Unveiling the Mysteries of Dark Matter, Dark Energy, and Antimatter (Part I)
Everything that we can see in our universe is known as matter - something that occupies space and has mass. However, our cosmos is also made up of substances that we cannot see such as dark matter and dark energy that affect our universe in ways more significantly than we had imagined. Normal matter can be observed in visible light or through telescopes to see them in other parts of the electromagnetic spectrums like ultraviolet or infrared. They're made up of atoms that can be further broken down into protons, electrons and neutrons. Despite being everywhere in our lives, it only takes up less than 5% of the entire universe whereas dark matter and energy take up most of the cosmos.
Dark Matter
Dark matter takes up space and has mass just like normal matter, but does not reflect or absorb light as of our understanding currently. It has been found that it comprises around 27% of the cosmos, but scientists still do not know what exactly it is. It was observed when the astronomer Fritz Zwicky was studying the galaxies part of the Coma galaxy cluster. The speed at which galaxies move depends on the galaxy cluster’s mass which would determine the gravity hold the galaxies together. However, the galaxies were moving so fast that the gravity that was present from the visible matter seen in the Coma Cluster was not able to hold it from flying apart from the cluster. Since they were not flying apart, this suggested there was an alternate matter that was adding to the gravity.
Evidence of Dark Matter
The first evidence for dark matter comes from observing galactic rotation curves. Vera Rubin confirmed the existence of dark matter by studying how individual galaxies rotated. She measured the wavelengths of light from stars in different parts of spiral galaxies to calculate the orbital speeds of those stars using the Doppler Effect. Measuring the orbital speeds of the stars based on their distances from the middle of the galaxy helped in understanding the distribution of mass throughout the galaxy. It was presumed that most of the mass and gravity of a galaxy would be concentrated in its center since the most visible stars were located there. This meant that the farther the star from the center, the slower its orbit should be since there was less gravity to hold the stars together.
Vocabubbleary: Dopper Effect is the shift in wavelength is proportional to the speed of the light source relative to the observer e.g. when light moves toward from us, the wavelength gets shorter whereas when light moves away from us, the wavelength gets longer
However, something unexpected was observed - stars far from the center of galaxies were moving at similar speeds to the closer stars. This was odd because the visible mass that they knew of was not sufficient to be the only thing keeping the rapidly moving stars in orbit, especially the stars in the sparsely populated regions. Calculations showed that at least 90% of mass in galaxies had to be invisible. Zwicky’s findings in the past had also reinforced her findings that there had to be “dark” matter and her conclusion was finally accepted by astronomers.
Another method is through gravitational lensing which is observing how gravity bends due to dark matter and distorts light from distant objects. The immense gravity of all the dark matter warps the space around the cluster, causing the light from background objects to be distorted and magnified. By studying how light is bent around these clusters, they can infer the distribution of dark matter around them. When astronomers looked at these gravitationally lensed galaxy clusters that distort the location of the galaxies within, they are able to reverse-engineer these changes and map it out. This indicates the location, amount and concentrations of dark and visible matter in the galaxy clusters.
Theoretical Models of Dark Matter
Scientists have some ideas on what dark matter could be made of; most think that it is comprised of non-baryonic matter. For some context, visible matter around us is called baryonic matter that are consisting of baryons - an all-encompassing name for subatomic particles luke protons, neutrons and electrons. Back to dark matter, when we’re talking of non-baryonic matter, one possibility of particles are WIMPS which stands for “weakly interacting massive particles”. These are believed to have thousands the mass of protons, but weak interactions that make it difficult to detect with the technology we have. They are also thought to be electromagnetically neutral due to the absence of light from the particles. There are efforts to detect the properties of these particles from witnessing their impacts on other matter or colliding them with each other through experiments in particle accelerators like the Large Hadron Collider.
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