According to the proverb, all good things must come to an end. Vacations give way to work; scrumptious candy bars come down to a last bite; even sci-fi shows (like Star Trek) have a final episode. Perhaps surprisingly, the adage even applies to the universe—or at least its capacity to form stars.
The universe began with no stars. Roughly 300 million years after the big bang, stars started forming (and continue to do so today). However, the birthrate of new stars varied significantly over the age of the universe. Recent studies of hydrogen—the fuel for star formation—reveal just how dramatically the birthrate has declined.
In order to affirm such a decline, astronomers need some measurable quantity of physical evidence that traces the rate of star formation in distant galaxies. The quantity of choice is the amount of Hα (or hydrogen-alpha) emission because massive stars (those more than 20 times the mass of the Sun) emit large amounts of Hα radiation and it is easy to detect with optical telescopes. An international team of astronomers used multiple telescopes to assemble a uniform sample of Hα radiation from galaxies with redshifts (distances) of 0.40, 0.84, 1.47, and 2.23.1 These redshifts correspond to look-back times of 4.2, 7.0, 9.2, and 10.6 Gya (billion years ago).
Comparing the amount of Hα from the different samples, they determined that the star formation rate started from a much higher value 11 Gya and has declined consistently since. In fact, half of the stars in the observable universe formed during a two-billion year period ending just over 8 Gya and the other half forming since then. Assuming the decline continues, the number of stars in the observable universe will grow by no more than 5 percent (above current values). The observable universe contains a trillion, trillion stars (or 1024). Thus, another 50 billion trillion (5×1022) stars will form—a large, but 95-percent-smaller number of stars.
The apologetic significance of this study lies not in the number of stars (5 percent) yet to form but in the fact that most of the finite budget of stars exists already. Our existence demonstrates the capacity of the universe to support life, and the Sun, one of the necessary trillion, trillion stars, plays a critical role in that habitability. The Sun provides the vast majority of the energy life uses to survive, reproduce, and shape Earth. Eventually, the Sun will exhaust its fuel and die—although this event will occur long after life ceases on Earth.
Thus, the “good thing” of star formation will come to an end. If the universe is all that exists, the end of star formation would be depressing. However, the Bible describes a new creation that awaits all those who follow Christ. In that new creation no good thing will come to an end.
- David Sobral et al., “A Large Hα Survey at z=2.23, 1.47, 0.84, & 0.40: The 11 Gyr Evolution of Star-Forming Galaxies from HiZELS,” Monthly Notices of the Royal Astronomical Society, accepted for publication.