One of the most confusing concepts in the already often confusing study of the universe is the idea of dark matter. Not to be confused with dark energy, dark matter is a name we have given for a hypothetical type of matter that can’t be seen but accounts for most of the matter in the universe.
When scientists began gathering numbers on all the matter and energy in the universe that we could see and detect, then plugged those numbers into computers to create models they quickly realized that something was missing, a big something! The models looked almost nothing like what we were seeing out in the universe. No one could figure out what exactly it was so the just called it dark matter, a place holder name.
We might not know what it is but we know it’s there because of the gravitational effects on the matter we can see, for example the way galaxies clumped together and rotate.
Just to clarify, dark energy has the opposite effect on matter. Where dark matter is pulling things together, dark energy is pushing stuff apart. Dark matter influences individual galaxies, while dark energy works on the entire universe as a whole. Like dark matter, dark energy cannot be detected directly and we only know it’s there because of affect on the universe.
The matter and energy we can see and detect actually only accounts for a small percentage of what is out there. The break down comes to about 4.9% ordinary matter, the stuff we know about, and about 26.8% dark matter and 68.3% dark energy. pretty crazy, right?
Because dark matter is just that, dark and unable to be seen, we know very little about it. It fact, we know more about what it isn’t, then what it is.
We do know that it is not an effect of the matter we can see. We also know that it is not just dark clouds of normal matter called, we would be able to detect that. And we know it isn’t antimatter, or else we could detect it interacting with normal matter. Finally we know it is not very large, think galaxy-sized, black holes or else we would see light bending around them a certain way.
But because we don’t know much about what it is there are still a few theories about what exactly could be happening. Most scientist have accepted the explanation that dark matter does exists and is composed of WIMPs, or weakly interacting massive particles that only interact through gravity and the weak force.
Scientists have made new simulations to map where dark matter might be and what it might look like. They are even beginning to make maps of it. So far they think that dark matter looks like a web woven together with regular matter. In some places it may be clumping together into lumps. In other places it looks stretched out and stringy with galaxies caught like insects in a spider web. Dark matter could be everywhere, all around us, binding everything together like a connective tissue.
It’s all a bit confusing, I know. Scientist are still learning about our universe and how it works and sometimes reality starts to sound very much like sci-fi, which I think is very cool.
What’s important to know is that there is “stuff” out there that is not like the everyday “stuff” we know and we can’t see it to figure out exactly what it is. We do know that it does affect the celestial objects and, eventually, i tt will determine the fate of our universe as a whole.
Featured image: As it departed its encounter with Saturn’s moon Dione, Cassini sailed above an unreal landscape blasted by impacts. The rising Sun throws craters into sharp contrast and reveals steep crater walls. At the far right, a medium-sized crater is bisected by a fracture, revealing a cross section of the impact site.
The seven clear-filter images in this mosaic were taken with the Cassini spacecraft narrow-angle camera on Oct. 11, 2005, at distances ranging from of 21,650 to 25,580 kilometers (13,450 to 15,890 miles) from Dione and at a Sun-Dione-spacecraft, or phase, angle of 154 degrees. Resolution in the original images ranges from 126 to 154 meters (413 to 505 feet) per pixel. The images have been re-sized to have an image scale of about 100 meters (330 feet) per pixel. North on Dione is 140 degrees to the left.