Astrophysics

3. The level at which something begins, or a doorway you step across into no return.
5. Describes a process you simply cannot stop, slow, or talk out of it; gravity behaves exactly this way.
6. What happens to a massive star's core when nothing is left to push back against gravity.
9. A boundary marking the limit of what you can see, including a famous point of no return in space.
10. Giving off light, literally; figuratively, the word for a mind or a smile that seems to glow from the inside.
11. Temporary support put up around something still being built, a favorite word in teaching for help that's slowly withdrawn.
13. The small surviving piece of something much larger that is otherwise gone.
14. Frustratingly hard to catch or pin down, whether it's a particle, a memory, or the right word at the wrong moment.
15. The band of colors hidden inside a beam of light, and a handy word for any range between two extremes.
16. An invisible surrounding shell of unseen mass around a galaxy, or a ring of light around a head in a painting.
17. A surviving trace left over from an ancient time, sometimes treasured, sometimes just outdated.
18. A statement or situation that seems to contradict itself yet may be perfectly true.

1. Spread thinly and widely rather than concentrated; also, to soften or calm a tense situation.
2. Having an enormous, eager appetite, whether for food or, more impressively, for books and ideas.
4. Based on real observation and evidence rather than theory or opinion alone.
6. A conclusion reached on incomplete evidence, in other words a well-dressed guess.
7. A vessel of fierce heat where new things are forged, and the perfect word for a trial that transforms someone.
8. The point at the heart of certain collapsed objects where the familiar rules of physics stop making sense.
12. The joining of light atomic nuclei into heavier ones, the very reaction that powers the stars.
14. Lasting only a short while, here today and gone by morning, like a white dwarf's fading glow or online fame.