Space and Physics
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What you'll discover in this article
- PSR J0437-4715, the closest and brightest millisecond pulsar to Earth, has experienced two changes to its pulsation.
- This is surprising, as the pulsation usually happens with a regularity that rivals atomic clocks.
- "This is the first time we are seeing two of them happen in a row," lead author Rami Mandow told IFLScience.
Millisecond pulsars are incredible objects. Take a stellar object a bit heavier than the Sun, shrink it down to the size of a city center, give it an exceptionally strong magnetic field, and then send it spinning hundreds of times per second. Voila! You have the most accurate natural clocks in the universe. Or are they?
New research, which is currently waiting for peer review, reports not one but two changes in the profile of millisecond pulsar PSR J0437-4715. This is the closest and brightest millisecond pulsar to Earth, and these “blips” suggest something might be happening around its extreme magnetic field.
For 44 years we always thought these were 'stable, accurate, cosmic clocks' – but now, we are starting to see that they might not be as stable as we once thought.
Rami Mandow
“For the first time ever, we're seeing two profile change events occurring consecutively on a millisecond pulsar,” lead author Rami Mandow, a radio astronomer from Macquarie University, told IFLScience.
“Profile changes are when the pulsar's very stable long-term profile undergoes an abrupt, sudden change and then recovers back over time. These events are very rare – we've only ever seen two other pulsars have profile change events in over 44 years since their discovery. This is the first time we are seeing two of them happen in a row.”
This pulsar has a mass of 1.4 times that of the Sun and a radius of around 11 kilometers (7 miles); it is orbited every 5.7 days by a white dwarf. It spins on its axis 173.68 times every second, sending a pulse of radio waves like a lighthouse.
A puzzle wrapped in an enigma
We do not know the process that produces the pulsating radio emission, and it is not exactly clear what is triggering these changes. Researchers do know that the changes are happening in the magnetosphere of the pulsar.
We will be able to build a summary of these phenomena to help us learn more about [...] what could cause these very stable stars to suddenly burp.
Rami Mandow
“We know that it occurs in the star's magnetosphere but are still baffled as to what causes it,” Mandow continued.
“These magnetospheres are complex environments, and these events tell us that something interesting is happening in the magnetosphere where on at least two occasions, a trigger is causing these events which disrupts the magnetosphere, and yet it seems to re-organise itself back to its almost exact configuration.”
The stability of this pulsar is in about one part in 1,000 trillion. This is similar to what we measure in the standard atomic clocks (the next-generation optical atomic clocks are more precise). This is why they are referred to as the most accurate clocks in the universe.
Other such occasional changes have been reported, and it might be that it is a common phenomenon that millisecond pulsars experience. We just might not have had the technology to spot it before.
“As our instruments become more sensitive, we will start to see more of these, and so, we are now assessing all the pulsars in our observing sample to try find more of these events.”
“Once we do, we will be able to build a summary of these phenomena to help us learn more about these magnetospheres and what could cause these very stable stars to suddenly burp.”
Wide-reaching impact
Mandow continued: “For 44 years we always thought these were 'stable, accurate, cosmic clocks' – but now, we are starting to see that they might not be as stable as we once thought. That has big implications for our fundamental physics experiments!”
We can never recreate these conditions on Earth.
Rami Mandow
Pulsars are used to study physics at extreme levels. Matter in pulsars is so compressed that one teaspoon of pulsar weighs as much as a mountain. The gravity is so high, that pulsars are extremely smooth. A mountain on one would be millimeters tall.
On top of that, millisecond pulsars are used as an incredible cosmic detector. Due to their precision, by studying them it is possible to measure variations as tiny as the effects of gravitational waves moving across the galaxy.
Collecting the data from all these pulsars, it is like having a galaxy-sized gravitational wave observatory. It is called the International Pulsar Timing Array. PSR J0437-4715 is visible from the southern sky, so if there are changes in its behavior, the Australian Parkes Pulsar Timing Array (PPTA) and South African MeerKAT Pulsar Timing Array might be affected.
“At the PPTA we've been timing it for decades, and now we need to study these events to work out if they introduce unmodelled noise into our experiment, as that can drown out the gravitational wave signals we are looking for,” Mandow told IFLScience.
“This is also the closest and brightest millisecond pulsar to Earth, so it gives astronomers a nice lab to study extreme physics in: extreme gravity, rapid rotation, powerful magnetic field – we can never recreate these conditions on Earth. For these experiments we really want this cosmic clock to be as stable as possible.”
It seems that the mysteries of pulsars continue, but the researchers won’t stop until they work things out.
The study has been submitted for publication in the Monthly Notices of the Royal Astronomical Society, and the preprint is available via arXiv.
