December 10, 2009
Before they become black holes, dying stars of a certain mass should form an entirely new class of stellar object called an electroweak star
When small stars die, they collapse to form neutron stars in which the Pauli exclusion principle prevents further collapse. Anything more massive eventually becomes a black hole (with the cut off at about 2.1 solar masses).
In recent years, however, astrophysicists have calculated that a star’s evolution into a black hole is more complex than originally thought. That’s because after the Pauli exclusion effect is breached, star stuff undergoes other nuclear phase transitions that release enough energy to delay collapse, albeit for a relatively short time.
For example, astrophysicists recently discovered a state between a neutron star and a black hole in which the star’s mass is supported by the energy released as nuclear matter is compressed into quark matter. So-called quark stars are thought to look very much like neutron stars so finding them will be tricky.
Today, De-Chang Dai at the State University of New York in Buffalo and a few buddies propose an entirely new type of star that forms after a quark star but before a black hole. Dai and colleagues point out that after the quark transition, there is one other phase transition predicted by the standard model of particle physicists.
This occurs when the quarks are squeezed so hard that they turn into a type of elementary particle called a lepton. Since leptons experience the electromagnetic force and the weak nuclear force but not the strong nuclear force, the team call this process electroweak burning.
Dai and co calculate that electroweak burning should generate enough energy to delay collapse for some 10 million years. That means there should be plenty of electroweak stars out there to see, if astronomers can find them.
Just what electroweak stars should look like, isn’t yet clear. Dai and co say that this will depend not on the star’s core where the electroweak burning takes place, but on the structure of its outer layer where the photons are produced that we’re likely to pick up on Earth. “Assessing the visibility of these fascinating new objects requires a careful modeling of their outer structure to determine the photon luminosity and spectrum,” says the team.
Calculating how this layer will behave is a difficult task but one the team say they’re working on for future publications. But here’s a tip, we won’t know for sure until Dai and co finish their number crunching but the smart money is betting that electroweak stars will be more or less indistinguishable from neutron stars. Shame!
Ref: arxiv.org/abs/0912.0520: Electroweak Stars: How Nature May Capitalize on the Standard Model’s Ultimate Fuel
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