Here on Earth, we pay a lot of attention to the Sun. After all, it plays a key role in our lives. But the Sun is only one of the billions of stars in our galaxy, the Milky Way. It is also quite small compared to other stars – most are at least eight times more massive.
These massive stars affect the structure, shape, and chemical composition of the galaxy. And when they run out of their gaseous hydrogen fuel, they go supernova. This explosion is sometimes so violent that it causes new stars to form from materials in the vicinity of the dead star.
But there is an important gap in our knowledge: astronomers do not yet fully understand how these original massive stars originally formed. So far, observations have provided only a few pieces of the picture.
This is because almost all of the known massive stars in our galaxy are located very far from our solar system. They also form in close proximity to other massive stars, making it difficult to study the environment in which they take shape.
One theory is that a spinning disk of gas and dust propels materials towards a growing star.
Astronomers recently discovered that over time, the funnel of matter into a forming star occurs at different speeds. Occasionally, a forming star absorbs huge amounts of matter, leading to an explosion of activity in the massive star.
This is called an accretion burst event. This is incredibly rare, with only three of the billions of massive stars in the Milky Way observed.
This is why astronomers are so excited about the recent observation of this event. Now, a team of astronomers can develop and test theories to explain how high-mass stars gain mass.
Following the first detection of an accretion burst in 2016, astronomers from around the world agreed to coordinate their efforts. The recorded bursts need to be verified and supplemented with additional observations, and this requires a collaborative global effort that led to the creation of the Maser Monitoring Organization (M2O).
A maser is the microwave (radio frequency) equivalent of a laser. The word stands for 'amplification of microwaves due to stimulated radiation'. Masers are observed with radio telescopes, and most of them are observed at centimeter wavelengths: they are very compact.
A maser flare can be a sign of an unusual event such as the formation of a star. Since 2017, radio telescopes in Japan, Poland, Italy, China, Russia, Australia, New Zealand and South Africa (HartRAO, in Gauteng province) have been working together to detect the explosion caused by the explosion as materials move into a massive star.
In January 2019, astronomers at Ibaraki University in Japan noticed that one such massive protostar, G358-MM1, was showing signs of new activity. The masers associated with the object have increased significantly over a short period of time. The theory is that masers become brighter when excited by an accretion explosion.
Subsequent observations showed that astronomers are observing for the first time – an explosion of a heat wave emanating from a source and passing through the vicinity of a huge forming star. Explosions can last from two weeks to several months.
Such explosions have not been observed in the previous two accretion bursts in massive stars. This could mean that this is a different type of accretion burst. There may even be many types of accretion bursts – a range of different types that act in different ways, depending on the mass and evolutionary stage of the young star.
Although explosive activity has subsided, masers are still much brighter than before the explosion. Astronomers are watching with interest to see if a similar explosion occurs again and on what scale.
This experience shows how valuable sky observation is from different parts of the globe. Collaboration is astronomy that is critical to important new discoveries.
James Okwe Chibuez, assistant professor at Northwestern University.
Sources: Photo: Katharina Immer / JIVE
