For the first 150 million years after the Big Bang, there were no galaxies, stars, or planets. There were no features in the cosmos.
Over time, the first stars started to form. As stars gathered, galaxies were created. Galaxies began to assemble in groups. Those clusters are made up of the galaxies and all the stuff between the galaxies. As clumps of matter collided with one another, the planets in our solar system began to take shape around the sun.
Galaxies, galactic clusters, and our solar system must all be interconnected. And gravity is that “glue.”
Some clusters have gas in the spaces between galaxies that are so hot that observatories using visible light cannot see it. The only methods for observing the gas are X-rays and gamma rays. Scientists investigate the gas and measure the volume of gas between galaxies in clusters. They concluded that there must be five times as much material in the clusters as what is seen as a result. The invisible, undetected stuff is referred to as “dark matter.”
What is Dark Matter?
Dark matter is a part of the universe that can only be seen by gravitational pull and cannot be seen with the human eye. Dark energy makes up 69.4% of the universe’s matter, while dark matter and “regular” visible matter make up the remaining 31.1%. (0.5 percent).
Fritz Zwicky, a Swiss-American astronomer, proposed the existence of dark matter, also known as the “missing mass,” after discovering in 1933 that the mass of all the stars in the Coma cluster of galaxies only made up about 1% of the mass required to prevent the galaxies from escaping the cluster’s gravitational pull.
For many years, the existence of this missing mass was disputed, but in the 1970s, American astronomers Vera Rubin and W. Kent Ford discovered a phenomenon that demonstrated its reality: the visible stars in a typical galaxy have a mass that is only 10% of the mass required to keep them orbiting the galaxy’s center.
In general, the orbital velocity of stars around the galactic center is unaffected by the distance between them; in fact, orbital velocity either stays constant over a range of distances or slightly increases rather than decreases as would be expected.
This requires a linear relationship between the star’s distance from the galaxy’s core and the mass of the galaxy within their orbits. Dark matter refers to inner matter that does not emit visible light.
What has happened since the confirmation of Dark Matters’ existence?
Gravitational lensing, or matter acting as a lens by warping space and distorting the passage of background light, has since the discovery of dark matter allowed astronomers to determine that dark matter dominates in galaxies and clusters of galaxies. The existence of this missing matter in the cores of galaxies and clusters of galaxies has also been inferred using the speed and heat of the gas that generates the observed X-rays.
For instance, the Chandra X-ray Observatory has witnessed the pull brought on by one galaxy cluster passing through the other in the Bullet cluster, which is made up of two merging galaxy clusters. The fact that the clusters’ mass is unaffected, however, indicates that dark matter accounts for the majority of the mass.
In the universe, matter makes up 30.6 percent of the total energy. Stars make up only 0.5% of the universe’s mass, and atoms heavier than hydrogen make up only 0.3% of that mass. What’s left is dark matter. It has been established that there are two distinct forms of dark matter. The well-known baryons (protons, neutrons, and atomic nuclei), which make up the first form of matter and account for about 4.5 percent of the cosmos, are also what give rise to brilliant stars and galaxies.
Most of this baryonic dark matter is expected to be found as a gas between and between galaxies. This baryonic or regular, component of dark matter has been identified by counting the number of elements heavier than hydrogen that was created in the first few minutes following the big bang, which occurred 13.8 billion years ago.
Dark matter, which makes up the remaining 26.1 percent of the universe’s mass, exists in an unidentified, nonbaryonic form. Galaxies and massive structures made of galaxies coalesced quickly from density fluctuations in the early universe, indicating that the nonbaryonic dark matter is relatively “cold” or “non-relativistic,” meaning that the galaxies’ cores and clusters of galaxies are made of heavy, slowly moving particles.
Since no light emanates from these particles, they are electromagnetically neutral. These qualities lead to the particles being referred to as weakly interacting big particles (WIMPs). Currently, it is unknown how these particles are made up specifically, and the standard particle physics model does not predict them. Other possible extensions to the standard model, however, including supersymmetric theories, predict imaginary elementary particles like axions or neutralinos that may be the missing WIMPs.
By observing their impact in a lab detector or their annihilations after interacting with one another, these invisible WIMPs are being found and their attributes are being gauged in unusual ways. There is also some hope that research at state-of-the-art particle accelerators like the Large Hadron Collider will shed light on their mass and existence.
Dark matter has been ruled out as a possible explanation for the apparent existence of “missing matter,” but gravitational alterations have been put forth instead. These modifications imply that ordinary matter may have a larger attractive force in galactic-scale conditions. However, the majority of the solutions are insufficient on theoretical grounds because they provide scant to no rationale for the modification of gravity.
These hypotheses also fail to explain the observation that dark matter and ordinary matter are physically separated in the Bullet cluster. This distinction demonstrates the physical reality of dark matter and its ability to be separated from ordinary matter.
