Massive Variable Star Mysteriously Disappears from Distant Dwarf Galaxy | Astronomy

James Marshall
July 1, 2020

The outburst may have resulted in the luminous blue variable being transformed into a less luminous star, which could also be partly hidden by dust.

Normally, when a star much larger than our sun reaches the end of its life, it erupts in an enormous 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. The European Southern Observatory's (ESO's) Very Large Telescope, however, couldn't find the star during two separate observing sessions in 2019 with different spectrograph devices.

After that outburst, the star may have dimmed so much that it would have been hard to see. The bloated orb was a superb example of a luminous blue variable (LBV) - a massive star approaching the end of its life and prone to unpredictable variations in brightness. That's still a mystery, but Allan's team has some ideas. The new telescope is scheduled to see first light in 2025. This is usually a long process, however as Ireland recently agreed to join ESO, we were able to apply for a fast-track observation reserved for important unusual events. "This time we used the X-Shooter instrument of the Very Large Telescope and were happy to find that this also pointed towards the star disappearing!"

However truly massive stars - such as the one at the center of the new study - shine so brightly that they leave evidence of their presence in the form of a light signature, that tells astronomers that they're there.

"This indicated the extreme nature of the massive star and was achieved by developing computer simulations", Allan said.

At the close of the outburst event, the luminous blue variable star could have transitioned into a less luminous stellar body that was cloaked in a thick view of dust comprising previously cast off matter.

The second, more exciting, explanation is that the star could have simply collapsed into a black hole. Given the star's estimated mass before its disappearance, it could have created a black hole measuring 85 to 120 times the mass of Earth's sun, though how this could have happened without a visible supernova is still an open question. What's left of the star either turns into a neutron star or a black hole. ESO is also a major partner in two facilities on Chajnantor, APEX and ALMA, the largest astronomical project in existence. Allan and his collaborators in Ireland, Chile and the USA wanted to find out more about how very massive stars end their lives, and the object in the Kinman Dwarf seemed like the flawless target.

What's more, the Kinman Dwarf showed no signs of a supernova, or star explosion, during the intervening years - leading the team to speculate the star may have collapsed directly into a black hole, instead of going supernova first.

Astronomers can, however, detect the signatures coming from the galaxy.

The Kinman dwarf galaxy is far enough away that it's hard to see what exactly is going on there. In the meantime, Allen and colleagues plan on performing additional observations with the Hubble Space Telescope.

This image of the dwarf galaxy PHL 293B was taken with the Wide Field Camera 3 (WFC3) onboard the NASA/ESA Hubble Space Telescope in 2011, before the disappearance of the massive star.

Other reports by Click Lancashire

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