Astronomers using ESO’s Very Large Telescope have observed an elaborate serpentine system sculpted by colliding stellar winds. The object, called 2XMM J160050.7-514245, is a Wolf-Rayet star system, and a likely source of one of the most energetic phenomena in the Universe — a long-duration gamma-ray burst.
The VISIR instrument on ESO’s Very Large Telescope captured this stunning image of the 2XMM J160050.7-514245 system. Image credit: ESO / Callingham et al.
Gamma-ray bursts (GRBs) are among the most powerful explosions in the Universe.
Lasting between a few thousandths of a second and a few hours, they can release as much energy as the Sun will output over its entire lifetime.
Long-duration GRBs — those which last for longer than two seconds — are believed to be caused by the supernova explosions of rapidly-rotating Wolf-Rayet stars.
Some of the most massive stars evolve into Wolf-Rayet stars towards the end of their lives.
This stage is short-lived, and Wolf-Rayets survive in this state for only a few hundred thousand years — the blink of an eye in cosmological terms.
In that time, they throw out huge amounts of material in the form of a powerful stellar wind, hurling matter outwards at millions of miles per hour.
Stellar winds in the 2XMM J160050.7-514245 system, nicknamed Apep after an ancient Egyptian deity, were measured to travel at an astonishing 7.5 million mph (12 million km/h).
These stellar winds have created the elaborate plumes surrounding the triple star system — which consists of a binary star system and a companion single star bound together by gravity.
Though only two star-like objects are visible in the image, the lower source is in fact an unresolved binary Wolf-Rayet star.
This binary is responsible for sculpting the serpentine swirls surrounding Apep, which are formed in the wake of the colliding stellar winds from the two Wolf-Rayet stars.
Compared to the extraordinary speed of Apep’s winds, the dust pinwheel itself swirls outwards at a leisurely pace, ‘crawling’ along at less than 1.2 million mph (2 million km/h).
The wild discrepancy between the speed of Apep’s rapid stellar winds and that of the unhurried dust pinwheel is thought to result from one of the stars in the binary launching both a fast and a slow wind — in different directions.
This would imply that the star is undergoing near-critical rotation — that is, rotating so fast that it is nearly ripping itself apart.
A Wolf-Rayet star with such rapid rotation is believed to produce a long-duration GRB when its core collapses at the end of its life.
“This is the first such system to be discovered in our own Milky Way Galaxy,” said Dr. Joseph Callingham, an astronomer at the Netherlands Institute for Radio Astronomy.
“We never expected to find such a system in our own backyard.”
The research is published in the journal Nature Astronomy.
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J.R. Callingham et al. Anisotropic winds in a Wolf–Rayet binary identify a potential gamma-ray burst progenitor. Nature Astronomy, published online November 19, 2018; doi: 10.1038/s41550-018-0617-7
