Fig12_11 Hubble diagram

Fig12_11 Hubble diagram

Fig. 12.11 . This plot of galaxy distance versus recession velocity is analogous to that obtained by Edwin Hubble (1889-1953), in his 1929 discovery of the expansion of the Universe (Fig. 12.10). The slope of the linear fit (solid line) to the data (dots) measures the expansion rate of the universe, a quantity called the Hubble constant, designated H0. The data shown here summarize eleven years of efforts to measure this constant by using the Hubble Space Telescope to determine the distances and velocities of Cepheid variable stars in nearby galaxies. The distance is in units of a million parsecs, or Mpc, where 1 Mpc is equivalent to 3.26 million light-years, and the radial velocity is given in units of kilometers per second, denoted as km s-1. The fit to these data indicate that H0 = 75 10 km s-1 Mpc-1, and that this constant lies well within the limits of 50 and 100 in the same units (dashed lines). [Adapted from Wendy L. Freedman et al., Final results from the Hubble Space Telescope Key Project to Measure the Hubble Constant, Astrophysical Journal 553, 47-72 (2001).]

Copyright 2010, Professor Kenneth R. Lang, Tufts University