‘Accretion Burst Event’

In a latest development, astronomers have found that the funnelling of matter into a forming star happens at different rates over time. Sometimes the forming star swallows up a huge amount of matter, resulting in a burst of activities in the massive star. This is called an accretion burst event.

Key-highlights of the findings:

• The international group of scientists, for the first time in history has been able to trace by masers and examine the subluminal propagation of a thermal radiation ‘heatwave’ emanating from an accreting high-mass protostar of the high-mass protostar G358-MM1.
• The object is eight times the mass of the sun; located at a distance of about 22,000 light years from Earth. 
• High-mass stars radically rebuild their surroundings and thus redetermine the structure and evolution of galaxies. One of the modern hypotheses is that high-mass protostars grow due to episodic accretion (an increase in mass due to the influx of matter from the surrounding objects).
• Large fragments of the surrounding matter fall on the star, dying in bright flashes.

What is Accretion Burst Event?

• Accretion burst event is incredibly rare. Till now, only three such events have been observed, out of all the billions of massive stars in the Milky Way.
• After the first detection of an accretion burst, in 2016, astronomers from around the world agreedin 2017 to coordinate their efforts to observe more.
  • Reported bursts have to be validated and followed up with more observations, and this takes a joint, global effort – which led to the formation of the Maser Monitoring Organisation(M2O).
• In January 2019, astronomers at Ibaraki University in Japan noticed that one such massive protostar, G358-MM1, showed signs of new activity. The masers associated with the object brightened significantly over a short period of time.
  • Follow-up observations with the Australian Long Baseline Array revealed something astronomers are witnessing for the first time– a blast of heat-wave coming from the source and travelling through the surroundings of the forming big star.
  • Blasts can last for about two weeks to a few months.

What is Maser?

• A maser (microwave amplification by stimulated emission of radiation) is the microwave (radio frequency) equivalent of laser.
• Masers are observed using radio telescopes and most of them are observed at centimetre wavelength. They are very compact.
• A maser flare can be a sign of an extraordinary 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 the country's Gauteng province) have been working together to detect a flare stimulated by a burst in the funnelling of materials into a massive star.

Formation of Stars:

• Stars are giant, luminous spheres of plasma. There are billions of them — including our own sun, in the Milky Way Galaxy. 
• Stars are born within the clouds of dust and scattered throughout most galaxies. A familiar example of such as a dust cloud is the Orion Nebula.
• Turbulence deep within these clouds gives rise to knots with sufficient mass that the gas and dust can begin to collapse under its own gravitational attraction.
• As the cloud collapses, the material at the center begins to heat up.
• Known as a protostar, it is this hot core at the heart of the collapsing cloud that will one day become a star.
• As the cloud collapses, a dense, hot core forms and begins gathering dust and gas. Not all of this material ends up as part of a star, the remaining dust can become planets, asteroids, or comets or may remain as dust.

Significance of the findings:

• The recent findings will help the astronomers to develop and test theories to explain how high-mass stars gain their mass.
• Furthermore, these findings promote the advantages of maser observations in understanding high-mass-star formation.