An article published in the journal “Nature Astronomy” reports the discovery of a binary system that includes a white dwarf pulsar, the second such object discovered so far. A team of researchers that includes some of those who discovered the first white dwarf pulsar identified J191213.72-441045.1, or simply J1912-4410, a binary system that also includes a normal star belonging to the red dwarf class. This new discovery offers new insight into what constitutes a new class of cosmic objects with the potential to develop models to describe their formation and behavior.
A white dwarf is what remains at the end of the life cycle of a medium-small mass star, such as the Sun. A more massive star can leave behind a neutron star instead, much more compressed than a white dwarf and with a much more powerful magnetic field, after the end of its life. Pulsars are a common type of neutron star, but in the past, it was assumed that, under certain conditions, even a white dwarf star could be a pulsar. The announcement of the discovery of a white dwarf pulsar in the AR Scorpii system published in February 2017 proved that this type of object did indeed exist.
Some of the researchers who studied the AR Scorpii system and other colleagues looked for other similar systems by examining binary systems with similar characteristics in various astronomical surveys. A follow-up study conducted with the ULTRACAM mounted on the New Technology Telescope (NTT) allowed, together with data collected with other instruments, to discover another binary system that’s very similar, J1912-4410. About 770 light-years from Earth, this system consists of two objects orbiting each other in a period of just over four hours.
The white dwarf pulsar in the J1912-4410 system emits a pulsation every 5.30 minutes with radio waves and X-ray emissions. Its mass is at least that of the Sun but its size is similar to the Earth’s. When a white dwarf forms, it’s extremely hot but slowly dissipates its heat, and the temperature below 13,000 Kelvin, which is relatively low, of the one in the J1912-4410 system indicates that it’s already ancient.
The discovery of this new white dwarf pulsar confirms the dynamo model supported by the researchers to explain the existence of this type of object. According to this model, this type of white dwarf has a powerful magnetic field and an advanced age while its companion is close enough for the white dwarf’s gravity to strip away its mass which causes it to spin rapidly.
The interactions between the white dwarf and the red dwarf appear to make the difference in the birth of a white dwarf pulsar. Magnetic fields form a central element in their behavior determining their characteristic pulsations. Being able to study two examples of this class of objects is useful to develop models that describe their formation and behavior. If follow-up studies of other candidate systems to host a white dwarf pulsar are successful, it will be possible to start comparing them to get more insights about them.
