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Since they were first discovered, galaxies have been a source of wonder. Many are arranged into beautiful spirals. But if they’ve been spinning for billions of years, wouldn’t their arms lose their slender shape?
These spirals should lose their shape in a very old universe. Indeed, the persistence of spiral arms suggests that the universe is very young.Large islands of stars, called “galaxies,” float in the inky blackness of space. The number of observable galaxies is estimated at 170 billion, each with billions or even trillions of individual stars. Such numbers fill an expanse we cannot even begin to fathom. When we behold these shimmering wonders, we naturally ask ourselves, “Where did all these gems come from?”
The first chapter of Genesis proclaims an unequivocal answer: on Day Four the Creator “made the stars also” (Genesis 1:16). The astronomers who reject God’s revealed history, however, are still struggling to find an alternative explanation.
One of their biggest challenges is the lovely spiral arms that grace so many galaxies. Simply put, these spirals should lose their shape in a very old universe. Indeed, the persistence of spiral arms suggests that the universe is very young.
Any robust account of galactic origins has a lot of explaining to do. Galaxies tend to be far apart and don’t appear to have much matter between them. For instance, our own galaxy, the Milky Way, is separated from the next closest galaxy of any notable size—the Andromeda galaxy (M 31)—by about two million light-years of black space.
Yet every galaxy is well-stocked with stars. The Milky Way and M 31, which are pretty ordinary galaxies, are filled with about 200 billion apiece, stretching about 100,000 light-years from end to end. Interestingly, other smaller galaxies often orbit larger galaxies, such as ours and M 31.
Galaxies come in two main types—spiral and elliptical. Elliptical galaxies appear, as the name implies, in elliptical shapes. Spiral galaxies, on the other hand, have a dense concentration of stars at their centers, called the nucleus, and graceful arms spiral outward from the nucleus, giving spiral galaxies a pinwheel appearance. Where did all this order and diversity come from?
The spirals generate the most commotion among astronomers. Beginning in the 1930s astronomers began to debate the structure and origin of spiral arms, a debate that continues today.
Before we look into the technical difficulties, we first must counter a common misconception. Many people believe that stars are plentiful within the spiral arms but nearly absent between them. In reality, the density of stars is about the same between the arms as within.
If so, why then do spiral arms look so bright? The reason is that spiral arms contain very hot, bright, blue stars. The light of these stars tends to dominate much of the visible spectrum, so the spiral arms stand out in photographs.
This was particularly true of the old black-and-white photographs, which were very blue-sensitive. In more recent red and infrared photographs, the spiral arms are much less pronounced because the more numerous red stars tend to dominate the light.
In addition to these very bright blue stars, a lot of dust and gas is present along the spiral arms. Some of this dust and gas is concentrated into “clouds,” called nebulae. Astronomers call the nebulae and blue stars “spiral tracers” because they trace out the locations of the spiral arms.
In the 1930s astronomers realized a problem, though. The outer stars needed more time to complete their orbit than the inner stars. As the distance from the center of a galaxy increases, the spiral arms ought to become unstable. That is, after a few rotations, spiral arms ought to smear out.
Astronomers debated for years whether spiral arms wound up or unwound, depending upon the direction of rotation. No matter which view they adopted, however, if galaxies are at least ten billion years old, as is generally thought, then no spiral arms should be left.
By the late 1960s astronomers thought they had an answer. They devised the spiral density wave theory. According to this concept, the spiral arms act like sound waves in the very thin space between stars (interstellar medium, or ISM). If an outside force compresses the interstellar medium, clouds of gas and dust would arise in the spiral arms. In addition, the compression of the gas would supposedly form stars.
According to this view, some of the new stars should be massive blue stars with very short lifetimes (only a few million years at most, not billions of years). These stars are critical to making this idea work, but because they supposedly don’t last long, there isn’t enough time for the “wave” to move along and leave behind the bright blue stars. So their theory proposed that the gravity of the galaxy stepped in to complete the process of collecting the material into stars.
The details of the spiral density wave theory have proven difficult to work out, but this viewpoint still has its diehard followers. By the 1990s astronomers looked at the small satellite galaxies as a likely mechanism to maintain spiral arms, though that has proven difficult to work, too.
In the last decade, astronomers discovered much evidence for dark matter, which only complicates the picture. Dark matter is very interesting in that it gives off no light, but since its total mass greatly exceeds the total mass of lighted matter, its gravity likely has the single greatest influence on structures within galaxies as well as the entire cosmos.
Evidence seems to show that dark matter is confined to the outer regions of galaxies. Most astronomers currently think that this dark matter may allow galaxies’ spirals to survive. However, the best evidence for dark matter—the higher-than-expected rotation of the outer portions of galaxies—may actually make the winding problem worse, not better.
Creationists long have argued that spiral arms should not exist in a very old universe, and so the persistence of spiral arms suggests that the universe is very young. However, because most evolutionary astronomers begin with an assumption that the universe is billions of years old, they are convinced that some mechanism must continue to uphold spiral arms. If they really had a satisfactory answer, they wouldn’t continually search for a new solution. Their failures show that creationists’ arguments should not be so easily dismissed.
Another wrinkle has developed in recent years. Astronomers have photographed very distant galaxies, about 12 billion light-years away. Assuming, for the sake of argument, a big bang happened 13.7 billion years ago, these galaxies are among the youngest in the universe. Though they differ subtly from nearby (and presumably older-appearing) galaxies, they appear otherwise identical to them. In other words, little evolution has occurred.
Within recent creation, we might expect distant galaxies to appear similar to nearby ones, but not with the evolutionary model. Once again, God’s Word sheds unwavering light on the origin and makeup of His grand universe.
Answers in Genesis is an apologetics ministry, dedicated to helping Christians defend their faith and proclaim the gospel of Jesus Christ effectively. We focus on providing answers to questions about the Bible—particularly the book of Genesis—regarding key issues such as creation, evolution, science, and the age of the earth.