Mystery as massive star 'vanishes' without a trace

01 Juillet, 2020, 05:38 | Auteur: Therese Cote
  • An image of the Kinman Dwarf galaxy taken by the Hubble Space Telescope

This illustration shows what the luminous blue variable star in the Kinman Dwarf galaxy could have looked like before its mysterious disappearance.

But when they pointed VLT to the galaxy in 2019, they could no longer find the telltale signatures of the star.

The other theory is that the star became less bright and partially obscured by dust, meaning it vanished from view. Alternatively, the team said the star may have collapsed into a black hole, without producing a supernova explosion.

When the big ones die, they go out with a bang, so to speak, so when astronomers made a decision to check in on what they believed was a large star in the Kinman dwarf galaxy almost a decade after it was last studied, they were shocked to discover that it was gone.

"It would be highly unusual for such a massive star to disappear without producing a bright supernova explosion", said Allan. ELT can image at high resolution very distant stars such as those in Kinman Dwarf, which is located more than 75 million light-years away.

From 2001 to 2011, the light from the galaxy consistently showed evidence that it hosted a "luminous blue variable" star 2.5 million times brighter than the Sun. Stars of this type are known to be temperamental, with dramatic shifts in their spectra and luminosity (inherent brightness). The new telescope is scheduled to see first light in 2025.

"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. What seems to be the most likely scenario is that the star was undergoing an outburst at the time when it was previously observed.

Scientists are not sure why the star can no longer be seen but believe there may be two possible explanations.

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Luminous blue variables are unstable stars prone to giant outbursts over the course of their life. It is possible that the star collapsed into a black hole without first triggering a supernova - a rare event, even in the context of dying stars.

This would be a rare event: our current understanding of how massive stars die suggests majority meet their end in a violent nova. Other telescopes were also used for the historical study; between VLT's spectrographs and these other observatories, astronomers easily confirmed the presence of the now-missing star in the older observations.

"As Hubble already imaged the galaxy prior to the star's disappearance, we are hoping this will enable us to confirm the star's disappearance and determine the true cause of its disappearance", Allan said.

However, the researchers can't rule out the possibility that the star went supernova in the period between 1995 and 1998 when no observations were available.

The team is composed of Andrew Allan (School of Physics, Trinity College Dublin, Ireland [TCD]), Jose J. Groh (TCD), Andrea Mehner (European Southern Observatory, Chile), Nathan Smith (Steward Observatory, University of Arizona, USA [Steward Observatory]), Ioanna Boian (TCD), Eoin Farrell (TCD), Jennifer E. Andrews (Steward Observatory).

ESO is the foremost intergovernmental astronomy organisation in Europe and the world's most productive ground-based astronomical observatory by far.

The archival search also revealed new information. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. ESO's Extremely Large Telescope will have a single 127-foot (39 meters) mirror, compared with the VLT's combined aperture of 107-foot (32 m) mirror across four telescopes.

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