2023-07-24 14:45:29
What appears to be a new type of stellar object has been discovered, as its behavior and characteristics do not fit with what is known about the physics of neutron stars.
A neutron star is created when a high-mass star exhausts its nuclear fuel and collapses in on itself. Part of it is ejected into space by a tremendous explosion (supernova), but the nucleus remains, compacted to such an extent that in atoms the electrons “embed” against the protons, giving rise to an exotic matter made mostly of neutrons. The resulting star made of this material is therefore called a “neutron star”.
The new finding is the work of a team led by Curtin University and the International Center for Radio Astronomy Research (ICRAR) in Australia. The Institute of Space Sciences (ICE), attached to the Higher Council for Scientific Research (CSIC) in Spain, has also participated in the research.
The stellar object is only the second of its kind detected so far. The first was discovered by Tyrone O’Doherty of Curtin University in Australia.
The strange new star, named GPM J1839-10, was discovered using the Murchison Widefield Array (MWA), a radio telescope in the western Australian outback. It is 15,000 light-years from Earth.
The first such object to be detected was transient and only shimmered in the sky for a few months. Instead, this new object can be located in archives of observations going back as far as 1988. ICE researchers Nanda Rea and Francesco Coti Zelati conducted follow-up observations of this new object using the Gran Telescopio Canarias (GTC), the optical telescope largest in the world, located in La Palma, Canary Islands, Spain, together with the XMM-Newton X-ray space telescope of the European Space Agency (ESA), and coordinated the physical interpretation of the results. “Discovering two systems of this type in such a short time tells us that they are very common in the universe,” says Nanda Rea, from ICE and the Institute for Space Studies of Catalonia (IEEC).
At first, the team couldn’t explain what they had found. In January 2022, they published a study on the matter in which they gave a first description of the enigmatic transient object that appeared and disappeared intermittently, emitting strong beams of energy three times an hour. Between July and September of that same year, the team scanned the sky using the MWA telescope. They soon found what they were looking for in the signal from GPM J1839-10, which emits bursts of energy lasting up to five minutes, five times longer than the first detected object of this type. Other telescopes served to confirm the discovery and obtain more information about the unique characteristics of the object. Among them, three CSIRO radio telescopes in Australia, the MeerKAT radio telescope in South Africa, the XMM-Newton space telescope and the Gran Telescopio Canarias.
Armed with the celestial coordinates and features of GPM J 1839-10, the team also began searching the observational archives of the world’s leading radio telescopes. They found results in the archives of the GMRT (Giant Meterwave Radio Telescope) in India, and the VLA (Very Large Array) in the US, which had records of observations dating back to 1988. “That was incredible, our telescopes recorded for the first time pulses from this object, but no one noticed and they remained hidden in the data for 33 years. They missed it because they didn’t expect to find something like this,” explains Natasha Hurley-Walker, from the research team.
“Long-period pulsars have been overlooked in radio surveys conducted so far. These soundings are designed to scan a wide area of the sky, but they only look at a particular region for a short amount of time, usually just a few minutes. This approach is very effective for detecting pulsars with spin periods ranging from milliseconds to seconds. However, unfortunately it falls short when it comes to capturing a sufficient number of consecutive long-period pulsar pulses”, says Coti Zelati, ICE researcher and IEEC member.
Artist’s recreation of the mysterious celestial body. (Image: ICRAR)
A stellar object below the ‘line of death’
Not all pulsars produce radio waves. Some are thought to lie below the so-called ‘death line’, a critical threshold where a star’s magnetic field becomes too weak to accelerate the particles responsible for radio waves. “We have studied in detail the emission from a possible slowly rotating pulsar or magnetar – using detailed computer simulations – and the bright emission from these systems, together with their slow rotations, challenges the current scenario for pulsar radio emission, which is below the so-called ‘lines of death’, says Rea.
The discovery has important implications for our understanding of the physics of neutron stars and white dwarfs, as well as the behavior of magnetic fields in extreme environments. It also raises new questions about the formation and evolution of magnetars and could possibly help unravel the origin of mysterious phenomena such as fast bursts of radio waves.
Professor Rea’s research group at ICE, in particular Celsa Pardo, Michele Ronchi and Vanessa Graber, have carried out further simulations to predict how many of these objects can be expected to be seen based on their still unknown nature. The Curtin University and ICE teams hope to discover more periodic radio bursts in the future, which could help to finally understand the nature of these fascinating and enigmatic objects.
The study is titled “A long-period radio transient active for three decades.” And it has been published in the academic journal Nature. (Source: Jorge Rivero / Alba Calejero / ICE / CSIC / NCYT from Amazings)
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