Quasars are the actively feeding supermassive black holes at the hearts of galaxies and can contain millions or even billions of times the mass of the Sun. It's believed they're the source of some of the highest energy cosmic rays detected. But there are also microquasars, where a star and black hole orbit one another. Material from the star accretes around the black hole, and the magnetic fields form jets that can also hurl cosmic rays with similar energies.

When a star like the Sun dies, it puffs away its outer layers, leaving behind its glowing core. Without fusion to keep it heated, the white dwarf slowly cools down over billions of years. Astronomers have discovered that 6% of massive white dwarfs pause their cooling for up to 10 billion years, providing a stable habitable zone for any planets nearby. This gives life a long time to develop under extremely stable conditions.