Pulsars emit incredibly powerful light. In some cases, where a pulsar is orbited by a companion star, the radiation can literally evaporate the unfortunate star. This is the merciless world of Black Widow pulsars, and astronomers have discovered one with the shortest period yet. The findings are reported in Nature.
The candidate black widow star system is known as ZTF J1406+1222. The system is made of three objects, one of which orbits far away from the pulsar. The other one is a brown dwarf so close to the pulsar that it challenges current assumptions on how these systems come to be. The black widow binary has a period of 62 minutes – far shorter than the previous record-holder at 75 minutes.
"This 62-minute orbit is remarkable because we don't understand how the stars could get into such a tight orbit," Dr Kevin Burdge, a postdoctoral scholar at MIT who performed the research while at Caltech, said in a statement sent to IFLScience. "The process of the pulsar ablating its companion should actually drive them apart. This is pushing the boundaries of what we thought possible."
The system was discovered using observations in visible light. Using the Zwicky Transient Facility (ZTF) instrument at Caltech's Palomar Observatory, the team was able to witness the system brightness vary by a factor of 13. Follow-up observations with NASA’s Chandra X-ray Observatory will provide new insights and hopefully confirm the nature of this system.
"Our data indicate we are looking at a black widow binary, but it could be something entirely new," Dr Burdge said.
"The population of black widows we've been finding so far with other wavelengths of light, such as X-rays, gamma rays, and radio waves, is probably biased because we haven't been catching all of them," says Burdge. "Now we have a new lens through which we can identify these systems."
The telescope was good enough to see the variation in the system brightness but not distinguish between the tiny pulsar – packing more than the mass of the Sun in a sphere with a diameter of just 20 kilometers (12.4 miles) – and the much larger brown dwarf. What they see is the heated surface of the brown dwarf, and can distinguish between the hotter “day” side that faces the pulsar and the slightly cooler “night” side.
The third star orbits the pair in over 10,000 years and it is located about 600 times away from them than the Earth is from the Sun. The system orbits in the galactic halo and the team believes it gets close to the galactic center, so further study might provide insights beyond the black widow pulsar physics.