Massive blue star disappears in unprecedented cosmic mystery

You’d think it would be hard to lose track of something 2.5 million times brighter than the sun. But there’s something strange going on with one such massive star in the Kinman Dwarf galaxy: It seems to have disappeared.

The star is of a type called a luminous blue variable and is located 75 million light-years away. It was studied by various astronomers between 2001 and 2011, who noted that the massive star was coming to the end of its life.

But when Ph.D. student Andrew Allan of Trinity College Dublin went to study it last year using the Very Large Telescope (VLT) to learn more about star death, he couldn’t locate it at all. “Instead, we were surprised to find out that the star had disappeared!” Allan said in a statement.

Artist’s impression of the disappearing star
This illustration shows what the luminous blue variable star in the Kinman Dwarf galaxy could have looked like before its mysterious disappearance. ESO/L. Calçada

The obvious answer would be that the star had indeed ended its life and died. But when this type of star dies, it typically explodes in an epic supernova which throws out tremendous energy in the form of light.

If that had happened in the Kinman Dwarf galaxy, the astronomers would have been able to detect it, but they saw no such evidence. “It would be highly unusual for such a massive star to disappear without producing a bright supernova explosion,” Allan said.

If this star has indeed died without undergoing a supernova, this would be the first time that a massive star’s life ending in this way has been observed. “We may have detected one of the most massive stars of the local universe going gently into the night,” said team member Jose Groh, also of Trinity College Dublin.

The team first looked for the star using the VLT’s ESPRESSO instrument, an instrument that uses four 8-meter telescopes in combination to look in the optical wavelength. When they couldn’t find the star using that, they tried another instrument called the X-shooter which looks across a wide wavelength range from ultraviolet to near-infrared. But that didn’t turn up anything either.

So then the team looked back at older data, and found indications that the star could have been experiencing a period of dramatic outbursts when it was last observed in 2011. They theorize that this outburst could have depleted the star so much that it became less bright and it is now hidden by dust.

Alternatively, the star could have collapsed into a black hole without producing a supernova, which would challenge the current understanding of how these massive stars die.

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