Wednesday, January 19, 2022

Focusing the Belt of Orion

I bet that at least once in your life you have raised your eyes to the sky attracted by that group of particularly bright stars that form the constellation of Orion. Among these stand out the three that make up the Belt of Orion, one of the most famous asterisms of the sky.

In particular, Mintaka, shown in the x-ray box, is a star that deserves attention: it is in fact a multiple system, consisting of five components.

Through a powerful telescope, three of the stars that make up the system can be identified. The most brilliant of these three is a triple system, which brings the total number of components to five.

Let’s focus on this last star system: by pure coincidence from Earth we see the secondary star transiting periodically in front of the primary star, causing a regular variation of brightness. Star systems in this configuration are called eclipse binaries and allow to derive with excellent precision both the mass of the two components and their orbital period. Astronomers have thus derived that the main component of the Mintaka system is a blue supergiant 25 times more massive than the Sun, while the secondary has a mass ten times that of the Sun and orbits the primary every 5.7 days. To these must then be added a third smaller star that orbits the other two every 350 years.

Credit: X-ray: NASA/CXC/GSFC/M.Corcoran et al.; Optical: Eckhard Slawik.

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