The motion of stars in the stellar nursery may reveal how they’re born
We never get a great view of the Lagoon Nebula from the UK, as it sits low on the horizon, just above the spout of Sagittarius’s Teapot asterism. It’s a shame, because this giant star-forming region, situated perhaps 5,000 lightyears from Earth, is a fascinating place. The bright nebula harbours stars which are only now forming, alongside some brilliant examples of young, massive stars whose influence shapes the nebula itself.
Trying to disentangle what is clearly a complex history has kept astronomers busy for centuries. The latest attempt, detailed in this month’s paper, uses data from ESA’s celestial cartographer, Gaia, to take a close look at the stars embedded in the nebula’s gas.
The nice thing about the maps produced by Gaia is that they show how stars move, as well as where they are. But as we should expect from the Lagoon, this only adds to the complexity. For starters, it turns out there are two separate clusters rather than just one, each expanding slowly. The first covers the whole of the nebula, while the second is concentrated in its western lobe; its presence probably reflects a second, distinct phase of star formation in the nebula’s complex past.
Picking up speed
Leaving the geography aside, the researchers are focused on thinking about how the stars move, measurements which can give us a clue into how clusters of stars like this form. We know that stars begin to form when a cloud of gas collapses under its own gravity, but we don’t know how fast this happens. The speed of the collapse has implications for understanding what stars can form. However, as we can’t sit and watch for the few million years it might take, it’s hard to measure.
This is where the velocity of the stars comes in. If the cloud collapses quickly, any forming protostars fall into its gravitational well, heading for the centre of the new cluste
