How Many Baryons Has Your Galaxy Lost?

Losing stuff seems to be part of life. For me, it’s the phone numbers I write down. Even though I write down important phone numbers in at least two different places, I still can’t find them when I need them.

Losing stuff is also part of the lives of all stars and galaxies. The difference is that such losses are good things. In fact, the timings and the rates of the losses must be fine-tuned for advanced life to ever be possible in the universe, thus providing additional evidence for the anthropic principle. (This principle states that the universe and its constituent bodies were designed in advance for the benefit of the human species.)

In a recent issue of the Astrophysical Journal, a team of four American astronomers, headed up by Xinyu Dai, established a strong inverse correlation between the depth of a galaxy or galaxy cluster’s gravitational potential well and the extent of baryon loss in the respective galaxy or cluster.1 The gravitational potential well depth refers to the strength of the gravitational attraction exerted by a galaxy cluster or a galaxy and is proportional to the mass density of the cluster or galaxy. Baryons are particles made up of three quarks and include protons, neutrons, antiprotons, and antineutrons.

The goal of Dai’s team was to explore the missing baryon, or baryon loss, problem in the nearby regions of the universe. They established the nature of the problem by comparing the primordial universe’s measured baryons density (from before star and galaxy formation) with current measured baryon densities for a number of relatively nearby galaxies and galaxy clusters. Maps of the cosmic microwave background radiation yield the primordial baryon density while the dynamics of satellite galaxies and results from gravitational lensing measurements determine the current baryon density of galaxies and galaxy clusters.

Figure 1: Galaxy Cluster Abell 370
Giant, dense clusters of galaxies like Abell 370 lose very little of their primordial abundance of protons and neutrons. Consequently, star formation tends to be both aggressive and early in the galaxies residing in such clusters.
Image credit: NASA/ESA/Hubble SM4 ERO Team/ST-ECF

Dai’s team found that the most massive of galaxy clusters (see figure 1) suffered virtually no loss of baryons over the 14-billion-year history of the universe. However, the researchers observed that the smaller the galaxy cluster mass, the greater the percentage of its baryons lost to intergalactic cluster space. They found the same kind of correlation for individual galaxies. The less massive the galaxy, the more of its original baryons supply it lost to intergalactic space. In verifying the tight inverse correlation between total mass and baryon loss, Dai’s team noted that galaxy clusters and individual galaxies of the same mass exhibit the same degree of baryon loss.

Though not commented on by Dai’s team, a specified degree of baryon loss is crucial for determining whether or not a galaxy and the cluster in which it resides is a candidate for supporting life. The specification is all the more demanding in the case of advanced life.

A low rate of baryon loss negates a galaxy’s chance of supporting advanced life. A low rate implies that galaxies will be jammed together too tightly for a galaxy’s structure to remain sufficiently undisturbed over cosmic history and that galaxies will be too large for advanced life. It also implies that much of a galaxy’s star formation will take place far too early in cosmic history (the first few billion years). For example, advanced life demands a spiral galaxy structure with star formation occurring steadily over the past 14 billion years.

Conversely, a high baryon loss rate implies galaxies spread too far apart from one another, too small in size, and a too delayed star formation history. For advanced life to be possible, the baryon loss rate for the host galaxy and the host cluster must be fine-tuned, that is, held at just-right values. Consequently, the baryon loss rate adds yet one more characteristic to the already very long list2 of cosmic and galactic features that must be fine-tuned for advanced life to be possible—strongly implying the work of an all-knowing, purposeful, all-powerful, and all-loving Creator.

1. Xinyu Dai et al., “On the Baryon Fractions in Clusters and Groups of Galaxies,” Astrophysical Journal 719 (August 10, 2010): 119–25.

2. Hugh Ross, Why the Universe Is the Way It Is (Grand Rapids: Baker, 2008), 119–24, 213–14; Hugh Ross, More Than a Theory (Grand Rapids: Baker, 2009): 243–44, 259–60.


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