Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have spotted comet-like stars in a young star cluster called Westerlund 1.
This image of Westerlund 1 was produced from data gathered by ALMA, combined with data from the NASA/ESA Hubble Space Telescope. Image credit: ESO / ALMA / NAOJ / NRAO / Fenech et al.
Discovered by Swedish astronomer Bengt Westerlund in 1961, Westerlund 1 is located approximately 15,000 light-years away toward the southern constellation Ara.
Also known as Ara Cluster and ESO 277-12, this object is one of the most massive young star clusters in our Milky Way Galaxy.
It is made up of around 200,000 stars and is relatively young in astronomical terms — at around 3 million years old it is a baby compared to our own Sun, which is some 4.6 billion years old.
Westerlund 1 is known to host a large amount of massive stars, many of them intriguing and rare types.
It is headlined by one of the largest stars ever discovered, named Westerlund 1-26.
This star is a red supergiant — although sometimes classified as a hypergiant — with a radius over 1,500 times that of our Sun. If Westerlund 1-26 were placed where our Sun is in our Solar System, it would extend out beyond the orbit of Jupiter.
The new observations of Westerlund 1 — led by University College London radio astronomer Danielle Marie Fenech — revealed comet-like ‘tails’ of material stretching away from some of the giant stars in the cluster.
Such tails are formed in the thick, relentless winds that pour from the cluster’s stellar residents, carrying material outwards.
This phenomenon is similar to how comets get their famous and beautiful tails.
“Comet tails in the Solar System are driven away from the nucleus of their parent comet by a wind of particles that streams out from the Sun. Consequently comet tails always point away from our Sun,” the astronomers said.
“Similarly, the tails of the huge red stars shown in the ALMA image point away from the core of the cluster, likely the result of powerful cluster winds generated by the hundreds of hot and massive stars found towards the center of Westerlund 1.”
“These massive structures cover large distances and indicate the dramatic effect the environment can have on how the stars form and evolve.”
The new ALMA observations are reported in a paper published in the journal Astronomy & Astrophysics.
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D.M. Fenech et al. 2018. An ALMA 3 mm continuum census of Westerlund 1. A&A 617, A137; doi: 10.1051/0004-6361/201832754
