Have you ever thought;
Why are the galaxies found in clusters?
Why are the galaxies so organised as they seemed to be?
If the speed of spinning galaxies is to faster to hold themselves, then why don’t the stars fly off into space?
Yellow portion indicates 5% normal matter,21% Dark Matter and 74% Dark Energy.
The major problem struck out when in the year 1932, Jan Oort calculated mass of the milky way galaxy was 10 times more than the mass of normal matter. The scientist then concluded that the circus master is nothing but gravity. Something is there which is more mysterious and in the form of the invisible matter because it posses mass and gravity. This invisible matter was termed as Dark Matter. It neither absorbs nor emits nor reflects light. Therefore, it can not be physically examined. It is a property of empty space but does empty spaces really empty?
If a table is kept in a dark empty room, it just that we are unable to see it but that does not mean the dark-room is empty. Similarly, in the case of dark matter consist of none baryonic material which doesn’t interact with normal matter at all.
“We know it is but we don’t know what it is”
LUX- Large Underground Xeon and BOULBY Underground Laboratories are the famous experiments working on the dark matter, 1000 of meters below the earth surface in America.
Then how do we actually get to know about them?
By their powerful effects in the universe.
1. Uniform speed of stars:
A body moving in a circular path has a centrifugal force i.e body having the capacity to go tendential but it does not happen due to gravity which is counter-balancing it. This is the reason, stars do not fly off into space. It was assumed that the speed of stars in the outer edge of the galaxy might be less as compared to the stars at the inner edge around our massive black hole Sagittarius A star but they found something really shocking, the speed of stars at outer edge was same as compared to inner ones 250 km/sec. Hence concluded there is some invisible matter which is providing gravitational pull and named as dark matter.
Due to gravitational lensing, we are able to observe light from distant galaxies.
The dark matter outside the galaxy behaves as a lens and produce a powerful gravitational force, results in bending of light.
Wilkinson Microwave Anisotropy Probe
In 2001, WMAP spacecraft was operated to collect the microwave signals which were an echo of light left after the big bang and generated a map which shows largest to smallest variation in temperature.
Here blue region indicates low temperature whereas red region indicates high temperature. The low-temperature region leads to the formation of visible matter and empty spaces containing dark matter.
Three believes of the universe:
1. If the energy density of the universe is more than the critical density, in simple words if the amount of gravity in the universe is more then it will slow its expansion and will again squeeze into a single point named as big crunch.
2. If there isn’t much gravity. It will keep on expanding forever.
3. The universe will expand to definite shape and then stops and termed as big freeze.
In 1932, Edwin Hubble came up with the result that most of the galaxies are red shifted i.e moving away, relative to us with faster and faster speed every second.
“This sounds like we know something! We Don’t”.
If everything in this universe has gravitational pull then how is this universe expanding?
There is some kind of energy in the empty space that making it accelerate to expansion against the wishes of gravity and termed as dark energy. Recently, a galaxy has been founded whose calculated mass is equal to the mass of visible matter. A galaxy with no dark matter –NGC1052-DF2.
We are unaware of 95% of the universe. Imagine someone asking you about your hometown where you are born and bought up and you don’t know about 95% things. I don’t think he will consider you as normal.
Dark matter is a crucial part of the universe.
“Without Dark matter, there would be no galaxies
Without galaxies, there would be no stars
Without stars, there would be no planets
Without Planets, there would be no humans”