Dark matter & Dark Energys

Submitted By :D.Surat

M.Sc. PhysicsDayalbagh Educational

Institute

Mysteries of the cosmos: Nature and Role of Dark Matter

& Dark Energy

What is Dark Matter and Dark Energy ?In our universe, we are chasing several mysteries one of them is the 95% of the invisible mass. The total part of the universe that we can observe only accounts for 5%, rest 25% is dark matter and 70% is dark energy.Dark Matter: An undetected form of mass that emits no light or no photons, but we know it must exist because we observe the effects of its gravity.Dark Energy: An unknown form of energy that is causing the universe to expand faster over time.

What Is the universe made of ?

“Normal” Matter ~ 5%

Dark Matter ~ 25%

Dark Energy ~ 70%

What is dark matter ?

Dark Matter is a kind of hidden matter which acts like a Gravitational pull to our universe.Dark meaning that it is not in the form of stars or planets we see. But it is something different from it.Although Dark Matter is not directly observed yet but its gravitational pull is experienced such as rotation of galaxies, gravitational lensing, cosmic microwave background radiation and so on.

Rotation of galaxies

Galaxies are collections of billions of stars. Most of the light from a galaxy comes from its center. This indicated that most of the galaxies stars and most of its mass is concentrated at its center. If gravity causes galaxies to rotate, as we assume it does, then outer stars should behave much like the planets of our solar system. Inner planets rotate faster and outer planets rotate slower. This is called Keplerian motion. In galaxies, however, both inner and outer stars rotate at about the same speed.

In order for gravity to cause this type of rotation, each galaxy must be surrounded by a super-massive halo of matter. No such halos, however, can be seen. So we conclude that they are made of dark matter.

What is Dark Energy ?

According to Stephen hawking big bang should be followed by a big crunch but according to Hubble's law the more distant are the celestial objects faster are they moving away from us.Which is contradiction to Stephen hawking’s statement. Which brings in an unknown kind of repulsive force believed to be dark energy.

The only thing we know about it is that it is a kind of repulsive force which causes the expansion of universe. It might be a gravitational pull of some other universe or something else we don’t know what it is, so we believe it to be dark energy.

Why are we interested in both ?

1. In future it might be possible that we might build such space crafts which could use the power from Dark Matter or Dark Energy, which will make them very fuel efficient as well as very fast.

2. Knowing properties of dark matter and dark energy we may predict actual shape and size of the universe.

At the end…

All of these points discussed in this presentation are the indirect evidences of Dark Matter and Dark Energy. We still Don't Know what they really are. They will always remain a mystery to us until we find the strong foundation for their existence.

Thank You…