Dark Matter In The Universe

This brief document will be over dark matter in the universe and why there are issues with the calculated mass of galaxies.

Table of Contents

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While measuring our own galaxy, we can see there must be a large amount of unknown matter here. We can’t see it or detect it. That is why it is such a big mystery. We first noticed this discrepancy because objects were not following the gravitational laws in the ways they should. So, dark matter is stuff that we can not see and gives off no detectable energy. Seems weird, for sure, but that is the consensus right now.

Expansion Of The Universe

Since we discovered the universe was expanding, there have been constant theories about why. Astronomers have also theorized how long the expansion would last. There is still no consensus on anything. Scientists have long thought that gravity would cause the expansion to stop. Intuitively, this would be the normal thought of most people. After all, gravity is strong and affects cosmic objects from vast distances away.

Thanks to the Hubble telescope, we know the expansion velocity of the universe has increased. This makes no sense at all. Something must cause the acceleration, obviously.

Scientists love a chance to name something new, so we now have dark energy. This dark energy, which is just a vague and generic placeholder, is our cause of universal acceleration.

Early physicists thought dark energy was just a property of space itself. What looks empty to you and me is not empty at all. It is full of energy and potential. In fact, Einstein thought that space could propagate more space. This could certainly be a hypothesis to expand the universe.

So, these are all the reasons that the observable mass of galaxies is way off. The mass is not just way off; it is magnitudes different than it should be.

Mass Of Galaxies

Estimating the masses of galaxies is hard. They are far away and we can only see faint details. So, we have to use indirect methods. These indirect methods are educated guesses based on their characteristics. The main such method is using the length of the galaxy arms versus distance from their galactic center. Then the velocities of these moving arms are calculated, which gives us a good estimate of mass.

These calculations are all done using Newton’s Laws. So far, these methods work on our own galaxy and others close by. They give us a range of mass to go by, which helps us infer that a lot of mass is missing. This is what astronomers have named dark matter.

For galaxies farther away, we have to use more indirect methods. This usually involves analyzing spectroscopic lines. When the lines change their width, this shows rotation speed. Of course, once we have that, then we can guess size and mass.

We have analyzed many galaxies in this way. In doing so, astronomers have realized that certain types of galaxies often come within a particular range of masses. This is great because, as we compile more information, we can make even better, more accurate guesses at these far away objects.

Matter We Can See

Astronomers think that most galaxies contain large amounts of dark matter. Spiral and elliptical galaxies have similar amounts of missing matter. So, the amount of dark matter may have nothing to do with the type of galaxy. All galaxies seem to have dark matter.

In fact, the accepted figure is around 27% dark matter per galaxy. I can’t say how they get a figure that precise. It’s done by people smarter than I. Regardless, that leaves inconsiderable matter that we can actually observe.


In this document, I tried to discuss the reason we are missing something. We are missing the cause of galaxies having much less mass than they should and why the universe is expanding faster and faster. These events are related, I feel. There is something big we are all missing. It just has not been discovered yet.