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An international team of researchers from the USA, Germany and Hong Kong used data from the already "late" Arecibo radio telescope in Puerto Rico, to discover a strange type of "spider star" in our galaxy, which defies the current classification.

Spider stars are a type of neutron star, or pulsars, which act like clocks in the sky, completing one rotation every 30 milliseconds and emitting a "pulse" of energy with each rotation. They are the compressed core of stars that in the past exploded into a supernova.

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They commonly pull material from companion stars in binary orbits, and use the momentum generated by “ingesting” the material to gain speed. But in rare and special cases, a neutron star orbits so close to its binary companion that it pulverizes its surface, ingesting vast amounts of material like a black widow spider dismembering and devouring a companion.

Arecibo radio telescope
Data from the “late” Arecibo radio telescope were used in the research. Image: NSF / US Government

There are two types of "spider stars": those that have a companion with a mass of less than one tenth of our Sun (usually from 0.02 to 0.03 solar masses) are called "black widow" (black widow). Those with larger companions, with more than a tenth of the Sun's mass, are the “redbacks”, the name given to the Australian black widow due to the red stripe on her abdomen).

In addition to size, there is a difference in behavior: redback companions often pass between the spider star and Earth, creating temporary eclipses. Black widow companions do not.

But the hybrid star found by astronomers is difficult to categorize: its companion causes eclipses, like a redback. But the estimated mass is 0.055 times the mass of the Sun, which is too heavy for a black widow, but too light for a redback. The exact mechanisms of how this binary system works are still a mystery.

The research was conducted with data collected by the Arecibo radio telescope between 2013 and 2018. But with its collapse early December further observations will be compromised. A comparable radio telescope is the 500-meter Aperture (Fast) Spherical Radio Telescope, which recently was opened for researchers around the world.

Source: Phys.org