The sun isn't the only source of radiant energy (visible light, IR, UV, etc) in a planetary system. Chemoluminescence and indeed heat itself (infrared (IR) emission) are other sources. I would think that living in a thermal environment closed off from the sun, creatures would be likely to evolve bioluminescent emitters/receptors or even fully developed IR Eyes in order to gain survival advantage.

1.) https://voices.nationalgeographic.org/2014/03/14/from-night-...