Virtually all the stars in any given cluster form at about the same time, thus star clusters expose cosmic history. Theoretically, the color and luminosity for any given star will change in a very predictable manner that strongly depends on the mass of the star and, to a far weaker degree, on the proportion of its mass made up of elements heavier than helium (the metals).
Picture wood burning on an open fire. When a wooden log is first ignited, it burns brightly and erratically with a yellow-white flame interspersed with blue. As the log settles into its main burning mode, its brightness becomes constant and its flame a steady yellow color. When all the fuel in a log is consumed, the remaining cinder emits an ever-dimming red glow.
Stars are much simpler systems than wooden logs. Unlike logs, they are gaseous through and through and about 98 percent of their matter is hydrogen and helium. Accordingly, the laws of physics predict with high precision exactly what color and what luminosity a star of a particular mass and age will manifest.
A simple plot of the observed colors and luminosities of several hundred to several thousand stars in a given star cluster informs astronomers as to how long ago that particular star cluster formed. Such a plot reveals a “main sequence” along which most stars lie, a line that runs from high luminosity with blue-white colors to low luminosity with orange-red colors. A star arrives on the main sequence after it starts burning hydrogen in its core and remains there throughout its core-hydrogen-fusion phase. A star’s position and length of stay on the main sequence depend critically on mass. The most massive stars (bright, blue-white stars) have main-sequence lifetimes of only a few million years. The least massive stars (dim red stars) may remain on the main sequence for a hundred billion years. When a star exhausts its supply of hydrogen in its core it undergoes rapid evolution or change in both its luminosity and its color, thus manifesting a dramatic turnoff from the main sequence. The turnoff point at which stars in a cluster depart from the main sequence determines the age of the cluster. The dimmer and redder the turnoff point, the older the cluster age.
Throughout the second half of the twentieth century, astronomers’ determinations of the main sequence turnoff point for the oldest star clusters provided the best estimates for the age of the universe. Measurements of the turnoff points for all the different kinds and sizes of star clusters also gave astronomers their best indicators of the history of the universe from the cosmic creation event to the present and, thus, their best tests of the big bang creation model.
Main sequence turnoff analysis of star clusters spectacularly confirmed big bang cosmology, though for a brief period in the mid 1990s such analysis sparked a so-called crisis in cosmology. This “crisis” occurred when ages for the oldest globular clusters (globular clusters are the first star clusters to form after the creation of the universe) based on main sequence turnoff analysis appeared to be slightly older than the age of the universe from measures of the expansion rate of the universe and from analysis of maps of the cosmic microwave background radiation. By the late 1990s and the first few years of the twenty-first century the crisis was resolved thanks to improvements in the distance measures to the relevant globular clusters (they proved to be slightly nearer and hence brighter than previously measured) and in the sensitivity of maps of the cosmic background radiation (which left no doubt that the universe had been continuously expanding for at least 13.5 billion years).
The second release of the WMAP produced a birth date for the universe of unprecedented precision, namely 13.73 ± 0.15 billion years.2 Such an excellent measure of the age of the universe opened a door of opportunity to subject the big bang creation model and the Bible’s story of cosmic creation and cosmic history to a much more rigorous test. If astronomers’ measurements of star cluster ages could come close to matching the accuracy of cosmic age measures from maps of the cosmic microwave background radiation, then a detailed comparison of the respective ages could deliver such a test.
With such a test in mind, a team of thirteen astronomers from Australia, Canada, and the United States embarked on a program to measure globular cluster ages by an entirely different method. This new method is based on the white dwarf cooling sequence. White dwarfs are stars in which all nuclear burning processes have ceased. Bright and white-hot at the time their nuclear furnaces shut down, they cool down in a manner that (relative to their mass and the epoch over which they have been cooling) produces very predictable colors and luminosities. Consequently, measurements of the colors and luminosities for several hundred white dwarfs in any given globular cluster will produce a determination for the age of that cluster.
The team had previously tested their new method on the globular cluster nearest to the Sun, namely Messier 4 (see here and here) situated about 7,200 light-years away.3 They determined Messier 4’s age to be 12.1 ± 0.9 billion years. This determination, however, was performed with the WFPC2 camera on the Hubble Space Telescope. The WFPC2 camera has since been replaced with the vastly superior Advanced Camera for Surveys. Using the new camera, the team repeated their method on the second nearest globular cluster, namely NGC 6397. They found its age to be 11.47 ± 0.47 billion years.4
Incredibly, the astronomers’ first measurement with this new method was twice as accurate as any other age measure for a globular cluster. Their second measurement was four times as accurate. The accuracy they achieved is now comparable to the WMAP’s precision in measuring the universe’s age. If the white-dwarf-cooling-method team were to use the same kind of error estimate analysis as the WMAP team (an error range that would have a 67 percent chance of being correct as compared with a 95 percent chance), their determined age for NGC 6397 would be 11.47 ± 0.23 billion years. Thus, the door is now wide open to put the biblical cosmic creation model to much more rigorous tests.
One such test performed by the white-dwarf-cooling-method team compared their age determination for NGC 6397 with the best one achieved through main sequence turnoff analysis. That main sequence turnoff analysis places NGC 6397’s age at 11.6 ± 1.0 billion years (where the distance used in the main sequence turnoff analysis is restricted to that which allows the main sequence and the white dwarf sequence to fit). In the team’s words, “the two methods are in complete agreement.”5 In other words, their much more precise measurements show no need to make any adjustment to the big bang creation model. To put it another way, the history of the universe according to the big bang model has passed yet another observational test and is more secure than ever before.
These measurements also established, relative to the creation of the universe, the formation date for the Milky Way Galaxy (MWG). Sound theoretical analysis links the formation of MWG’s system of metal-poor globular clusters (of which NGC 6397 is one) with the formation of the MWG. Therefore, the MWG formed about 2.1 billion years after the cosmic creation event. This timing coincides with the cosmic epoch of most aggressive star formation. Whether or not the timing of the MWG’s formation date proves to be a design feature for the possible existence of life (human beings in particular) awaits future research and analysis.
The team concludes their research study by pointing out that until the launch of the James Webb Telescope (the scheduled replacement for the Hubble Space Telescope) their new method will be limited to nearby globular clusters. This is because the coolest white dwarfs are extremely faint. Given current technology, their method will be confined to a reanalysis of Messier 4 and two more globular clusters, NGC 6752 and 47 Tucanae. Even so, with their method applied to four globular clusters, the big bang creation model can be developed in more detail and put to even more rigorous tests. We at Reasons To Believe confidently predict that the big bang creation model that the Bible so eloquently described more than two thousand years before any scientist dreamed of the concept will pass these future tests with flying colors.