The Milky Way galaxy is believed to have approximately 200 billion stars orbiting a black hole weighing four million times as much as our Sun. But the gravitational effects of the Milky Way suggest the galaxy is much, much heavier than what we can see. Recent estimates suggest the galaxy weighs around 1.5 trillion solar masses, which means something heavy in the Milky Way is hiding in plain sight. Dark matter could be this mysterious something, giving the Milky Way more mass than the sum of all objects we can observe.
Dark matter is a former of yet undiscovered matter, which does not interact with the electromagnetic force.
Dark matter is called dark because it does not emit light and it does not reflect light, making it virtually impossible to observe.
There is also no clear consensus on what exactly dark matter is and where it fits in the accepted model of particle physics.
One theory dubbed Supersymmetry suggests all known particles in the Standard Model – fundamental particles such as electrons, quarks bosons and muons – are paired with a partner particle of dark matter.
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Another theory stipulates dark matter is built from small, undetectable black holes scattered around the galaxy.
US space agency NASA explained: “More is unknown than is known. We know how much dark energy there is because we know how it affects the universe’s expansion. Other than that, it is a complete mystery.
“But it is an important mystery. It turns out that roughly 68 percent of the universe is dark energy. Dark matter makes up about 27 percent.
“The rest – everything on Earth, everything ever observed with all of our instruments, all normal matter – adds up to less than 5 percent of the universe.
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“Come to think of it, maybe it shouldn’t be called ‘normal’ matter at all since it is such a small fraction of the universe.
Whatever the case may be, all estimates show dark matter is the dominant substance in the universe, accounting for about 85 percent of matter.
For comparison, all forms of normal matter, which our cars and bodies are built from, only comes in at around five percent.
One way in which astronomers want to look for signs of dark matter in the Milky Way is the Extremely Large Telescope (ELT).
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The ELT is an under-contraction ground telescope in Chile, which after completion, will be the world’s largest astronomical observatory.
According to the European Southern Observatory (ESO) in Germany, the ELT will hunt for signs of extraterrestrial life, will measure the properties of planets and galaxies, and will hunt for dark matter.
Scientists are also looking to learn more about the mystery substance by colliding together beam of particles accelerated to the speed of light.
When particles in accelerators like the Large Hadron Collider (LHC) in Switzerland collide, they are turned into pure energy, from which new particles emerge.
Particle detectors are then used to pick out and measure what is created in the process, in the hopes we can better understand the nature of dark matter.