Experts classify these disparate binary star systems by the names of spider species whose females sometimes devour their smaller mates.
An international team of astronomers discovered the first gamma-ray eclipses from a special type of binary star system called ‘spider systems’. The scientists reviewed data from more than a decade of observations from NASA’s Fermi Gamma-ray Space Telescope to find seven such systems. The eclipses allowed them to determine the inclination of these systems in relation to our line of sight and calculate the mass of the pulsars, they reported Thursday.
Measure the masses of pulsars A ‘spider’ binary star system is made up of a pulsar (superdense, rapidly rotating remnants of a star that exploded in a supernova) and its low-mass companion star. “One of the most important goals of studying spiders is trying to measure the masses of pulsars,” said Colin Clark, an astrophysicist at the Max Planck Institute for Gravitational Physics in Germany who led the work. “Pulsars are basically balls of the densest matter we can measure. The maximum mass they can reach constrains the physics within these extreme environments,” he added. Why are eclipses necessary? Researchers can calculate the masses of these systems by measuring their orbital motions. Visible-light observations can measure how fast the companion is traveling, while radio measurements reveal the speed of the pulsar. However, to avoid potentially misleading estimates, it is essential to determine the tilt of the system relative to our line of sight.
Given the immense energy of the gamma rays generated by the pulsar, they will travel in straight lines, unaffected by debris, unless blocked by the companion. In other words, it eclipses it. In this way, the inclination in our line of sight, the speeds of the stars and the mass of the pulsar can be calculated very precisely. The first known ‘black widow’, B1957, discovered in 1988, has an estimated mass of 2.4 times that of the Sun, making it the heaviest known pulsar right at the theoretical mass limit between pulsar and hole black. “There is a quest to find massive pulsars and these ‘spider systems’ are thought to be one of the best ways to find them,” said Matthew Kerr, a physicist at the US Naval Research Laboratory and co-author of the newly published paper, this Thursday, in Nature Astronomy. “Before Fermi, we only knew of a handful of pulsars that emitted gamma rays,” said Elizabeth Hays, a Fermi project scientist at NASA Goddard Space Flight Center, USA. “After more than a decade of observations , the mission identified more than 300,” he stressed.
How are these systems formed? Spider systems develop because one star in a binary ages faster than its partner. When the most massive star explodes in a supernova and then becomes a pulsar. The emitted gamma rays create pulses so regular that they rival the precision of atomic clocks. Initially, the pulsar “feeds” on its companion, extracting its gas, but when it begins to spin more rapidly, the feeding stops and the intense streams of particles and radiation generated superheat the front side of the companion and erode it. Why spider names? Experts classify these systems by the name of spider species whose females sometimes devour their smaller mates. In this way, the so-called ‘black widows’ contain companions with less than 5% of the mass of the Sun. For their part, the systems called ‘red-backed spiders’ harbor larger companions, both in size and mass, than They weigh between 10% and 50% of the mass of the Sun.