The Dark Universe
From Black Holes, Dark Energy to Dark Matter: Explore the mysterious and most curious parts of our universe.
Black Holes
A Singularity is a point in space with infinite density and zero volume. This can occur when an old and massive star’s fusion reactions start to die out, and the entire star collapses in on itself due to the instability of the core. This collapse proves to be so powerful that the entire mass of the star compresses down into a point of zero volume, thus also infinite density. The Event Horizon defines the point at which the gravitational strength of the black hole becomes so great, that light itself can no longer escape its grasp! This is why black holes appear black, because you are looking into the point at which absolutely nothing can ever make it to your eyes. This point can also be referred to as the Schwarzschild Radius, which is a calculated radius from the center of mass of any object where light cannot escape. For most objects though, this does not really matter because most of the mass exists on the outside of this radius. For example, the Schwarzchild radius of the Earth is only about the size of a marble, meaning it is just about insignificant. Any object whose Schwarzchild radius extends beyond its own radius is thus a black hole.
Image Credit NASA
The Expansion of the known universe
Video Credit: NASA
Black holes have some other notable features as well. Mainly, the Accretion Disk is the warped ring of light that we would see around a black hole, given that we were close enough. The observed light around a black hole also appears brighter on one side than the other. This is because the extremely fast spinning of the disk near the black hole causes Doppler shifts to the light, which is referred to as Doppler Beaming. This effect can also be seen in the black hole’s Particle Jets. Particle jets occur when material near the inner edge of the disk gets shot out in a line away from the black hole. We can observe this because the jet that shoots out towards us is considerably brighter, again due to the Doppler beaming!
Image credit: NASA
Primordial black holes are a theoretical type of black hole that could have formed very soon after The Big Bang in the inflation period. The idea is that these black holes would not have needed the collapse of a star to have formed like the way we know they are formed now (the actual mechanisms for their formation are a bit too complex to be discussed in this article!). These primordial black holes have many scientific implications: They could have helped form early galaxies, they are a possible explanation for the theory of dark matter, and they could even explain the lack of magnetic monopoles (a theoretical type of magnetic field where there is only a “north” end, or only a “south end”. These types of magnets as of now, have never been observed).
Dark Energy
The expansion of the universe, though nothing has been proved to be certain, is best explained by the theory of dark energy. Dark energy is a hypothetical form of invisible energy that fills all of space and drives the ever-increasing rate of expansion of our universe. Dark energy is estimated to account for nearly 70% of all energy in the entire universe! Despite this, dark energy is not something that we have directly observed, but rather something that we understand based on otherwise inexplicable cosmic events.
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The first observed evidence for dark energy came from looking at distant supernovae. Supernovas are known to have a constant luminosity, which means that we can accurately measure their distance. From
this, observed redshifts in their light indicated that they were moving away from us at a constantly expanding rate. It is worth noting that the properties of dark energy itself are entirely unknown, it is just the name that scientists have given to explain the causes of the observed effects (mainly the expansion of the universe). Dark energy remains an evolving field of study, and
the ESA’s Euclid missions (launched just in 2023) will help explain some of the unknowns by mapping the expansion of matter in the observable universe. NASA’s Nancy Grace Roman Space Telescope also aims to help solve some of these mysteries, with a planned launch in 2027, the Roman telescope will also be observing and mapping the effects of dark energy and dark matter.
Image Credit: NASA
Dark Matter
In 1933, Swiss-American scientist Fritz Zwicky observed an anomaly within the galaxy cluster named Coma. He discovered that there was an enormous amount of unaccounted-for mass in this cluster that would have been needed in order for the many stars to not escape its gravitational influence (in fact, only about 1% of the needed mass could be observed!). In the 1970s, American astronomers Vera Rubin and W. Kent Ford confirmed that in every observed galaxy, only about 10% of the mass required to maintain stable orbits actually comes from visible stars.
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Thus, scientists are led to believe that there must be enormous amounts of mass out there that we currently have no way of directly observing, hence the name “dark” matter. In fact, it is estimated that roughly 30% of all matter in the known universe. The working theories for where all of this unseen mass actually resides are that it is either within some as of yet unobserved subatomic particles, or that it is from those previously mentioned primordial black holes. Again,
however, the existence of dark matter has not been seen directly, but rather we can theorize about its nature based on holes in our observations. The Roman Telescope also aims to shine more light on the existence of dark matter and help scientists make more accurate theories regarding its unknown mechanics.
Image Credit: NASA