What is Sheliak?


Sheliak is the third brightest star in the constellation Lyra. It is about 900 light years from us, which means that its light takes 900 years to reach Earth (if we were on Sheliak we could look at the Earth as it was in the Middle Ages!).

Since its discovery, Sheliak was always thought to be a solitary star, until in 1784 the English astronomer John Goodricke observed that its light increased and decreased periodically, about every 13 days. At the time, this characteristic had been noted in very few other stars, and Goodricke was the first to make a very counterintuitive hypothesis: according to him, the variation in light (which is why it is called a variable star) occurred because there were two stars orbiting around each other; the light increased and decreased because the two stars were positioned so that they rotated past each other, generating an eclipse each time. It was with this discovery that Goodricke defined the class of eclipsing variable stars.

Sheliak is the prototype on which the class of Beta Lyrae variables was founded, i.e. stars, large and even tens of times heavier than the sun, that orbit so close to each other that they can no longer be spherical; the enormous gravitational force that attracts them to each other distorts their very shape, eventually making them elliptical.

The two stars of the Sheliak system have been so close to each other since their birth billions of years ago, then the more massive of the two expanded into a giant and began to lose some of its own matter to space. From that moment, the companion star, dangerously close, began inexorably sucking up the gases expelled by the giant, and in ‘a few’ million years it has already become the most massive in the system. A veritable theft of matter!

Curiosity: in 2006, a third star was observed that is thought to be gravitationally bound to the two, in which case Sheliak would be a triple star system.

It is easy to observe the constellation Lyra, especially in the summer, because one of its constituent stars is Vega, one of the brightest in our sky.

It was on a summer evening that, at the end of a day of rehearsals, the three of us took a walk along the Lungarno in Florence. We were desperately searching for a name for our trio, but months had passed without coming up with a convincing idea.

At that moment, sitting on a bench discussing a few possibilities, it occurred to us to look at the clear night sky above our heads. Emanuele immediately opened an app on his phone and pointed it at the sky, where we could see the brightest star, to find out what was above us at that moment. That’s how we discovered Sheliak, a name that was given to the star by the Arabs and which means “harp”, an instrument whose strings are reminiscent of both the piano and the strings. Moreover, the Lyra is itself the constellation that represents music, harking back to timeless myths including that of Orpheus. Having come across that very star at that very moment was a coincidence that affected us greatly, and so we decided that Sheliak would be our name.