The gravity of neutron stars is so strong that atoms collapse to form a dense mass of neutrons. The interior of objects can be dense enough to enable quarks to escape the confines of their nuclei. Thus, it is difficult to imagine neutron stars as active celestial bodies with tectonic crusts and perhaps even mountains.
But we have evidence to support this idea. Through gravitational waves, we can learn more.
It turns out that one of the reasons we know these stars are active is because of pulsars The universe today From his report. Pulsars are neutron stars that emit powerful beams of radio light from their magnetic poles. When these poles point toward the Earth, we see a series of regular pulses.
The pulsations are so regular that we can use them as a kind of cosmic clock, measuring almost everything from the ripples in spacetime caused by the first moments of the Big Bang.
Because neutron stars radiate energy, their rotation speed gradually slows down over time. We can easily observe this slowdown in pulsar data. However, sometimes it “stucks”, in which case its rotational speed jumps slightly. This can only happen if the shape of the neutron star suddenly changes.
Just as earthquakes can cause a measurable change in the Earth's rotation, starquakes also change the rotation of a star. So there is some kind of tectonic activity going on in neutron stars, but we don't know exactly what it is.
One idea is that neutron stars have a fairly thin but solid crust, similar to that of rocky planets. As the neutron star cools over time, this crust cracks and bends, creating earthquakes, fissures, and perhaps even mountains.
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Although this seems like a reasonable model, it is difficult to prove because we only notice the gap when something dramatic happens. Imagine trying to study Earth's mountains when we can only record data from earthquakes. But as the study published on arXiv shows, there are other ways to study mountains of neutron stars. This is where gravitational waves come into play.
Gravitational wave astronomy is still a young field, but it is already possible to collect data on neutron stars. When these merge, they create an energetic burst of gravitational waves, similar to merging black holes. By combining observations of gravitational waves of merging neutron stars with optical data, astronomers have been able to study the interior of neutron stars. This new study takes that idea a step further.
If a neutron star has a surface bulge, it is asymmetric. This means that as it rotates, the neutron star emits continuous gravitational waves. These waves are not very intense, but they contain a lot of information about the overall shape of the body.
If we can observe these waves over time, we can even study how a neutron star oscillates due to the dynamic motion of its surface. In the case of neutron stars with intense magnetic fields, called magnetars, we can even study how magnetic fields can distort the shape of the neutron star, which could play a role in fast radio bursts.
Of course, all of this requires the ability to detect faint gravitational waves, and this is where astronomers are most optimistic. Currently, the most accurate gravitational wave data we have can only place an upper limit on the size of mountains of neutron stars.
However, we can only say that it is not huge, which we already know. But as the next generation of gravitational observatories becomes operational, it may become within range of observation. There are still many challenges, but they do not seem insurmountable. So, in the data to come, gravitational waves could revolutionize our understanding of neutron stars, just as they revolutionize our understanding of black holes today.