204
13 Cosmological Preliminaries
Fig. 13.1 Hubble’s original data. Black dots represent individual galaxies and the solid line is a
best fit to these. Open circles represent groups of galaxies and the dashed line is a best fit to these.
See Fig. 13.2 for more recent data at larger distances
interest; in particular the distances are not accurate. Figure 13.2 shows more recent
data based on the use of type 1a supernovae (SN 1a) as standard candles rather than
entire galaxies (Kirshner 2004).
The Hubble constant is generally considered to be the present value of a slowly
varying function of time, as we will study in detail. Its presently measured value using
Hubble’s technique is about H 0 = 74 (km/s)/Mpc, with distances in megaparsecs
as used by astronomers, or 1/(14 × 10
9 year) in light years; we will say more about
this value below and in Appendix 1 (Reiss 2019).
If we ponder Hubble’s law for a moment we see that it tells us that all the galaxies
and their stars would have been much closer together at about 14 × 10
9 year ago.
Fig. 13.2 The Hubble diagram for type 1a supernovae out to about 700 Mpc (Kirshner 2004)
13 Cosmological Preliminaries
Fig. 13.1 Hubble’s original data. Black dots represent individual galaxies and the solid line is a
best fit to these. Open circles represent groups of galaxies and the dashed line is a best fit to these.
See Fig. 13.2 for more recent data at larger distances
interest; in particular the distances are not accurate. Figure 13.2 shows more recent
data based on the use of type 1a supernovae (SN 1a) as standard candles rather than
entire galaxies (Kirshner 2004).
The Hubble constant is generally considered to be the present value of a slowly
varying function of time, as we will study in detail. Its presently measured value using
Hubble’s technique is about H 0 = 74 (km/s)/Mpc, with distances in megaparsecs
as used by astronomers, or 1/(14 × 10
9 year) in light years; we will say more about
this value below and in Appendix 1 (Reiss 2019).
If we ponder Hubble’s law for a moment we see that it tells us that all the galaxies
and their stars would have been much closer together at about 14 × 10
9 year ago.
Fig. 13.2 The Hubble diagram for type 1a supernovae out to about 700 Mpc (Kirshner 2004)