European astronomers have detected an unprecedented binary system featuring two hot blue O-type stars in orbits so tight they're actually touching each other — and they're not entirely sure what will happen when the stars complete their massive merger.


Located in the Giraffe Constellation, MY Camelopardalis (MY Cam for short), is one of the most massive binary star systems ever discovered. Individually, the two hot blue O-type stars contain 32 and 38 times the mass of our sun.

MY Cam is an eclipsing binary system in which one star passes in front of the other each time an orbit is completed. It has the shortest orbital period ever detected in a binary pair — a mere 1.2 days. The resulting changes in the brightness of the system is what enabled astronomers from the University of Alicante to confirm that it was in fact a binary system and not one massive star.


An illustration of MY Cam to scale at the quadrature phase. (J. Lorenzo et al./University of Alicante)

But given their immense size, they have to be in extremely close orbits to make a full turn so quickly. This means the stars are actually touching each other and that the material on their outer layers are forming a common envelope. Physicists call it a 'contact binary.' Both components are churning away on the main sequence, and are probably not far from the initial zero-age main sequence.

Indeed, the astronomers say that MY Cam is a young system that formed about two million years ago. Its current configuration may very well be the one it was born into, but it wasn't meant to last. According to the researchers, the system will eventually merge and create one massive single object. But some theoretical models are predicting an extremely fast merger process culminating in a massive release of energy in the form of an explosion.

That said, many astrophysicists believe that the merger of close binaries are the most efficient way to generate extremely massive stars. If true, MY Cam is the first example of such a system.


Read the entire study at Astronomy & Astrophysics: "MY Camelopardalis, a very massive merger progenitor".

Image: J. Lorenzo et al./University of Alicante