text: This man hypothesized that new matter was poured into our universe from spiral galaxies from other dimensions in his book Astronomy and Cosmogony.
full_question: This man hypothesized that new matter was poured into our universe from spiral galaxies from other dimensions in his book Astronomy and Cosmogony. Donald Lynden-Bell derived this astronomer's "strong" theorem, which states that the distribution function of a steady state system with regular orbits can be written exclusively as functions of the action integrals. He names a quantity that is equal to the square root of fifteen, times Boltzmann's constant, times temperature, all over four pi, times big G, times the mass per particle times mass density. That quantity named for him is derived by setting the free-fall time equal to the sound-crossing time and determines when his namesake instability will induce structure formation. For 10 points, name this scientist, who names the critical length under which a molecular cloud will undergo gravitational collapse, thus causing star formation to begin
first_sentence: This man hypothesized that new matter was poured into our universe from spiral galaxies from other dimensions in his book Astronomy and Cosmogony.
raw_answer: Sir James Hopwood Jeans [or Jeans length; or Jeans theorem]