Guest post: Some stars have a pulse – and astronomers have cosmic stethoscopes
Research impact and institutes 4 May 2023
MSc Science Communication student Lucinda Shirreffs sets focus on those most compelling of stars: pulsars.
An international team of astronomers has made a breakthrough with one of the strangest, most fascinating types of stars in the cosmos.
Using the unmatched sensitivity of the MeerKAT radio telescope, which consists of an array of 64 radio telescopes in the Karoo desert in South Africa, the distinctive pulses of spinning neutron stars – pulsars – have been measured in greater accuracy than ever before.
Just like the pulse of a human heart can tell doctors what is going on in the body, the pulse of these extraordinary stars can tell astronomers what is happening inside them.
What’s in a name?
Pulsars are a variety of neutron stars with twin beams of electromagnetic radiation emitting from each of their magnetic poles.
These stars spin extremely quickly, rotating over 43,000 times per minute when they first form, gradually slowing down as their interiors cool into a superfluid. The spinning and twin beams of radiation combine to create a lighthouse effect when the stars are oriented with a beam shining at Earth, making them extremely distinctive to astronomers.
Perhaps one of the most mind-blowing things about neutron stars is their size. Unlike most astronomical objects – so large the human mind can barely comprehend them – neutron stars exist on a far more familiar scale. On average, these stars are only 20 kilometres (12 miles) in diameter – about the same size of the Isle of Man. Despite how tiny they are, neutron stars typically have a mass one and a half times that of the sun. This makes them the densest objects in the universe – one cubic centimetre of neutron star material would weigh about one trillion kilograms on Earth.
All neutron stars are highly magnetised, being on average over a trillion times stronger than Earth’s comparatively puny magnetic field. Even over 60 years after their famous discovery by Jocelyn Bell Burnell, the remarkable qualities of these objects can make them seem stranger than (science) fiction.
Finger on the pulse
This new pulsar breakthrough comes in the form of the largest and most accurate pulsar survey ever, published by a team of collaborative international scientists in Monthly Notices of the Royal Astronomical Society.
The Thousand Pulsar Array (TPA), a database of over 1,200 known pulsars as measured by the MeerKAT telescope, has spearheaded this success. Data in the TPA constitutes over one third of all known pulsars. The data, detailing the over one million individual pulsar flashes recorded, is published in two parts – one of which is directed by The University of Manchester.
Dr Patrick Weltevrede, a Senior Lecturer in Pulsar Astrophysics in Manchester’s Department of Physics and Astronomy, describes: “Observing a pulsar is like checking the pulse… revealing the particularities of its ‘heartbeat’. Each individual pulse is different in shape and strength.”
What’s the prognosis?
Some of the findings from the TPA show peculiarities in the form of ordered diagonal stripes surrounding the star. These leave distinctive markers in the pulses given off by the pulsar in question and show up when the star is digitally visualised.
Dr Xiaoxi Song, a PhD student at Manchester, says: “The superb quality of the TPA data and our sophisticated analysis allowed us to reveal these patterns for many pulsars for the first time.”
These strange stripes are theorised to be caused by massive, swirling lightning storms, shattering across the thin upper atmosphere of the pulsar. Neutron stars that have these distinctive lightning storms must be newly-formed, because they calm down after a few million years.
Models predict that the ionising gas surrounding these stars continually discharges in a way not dissimilar to lightning storms here on Earth, funnelling charged particles and radio electromagnetic radiation along the pulsar’s brutally strong magnetic field. There, it blasts out from the poles to create those magnificent twin beams.
The potential power to produce this observed electromagnetic radiation is called the “spin-down power”. In accompanying research from the University of Oxford, Dr Brettina Posselt explains: “We find that the most important property governing the radio emission of a pulsar is its so-called spin-down power… Some of this spin-down power is used to produce the observed radio waves.”
As the pulsar ages, there is evidence that it loses some of this power. The data in the TPA shows pulsars with a variety of levels of spin-down power, making it an ideal database for astronomers wanting to research the ageing process of some of the strangest stars in the universe.
The future of pulsar research
The work of the MeerKAT team – which recently received the prestigious Group Award of the Royal Astronomical Society – has paved the way for a future of pulsar research, especially pertaining to the mysterious process by which pulsars age and die.
Putting a cosmic stethoscope up to the beating heart of the universe has offered astronomers from Manchester and across the globe invaluable insight into some of the strangest stars out there.
One day, those ‘heartbeats’ will stop, and with this pioneering research astronomers are beginning to understand how.
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Words: Lucinda Shirreffs
Images: Kevin Gill, The University of Manchester, Shutterstock
