Asteroseismology and the History of Stars

Asteroseismology and the History of Stars

Stars are like people: They are unstable when young and when old. Stability is something stars manifest only when they reach middle-age.

Recently, a team of 58 astronomers from 14 different countries accurately determined the properties of a star that has transitioned from middle to old age by combining ground-based spectral observations with measurements from the Kepler satellite mission.1 The primary goal of the Kepler Mission is to discover and measure the properties of extrasolar planets in the solar neighborhood. The astronomy team noted, however, that the high sensitivity photometers on board the Kepler satellite (see figure 1) can also be used in combination with high quality spectra to determine the vibrational oscillations of older stars. Such determinations can yield both accurate diameters and precise ages for these stars. Astronomers, in turn, can use these diameters and ages together with detailed theoretical models for stars’ burning history to produce a much more detailed and accurate understanding of the birth, development, and death of stars throughout cosmic history. Such an understanding can lead to a more refined big bang creation model, give more insight into the design of the Milky Way Galaxy and solar system for the benefit of advanced life, and offer yet another refutation of young-universe creationism.

All stars experience vibrational oscillations. For stars similar in age and size to the Sun, these oscillations are minimal and, except for bright relatively nearby stars, very difficult to measure with any precision. However, once a star gets past its middle age these oscillations begin to grow to increasingly larger amplitudes. For the full range of conceivable theoretical models for stars’ burning history, the oscillations’ amplitude, frequency, and spectral response depend very sensitively on the age and the diameter of the star. The astronomy team’s goal was to demonstrate the capability of using Kepler photometry to accurately measure both the diameter and the age of older stars.

The team chose the subgiant star KIC 11026764 for the test case. KIC 11026764 is bright and falls into the same spectral category (G-type) as the Sun. G-type stars rank as the best studied stars, both observationally and theoretically. The team determined KIC 11026764’s diameter to be 2.05 ± 0.03 times that of the Sun and its age to be 5.94 ± 0.05 billion years.2 That is, both measurements were achieved with an unprecedented accuracy of 1 percent.

Such precision means that astronomers can make similar measurements on many more older-type stars and thereby dramatically improve their understanding of stellar evolution (stellar burning history). This improved knowledge, in turn, will provide astronomers with a more detailed big bang creation model and, thus, a more definitive test of biblical cosmology.

In one context the team’s research already yields a definitive test. Even the measurements made on just the one star, KIC 11026764, grants yet one more disproof of a particular creation model, namely young-universe creationism. The team not only calculated possible statistical errors in their measurements of KIC 11026764’s diameter and age, they also determined the maximum range of possible values for the full array of theoretical models for this subgiant star’s history conceivably permitted by the universe’s physical laws. That maximum range lies between 5.05 and 6.83 billion years. A minimum age of 5.05 billion years for KIC 11026764 clearly rules out the claim by young-universe creationists that the universe and Earth are no older than about ten thousand years.     

Figure 1: The Kepler Spacecraft   
The Kepler Mission is a NASA space-born telescope designed to discover planets orbiting about other stars. Kepler uses a photometer to continuously monitor the light output of over 145,000 stars within a fixed field of view.
Image credit: NASA

  1. T. S. Metcalfe et al., “A Precise Asteroseismic Age and Radius for the Evolved Sun-Like Star KIC 11026764,” Astrophysical Journal 723 (November 10, 2010): 1583–98.
  2. Ibid., 1594.