Life around Cepheid Variable stars
Are there any unique challenges life would face evolving on a planet orbiting a Cepheid Variable star? I'm aware this is a broad question, so to narrow it down, consider this a question about Great Filters, in the sense of the Fermi Paradox. What sorts of challenges unique to a Cepheid Variable star could prevent life from evolving to human-level intellect?
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Stars that become Cepheid variables stay in this phase of their lives for only a short period of time, and after they leave the main sequence. While their properties vary (in particular, Cepheids are divided into two groups, Type I (Classical) Cepheids and Type II Cepheids) there are a few characteristics they have in common:
- Masses of anywhere from 3 to 20 solar masses
- Ages of a few tens of millions to a few hundred million years
- Luminosities on the order of $\sim10000L_{\odot}$
- Pulsation periods of a few days
- Luminosity changes of 0.5 to 2 magnitudes
Most of these are problematic for various of reasons. The key one is that there's not enough time for life to evolve around a Cepheid, in all probability. Furthermore, given how hot these stars are, most of their light will be at ultraviolet wavelengths, rather than optical wavelengths. This means that photosynthesis would require pigments unlike the chlorophylls we see on Earth; I'm actually not sure whether pigments optimized for these wavelengths even exist.
I'd argue that the swings in luminosity wouldn't be a problem for life, at least, for the same reason that eccentric orbits aren't problematic for life: only the mean flux a planet receives matters. If you could solve the timescale and spectral problems, the pulsations likely wouldn't be too problematic.
I should note that these issues may arise for other types of (lone) variable stars, too. Take the cases of (for instance) Beta Cepheid variables and rapidly oscillating Ap stars, which have masses similar to Cepheids. They're hotter than solar-type stars and more massive, and so they evolve quicker and emit substantially more UV light than visible light - not great for most kinds of life. On the other hand, cool, low-mass stars like Mira variables are likely to be more conducive to habitability, even if - as is true for most variable stars - their time as variable stars is brief.
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