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A team of astronomers led by Lucas Ellerbroek – doctoral candidate at the University of Amsterdam (UvA) – witnessed the rare birth of a massive star.

Geboorte zware ster

A team of astronomers led by Lucas Ellerbroek – doctoral candidate at the University of Amsterdam (UvA) – witnessed the rare birth of a massive star. The team observed the star – still in the process of formation – with the new spectrograph X-shooter, at ESO’s Very Large Telescope (VLT) in Chile. The star is hidden deep in a star formation area near the Vela constellation. Additional observations with Sinfoni, another VLT instrument, confirmed the existence of a gaseous disk around the star and perpendicular jet streams emitting particle matter. The findings were published yesterday in Astrophysical Journal Letters.

The exact process behind star formation is one of the most important unresolved questions facing contemporary astronomers. The formation of massive stars (10-100 times heavier than the sun) is an especially puzzling mystery. This is because massive stars are rare – only 1 in every 10,000 stars is massive – and have a short lifespan: a few million years compared to the sun’s 10 billion-year lifespan. The formation process of massive stars is approximately 100 times faster. Young massive stars are also more difficult to find, located at the heart of enormous gas and dust clouds that are almost impenetrable to visible light.

Using X-shooter, the world’s most sensitive spectrograph, the team of astronomers were able to observe the visible light – highly weakened – that surrounds a massive star during the formation process. The team then used Sinfoni to take a photograph clearly showing the jet streams in near infrared light, which can penetrate dust clouds slightly more easily

Are the formation processes of massive and low-mass stars comparable?

When a low-mass star is formed, part of the matter is channelled onto the star itself via a slowly rotating disk; the remainder is expelled from the system by jet streams. Astronomers are trying to find out whether this scenario also applies to mid-sized and massive stars. The new observations would seem to confirm this, although the processes are much faster and more powerful.

‘As we know from our observations of the X-shooter spectrum, the matter in the jet stream travels away from the star in two opposing directions. Measuring the speed at which this matter travels and tracing it back to the source allows us to find out more about the star’s past behaviour,’ Ellerbroek explains. ‘We’re basically conducting a form of stellar archaeology. Amongst other discoveries, we’ve learned that the formation process is erratic rather than gradual.’ Ellerbroek and UvA professor Lex Kaper are two of the first astronomers to use the new X-shooter. Kaper: ‘The X-shooter is the first of a new generation of instruments at the VLT. Where we previously had to record small sections of the spectrum at a time, we can now record the entire spectrum at once, from ultraviolet to infrared (300 - 2500 nm). This is especially useful in studying this type of object, where we have no idea in advance what the spectrum might contain.’