabric of space-time, distortions that could drive up vacuum energy.

Surprisingly, the researchers found the vacuum energy in the neighborhood of a neutron star could ?keep building exponentially, depending on the size and mass of the neutron star.

This could rapidly cause the vacuum energy to exceed the neutron star's combined mass and energy. The neutron star could then either collapse to form a black hole or explode and shed a significant fraction of its mass ? the intricate calculations as to what exactly might occur are not yet complete, Vanzella said.


The vacuum awakens

?The scientists' model analyzed the effect of gravity on a so-called "scalar field" that could represent anything from a simplified version of the electromagnetic field to an as-yet-undiscovered particle.

One potential criticism is that the researchers do not know of any specific field with the features to cause this "vacuum awakening."

Still, "95 percent of the energy of the universe is in forms which we don't know what they are ? they are generically called 'dark matter' and 'dark energy,'" Vanzella told "In principle, there is plenty of room for new or yet-to-be-discovered fields in nature."

If astronomers ever do see these kinds of dramatic changes in neutron stars, the discovery could shed light on a hitherto unknown kind of force, Vanzella said.

By the same token, if scientists detect neutron stars that are stable despite conjectured forces, they can rule out the existence of those forces.

The scientists detailed their findings in the Oct. 7 edition of the journal Physical Review Letters.