Astronomy: Stars become more hostile to life as the Universe ages

Due to the changing composition of newly forming stars, the universe becomes less favorable for the emergence of life as it ages. This is the result of an investigation into the connection between the so-called metallicity of stars and the ability of their planets to build up a protective ozone layer. Stars made of less heavy elements – in astronomy “metals” – emit more life-threatening UV radiation, but this is composed in such a way that dense ozone layers can form. The more heavy elements there are in the stars, the thinner the protective ozone layers.

As the research team from the Max Planck Institutes for Solar System Research and Chemistry and the University of Göttingen now explains, they wanted to find out what connection there is between the composition of stars and the formation of protective ozone layers around their planets. On earth, this combination of three oxygen atoms protects all life from cell-damaging UV radiation. Such a shell in the atmosphere is therefore considered an important prerequisite for the emergence of complex life.

Visualization of the finding

(Image: MPS/

At the same time, the team explains that ultraviolet radiation in combination with oxygen can both destroy ozone (long-wave UV-B radiation) and create it (short-wave UV-C radiation). According to the study presented here, it is precisely the ratio of these two variants to one another that depends on the metallicity of the stars, i.e. the content of heavy elements. In the case of stars with relatively few heavy elements (“metal-poor”), UV-C radiation predominates, which is why they are likely to create a dense ozone layer on planets. In the case of metal-rich stars, this protective shell is “significantly poorer”.

The main aim of the research group was to determine which stars would be particularly worthwhile in the search for extraterrestrial life. She did that, but at the same time made a far-reaching discovery. Because the heavy elements (in astronomy, all elements except hydrogen and helium are “metals”) are formed inside dying stars, and each generation therefore exhibits higher metallicity, the universe becomes more hostile to life. At the moment, however, the search is not hopeless, after all we know of a star that “accommodates complex and interesting life forms on at least one of its planets”. The entire work has been published in the journal Nature Communications.


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