When a star dies, there are a few different forms the stellar corpse can take. Now researchers have added another variety of ‘dead' star to the list: the electroweak star.
Although astrophysicists have only speculated about the existence of electroweak stars for a short time (see "Why Are Quark Stars So Strange"), scientists at Case Western Reserve University, Ohio, have detailed new predictions about the electroweak star's characteristics in a new paper submitted to the journal Physical Review Letters.
When a star dies, depending on its mass, it has several options. When a sun-like star runs out of fuel, it puffs up into an angry red giant, eventually losing its outer layers to space, leaving a compact mass of "electron degenerate" matter behind. This remnant is called a white dwarf, the kind of star our sun will turn into in about 4 billion years time.
However, larger mass stars may explode as supernovae, leaving behind rapidly spinning neutron stars (composed mainly of neutron degenerate matter), or even collapse entirely to form black holes. But these scenarios of gravitational collapse may only be part of the story.
Intermediate stages of collapse are theorized, including a type of "strange" quark star. Its strangeness indicates the remaining dense matter is composed mainly of strange quarks, a stage of collapse even more dense than the neutron star (neutrons have effectively been crushed out of existence, leaving their constituent quarks behind). This material would therefore be (you guessed it) quark degenerate matter.
So the quark star could be a stage of collapse between a massive neutron star before it collapses in on itself to form a black hole. But wait! The electroweak star could be yet another phase after the quark star, just before black hole doom.
These extreme electroweak stars will "burn" quarks, converting them into smaller particles called leptons, generating massive quantities of energy, flooding space with neutrinos (extremely weakly interacting particles that pass through matter like ghosts). The quark energy released would create an outward pressure preventing the force of gravity from pulling all the matter into a single point (i.e. a black hole).
Under such extreme conditions, the electromagnetic and weak forces effectively become one single force, hence the name "electroweak." The only other time we think such an extreme state of matter existed was moments after the Big Bang, just before the electromagnetic and weak force became the separate fundamental forces see measure today.
"This is a process predicted by the well tested Standard Model of particle physics," said Glenn Starkman, the lead researcher in this study, in an Institute of Physics article last year. "At ordinary temperatures it is so incredibly rare that it probably hasn't happened within the visible universe anytime in the last 10 billion years, except perhaps in the core of these electroweak stars and in the laboratories of some advanced alien civilizations."
Stability in Electroweak Stars?
Starkman's 2009 study (with De-Chang Dai and Dejan Stojkovic of the State University of New York in Buffalo and Arthur Lue of the Massachusetts Institute of Technology) suggested that the electroweak star would be a very short unstable phase, possibly lasting for less than a second. In his group's 2010 Physical Review Letters publication, this period has been revised and calculations suggest electroweak stars could persist for 10 million years or more.
Also, it is thought that the quark burning phase will consume huge quantities of mass inside the electroweak star, saving it from ever having the gravitational potential to collapse into a black hole.
As the majority of radiation would be in the form of neutrinos, a very small fraction of the energy will be emitted as electromagnetic radiation (i.e. light), making these objects very hard to detect. "But to understand that small fraction, we have to understand the star better than we do," Starkman says.
Although it's exciting to think that another type of star may exist out there, some scientists are cautious, pointing out that the extreme energies generated through quark burning may destroy the star all together, stripping the outer layers of the electroweak star away.
"It highly implausible that such an electroweak star would exist," said Paolo Gondolo of the University of Utah.
So, according to our understanding as to how the universe works, electroweak stars might be possible, but they won't be easy to detect, if they're detected at all.
Image: The Helix Nebula as seen by NASA's Spitzer infrared space telescope (NASA).