Creation Science Issues

Ages of Stars

First Published October 2014

Not many astronomers are young earth creationists, and this isn’t surprising. The evidence for an old universe is absolutely, totally overwhelming. YECs really have to jump through all sorts of hoops to try to account for this evidence in a 6000 year timeframe. I’ll talk more about this below.

The word “evolution” is used in astronomy to refer to the progress of a system over time, and has no relation to biological evolution. Evolution of stars, then, is the way stars develop from when they first form, right through their lifetime. The general principles were worked out in the 1950’s, mainly by the famous British astronomer, Fred Hoyle. Observational evidence is in impressive agreement with theory, and the theory is based directly on the principles of nuclear physics.

A star first forms when a large cloud of gas contracts under its own gravitation. This gas is mainly hydrogen, with some helium and small amounts of heavier elements. As it contracts, it warms and the central pressure increases. Eventually the central pressure and temperature become high enough for nuclear fusion to begin, in which two hydrogen nuclei combine to form one helium nucleus. Actually there are several different reactions which occur, but the end result in each case is a helium nucleus. The mass of this nucleus is less than the combined mass of the hydrogen nucleii, so the difference is emitted as energy, mainly gamma ray photons.

After this, the new star enters a period of stability, with most of the hydrogen “burning” occurring in the central part of the star. The brightness and the color of the star depends only on its mass. Heavier stars are brighter and hotter, and so are bluer. Lighter stars are dimmer and redder. We can plot stars’ luminosity vs. temperature on the well-known Hertzsbrung-Russell diagram. This one, and all the other graphics in this article, are from Wikipedia:

Young stars fall along the line called “main sequence”. Our Sun is at point 1 on the main sequence.

Once stars burn all the hydrogen in their central core, changes take place which cause the star to move off the main sequence. Our Sun will reach this point in around 5 billion years, having already been on the main sequence for about the same length of time. Very massive stars may reach this point in just a few million years, since they burn their hydrogen at a much faster rate. Very low mass stars may stay on the main sequence for hundreds of billions of years (and so have not had time to move off the main sequence yet, since the universe is only 13.7 billion years old.)

The changes that take place vary according to the mass of the star, but all cause the star to move upwards and somewhat to the right, above the main sequence line on the H-R diagram. What occurs is that when hydrogen burning ceases in the core, there is no longer enough radiation pressure to balance gravity, so the core shrinks and becomes denser. The region of the star in which hydrogen burning occurs moves outwards to become a “shell” around the (mainly helium) core. This region has greater density than the original core, and also greater surface area than the original burning area, so the energy generation increases and the star becomes brighter. In order for the increased radiation to be able to leave the star, its outward regions have to expand. The star is on its way to becoming a “red giant”, up towards the top right area of the H-R diagram.

What happens next can be extremely complex, and varies according to the mass of the star. If you are interested, you can look at the Wikipedia article on Stellar evolution for more detail.

But briefly, if the star is not much more massive than the Sun, the core eventually becomes stable as electron degeneracy pressure can balance gravitation, and once all the hydrogen is gone the star becomes a white dwarf. However if the star is more massive than the Chandrasekhar Limit (about 1.4 solar masses) electron degeneracy pressure is insufficient to balance gravitation, so gravitational contraction continues, and the pressure and temperature of the core become sufficient for helium to start fusing to heavier elements. (Traces of these heavier elements can eventually convect to the outer region of the star, and can be observed in the star’s spectrum.) Eventually when this process produces Iron-56, the core consumes energy rather than generating it. This causes catastrophic collapse of the core to a neutron star or, if massive enough, a black hole. This happens in just seconds. A colossal shock wave is produced which blows off the entire outer region of the star, and we have a Type II Supernova. These explosions throw huge amounts of material off into interstellar space, including the heavier elements which were generated in the final stages of fusion before the explosion. This, incidentally, is the way that heavier elements come to exist in interstellar space.

This general picture of stellar evolution is confirmed when we look at globular clusters. These are huge clusters of stars commonly found in the outer regions of galaxies. They typically contain hundreds of millions of stars, and these presumably all formed around the same time.

This makes globular clusters an excellent observational test for the stellar evolution theory. Here is the H-R plot for one globular cluster, M3:

Globular Cluster M3

You can plainly see the main sequence stars, and also that at a certain brightness there is a “kink”, as most of the more massive stars in the cluster have by now evolved off the main sequence, up and to the right. The few brighter, bluer stars that are still on the main sequence are dubbed “blue stragglers” and are currently accounted for as mainly being members of a binary system where the larger star’s outer regions (mainly hydrogen) have been “gobbled up” by the smaller star, which consequently appears to be much younger than it actually is. (YECs claim blue stragglers represent a problem for an old universe. They don’t. This is yet another case of a phantom problem.)

