New-style star accretion bursts dazzle astronomers at NWU and around the world

The meaning of the term "accretion burst" is expanding. In a rare glimpse at how high-mass stars grow even larger, an astronomer from the North-West University (NWU) has been part of a 15-country research team that has observed star bursts - or growth spurts - previously unknown to humankind.

"It is a privilege to be at the cutting edge of humanity's efforts to understand space and celestial bodies, and to have witnessed star behaviour that is entirely new," says Associate Professor James O Chibueze of the NWU's Centre for Space Research.

He and Dr SP van den Heever*, also from the Centre for Space Research, are part of an international team of astronomers who have been studying the G358-MM1 high-mass protostar - a young star located approximately 22 000 light years away from Earth.

While the two NWU astronomers have been observing this young star from the Hartebeesthoek Radio Astronomy Observatory, a branch of the South African Radio Astronomy Observatory (SARAO), near Krugersdorp, other astronomers have been keeping an eye on it from observatories in Australia, China, Germany, Korea, Japan, Ireland, Italy, the Netherlands, Poland, Russia, Chile, the United Kingdom and the United States.

What makes G358-MMI so special is that it has been displaying growth spurts that astronomers say are unique. "The star event we have been observing is the first of its kind to have been recorded from Earth," says the NWU's Prof Chibueze, who is among the co-authors of a letter published in Nature Astronomy, one of the world's top-rated academic journals.

He says the growth bursts of high-mass protostars like G358 are seldom seen by astronomers as these events are rare and difficult to observe directly. In this case, however, the global research team has been using what is known as "maser" emission phenomena to study the star.

Maser is similar to laser but uses microwaves instead of light waves and can be used to monitor and measure activity in space.

Using maser observation, astronomers have been able to capture "heat waves" emanating from the star during what is thought to be growth events. These waves of heat were found to be only slightly slower than light.

While this heat-wave phenomenon has been observed twice before in other high-mass protostars, G358 is different because of the variety of the bursts. To quote the letter in Nature Astronomy: "The G358-MMI event may therefore represent a new species among a 'zoo' of high-mass protostar accretion burst varieties."

What's more, this 'zoo' is likely to diversify as the research team around the world continues to keep tabs on this young star's activity.

Says Prof Chibueze: "The team's discoveries are hugely exciting and we are hopeful that further investigation will reveal more about the physical processes taking place within the G358 star. New horizons are opening up in space and it is wonderful that NWU and South Africa are part of it."

* Currently at the South African Radio Astronomy Observatory (SARAO).

Credit: The research is led by Dr Ross A Burns and the contribution of the Maser Monitoring Organization (M2O) is acknowledged.