The Intriguing Mystery of Dark Matter

Dark matter is something that has many scientists baffled and many more curious. Its existence is widely accepted, for good reason. If it doesn’t exist, observational astronomy displays violations of basic physical laws. Before we can dismiss dark matter to the realm of theoretical science that has nothing to do with us, it should be pointed out that it could have an enormous impact on the earth, solar system, and life, in ways that we can’t begin to guess about.

Dark Matter Theory Beginnings

The theory of dark matter is around 100 years old. It is based on direct observational data and the laws of physics. To understand the idea, we need to look no farther than our own Milky Way galaxy.

Our galaxy is a collection of hundreds of billions of stars, held together primarily by gravitational forces. Looking at the Milky Way from the edge and far enough away that all of it could be seen, it looks rather like a phonograph record or CD viewed edge on, except that near the middle, the galaxy is much thicker. This simply means that there are more stars there, closer together. There are fewer stars near the edge of the galaxy. Our own solar system is closer to the edge of the galaxy than it is to the middle.

Galactic revolution

As is common in the universe, spiral galaxies like the Milky Way spin around the center. Planets and stars also spin, and even black holes spin, so this is not a surprise. This is also in keeping with the visual image of a phonograph record spinning on a turntable.

There is a distinct difference, however. A record is solid. Although the stars in the Milky Way are linked gravitationally, the galaxy is decidedly not solid. This becomes important later.

At the distance of our solar system from the center of the galaxy, the galaxy is spinning at about 250 to 300 kilometers per second or just under 9.5 million km per year and it takes over 200 million years for it to revolve one time. It is very important to note, though, that the nearer to the center of the galaxy an observer is, the faster the spin or rotation is. This can be easily seen with the phonograph record. Near the center of the platter, the record spins substantially faster than at the edge.

Remember that the galaxy isn’t solid. If the rotation is greater than the gravitational pull that holds the galaxy together, the stars at the edges of the galaxy will be flung out into the void between galaxies. If the rotation isn’t fast enough, the galaxy will collapse in on itself. As it happens, the Milky Way appears to be quite stable, which means that the gravitational pull balances the spin so that it is neither collapsing nor expanding.

Herein lies the issue. Since astronomers can measure the spin at the observable edge of the galaxy, and at the center, they can calculate the mass that is necessary to balance the rotation. A remarkable thing happens when all the math is done. Using visual telescopes, radio telescopes, and telescopes operating in gamma, x-ray, infrared, and ultra-violet, the observable matter within our galaxy isn’t nearly enough to balance the spin.

Even accounting for the mass of the black holes at the center of the galaxy and extrapolating such things as dust clouds, gas clouds, burned out stars, and very cool stars that are difficult to detect, at the velocity it is rotating, it should be shredding itself, flinging stars out of the galaxy continually. This isn’t happening.

Further corroboration

Applying the same basic principles of physics, mathematics, and observing other galaxies, we can see that the same thing is occurring outside the Milky Way. It appears to be the rule, rather than the exception. Although it is still a theory since we’ve never been able to actually see it, this is the point of dark matter. Whatever dark matter is, its something we can’t see with our telescopes, but which provides the additional mass necessary to balance the rotational spin of the Milky Way. Nothing else comes close to explaining what is observed.

How much of the unseen mass would be necessary to keep the galaxy intact? That is the staggering part. Everything we can see or detect; gas, dust, stars, planets, asteroids, moons, and so forth, only accounts for about 10% or less of the mass needed in order to keep the galaxy from flying apart. That means that 90% or more of the mass has to come from dark matter and/or dark energy. (Dark energy needs to be discussed separately.)

This means that nine-tenths of our galaxy is unseen and undetectable by our current level of technology. We don’t know what the dark matter is or what properties it has, which also means that it could be directly impacting the earth, life on earth, the climate, and so on, without us even being aware of it. This is anything but absurd reasoning. We can’t see air, but we know it exists and has an enormous impact on earth. 

None of this is speculation, either. The fact that we can’t detect dark matter makes little difference, for that matter. Astronomers are fairly certain that black holes exist, yet we can’t see them or directly measure them. Indirectly, we can make measurements. In a similar way, we can’t see dark matter or directly measure it. If we could, we’d have a better idea about its properties. However, we can indirectly make measurements. That is exactly what measurements of the missing galactic mass are; indirect measurements.

What we do know with fair certainty, especially based on how much dark matter would be needed to balance against the rotational spin, is black matter either exists or the laws of physics are totally wrong. That is always a possibility. However, it isn’t likely.