It is possible for planets to get gravitationally ejected from a developing solar system and thenceforth wander alone through the galaxy. Current estimates are that there are a lot of these. Of course we normally think that a planet would need the energy from a sun, a star, to power any possibility of life. But a new study has raised the intriguing possibility that a supermassive black hole or Active Galactic Nuclei (AGN) gives off sufficient ultra-violet light to produce a Goldilocks zone from maybe 100 to 140 light-years from a Sag A* size AGN in where the radiation is not so severe that it would strip any atmosphere from the planet but sufficient UV would be available to power photosynthetic life. Moreover copious UV could break apart molecules to make the building blocks of life more available. The paper estimates that there could be a billion free-floating planets in the Goldilocks zone of our own galaxy.
Two major experiments are reporting (8th Nov 2017) that they have been unable to detect any signals at all from dark matter – XENON1T in Italy and PandaX in China.
These experiments were based on the favoured theory of SuperSymmetry in which dark matter consist of Weakly-Interacting Massive Particles (WIMPs) that would interact, but only rarely with ordinary matter, and carry large mass.
Such detectors will continue to be developed, but alternative theories are now being taken more seriously – axions (a type of massive exotic photon) are one candidate. But it is also possible that the dark matter (whose gravitational effects are not disputed) exists in a ‘sector’ of the universe completely hidden from us, or that the theory of gravity needs modification in the large scale.
Update 19th Nov 2017: Despite the above failure to detect WIMPs, the Astroparticle Physics European Consortium (APPEC), which coordinates funding plans, has proposed scaling up the same experiments – instead of using 3 tonnes of noble gas, they would use 30 tonnes! There has been criticism that following this same line of research “will turn the dark-matter field into a desert of ideas.”
Update 2nd Dec 2017: A Chinese spacecraft (DAMPE) which is designed to measure cosmic ray properties, has confirmed an anomolous disruption in the curve when plotting number of particles against energy of those particles. This cannot be explained within existing physics knowledge, and is possible a pointer to darm matter WIMP annihilation. Futurism article