The gravity of neutron stars is so strong that atoms collapse into a dense mass of neutrons. The interior of objects can be dense enough for quarks to escape from 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. And through gravitational waves, we can learn even more.
One of the reasons we know these stars are active is pulsars, it turns out Universe Today from his report. Pulsars are neutron stars that emit powerful beams of radio light from their magnetic poles. When these poles are directed towards the Earth, we see a series of regular pulses.
The pulses 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 deceleration in the data of pulsars. Sometimes, however, they ‘break down’, in which case its rotation speed jumps a bit. This can only happen if the shape of the neutron star suddenly changed.
Just as earthquakes can cause a measurable change in the Earth’s rotation, starquakes also change the star’s rotation. 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 rigid crust, similar to that of rocky planets. As the neutron star cools over time, this crust cracks and bends, leading to earthquakes, fissures, and perhaps even mountains.
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While this seems like a reasonable model, it’s hard to prove because we only notice the gap when something dramatic happens. Imagine trying to study the 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 the mountains of neutron stars. This is where gravitational waves come into play.
Gravitational wave astronomy is still a young field, but it has already been 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 gravitational wave observations of merging neutron stars with optical data, astronomers were able to study the interior of neutron stars. This new study takes this idea a step further.
If a neutron star has a surface bulge, it is asymmetric. This means that during its rotation, the neutron star emits continuous gravitational waves. These waves are not very intense, but they would contain a lot of information about the general shape of the object.
If we can observe these waves over time, we can even study how the neutron star wobbles due to the dynamic movement of its surface. In the case of neutron stars with intense magnetic fields, so-called magnetars, we could even study how the 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 being able to detect these faint gravitational waves, and here astronomers are a little more sanguine. Currently, the most accurate gravitational wave data available to us can only set an upper limit to the magnitude of neutron star mountains.
Even so, we can only say that they are not huge, which we already knew. But as the next generation of gravity observatories come into operation, it may come within range of observation. There are still many challenges, but they do not seem insurmountable. So in the coming data, gravitational waves could revolutionize our understanding of neutron stars, much like they are revolutionizing our understanding of black holes today.
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2024-01-05 20:54:49
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