Using information from NASA's Fermi Gamma-ray Space Telescope, scientists have identified the first gamma-ray eclipses from a "spider" binary star system.
A pulsar, or the superdense, rapidly revolving remnants of a star that erupted in a supernova, is present in each of these spider systems.
Seven spiders that experience these eclipses, which happen when the low-mass companion star crosses in front of the pulsar from Earth's perspective, were discovered by an international team of researchers who combed through more than ten years of Fermi observations.
Spider Systems
Spider systems occur when one star in a pair evolves faster than its partner. The more massive star's supernova leaves a pulsar behind and this remnant generates several light beams, including gamma rays.
A spider pulsar begins by siphoning a stream of gas from its companion. The feeding ends as the system develops and the pulsar speeds up, producing radiation and particle outflows that superheat and destroy the companion's facing side, according to NASA.
Scientists categorize spider systems into two groups, each named for a species of spider whose females occasionally consume their smaller partners.
Companions of black widows have a mass less than 5% that of the Sun. Larger companions are found in redback systems, ranging in mass from 10% to 50% of the Sun.
NASA explains that scientists can estimate the masses of spider systems by studying their orbital motions. The speed of the companion can be determined by visible light studies, whereas the pulsar's speed can be determined by radio measurements.
Visible light is typically used to estimate the tilt's angle, although NASA notes that this method has certain limitations. The superheated side of the companion's orbit changes our view of it, causing a tilt-dependent variation in visible light.
As astronomers continue to learn more about the phenomenon of superheating, differing pulsar masses have occasionally been predicted by models with various heating regimes.
Gamma rays, on the other hand, are only produced by the pulsar and have such high energy that, unless the companion blocks them, they move in a straight line untouched by debris.
Gamma Rays in Spider Systems
NASA adds that gamma rays disappearing from a spider system's data set indicate that the companion has overtaken the pulsar. They then can determine the system's tilt toward the Earth's line of sight as well as the speeds of the stars and the mass of the pulsar.
After examining the Fermi data, scientists discovered 15 missing gamma-ray photons. The gamma-ray pulses from these objects are timed with such precision that the team was able to identify the system was eclipsing from the 15 photons missing for a decade.
The pair is 84 degrees inclined, and the pulsar's mass is only 1.8 times as much as the Sun, according to their calculations.
"There's a quest to find massive pulsars, and these spider systems are thought to be one of the best ways to find them," Matthew Kerr, co-author of the study, said in a statement.
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