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Across
  1. 6. limit: The upper boundary to the mass of a white dwarf.
  2. 8. dwarf: An object, midway in size between a planet and a star, with a mass about 1/100 that of the sun.
  3. 9. Diagram (HR diagram): A plot of luminosity against surface temperature or spectral type for a group of stars.
  4. 11. dwarf: A low-mass star that has exhausted most or all of its nuclear fuel and has collapsed to a very small size.
  5. 12. magnitude: A measure of the luminosity of an object like a star.
  6. 16. bulge: The central part of a galaxy.
  7. 19. star: A star of extremely high density composed almost entirely of neutrally charged subatomic particles.
  8. 21. hole: A collapsed, massive body whose escape velocity is equal to or greater than the speed of light.
  9. 22. sequence: Middle-age stars that can be found running diagonally through the middle of an HR diagram.
  10. 23. radius: The distance from the center of a black hole to its event horizon.
  11. 25. galaxy: A large assemblage of stars without radial symmetry.
  12. 26. Variables: Stars that pulsate radially, varying in both temperature and diameter, to produce brightness changes with a well-defined stable period and amplitude.
  13. 30. A cloud of interstellar gas or dust.
  14. 31. A large assemblage of stars, gas, dust, and dark matter orbiting a common center.
  15. 32. galaxy: A flattened, rotating, large assemblage of stars with pinwheel-like arms of interstellar material and stars winding out from its nucleus.
  16. 34. The outermost extent of a galaxy with a sparse distribution of stars.
Down
  1. 1. A star of very high luminosity and relatively low temperature.
  2. 2. Object: One of the 107 galaxies, nebulas, star clusters, and other deep sky objects classified with an M followed by a number.
  3. 3. An explosion that marks the final stage of stellar evolution.
  4. 4. brightness: A measure of the observed light received from a star or other object.
  5. 5. A star of large luminosity and radius.
  6. 7. A variable radio source of small angular size that emits very rapid radio pulses in very regular periods.
  7. 10. horizon: The surface at which the escape velocity of a collapsing star is equal to the speed of light.
  8. 13. classes: The classification of stars according to their temperatures using the characteristics of their spectra.
  9. 14. galaxy: An assemblage of stars, oval in shape, that contains no conspicuous interstellar material.
  10. 15. disk: The main portion of a galaxy. Consists of a nucleus, bulge, and spiral arms.
  11. 16. A star that experiences a sudden outburst of radiant energy, temporarily exponentially increasing its luminosity.
  12. 17. An object of very high redshift that looks like a star but is extragalactic and highly luminous.
  13. 18. molecular clouds: Large, cold, interstellar clouds with large diameters where massive stars form.
  14. 20. Velocity: The rate at which an object must travel in order to break free of the influence of gravity.
  15. 24. cluster: A spherical collection of stars that orbits a galactic core as a satellite.
  16. 27. system: Two stars that revolve around each other.
  17. 28. sequence: A morphological classification scheme for galaxies. Often described as a tuning fork, after the shape of the diagram created from it.
  18. 29. A theoretical point of zero volume and infinite density to which any black hole must collapse.
  19. 33. The apparent displacement of a nearby star caused by the revolution of the Earth around the sun.