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Across 1. A swelling giant star. 4. Objects attracted to a protostar but too small to become a star. 7. Cataclysmic explosion of a swelling star. 8. The joining of two atomic nuclei. 9. Describes the situation of a star during the main period of its life. 10. Name of a star 'to be'. 11. The process through which nuclei split. 13. Particle that absorbs the neutron in nuclear fission. 16. Plural of nucleus. 18. e.g., Sun 19. Released when fission occurs. 20. Process by which energy is released in stars. 21. A rather smeggy programme. 22. Absorb surplus neutrons.

Down 2. Force that pulls together dust and gas to form stars. 3. Type of reaction that nuclear fission is classified as. 5. What remains after a supernova occurs. 6. The water acts as this as it slows down the fission neutrons. 12. The majority of nuclear reactors use this element in 235 form. 14. Fusion occurs when a star is in this phase. 15. Occurs when a star fades out and becomes cold. 17. The star becomes this when it collapses under its own gravity.