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ESO/Callingham et al.
ESO/Callingham et al.

Award for finding the most extreme stellar object in the Universe

Joseph Callingham from the Leiden Observatory receives the Louise Webster Prize for outstanding post-doctoral research. The prize is awarded by the Astronomical Society of Australia for Callingham’s search for the most extreme object in the Universe.

The most extreme stellar object so far

Callingham discovered the brightest and most extreme stellar object found so far in the Universe. Dubbed Apep, after the ancient Egyptian god of chaos, it comprises at least three massive hot stars enshrouded in spectacular spiralling plumes of dust. Calligham and colleagues demonstrated that Apep is generating two types of stellar wind, one moving six times faster than the other – a profoundly strange result. Since the finding was first reported in Nature Astronomy in 2019, the work has ignited many new research projects and generated hundreds of media stories.

A feather in the storm

‘Apep has confounded our ideas about how massive stars end their lives,’ Callingham says. ‘When the most massive stars in our Universe near the end of their lives, they produce incredibly fast winds ( over a 1000 km/s) that carry away a huge amount of a star's mass. These massive stars are often found with a partner, in which the fast winds from the dying star can collide with its companion to produce exotic dust patterns.’ The Apep star system, on the other hand, is adorned with a spectacular dust pinwheel that is moving much slower than the wind within the system. ‘This is equivalent to finding a feather not moving at all in the middle of a cyclone,’ Callingham explains.

That's how modern science works

The path that led to the discovery of Apep started when Callingham was still a Master’s student in Australia and took until his arrival in the Netherlands to solve the case. ‘Surrounded by an international team of experts that made it all possible,’ he says. ‘Making a discovery in astronomy is always exciting. However, while some discoveries have an immediate and obvious scientific impact, other discoveries require a period of incubation to tease out their wide-ranging implications. The discovery and study of Apep, fits well into the latter group. It is a great microcosm for how modern science works.’ 

Callingham wrote a special blog piece for Nature Astronomy about this journey – Riding the serpent: The discovery and study of Apep.

No solo achievement

Callingham was incredibly surprised and delighted when he found out about the prize. ‘I feel very privileged to be given this award. However, that delight is also accompanied by the apprehensive feeling that what I think was a team achievement is being awarded to a single person. I am extraordinarily fortunate to have had a great team around me that made it possible to discover Apep, and solve some of its enigmas.’

IInfrared image by the Very Large Telescope. ESO/Callingham et al.

Start of an astronomical journey

Callingham is currently still working on solving some of the unknowns associated with Apep, together with students at Leiden Observatory. ‘Furthermore, I have been spending a significant amount of time looking for stars and exoplanets with LOFAR, a large radio telescope that detects extreme low frequencies and is headquartered in the Netherlands. Apep really represents the start of my journey into studying stellar and exoplanetary science.’

Honouring stargazers at annual conference

The Astronomical Society of Australia (ASA) is Australia’s professional body for astronomy. It honours six Australian astronomers during their annual conference on 14 June 2021 at the School of Physics at The University of Melbourne.

The Louise Webste prize that Callingham receives was named after Dr Louise Webster. She was an inaugural staff astronomer at the Anglo Australian Observatory. She passed away in 1990 at the age of 49, after a long illness. The prize recognises outstanding research by a scientist early in their post-doctoral career.

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