We still haven’t detected dark matter directly but we may have gotten our first hint from equipment aboard the International Space Station (ISS). An Alpha Magnetic Spectrometer (AMS) on board has been detecting massive numbers of cosmic ray positrons. These particles occur theoretically when dark matter is annihilated. They are the antiparticle to electrons, a form of antimatter, and have the same very small mass. In our Universe they tend not to hang around too long.
So what is dark matter?
Cosmologists have identified dark matter as one of two key missing ingredients that make up the total mass of our Universe. The matter we see in visible light, stars, nebula, planets and galaxies represents only 4% of the Universe’s total mass. Invisible matter accounts for another 23%. And formless energy accounts for the rest, 73% in total. We know this because of a European Space Agency robotic spacecraft that conducted a census of the Universe over a 15-month period starting in 2008. These findings were further confirmed by a NASA satellite in 2011. And now with the findings on the ISS it is clear that we are beginning to understand if not see dark matter.
Because we live in the visible Universe it is hard to get the hang of what is really happening in the parts we cannot see. And only in the last year have we begun to understand a little more about this unseen Universe. It appears that it may very much act like the visible matter we see. That means there is more than one type of dark matter just like visible matter. And like visible matter, dark matter can form into disks and maybe even dark stars surrounded by dark planets.
Further speculation leads to other potential scenarios. Is it possible there could be dark life on dark planets? Maybe there is even someone writing a blog about visible matter at this moment living on a dark matter version of Earth. And when you consider that dark matter is far more abundant than visible matter, maybe we in the visible Universe are the exception and not the rule.
So now we get to the statement that is the title of this posting: why dark matter matters!
Because by the force of its much larger mass it serves as the glue that keeps the Universe we see from flying apart. And dark matter isn’t invisible but has been described as “a black cat eating licorice in a coal bin.” It absorbs light. It doesn’t react to cosmic radiation. But those positrons are a key clue to its existence. And in the near future a new European space observatory called Gaia will be launched with the goal to map a billion stars within the Milky Way, our galaxy. That mapping should detect anomalies that will allow us to detect what is virtually invisible, the galaxy’s dark side containing dark stars and nebulae and even dark planets and moons.
For today at least we know what we know, that dark matter is important. It is as much a product of the Big Bang as the visible matter from which we are made. Without it we would cease to exist.
Now if we could only figure out dark energy, the remaining 73% of the Universe. But that’s a topic for another day.