(ORDO NEWS) — Scientists at the University of Turku (Finland) studied the neutron star Hercules X-1, located at a distance of 21 thousand light years, and found that it precesses like a spinning top.
Hercules X-1 is an X-ray pulsar, which, as the researchers found out, belongs to the accreting class. The source of energy that feeds the X-rays is the matter flowing from the companion star.
The object was observed using the International X-ray Polarimeter Explorer (IXPE) spacecraft, which measures the polarization of X-rays.
The observed degree of linear polarization, in which the electric field vector of electromagnetic radiation oscillates in the same plane, was about 10 percent, well below the theoretical expectation of 80 percent for this object, and remains low throughout the pulsar’s rotation cycle.
The degree and angle of polarization varied depending on the phase of rotation of the pulsar, which made it possible to measure the position angle of rotation of the object and the slope of the magnetic field, which is a key quantity for modeling the radiation of a pulsar.
The simulation showed that the observed polarimetric characteristics of the system from the point of view of an observer from the Earth correspond to a shift of the pulsar’s axis of rotation relative to the angular momentum of its orbit in the binary system by 20 degrees.
This is a strong indication of the precession of a neutron star, when the axis of rotation changes its position in space. It is expected that definitive evidence of precession will come later when IXPE observes Hercules X-1 in another phase of the precession cycle.
IXPE was launched on a Falcon 9 rocket from Cape Canaveral in December 2021 and is now 600 kilometers above the Earth’s surface. The mission is a collaboration between NASA, the Italian Space Agency and scientists from 13 countries.
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