Dark Matter

WTT Weekend Feature – Understanding of dark matter gets closer

The universe is a pretty big place. Undoubtedly, there will be a lot of mysteries to solve, if we ever reach the stars. But our fundamental understanding of the universe can be furthered here on Earth, or a relatively short distance above in orbit. One of the greatest mysteries being investigated by scientists is the composition of the universe itself. Dark matter is meant to be a key component. But what is this dark matter, and how do we find it?


WTT Weekend Feature – universal mystery

dark matter

Image credit – National Geographic

It might surprise you to learn that baryonic matter – the stuff we see, touch and feel on a daily basis – only makes up an estimated five per cent of the universe’s matter and energy content.


Yes, just five per cent. Let that sink in for a moment. All of the stars, planets and gas in the universe makes up a tiny proportion of the place.


The rest of it is apparently made of Dark Energy (68 per cent) and Dark Matter (27 per cent). Neither of these two things are understood because very little makes sense. Indeed, the phenomenon has been known for some time due to anomalies in galactic orbital mechanics, but never been explained.


dark matter

Artist’s impression of Pioneer 10 near Jupiter. Image credit – NASA


Of course, there are competing theories as to why these anomalies exist. One theory, MOdified Newtonian Dynamics (MOND), postulates that gravity might not behave precisely as Isaac Newton’s equations set out. There were unexplained anomalies closer to home that proponents of this theory bring about, such as Pioneer 10 being 400,000 kilometres away from where it should be. The cause was later determined to be heat leaking from the craft causing a minute drift in its course.


However, such alternate theories are not supported by evidence, such as gravitational lensing and even observations of the behaviour of light in other circumstances.


WTT Weekend Feature – Orbital strangeness

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Stuff spins around galactic centres much faster than they should. Dark matter is one explanation for this anomaly. Image credit – Wikipedia


The first clue that the universe wasn’t acting in the way scientists expected was when Lord Kelvin of absolute zero fame theorised that the amount of observable matter in the Milky Way didn’t account for the speed at which the galaxy spun around the central core. Even accounting for the supermassive black hole in the centre, the outer parts were travelling too quickly.


Lord Kelvin suggested this might be due to the majority of matter being “dark bodies”. Evidence continued to mount, the most conclusive was from Vera Rubin and Kent Ford in 1978. Using edge on observations of other galaxies, the phenomenon of stars travelling faster than they should be was seen elsewhere in the universe.


WTT Weekend Feature – What’s dark matter exactly?

dark matter

Here’s Neil deGrasse Tyson inside a neutrino detector. Neutrinos are weird and could be a kind of Weakly Interacting Massive Particle.


The answer to this question is just what scientists are seeking through experimentation and data gathering. There are two competing theories about just what more than a quarter of the universe is comprised.


The first are WIMPs or Weakly Interacting Massive Particles (by the way, I love science acronyms). These are as yet undiscovered and totally unknown types of subatomic particles that do not interact with the rest of the universe’s matter. They have mass, but we just can’t yet detect them with conventional means.


The other competing theory is that dark matter consists of MACHOs – MAssive Compact Halo Objects – which are cold and otherwise undetectable. But given their spread throughout the galaxy, accounts for the observed discrepancy.


WTT Weekend Feature – Enter the Monkey King

dark matter

The Chinese DAMPE “Wukong” satellite being launched in 2015. Image credit – Sputnik International


China’s DArk Matter Particle Explorer satellite (DAMPE) is currently in orbit looking for signs of dark matter. These signs would help scientists understand its nature, and just how to find the stuff and study it with some manner of consistency.


The satellite is nicknamed Wukong, after the mythical Monkey King of Journey to the West and which inspired the modern anime classic of Dragonball. Wukong in Chinese means “understanding the void”, an apt name for a satellite designed to learn about the nature of the universe itself.


In essence, the satellite is in orbit to look for the signature of WIMP decay. It does this by detecting and analysing cosmic rays, their energy, direction and even electron/positron pairs. Theoretically, the spread of energies of such incoming cosmic waves should be smooth and predictable.


However, there are signs that there might be a break in that nice smooth curve that could be caused by certain types of matter/antimatter collisions. And such an anomaly, if it were to be confirmed, could be smoking gun evidence that WIMPs are out there, waiting to be found. Indeed, Wukong has confirmed the break in this curve exists after 530 days in orbit and 1.5 million detections.


WTT Weekend Feature – What does this mean?

dark matter

The cosmic background radiation map. Dark matter influences some of the shape and distribution of this map. Image credit – NASA


Confirmation of this hypothesised anomaly does not mean that the existence of WIMPs has been conclusively proven or even disproven as yet. However, it does point scientists in the direction in which their research should continue. Certainly, the anomaly in the curve of detections needs to be studied further to understand the implications. It could mean nothing, but it could mean everything in the search for dark matter.


The search for knowledge and understanding continues, one step at a time. And we have a satellite named the Monkey King to thank for this latest snippet of knowledge.

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