Astronomer Steve van Straaten studied the time variations in the X-ray emission from various binary stars. He found that one of the binary stars had a vibrational frequency of 1330 Hz. This means that the intensity of the X-rays emitted changes 1330 times per second. That is the highest frequency ever measured for such a variation. The researcher used this information to determine the upper limit for the size and mass of the neutron star.
Neutron stars consist of the most compacted material in our universe. They have a mass comparable to that of our sun but they are about one quadrillion times smaller. If a neutron star and a normal star rotate around each other, matter can pass from the normal star to the neutron star. This happens as soon as the gravitational force of the normal star is no longer strong enough to stop its outer layers from being pulled away by the attractive force of the neutron star.
The matter originating from the star will move to the neutron star in a spiralling trajectory. The inner part of such a spiral-shaped disk and the surface of the neutron star are so hot that they emit high-energy X-rays. Changes in the intensity of this radiation are related to the movements of matter in the disk.
Van Straaten discovered that a relationship between the various movements around the neutron star is the same for different binary stars. Astronomers can use this discovery to develop new models for movement in the vicinity of a neutron star.
The research was funded by the Netherlands Organisation for Scientific Research.