NASA’s X-ray telescope on the ISS measures the closest millisecond pulsar to Earth, providing new insights into neutron stars and their properties.
Astronomers have successfully measured the mass and dimensions of the closest millisecond pulsar to Earth using a NASA X-ray telescope mounted on the International Space Station (ISS). This pulsar, known as PSR J0437-4715 (PSR J0437), is located approximately 510 light-years away in the constellation Pictor.
What is a Millisecond Pulsar?
Millisecond pulsars are a type of neutron star born from the remnants of massive stars. Unlike typical neutron stars, millisecond pulsars spin hundreds of times per second, emitting beams of radiation and matter from their poles. These beams sweep across the universe, making pulsars resemble powerful “cosmic lighthouses.”
Discovering PSR J0437-4715
PSR J0437-4715, the closest millisecond pulsar to our solar system, spins 174 times per second. This rapid rotation causes it to emit X-rays and radiowaves towards Earth every 5.75 milliseconds, making it a precise cosmic timekeeper.
Using data from NASA’s Neutron Star Interior Composition Explorer (NICER) on the ISS, scientists determined that PSR J0437 is 14 miles (22.5 kilometers) wide and has a mass 1.4 times that of the Sun. Additionally, they discovered that its hot magnetic poles are misaligned.
The Role of NICER and Advanced Modeling
The team employed a modeling method called “pulse profile modeling” to analyze NICER’s X-ray data. They then used the Dutch national supercomputer Snellius to create simulations of PSR J0437.
“Before, we were hoping to calculate the radius accurately and show that the hot magnetic poles are not directly opposite each other on the stellar surface,” said team leader Devarshi Choudhury of the University of Amsterdam. “And we just managed to do both!”
Formation and Characteristics of Neutron Stars
When stars with masses between eight and 25 times that of the Sun exhaust their nuclear fuel, they undergo gravitational collapse, leading to a supernova explosion. The core’s collapse forms a neutron star with a mass between one and two times that of the Sun but a significantly smaller diameter of around 12 miles (20 kilometers). This density is so extreme that a sugar cube of neutron star matter would weigh about 1 billion tons on Earth.
The rapid spin of neutron stars is due to the conservation of angular momentum, similar to how an ice skater spins faster by pulling in their arms. Neutron stars can also gain additional spin speed from a companion star by stripping material from it.
PSR J0437’s Companion Star
PSR J0437 likely engaged in this fascinating process, as it possesses a helium-rich companion white dwarf star, whose mass is only a quarter of that of the Sun. This significant disparity in mass suggests that PSR J0437 has stripped away the outer layers from its companion star. By doing so, it has managed to achieve its extraordinarily high spin rate. The interaction between PSR J0437 and its companion is a remarkable example of stellar dynamics, where the pulsar’s gravitational influence has profoundly altered the evolution of the white dwarf, effectively peeling away its outer layers and thereby enriching itself with helium. This process not only explains the high spin rate of PSR J0437 but also provides insight into the intricate dance of binary star systems and their complex evolutionary pathways.
Implications of PSR J0437’s Measurements
The mass of PSR J0437 indicates that the maximum mass of neutron stars might be lower than some theories predict. This finding aligns with recent observations of gravitational waves.
“That, in turn, fits nicely with what observations of gravitational waves seem to suggest,” said Anna Watts, a neutron star expert at the University of Amsterdam.