Now where I am headed with all this, is that the whole study of stellar evolution presents us with a totally convincing case for the age of the universe. The theory is borne out in the observational evidence to an impressive degree. For example, we can observe the presence of heavy elements in the spectra of massive stars, and nuclear and quantum physics tell us how long it has taken for this to happen. The H-R plots for globular clusters tell us exactly how old the cluster is. This evidence is so strong, that if God had just created these objects recently with an appearance of age, he would be deceiving us exactly as he would have done if he had created fossils in rocks as false evidence. There’s no difference. YECs have rightly now rejected the second idea, and should reject the first.

There have been some recent attempts to account for this evidence by admitting long ages in the remote universe, and invoking massive expansion of the universe on Day 4 of Creation Week, Earth time, which would cause colossal time dilation, so that billions of years could elapse in the remote universe, all on Day 4 (Earth time). You can read about these theories here:

A new cosmology: solution to the starlight travel time problem

How do spiral galaxies and supernova remnants fit in with Dr Humphreys’ cosmological model?

In order to avoid the accusation that I’m ignoring these theories, I’ll concentrate nearby, on our own galaxy. The globular clusters that have been closely studied are all in or around our own galaxy. Moreover, our galaxy contains “halo stars”. These, like globular clusters, have orbits which are not in the plane of the galactic disk. They are all of comparative low mass, and spectroscopic study reveals that they have a very low percentage of elements other than hydrogen. This is consistent with them being very old, so that they formed soon after the big bang, before there had been many supernovae to throw heavier elements out into interstellar space. Presumably they became associated with our newly-forming galaxy very early, before the disk developed, and this would account for their orbits. The same would apply to globular clusters.

Now the YEC argument about massive time dilation would not work here. This theory is invoked to account for the “distant starlight” problem (see Distant Starlight). However within our own galaxy, the longest time that light needs to travel to us is a hundred thousand years, not billions. Yet these halo stars and globular clusters are billions of years old! Well, maybe the time dilation occurred closer in, near our own solar system? But that wouldn’t work either, because the gigantic expansion that would be needed to cause the time dilation would have totally disrupted our galaxy, so we wouldn’t have a galaxy at all!

Now, consider our Sun and the nearby multiple system, Alpha Centauri (4 light years distant). The two major stars in this system are Alpha Centari A with about 110% of the Sun’s mass, and Alpha Centauri B with about 90%. These stars are both on the main sequence, are very similar to our Sun, and neatly bracket it in mass. Are we supposed to believe that these formed in the regular way over billions of years, while our Sun was simply created by God in its present form, with an appearance of age, 6000 years ago? How deceptive would that be? These stars are so similar in every way. And if they were just created, fully formed, on Day 4, what about all the very similar stars much farther out in our galaxy? Where should we draw the line between fully-formed creation and “regular” formation of stars, with time dilation? Isn’t this all starting to sound a bit ridiculous?

There is another issue. I’ve shown that there is overwhelming evidence that stars form over very long periods of time, and evolve according to well-understood physical processes. Our Sun, too, has every appearance of a mid-sized main sequence star, around 5 billion years old. Moreover it’s now in a stable mid-life state. Gamma-ray photons are generated by hydrogen fusion in the core, and work their way outward by travelling a few millimetres in a random direction, getting re-absorbed by the solar plasma, then getting re-emitted. It takes some tens of thousands of years for a photon to reach the outer layers by this process, and when they get there heat transfer is by convection rather than radiation. YECs don’t dispute this. Yet they claim that this length of time for energy to reach the surface of the Sun isn’t a problem, since God created the Sun already in a thermal balance, and photons travelling outward aren’t actually carrying information. So, they claim, this isn’t the same as the distant starlight problem. Here, earlier YEC thinking had God creating light in transit, carrying information about stellar events which hadn’t really happened. The YECs rightly dropped this idea. But they say the situation with the Sun is different, since the photons aren’t carrying information. In response we might easily claim that the solar photons are actually carrying information, namely that they were generated by fusion in the core. After all, they have exactly the right amount of energy for a main sequence star of the Sun’s mass. You decide which makes more sense.

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