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Scientists use rotating neutron stars to calibrate atomic clocks

Pulsar SXP 1062
Image: ESA / XMM-Newton / L. Oskinova / M. Guerrero; CTIO / R.Gruendl / Y.H. Chu

The European Space Agency synchronizes an atomic clock with distant, rapidly rotating neutron stars, called pulsars.

The efforts made by GMV, a private company together with the University of Manchester and the National Physics Laboratory of the United Kingdom, are used to improve the clocks used in the global Galileo satellite navigation system, such as GPS, but for Europe. The PulChron pulsar-based system combines the long-term stability of pulsar measurements with the accuracy of vibrating atoms to create more accurate clocks.

Physicist Jocelyn Bell Burnell discovered pulsars in 1967 when she noticed a radio signal varying with a period of 1.34 seconds in data from the Interplanetary Scintillation Array at the Mallard Radio Astronomy Observatory. Today we know that pulsars are neutron stars, small but incredibly dense coiled centers of larger stars that emit a beam of radiation, rotating with surprising regularity.

Although they are interesting in themselves, scientists now use regular rotation of pulsars as tools, for example, observing their arrays to search for gravitational waves. And their exact frequency makes them excellent time keepers.

In the end, the clock is just something that ticks at well-understood intervals that can be used to measure time. PulChron receives its measurements from five radio telescopes belonging to the European array Pulsar Timing Array, which monitor 18 pulsars. At the same time, atomic clocks have a characteristic frequency that makes up their “tick” by fine tuning the laser to excite the atom, and then translating the laser frequency to a useful interval.

But some atomic clocks, such as those based on hydrogen, which are excited by microwave lasers, can drift at longer intervals without another system to correct them. The clocks used by Galileo require re-synchronization with the atomic ground clocks every few hours. The PulChron project hopes to add the long-term stability of pulsars to control the atomic clocks, both for Galileo and potentially to tune UTC or coordinated time.

This is just a demonstration, according to the ESA bulletin. Nor is it the first hours of a pulsar — ​​but it's nice to see that some of the largest and smallest timekeepers in the universe function together to help us humans move.

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