Readers ask about the size of the Milky Way, ancient rainforests and COVID-19
Milky Way matters Computer simulations and observations of nearby galaxies helped astrophysicists determine that the Milky Way stretches nearly 2 million light-years across, Ken Croswell reported in “Astronomers find Milky Way’s edge” (SN: 4/25/20, p. 8). Reader John Montany thought that the Milky Way must be more massive than previously thought. “I have read other articles that have reported discoveries of previously unknown mass in the universe,” Montany wrote. “Taken collectively, are these discoveries changing theories of dark matter as an explanation for gravitational observations?” No, Croswell says, the new work does not suggest the Milky Way has more mass and doesn’t change estimates for how much dark matter the universe has. “Most astronomers believe that dark matter explains such observations as the high velocities of stars in dwarf galaxies and the high velocities of galaxies in galaxy clusters,” he says. “Without the gravitational force exerted by this dark matter, stars in typical dwarf...