Only 15% of the universe’s total mass is believed to be made up of regular stuff, according to astronomers’ estimates. According to CERN(opens in new tab), dark energy, which astronomers refer to as the accelerated expansion of the universe, accounts for about 27% of all the mass-energy in the cosmos (the European Organization for Nuclear Research).
With the use of a variety of instruments, astronomers may determine the total mass of the universe and contrast it with the mass of “normal” (also known as “baryonic”) matter. Comparing two measures is the most straightforward method.
Astronomers can determine an object’s mass by first measuring the total amount of light that huge structures like galaxies release. The projected amount of gravity required to hold the substantial construction together is the second measurement. The same conclusion is reached when scientists compare these measurements of galaxies and clusters throughout the cosmos: There isn’t nearly enough typically light-emitting stuff in the universe to account for the gravitational force required to hold those things together. Dark matter is therefore the only type of matter that might exist.
The ratio of dark matter to normal matter varies among galaxies. While some galaxies are nearly empty of normal matter, others almost entirely lack dark matter. However, each measurement yields the same typical result: Approximately 85% of the universe’s mass does not emit light or interact with it.
Not enough baryons: Astronomers can confirm this finding in a variety of other methods. An example of gravitational lensing is when a large object, such as a galaxy cluster, warps space-time so much that any light passing through it is bent. The quantity of mass that we observe from light-emitting objects can then be compared to the mass required to explain the lensing, further demonstrating that there must be hidden extra mass.
Computer simulations can be used by astronomers to examine the development of massive structures. Our universe was far smaller than it is now billions of years ago. We wouldn’t see any galaxies now if the cosmos had to rely just on the ordinary, visible matter because it takes a long time for stars and galaxies to evolve. According to a presentation by cosmologist Joel Primack, the formation of galaxies requires dark matter “pools” for the normal matter to gather in. (new tab opens)
The first protons and neutrons were produced when the universe was barely a dozen minutes old, according to cosmologists. Cosmologists can estimate how much hydrogen and helium were created over that period using our knowledge of nuclear physics.
The hydrogen-to-helium ratio in the current cosmos may be predicted with high accuracy by these calculations. According to astronomer Ned Wright, these values correspond with observations of current galaxies and clusters and also suggest an absolute limit to the amount of baryonic matter in the universe (opens in new tab).
Alternatives to dark matter: As an alternative, it’s possible that our theories of gravity—which are founded on Newton’s equations and Einstein’s general relativity—are incorrect.
These hypotheses can be modified by astronomers to explain dark matter in specific situations, such as the motions of stars within galaxies. However, there are still a number of observations of dark matter around the universe that cannot be explained by anything other than gravity.
All available evidence suggests that dark matter is made up of unidentified particles. It solely communicates with us through gravity and has no interactions with light or ordinary matter. In fact, according to astronomers, you are currently being flooded with trillions of trillions of dark matter particles. Soon, researchers think, they will be able to identify this enigmatic aspect of the cosmos.