Using a VISIR receiver mounted on the Very Large Telescope (VLT) of the European Southern Observatory (ESO), astronomers obtained a unique image of a massive triple star system, enveloped in an elegant dust cloud. The object, living at a distance of about 8 thousand light years from Earth, may be the first precursor to the future gamma-ray burst.
This is the first such system discovered in our Galaxy. We did not hope to find such a thing literally under our noses.
-Joseph Kallingam, lead author of a study from the Netherlands Institute of Radio Astronomy
The system, which is a nest of massive stars surrounded by a dust swirl, is officially known as 2XMM J160050.7-514245. However, astronomers invented for this amazing object a more memorable nickname in honor of the ancient Egyptian deity, a huge snake, personifying chaos – Apep. This name was given to the cosmic structure for its curved shape.
Wolf-Rayet stars and gamma-ray burst
Gamma-ray bursts – perhaps the most powerful explosions in the universe. Continuing from a few thousandths of a second to several hours, they emit as much energy as the Sun emits during its entire existence. Prolonged emissions — that is, those that last more than two seconds — are believed to be caused by supernova flashes, into which the rapidly rotating massive Wolf-Rayet stars at the end of their life path turn.
This stage of development of the star is very short: the Wolf-Rayet stars remain in this state for only a few hundred thousand years, literally a moment on a cosmological scale. During this time, they emit huge amounts of matter into the surrounding space in the form of a powerful stellar wind, the speed of which reaches millions of kilometers per hour. The measured speed of the stellar winds at Apepe is truly amazing: 12 million kilometers per hour, which is faster a hundred thousand times the most powerful hurricanes on Earth.
It was these stellar winds that formed the complex curved structures surrounding the triple star system, which consists of a double star and its companion: a single star associated with double gravitational forces. Although we see only two star-shaped objects in the picture, the brighter of them is in fact a binary system. This duet also gave rise to serpentine eddies surrounding Apep at the junction of oncoming stellar winds from two Wolf-Rayet stars.
Compared with the dizzying speed of stellar winds in Apepe, the dusty carousel spins outwardly slowly and lazily, crawling at a speed of just some two million kilometers per hour, or even less. The striking discrepancy between the speeds, apparently, is the result of the fact that one of the stars of the binary system emits both fast and slow wind, and in different directions.
This may indicate that this star is in the stage of near-critical rotation — that is, it rotates so fast that it almost breaks into pieces. It is believed that at such a high rotational speed, the Wolf-Rayet star eventually experiences a gravitational collapse and generates a long gamma-ray burst.
A triple star system discovered in which one of the stars tears itself apart
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