Friday, January 15, 2021

What can two stars like Mu Cephei (above) and 119 Tauri (below) have in common?

You can easily understand this by comparing the two images. Both have an intense red color: Mu Cephei and 119 Tauri are in fact the two reddest stars visible to the naked eye from Earth.
This is due to their nature. Both are in fact two red supergiants with a very low surface temperature: 3800 Kelvin for 119 Tauri, just 3000 Kelvin for Mu Cephei.
Both stars are in the final stages of their evolution. They have in fact finished burning the hydrogen inside their core and have begun to melt the heavier elements such as helium. The life of these two stars will end in a few million years, when they explode into supernovae.
From Earth, the two stars appear as two red dots of fourth magnitude. Mu Cephei is 3,000 light-years away from Earth, 1,200 light-years further away than 119 Tauri.
Since from our planet they appear of the same magnitude we must deduce that Mu Cephei is much brighter than 119 Tauri.
Indeed Mu Cephei is 350,000 times brighter than the Sun, while 119 Tauri has a brightness 66,000 times greater than that of the sun.
The diameter and mass of the two stars are also different. Mu Cephei has a diameter of 1400 times that of the Sun and a mass 19 times that of our star. The diameter of 119 Tauri is instead 600 times greater than that of the Sun, while its mass is 14 times that of the Sun.
Credit: Greg Parker, Noel Carboni, New Forest Observatory.

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