Super Star

An enlargement of the cluster from the original image, linked below.  Credit: ESO

An enlargement of the Westerlund cluster of stars from the original image, linked below. Credit: ESO

The star at the heart of this story is called Westerlund 1-26 or just W 26, it is about the biggest star we know of in our galaxy. It is some 1,500 + times the size of our sun! As the press release below tells, the star is in the process of dying, surly to become a black hole.

The star W 26 is part of a cluster of stars especially notable because of the large number of very massive stars.

The cluster was discovered in 1961 by Bengt Westerlund. The cluster was difficult to study for a long time because of dust and gas clouds and is one of the reasons distance estimates vary so much, last estimate I saw was a little over 4,900 pc, or around 16,000-light years.

The problem of the gas and dust doesn’t seem to be much of a problem for a very amazing telescope the VLT Survey Telescope. If the telescope isn’t cool enough, the camera on it, the OmegaCAM is incredible!

From the ESO (use this link to see the original image):

This new picture from the VLT Survey Telescope (VST) at ESO’s Paranal Observatory shows the remarkable super star cluster Westerlund 1 (eso1034). This exceptionally bright cluster lies about 16 000 light-years from Earth in the southern constellation of Ara (The Altar). It contains hundreds of very massive and brilliant stars, all of which are just a few million years old — babies by stellar standards. But our view of this cluster is hampered by gas and dust that prevents most of the visible light from the cluster’s stars from getting to Earth.

Now, astronomers studying images of Westerlund 1 from a new survey of the southern skies [1] have spotted something unexpected in this cluster. Around one of the stars — known as W26, a red supergiant and possibly the biggest star known— they have discovered clouds of glowing hydrogen gas, shown as green features in this new image.

Such glowing clouds around massive stars are very rare, and are even rarer around a red supergiant— this is the first ionised nebula discovered around such a star. W26 itself would be too cool to make the gas glow; the astronomers speculate that the source of the ionising radiation may be either hot blue stars elsewhere in the cluster, or possibly a fainter, but much hotter, companion star to W26.

W26 will eventually explode as a supernova. The nebula that surrounds it is very similar to the nebula surrounding SN1987A, the remnants of a star that went supernova in 1987 [2]. SN1987A was the closest observed supernova to Earth since 1604, and as such it gave astronomers a chance to explore the properties of these explosions. Studying objects like this new nebula around W26 will help astronomers to understand the mass loss processes around these massive stars, which eventually lead to their explosive demise.

Notes
[1] This picture forms part of a detailed public survey of a large part of the Milky Way called VPHAS+ that is using the power of the VST to search for new objects such as young stars and planetary nebulae. A spectacular recent picture of the Prawn Nebula was made using observations from the same survey.

[2] This nebula is thought to have surrounded SN1987A’s progenitor star since before it went supernova.

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