Astronomershave found the most massive neutron star yet measured ? one nearly twice themass of our sun. The discovery indicates that, as their name suggests, these stellarremnants really are made mostly of neutrons, as opposed to more exoticparticles.
Neutronstars are fast-spinning remnants left behind in the aftermath ofsupernovas: huge star explosions where protons are crushed together withelectrons to form neutrons. They are typically small, with diameters of about12 miles (19.3 km) or so, but yet so massive they weigh as much as the sun.
"We didn't really know for sure that neutron stars could getquite this massive until we made this measurement ? it was very surprising andexciting," researcher Paul Demorest, an astronomer at the National RadioAstronomy Observatory, told SPACE.com. "The typical thinking was that mostneutron stars clustered pretty tightly around 1.4 solar masses."
What's it really made of?
Whileastronomers have long thought that neutron stars are composed solely ofneutrons, some scientists have recently proposed they might also contain moreexotic subatomic particles as well, such as hyperons and kaon condensates,which possess so-called "strangequarks."
Althoughquarks ? the building blocks of protons and neutrons ? are generally thought toalways be confined atomic nuclei in nature, some researchers had also suggestedneutron stars might contain unbound "free quarks."
Todetermine the neutron star's mass, researchers measured a delay in the traveltime of its radio pulses resulting from them getting distorted by the companionstar's gravitational field. This effect, called the Shapiro delay, variessystematically as the paired stars orbit each other, and precise analysis of itallowed scientists to determine the white dwarf's mass.
Sincethe investigators know the orbital characteristics of the binary system as awhole, knowing the companion star's mass enabled them to calculate the pulsar'smass as well.
"Wegot very lucky with this system," said researcher Scott Ransom, anastronomer at the National Radio Astronomy Observatory in Charlottesville, Va.
"Thisunique combination made the Shapiro delay much stronger and thus easier tomeasure," Ransom added.
Thescientists narrowed the pulsar's mass to 1.97 times the mass of the sun, giveor take 0.04 solar masses.
Thesenew findings could also shed light on the origins of gamma ray bursts, the mostpowerful explosions in the universe. A leading explanation for the cause of onetype of gamma-rayburst ? the "short-duration" bursts ? is that they are caused bycolliding neutron stars. The fact that neutron stars can be as massive as PSRJ1614-2230 hints these collisions would be powerful enough to generate thesebursts.
"Pulsarsin general give us a great opportunity to study exotic physics, and this systemis a fantastic laboratory sitting out there, giving us valuable informationwith wide-ranging implications," Ransom said. "It is amazing to methat one simple number ? the mass of this neutron star ? can tell us so muchabout so many different aspects of physics and astronomy."
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