As we’ll discuss later in this article, it has been discovered using the Hubble constant and measurements of supernovae of distant stars that the universe is not contracting, nor is it static (as Einstein thought), but instead, the universe is expanding, and the expansion is speeding up. To account for this, a hypothetical form of energy known as Dark Energy has been proposed and is being investigated by leading astrophysicists and cosmologists. Whether it is a scalar property of space time itself, as proposed through a cosmological constant, or something dynamic, known as quintessence, is a matter of large debate, but current astrophysics places a full 74% of the energy in the universe as being dark energy.
Dark matter (different from Dark Energy) is a type of matter that has been proposed to exist to explain gravitational effects within galaxies. When astronomers were able to measure the mass of galaxies and the orbital speed of stars within a galaxy, they noticed discrepancies between the expected results and the calculated results. Thus, a new type of matter was classified as dark matter, which is matter that is simply not detected using current measurement techniques involving electromagnetic radiation.
Cosmic microwave background radiation, or CMBR, is a form of electromagnetic radiation that fills the universe and is left over from the Big Bang. Two Bell Telephone employees were working on a radiometer for satellite communication experiments, when they discovered 3.5 K in excess temperature that they could not account for. The CMBR is essentially the remaining radiation left from a previous stage in the universe’s history, currently theorized as the Big Bang.
After discovering the various planets and non-planetary objects in our solar system, astronomers began looking at other stars in attempts to discover new planets. By analyzing the light spectra coming from distant stars, and also their brightness plotted over time, astronomers have been able to discover a large number of planets, starting in 1992 with the discovery of several planets orbiting a pulsar.
Black holes, which are largely known due to Stephen Hawking’s work, are a region of space where nothing, not even light, can escape, due to the massive gravitational pull from a single point in space with infinite density, known as a singularity. Beyond the event horizon, nothing can be seen and nothing can escape. Now, astrophysicists believe that black holes form as the result of larger stars collapsing and the electron and neutron degeneracy pressure cannot hold even atoms intact. Astrophysicists now believe that super-massive black holes exist at the center of most spiral galaxies and most galaxies in general.
General relativity is one of the theories presented by Albert Einstein, which proposes a unified description of gravity as a property of space and time, and allows for proper explanation of redshift of light and bending of light by massive objects. Largely verified through a variety of tests, one of the most famous proofs of general relativity occurred during a solar eclipse, during which the light from visible stars was mapped and extrapolated to locate the stars, which appeared in a different place than the stars actually were, due to the warping of light.
Hubble’s Law allowed for the calculation of the speed at which galaxies are receding away from Earth, which demonstrates that galaxies are moving away from us, and thus provided the general basis for the Big Bang Theory. This then later contributed to the work by astronomers that demonstrated that galaxies are expanding away from us even faster than predicted, based on the redshifts of distant supernovae, as mentioned earlier in this article.
Gamma ray bursts are, quite literally, bursts of gamma rays coming from distant galaxies, that are suspected to come from extremely energetic explosions. GRBs are the most luminous electromagnetic events in the universe, and most astrophysicists believe that GRBs come from supernova explosions and occasionally the merger of binary neutron stars.
Thanks to the use of redshifting measurements, the discovery of cosmic background radiation, and the age of the globular clusters of ancient stars in galaxies, astrophysicists have been able to calculate the age of the universe, which is currently estimated at 13.75 billion years.
As mentioned previously, the discovery of the CMBR, redshifting, and the faster than expected recession of galaxies led astronomers and astrophysicists to theorize the Big Bang, which is currently accepted as the model for the formation of the universe. The Big Bang was not an explosion within space and time, but instead, the creation of spacetime from nothing. While implications for our role in the universe, the possible existence of other universes, and what, if anything, occurred before, are the subject of speculation, the Big Bang model has survived a variety of tests and scrutiny to become widely accepted. However, with the discovery of the CMBR, it was discovered that the temperature of the universe is widely uniform, which would be impossible through traditional thermal interactions (the concept of the universe being flat, homogeneous and isotropic is known as the cosmological principle). Thus, Inflationary Theory was introduced, which suggests that the universe started with extremely rapid exponential expansion, driven by a negative pressure energy (somewhat reminiscent of Dark Energy), but before inflation, the universe was causally connected and thus had a balanced temperature.