Neutron stars, some of the most extreme objects in the Universe, are formed from the collapsing nuclei of supergiant stars. Despite having a mass that exceeds that of the sun, they are compressed to the size of a small city. The study of neutron stars can provide valuable insights into the behavior of matter in unique and extreme conditions that cannot be replicated on Earth.
NASA is actively involved in the study of neutron stars through the Neutron Star Interior Composition Explorer (NICER) mission. This X-ray telescope, located on the International Space Station, captures X-ray radiation emitted from hot spots on the surface of neutron stars, where temperatures can reach millions of degrees.
Recently, scientists managed to measure the mass of a neutron star using radio signals from the rapidly rotating pulsar PSR J0437-4715. These measurements helped determine the star’s radius, providing valuable information about the composition of matter inside it.
Neutron stars are composed of matter so dense that it surpasses the density of atoms and exists on the brink of collapsing into a black hole. Understanding how matter behaves under such extreme conditions is crucial for testing our understanding of fundamental physics.
One of the primary objectives of the NICER mission is to study the PSR J0437-4715 pulsar, which is the closest and brightest millisecond pulsar known. This pulsar spins at a rate of 173 times per second, and observations of it have been ongoing for nearly three decades using the Murriyang radio telescope in Australia.
The scientific team had to overcome challenges related to modeling hot spots on the neutron star’s surface due to X-ray radiation from a nearby galaxy. By utilizing radio waves, they were able to independently measure the pulsar’s mass, a crucial step in accurately determining its properties.
The measurement of the neutron star’s mass was made possible by the Shapiro effect, as described in Einstein’s theory of relativity. The pulsar was found to have a mass equivalent to 1.42 times that of the sun, with a radius of 11.4 kilometers. These findings help to refine models of the internal structure of neutron stars by ruling out certain equations of state.
Further insights into the composition of matter inside neutron stars have been gained through observations of gravitational waves from colliding neutron stars and resulting explosions, known as