Around 1,350 light years away from Earth is a star called TOI-2155. It’s a little bigger, heavier and hotter than the Sun, and it’s not particularly interesting or unusual in itself.

But orbiting around TOI-2155 is something very interesting indeed: a much smaller object called TOI-2155b, which we only know about by observing the tiny changes in light from the host star when the smaller object passes in front of it.

What is TOI-2155b? A mini-star? A giant planet? Or something in between? I’m glad you asked.

As my collaborators and I write in a recent paper in The Astronomical Journal, we’re not yet sure whether TOI-2155b is quite a star. But it seems to live on the fascinating boundary between a celestial beacon blazing through the heavens and a failed star that never quite ignites sustained hydrogen fusion.

Stars start out as huge blobs of gas in space – but........

© The Conversation