Astronomers have announced the discovery of a magnetized neutron star which seems to have an entirely solid surface.
As far as current scientific knowledge goes, stars are massive celestial bodies that consist primarily of gas and plasma, and do not have a solid surface. The gravitational forces that act on the gases in a star cause them to compress and heat up, eventually leading to nuclear fusion reactions in the core that produce light and heat.
While there are various types of stars, such as red giants, white dwarfs, and neutron stars, none of these types are known to have a solid surface. But that changes now.
An multinational group of 50 researchers analyzed information from the Imaging X-ray Polarimetry Explorer (IXPE), a satellite that NASA and the Italian Space Agency launched in December 2021. Their findings were published in the journal Science. The researchers collected data on the neutron star with the oblique designation 4U 0142+61.
Neutron star 4U 0142+61 is a pulsating X-ray source located in the constellation Cassiopeia, approximately 13,000 light-years from Earth. It is a type of neutron star known as an anomalous X-ray pulsar (AXP), which is characterized by its unusual X-ray emission and strong magnetic field.
4U 0142+61 was first discovered in the 1980s as a persistent X-ray source, and later identified as a pulsar through its periodic X-ray emission. The pulsation period of 4U 0142+61 is around 8.7 seconds, and it exhibits a high degree of stability over long periods of time.
One of the most remarkable features of 4U 0142+61 is its extremely strong magnetic field, which is estimated to be around 10^14 Gauss. This makes it one of the most strongly magnetized neutron stars known, and it is thought to be responsible for the pulsar's unusual X-ray emission.
The X-ray emission from 4U 0142+61 is believed to be powered by the decay of the pulsar's magnetic field, which creates a hot, magnetized plasma around the neutron star. The X-rays are emitted as the plasma interacts with the strong magnetic field, and the periodic pulsations are thought to be caused by the rotation of the neutron star and its magnetic field.
Overall, neutron star 4U 0142+61 is an important object of study for astronomers, as it provides insights into the properties and behavior of neutron stars, as well as the mechanisms that produce high-energy radiation in the universe.
Recent observations of 4U 0142+61 using X-ray telescopes have detected "quasi-periodic oscillations" in its X-ray emission. These oscillations are thought to be caused by vibrations or seismic waves traveling through the crust of the neutron star, indicating that the crust is solid.
4U 0142+61 is actually a solid body or so it appears. Based on the most recent information from IXPE, the researchers in Science claim that it is very improbable that the energy originating from 4U would be "compatible with the existence of an atmosphere and just marginally compatible with a condensed surface."
The atoms in this solid crust, which is most likely formed of iron, would be warped, losing their spherical shape and being stretched and extended in the magnetic field's direction instead.
These magnetic forces would hold the ions together to create a lattice. In other words, the surface could not be made of neutrons but rather of "normal" stuff, such as the iron that makes up Earth.
"This was completely unexpected. I was convinced there would be an atmosphere," one of the study's lead authors, professor Silvia Zane, a member of the IXPE science team, said in a statement. There could be an alternative explanation here, but so far, there isn't enough data to explore these other possibilities. "A next step is to observe hotter neutron stars with a similar magnetic field, to investigate how the interplay between temperature and magnetic field affects the properties of the star's surface."
Reference(s): Research Paper, News Statement