Saturday, June 12, 2021

Talking about Trappist 1

Over the past three years you have surely heard of Trappist 1, the star that became famous when, in February 2017, the discovery of seven Earth-sized planets in orbit around it was announced.

As you can see from this simple illustration, Trappist 1 is a very different star from our Sun.

Trappist 1 is in fact an ultra-cool red dwarf that has a surface temperature of just 2500 K (for comparison, the solar temperature is 5700 K). Trappist 1's diameter is also just 11% of that of the Sun, making it slightly larger than Jupiter.

The mass of the red dwarf, however, is 85 times higher than that of the gas giant, therefore equal to just 8% of the mass of the Sun.

Trappist 1 therefore has just enough mass to be a star: in fact, if it had been lighter, the temperature of its core would never have reached the temperature necessary for hydrogen burning and consequently it would have been cataloged as a brown dwarf.

As we can now imagine, the brightness of Trappist 1 must be much lower than that of our star. It has been estimated that the red dwarf emits just 0.05% of the radiation emitted by the Sun, mainly concentrated in the infrared region of the electromagnetic spectrum.

Trappist 1, like most red dwarfs, is also characterized by very violent variable phenomena, such as flares (i.e. eruptions of matter from the photosphere) that may perhaps be able to wipe out the atmosphere of the planets orbiting around it.

Credit: ESO.

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