Artist’s impression of the disc and outflow around the massive young star. Credit: A. Smith, Institute of Astronomy, Cambridge.
A young star, located almost 11,000 light years away could help us understand how the most massive stars in the Universe are formed. This young star, already >30 times the mass of our Sun, is still in the process of gathering material from its parent molecular cloud, and may be even more massive when it finally reaches adulthood. The researchers, led by a team at the University of Cambridge, have identified a key stage in the birth of a very massive star, and found that these stars form in a similar way to much smaller stars like our Sun – from a rotating disc of gas and dust.
In our galaxy, massive young stars – those with a mass at least 8X greater than the Sun – are much more difficult to study than smaller stars. This is because they live fast and die young, making them rare among the 100 billion stars in the Milky Way, and on average, they are much further away. “An average star like our Sun is formed over a few million years, whereas massive stars are formed orders of magnitude faster – around 100,000 years,” said Dr John Ilee. “These massive stars also burn through their fuel much more quickly, so they have shorter overall lifespans, making them harder to catch when they are infants.”
The protostar that Ilee and his colleagues identified resides in an infrared dark cloud – a very cold and dense region of space which makes for an ideal stellar nursery. However, this rich star-forming region is difficult to observe using conventional telescopes, since the young stars are surrounded by a thick, opaque cloud of gas and dust. But by using the Submillimeter Array (SMA) in Hawaii and the Karl G Jansky Very Large Array (VLA) in New Mexico, both of which use relatively long wavelengths of light to observe the sky, the researchers were able to ‘see’ through the cloud and into the stellar nursery itself.
By measuring the amount of radiation emitted by cold dust near the star, and by using unique fingerprints of various different molecules in the gas, they determined the presence of a ‘Keplerian’ disc – one which rotates more quickly at its centre than at its edge. “This type of rotation is also seen in the Solar System – the inner planets rotate around the Sun more quickly than the outer planets,” said Ilee. “…it suggests that massive stars form in a similar way to lower mass stars, like our Sun.”
The undergraduate carrying out the work, Pooneh Nazari, said, “My project involved an initial exploration of the observations, and writing a piece of software to ‘weigh’ the central star.” From these observations, the team measured the mass of the protostar to be over 30X the mass of the Sun. In addition, the disc surrounding the young star was also calculated to be relatively massive, 2-3X the mass of our Sun. Dr Duncan Forgan said, “Our theoretical calculations suggest that the disc could in fact be hiding even more mass under layers of gas and dust. The disc may even be so massive that it can break up under its own gravity, forming a series of less massive companion protostars.”
The next step for the researchers will be to observe the region with the Atacama Large Millimetre Array (ALMA), Chile. This powerful instrument will allow any potential companions to be seen, and allow researchers to learn more about this intriguing young heavyweight in our galaxy. http://www.cam.ac.uk/research/news/astronomers-identify-a-young-heavyweight-star-in-the-milky-way
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