Here's What We Know About Dark Matter

stellar nursery star birth universeDark matter. It’s out there.

Today, NASA and European Space Agency scientists announced that they’ve detected the first hints of dark matter from a detector on the International Space Station.

What is dark matter?

Dark matter makes up about a quarter of the universe, but we don’t really know what it is. We can’t visibly detect it because it does not emit or absorb light — hence its “dark” name — but based on our knowledge of the universe, something must be out there, creating mass that we can measure but can’t see.  

Because dark matter doesn’t interact with light waves, or create them, we can’t detect it in the usual ways. But we can see its effect on gravity. The more massive something is, the stronger its gravitational pull.  

When we observe the universe, we detect more gravity acting between stars, galaxies, and clusters of than what we can account for based on what we can physically see. 

A recent new survey of the Big Bang’s afterglow showed that there is actually a tad bit more dark matter in the universe than we thought (and a few other neat things). 

Dark matter is just one of the crazy mysteries of our universe — the other is dark energy.

In reality the universe that we know and love and expedience on a daily basis is just 4.5 per cent of the universe that exists — that’s how much “ordinary matter” exists.

According to NASA, “we know much more about what dark matter isn’t than what it actually is.”

  • “It is not in the form of stars and planets that we see. Observations show that there is far too little visible matter in the Universe to make up the 25% required by the observations.
  • It is not in the form of dark clouds of normal matter, matter made up of particles called baryons. We know this because we would be able to detect baryonic clouds by their absorption of radiation passing through them.
  • Dark matter is not antimatter, because we do not see the unique gamma rays that are produced when antimatter annihilates with matter.
  • We can rule out large galaxy-sized black holes on the basis of how many gravitational lenses we see. High concentrations of matter bend light passing near them from objects further away, but we do not see enough lensing events to suggest that such objects to make up the required 25% dark matter contribution.”

So what is it? Basically it’s a theoretical mystery particle. Possibly even more than one particle; there could be multiple factors at play to make up this mystery.  It could be what’s thought of as a “supersymmetrical” particle — those that mirror the particles in ordinary matter. There are a few options of what they are.

One theory, which based on today’s findings is less likely, is that “dark matter” could not be dark matter at all, but instead be a version of normal matter, known as MACHOs — Massively Compact Halo Objects. These objects would be black holes or neutron stars that have traveled far from their detectable traces like gas clouds. Many lines of evidence have indicated that this isn’t likely to be what’s causing the dark matter problem, because we would have seen evidence of them.

Or, there would have to be a huge (like, really huge) number of brown dwarves out there. Brown dwarves are stars that are 8 per cent the size of our sun. They are too small to spark hydrogen fusion, so they don’t shine like suns. Based on calculations, though, they could only account for 20 per cent of dark matter.

Dark matter could also be made of a particle called axions — light particles that interact in ways that would account for dark matter. They don’t have much mass, but they could have a large, widespread population because they were made in really high numbers during the creation of the universe. They haven’t been detected yet.

The third, and most likely, theory is that dark matter may be made of theoretical particles called WIMPs — Weakly Interacting Massive Particles. They have mass like normal particles but they don’t interact with normal matter in other ways. Basically, they were invented to make physics work and explain dark matter.

These WIMPS interact with normal matter through the force of gravity and the weak force.

As we learn more and get more data we’ll get a better understanding of what makes up dark matter — and our universe.

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