Inside the Christmas Tree Cluster

Scan the depths of our galaxy with a telescope and you may spot this festive cloud of star dust

Among the many festivities of Christmas, trees with twinkling lights that line the streets and stand in houses are a common sight. But one Christmas tree stands much further afield: shining roughly 2,600 light-years away, it puts the centrepiece of our living rooms to shame. With fiery baubles furnishing its wispy shape, the Christmas Tree Cluster is a galactic display to behold.

As the largest Christmas tree in the universe, this formation of stars, dust and gas covers a width of about 30 light years with its natural sparkle. The cluster was first discovered in the 18th century, but modern telescopes can capture high-quality images like this one, using a series of filters to produce an electrifying assortment of colours. A bit of imagination and a tilt of your head is all you need to see how the Christmas Tree Cluster got its name.

So how does the triangle of galactic gas mimic these Christmassy shapes and tones? The bauble-like blue stars dispersed throughout the tree are actually young, hot stars that are more massive than our Sun. The tree’s hazy red body is given its colour by its exposure to the ultraviolet light emitted by the ‘baubles’.

Adhering to this magical theme, the festive cluster is found in the constellation of the unicorn (Monoceros), part of the NGC 2264 region. In clear conditions this spectacle is visible to the naked eye, with the brightest of its stars, known as S Monocerotis, bringing your gaze to the galactic tree’s base.

Image credit: © ESO

This article was originally published in How It Works issue 139, written by Ailsa Harvey

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