Dragging effect of space-time detected in white pulsar-dwarf system

If a very massive object, such as a planet or star, rotates, it literally drags the surrounding space-time with it. It is a phenomenon predicted by Einstein’s general relativity also known as the “dragging effect” or the Lense-Thirring effect (from the two Austrian physicists Josef Lense and Hans Thirring who in 1918 first derived the effect within general relativity).

This effect also exists on Earth in relation to its proximity to the Sun but in our case, it is extremely small so that it has been very difficult to measure for years. The effect, however, is more pronounced with heavier and more massive objects, such as white dwarfs or neutron stars. And it is by studying a binary system composed of a white dwarf and a pulsar that researchers have found direct evidence of this effect.

The researchers, led by Vivek Venkatraman Krishnan of the Max-Planck-Institut für Radioastronomie, have in fact observed a pulsar characterized by a narrow and fast orbit around a white dwarf that has a mass similar to that of the Sun. The pulsar makes a full circle around this white dwarf in less than five hours, whizzing at a speed of over one million km/h. The two bodies are very close together and less than the diameter of the Sun.

Measuring the timing of the arrival of the very short pulses of the pulsar towards Earth, data found over a period of almost twenty years, the researchers concluded that it is the Lense-Thirring effect that causes a sort of drift, slow and long term, of the way in which the pulsar and the white dwarf orbit around each other.

It is the dragging of the same space-time that causes the orientation of the pulsar to slowly change while it revolves around the white dwarf. Among other things, this new study confirms a hypothesis, contained in other previous studies, according to which white dwarf of this binary system, called PSR J1141-6545, was formed before the pulsar. Such binary systems are considered quite rare.

This study, among other things, could also be useful to understand what is inside a white dwarf: despite decades of research, it is not yet known how matter is arranged inside this very strange cosmic object given the conditions inside it, conditions of very strong gravity to which the same matter is subjected and which are not reproducible in the laboratory.