Astronomers measure the heartbeat of rotating stars

An international team of scientists has used the MeerKAT radio telescope to observe the pulsating heartbeat of the Universe as neutron stars are born, forming swirling lightning storms that last millions of years.

Radio pulsars are spinning neutron stars from which we can observe bursts of radio waves like pulses of light from a lighthouse. With masses about one and a half times the mass of the Sun and sizes of only about 25 km, neutron stars are the densest stars known. They rotate extremely rapidly, typically once every thousandths of a second to once every tens of seconds, only gradually slowing down as they age.

Now a team of astronomers has released the largest pulsar survey ever Monthly Bulletins of the Royal Astronomical Society.

Neutron stars are also the strongest magnets in the universe, on average a million times stronger than the strongest magnet on Earth. Such extreme properties provide an opportunity to test the laws of physics with exceptionally high accuracy. Even 60 years after their discovery, fundamental questions about the nature of these exotic objects remain.

No two pulsars are alike, and advancing in these exciting areas of physics requires delicate observations of as many pulsars as possible. The Thousand Pulsar Array (TPA) project is an international collaboration aimed at pursuing these goals by utilizing the unprecedented sensitivity of the MeerKAT radio telescope. This consists of 64 antennas in the Karoo Desert in South Africa and is a stepping stone towards the Square Kilometer Array, in which the UK is a leader.

The results will be published in two parts, one of which will be led by researchers from the University of Manchester, detailing the results of the study of over one million individual flashes recorded. The flash sequence can be visualized as a pulse train.

dr Patrick Weltevrede from the University of Manchester said: “Observing a pulsar is like checking the pulse of a pulsar and revealing the peculiarities of its ‘heartbeat’. Every single pulse is different in shape and strength.”

Some pulsars visualize ordered patterns of diagonal stripes. dr Xiaoxi Song, Ph.D. Student at the University of Manchester explains: “The excellent quality of the TPA data and our sophisticated analysis allowed us to reveal these patterns for many pulsars for the first time. These patterns can be explained by the thunderstorms swirling around the star. The results point to something fundamental about how pulsars work.”

After the pulsar’s birth, the thunderstorms swirl rapidly and chaotically around the star. After a few million years, thunderstorms die down and patterns become slower and more steady. This turns out to be the opposite of what models predict. Eventually, after a few billion years, lightning will stop altogether and pulsars will no longer be detectable.

The MeerKAT team recently received the prestigious Royal Astronomical Society Group Award, and the TPA project has now achieved an extraordinary milestone: detailed observations of more than 1,200 pulsars, representing more than a third of the known pulsars.

In accompanying work, led by researchers from the University of Oxford, the statistical properties of the pulse shapes are presented. dr Bettina Posselt explains: “We find that the most important property that determines the radio emission of a pulsar is its so-called spin-down power. It quantifies the energy a neutron star releases every second as its rotation slows down, and this spin-down power is used to generate the observed radio waves.”

Models predict the ionized gas surrounding the star is continuously discharging, akin to thunderstorms, that creates the radio pulses. The new data show that the spin-down power affects how high above the neutron star’s surface the radio emission occurs and how much energy the charged particles have. Because there is evidence that spin-down power decreases with age, and the 1,200 pulsars exhibit a wide range of spin-down power, the TPA data are ideal for studying neutron star aging.

The new data show that even the lowest spin-down power pulsars emit intense radio emissions and can be detected over long distances. This result suggests that a larger population of pulsars may yet to be discovered than previously anticipated.

The TPA data of both projects are now publicly available. They allow the international community to conduct further studies both on the properties of these pulsars and on those of the interstellar space in between.