With Dark Matter, Things Are Not What They Appear to Be
By Dr. Gary Deel, Ph.D., J.D.
Faculty Director, School of Business, American Military University
Today, we have four great observatories in space: the Hubble Space Telescope, the Spitzer Space Telescope, the Chandra X-Ray Observatory, and the Compton Gamma-Ray Telescope.
Why do we put telescopes in space? The answer is simple. Our atmosphere distorts incoming light in ways that make resolving fine image details very difficult. This distortion is actually what causes stars to “twinkle” in the night sky from the perspective of observers on the ground. By putting telescopes in space, we circumvent the obstacles caused by our atmosphere in the pursuit of high-quality cosmic images.
Because there is no atmosphere in space, telescopes in orbit are not affected by atmospheric distortion. But there are other factors in space that distort images.
Get started on your Space Studies Degree at American Military University.
In the early 20th century, Albert Einstein showed that the gravity of an object is actually just the amount by which the object curves the fabric of space-time toward its center of mass. Imagine grabbing the center of a spider web and making a fist so that it pulls all the outer edges of the web into the center. This is the effect that gravity has on the fabric of space-time, but in three dimensions.
High Mass Objects in Space Can Cause a Phenomenon Known as Gravitational Lensing
Because of this stretching and curving effect on space-time, high mass objects in space can actually cause an observational phenomenon known as “gravitational lensing.” This occurs when a distant object behind a high mass object actually appears larger and brighter to an observer because of a magnification effect caused by gravity.
To illustrate how this effect works, imagine staring at me from across a large room. I am about two feet in front of the wall at the far end of the room opposite you. An ant is crawling on that wall just to the left of me. From where you’re standing, you can barely see the ant because it’s hardly discernible at such a distance.
But now suppose I hold out a magnifying glass to my left at just the right position and angle it such that it allows you to see the ant in much greater detail from your vantage point across the room.
High Mass Objects Stretch Space-Time and Magnify the Light from Distant Objects behind Them
This is essentially how gravitational lensing works. High mass objects stretch space-time and magnify the light from distant objects behind them. And we’ve actually used this phenomenon on many occasions to observe distant objects that happen to reside behind high mass, closer objects such as stars and galaxies.
As such, we know that if a telescope is aimed at a distant object and there happens to be a nearer high mass object somewhere in the peripheral foreground, the view of the distant object will be distorted and magnified. And if we’re not careful to note this circumstance, we might be fooled into thinking that the distant object is much bigger and brighter than it actually is.
But so long as no high-mass objects are present in the intervening space between a telescope and its target, it’s safe to assume that what we see is more or less what actually exists.
Or at least we thought so for decades. But as science has evolved, we’ve learned that the universe might be more than meets the eye. Enter dark matter.
Dark matter was discovered by astronomer Fritz Zwicky in 1933. It is a theoretical construct that we assume in models of our universe for mathematical stability. Zwicky was studying distant galaxies, which are giant spinning disks of billions of stars, held together by their collective gravitational attraction.
As Zwicky was making his observations, he noticed something peculiar. He calculated that, if one adds up all the gravity one would expect from all of the stars in a particular galaxy, it isn’t nearly enough to hold the galaxy together. Not even close.
In fact, the average galaxy’s stars exert less than one percent of the gravity needed to maintain that galaxy’s form. According to the math, these galaxies should simply fly apart from the centrifugal forces at work. But they obviously don’t. So something else is creating the other 99 percent of the gravity needed to keep the galaxy together.
Zwicky didn’t have an answer. Actually, we still don’t even know for sure today. But we know there must be some large mass unaccounted for. It doesn’t seem to interact with any light because we haven’t been able to observe it, but we see its gravitational influence nonetheless. So we know it’s there. We call this mystery mass “dark matter.”
Experts Have Been Trying to Determine What Dark Matter Is
Ever since Zwicky deduced its existence, experts have been trying to determine precisely what dark matter is. Based on large-scale gravitational calculations, astronomers estimate that 27 percent of all the mass in the entire universe must be dark matter. But again, we can only infer details about dark matter from its gravitational interaction with ordinary matter. We have no other evidence with which to work.
Originally, we thought that most dark matter — whatever it is — would be bound up in the centers of galaxies as it coalesced with regular matter. A 2012 study looked at the distribution of dark matter based on gravitational dynamics. The study found that dark matter is actually spread far beyond the outermost stars that we see with our telescopes. In fact, the study propounded that dark matter might actually saturate much or all of the intervening space between galaxies.
What does this have to do with gravitational lensing and viewing our universe with space telescopes? In the past, if we wanted to avoid any distortion from gravitational lensing in viewing distant objects, we would simply ensure that there weren’t any high-mass objects — stars, galaxies, and the like — in the foreground between our telescope and the object we’re aiming at. However, now that we have reason to suspect that dark matter might permeate the intergalactic space all around us, we have to wonder: How much is the gravitational lensing from such dark matter distorting what we think we’re seeing in our night skies?
It’s possible that the effect of dark matter’s gravity on our views of deep space could be negligible. But it’s also possible that high-mass concentrations of dark matter in otherwise empty regions of space — which we can’t yet detect due to a lack of interaction with actual matter — could be turning our view of the universe into a veritable kaleidoscope of the cosmos.
About the Author
Dr. Gary Deel is a Faculty Director with the School of Business at American Military University. He holds a J.D. in Law and a Ph.D. in Hospitality/Business Management. Gary teaches human resources and employment law classes for American Military University, the University of Central Florida, Colorado State University and others.