Science lovers are always extremely curious about dark matter and dark energy, and want to know what really this strange thing is. But this recent phenomena is already troubling the scientists much, and truly, they couldn’t observe it completely. This doesn’t mean that we don’t know anything about them, observing them for years; we now know some of the characteristics of them.
Our planet earth, the sun, stars, galaxies, you, and me even your dog is made of proton, neutrons, and electrons which are wrapped together into atoms. The 20th century’s most surprising finding that has amazed all the astrophysicists is the fact that only 5% of the universe is made up of ordinary or baryonic matter. And the rest of the universe is made of a bizarre and imperceptible matter. To specify it, they named it Dark Matter.
Dark matter was first referred as the Missing Mass, the name was provided by Fritz Zwicky, a Swiss American astronomer who first hypothesized the existence of the dark matter. Also, he was the one to discover that the mass of every star in the Coma Cluster of the galaxies gave about one percent of the mass which is necessary for not letting the galaxies to escape from the gravitational pull of the cluster.
Later, this missing mass became the talk of the town until the American astronomers Vera Rubin and Kent Ford confirmed it exists by observing a close phenomenon. Which is the mass of the stars visible within a typical galaxy is only about 10 percent of which is needed to keep those stars orbiting the center of the galaxy.
In simple words, the orbital speed of a star with which they orbit their galaxy’s center is independent of their separation from the center. The orbital velocity is either continuous or increases slightly with the distance rather than decreasing as expected.
To account for this, the galaxy’s inner mass within the star’s orbit must increase in a straight line with the star’s distance from the center of the galaxy. When no lights were seen from this inner mass – it was named dark matter. But, wait a minute, from the statement, it looks like the complete proof about the dark matter is yet to be found and what we have is just hypothesis.
Still, astronomers and scientists are very confident about the existence of it because of the gravitational effects it appears to have on galaxies and galaxy clusters. For example, according to standard physics, stars at the verge of a spinning, spiral galaxy should travel much slower than those near the galactic center, where the visible matter of a galaxy is concentrated.
But according to the observations, stars orbit at more or less the equal speed regardless of where they are in the galactic disk. If someone agrees that the boundary stars are feeling invisible mass’s gravitational effect (We now know as the dark matter) in a ring around the galaxy, then all these spooky results make sense.
It was thought that the dark matter could explain many mysteries about the universe which astronomers have observed in the deep and dark universe. For instance, the picture of galaxies containing strange rings and arcs of light could be described as if the light from even more faraway galaxies are being contorted and magnified by giant and imperceptible clouds of dark matter in the foreground, the phenomenon is known as Gravitational Lensing.
Although not everything, scientists have created some theories of what dark matter could be. The easiest one is the dark matter consists of foreign particles which don’t interact with ordinary particles or any kind of light but it still applies gravitational pull.
Many researchers and scientists including the one at Large Hadron Collider of CERN are working to figure out more about the dark matter.
So, leaving the 95% unknown universe, the 5% we know is made of just five percent ordinary or baryonic matter and 25% of it is made of the mysterious dark matter. So what is the other 70% consists of? Well, from here the dark energy comes into play.
Dark energy is more spooky and mysterious than dark matter. The discovery of dark energy shocked all the scientists in 1990. Before the discovery, physicists thought that the attractive force of gravity would slower the universe’s expansion over time.
But when a couple of teams tried to measure the deletion rate, they found something unexpected; very much unexpected. Their findings told that the expansion was actually speeding up! Scientists now believe that some kind of repulsive force is driving the accelerated expansion of the universe generated by quantum fluctuation; in otherwise empty space.
So what’s next? The unknown force is becoming stronger as the universe is expanding. Scientists have neither logical explanation nor even a plausible hint about dark energy.
One idea says that the dark energy is a fifth and previously unknown type of fundamental force called quintessence, which fills the universe like a fluid. Some scientists also indicated that the dark matter’s known properties are consistent with a cosmological constant.
In 1917, Albert Einstein theorized a new type of cosmic repulsive force which was represented as the cosmological constant. Einstein unwillingly placed it in his Theory of General Relativity to prevent the attractive force of gravity and to explain such universe which is supposed to stay static.
But the universe is expanding; which was also proved by an American astronomer Edwin Hubble. He proved that the universe isn’t static but expanding. After it was proven, Einstein referred to the addition of this constant as his greatest blunder.
That was sad. Although, the measured amount of matter in the universes’ mass-energy budget was unlikely low, hence, some cosmological constant like missing components were needed to make up the deficit. As direct evidence began to come, it was renamed as dark energy in 1998. However, scientists are helpless to answer why the strange force exists in the universe.