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The main focus of this paper is to explore the latest theories regarding dark matter and dark energy and their relationship. These theories explain the Universe's accelerated expansion rate and also provide insight into why galaxies remain intact despite appearing to lack sufficient mass for gravitational cohesion. This is especially intriguing considering that galaxies rotate at speeds that should disperse their starry elements away from the center.
Dark Matter Dark Introduction Recent discoveries are challenging our understanding of the universe, causing some to struggle with comprehending these new findings.
Advanced technologies like radio telescopes and the Hubble Space Telescope play a crucial role in unveiling mysteries of the cosmos. The concepts of dark matter and dark energy are emerging to shed light on the composition of our universe.
Scientists have been puzzled for years by the complex task of studying the composition, significance, and connection of dark energy and dark matter. The mystery surrounding dark matter is due to our focus on visible entities, leading to many unexplained phenomena.
In 1933, astrophysicist Fritz Zwicky found that the galaxies in the Coma Cluster of Galaxies were moving at speeds too fast to be bound by gravity. Vera Ruben and Kent Ford's research on galaxy rotations backed up Zwicky's discovery. Zwicky suggested that these galaxies must have additional mass in the form of invisible matter, now referred to as dark matter (Hooper, 2013).
Scientists in the 1970’s used computer simulations to theorize that our galaxy lacked the necessary mass to maintain stability, leading to the potential disintegration caused by rotational forces (Hooper, 2013; Panek, 2010).
Despite being undetectable through direct means due to its limited interaction with regular matter, dark matter's presence can be inferred through its observable effects (Panek, 2010).
Dark matter's powerful gravitational forces are evident in its ability to distort light, a phenomenon called gravitational lensing (Rishwanm, 2008). This effect is typically seen in galaxy halos, as shown in Figure [ 1 ] from the Hubble Space Telescope. NASA/ESA Dark Matter Composition Theories remain uncertain due to the lack of direct observation or measurement of dark matter.
Scientists use gravitational lensing to understand the quantity and distribution of dark matter in the Universe. To solve the puzzle of dark matter, they have investigated various theories including black holes, Massive Compact Halo Objects (MACHOs) composed of baryonic matter with low radiation emission, brown dwarf stars that cannot undergo hydrogen fusion yet can still warp light, and particles (Rishwanm, 2008).
Black holes, brown stars, and MACHOs are unlikely to meet the quantitative criteria for the amount of dark matter in existence (Rishwanm, 2008). According to a NASA sponsored website, a favored model for dark matter is that it is mostly composed of exotic particles formed when the Universe was a fraction of a second old (NASA, 2012, p. 1). Some particles considered are neutrinos, axions, and Weakly Interacting Massive Particles (WIMPs). The current and most popular theories amongst astrophysicists to explain what dark matter is made up of are WIMPs and axions.
According to Caldwell and Kamionkowski (2009), WIMPs and axions are considered as candidates that have passed long-standing theoretical scrutiny. WIMPs, similar to neutrinos, have weak interactions with ordinary matter and are naturally found in extensions to the standard model of particle physics (p. 587). The Role Dark Matter Plays Galaxies rotate at speeds that are too fast to maintain their stars orbiting around the center without veering off in a different direction or decelerating based on the visible or luminous mass present within the galaxy ("Dark Energy, Dark Matter," 2012).
American theoretical physicist Kaku Michino discussed in a series called The Dark Matter & Dark Energy how dark matter forms a halo around galaxies, maintaining their constant rotation speeds and adding mass to them (Rishwanm, 2008). This results in dark matter exerting an attractive force on a galactic scale, increasing gravity at the galaxies' centers. The concept of Dark Energy was also presented in the discussion.
The theory of dark matter entail attractive forces, it makes sense that the Universe would slow its expansion and then start contracting due to gravitational mechanics, or at least that the rate of expansion would decrease. However, scientists have observed that instead of slowing down, the expansion rate of the Universe is actually increasing, which goes against logical expectations. In the 1990s, two groups of astronomers investigating the deceleration of the Universe's expansion found evidence of acceleration (Panek, 2010).
According to Panek (2010), astronomers used the brightness of supernovas as references for their measurements because these exploding stars are bright and have relatively short lifespans. They compared the actual brightness of supernovas with how bright they should appear at different locations in the Universe if the rate of expansion was uniform. The unexpected finding that the expansion of the Universe was accelerating suggested that gravity was not the leading force in the Universe's evolution.
The enigmatic force recently uncovered was labeled dark energy by an astronomer. Interestingly, physicist Albert Einstein first proposed the concept of a cosmological constant in 1917 to create stable, everlasting solutions to his field equations. This idea was based on the belief that the Milky Way was the entirety of the Universe and the observed lack of systematic expansion or contraction in its stars' movements (Kirshner, 2003, p. 1914). Einstein later regretted this notion, referring to it as his biggest mistake upon learning about Hubble's research on cosmic expansion.
Dark energy, comprising approximately 75% of the Universe, is theorized to counteract gravity and contribute to universal expansion. This concept challenges traditional understanding of gravity and highlights our limited knowledge of the cosmos. According to Caldwell & Kamionkowski (2009), dark energy is a repulsive force originating from the gravitational field of a negative-pressure fluid created by thermal molecular motions.
Dark energy, identified as the fluid in question, is surrounded by various theories. One theory proposes that dark energy may be a cosmological constant or a result of cosmic expansion. According to Banchi & Rovelli (2010), as the Universe expands, space also expands like an inflating balloon, causing galaxies to move farther apart. Einstein introduced a repulsive vacuum energy to counteract the attractive force of gravity, although this idea was initially applied incorrectly to a static universe (Rishwanm, 2008). The cosmological constant is believed to correspond with the characteristics of dark energy. In the early stages following the big bang theory's formation of the Universe, galaxies and stars were close together and dark matter's influence slowed down the initial explosion's expansion.
As the Universe expands, the distances between galaxies grow larger and dark matter's influence diminishes in comparison to dark energy. Some astrophysicists suggest that this shift towards a repulsive force could be driving the accelerating expansion of the Universe, believed to have started approximately five billion years ago. Recent technological progress has unveiled new findings prompting a reevaluation of our understanding of the cosmos.
The evidence of dark matter, confirmed through gravitational lensing, explains the missing mass required for maintaining stellar cohesion in galaxies as well as their puzzling fast rotational speeds. Additionally, the discovery of the Universe's accelerating expansion prompted the investigation of the repulsive forces causing galaxies to move apart, a force known as dark energy.
Studies have revealed the opposite correlation between dark matter, an attractive force, and dark energy, a repulsive force. Initially, in the early Universe when galaxies were closer together, the dominant force was dark matter's attractive force. However, as they moved farther apart, the repulsive force of dark energy became stronger and accelerated the rate of expansion.
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