Cosmic proportion
What is universe comprised of? Simply the answer to this question is it is composed of 95% stuff that don’t even need to interact with anything we know. But we can feel its effect by observing at the remaining 5% regular stuff.
Dark Matter & Dark Energy (Majority of universe)
In cosmology, dark matter is exotic form of matter, which doesn’t interact with any form of radiation, making it hardly detectable, but its presence can be felt by the gravitational effects. Dark matter is postulated to explain the rotation curve of the spiral galaxy accounting the missing mass of universe. According to modern cosmology, in the large scale structure of universe, dark matter dominates the regular matter that we are familiar of. It is more massive than the galaxies and galactic clusters.
Only 4% of total energy density can be felt from the observation which infers the regular matter. And from the gravitational effect, we can see that 22% is occupied by dark matter. The remaining 74% is occupied by dark energy , even stranger ingredient of universe.
In physical cosmology, dark energy is hypothetical form of energy, that permeates all of space and accelerate the rate of expansion of the universe. It is widely accepted intuition about the accelerated expansion of universe.
Some cosmologist believe that source of dark matter is massive bodies like primordial black holes, while other astrophysicist believe that dark matter comes in the form of fundamental particles that doesn’t interact with any form of radiation.
Physical astronomy concludes that most of the matter in the universe is dark, i.e, those can’t be detected through electromagnetic radiation. Those stuffs can’t be seen directly- so what makes us think that it exist at all? Scientists indirectly infer the notion of dark matter, from the different motion of heavenly bodies at different scale, like stellar, galactic and even cosmic.
For each observation, the basic principle is that if we measure velocities in some region, then for given velocity, there has to be enough mass to gravitate, in order to have static equilibrium. When we do these observation on large scale,it turns out that the amount of mass of body not interacting to electromagnetic radiation is much more in comparison to those who does. So, this missing mass can be assigned to dark matter.
Dark matter usually are 2 broad catagories.
- Baryonic
- Non baryonic
Baryonic dark matter is made of regular stuffs, but fails to interact with electromagnetic radiation.
Non baryonic dark matter may be composed of tiny fundamental particles. These may be massive and these particle may have built of something we call dark matter, which we think exist. Non baryonic dark matter can be of two types:
- Hot dark matter
- Cold dark matter
Hot dark matter is postulated to have particles with nearly 0 rest mass. As, relativity suggests, lesser the rest mass, higher the velocity, these particle must have high kinetic energy and if we imply kinetic theory of gasses, they must heat up.
Cold dark matter is hypothesise to be comprised of very massive and have sub relativistic velocities, forming the cold gasses.
The core difference between cold dark matter and hot dark matter is the key role for the formation of structure, because the hot dark matter tries to wipe out the structure on small scale because of higher velocities.
Regular matter (a tiny minority)
Galaxies:
A galaxy is a gravitationally bound system of stars, stellar remnants, interstellar gas, dust, and dark matter. They are vast cosmic islands of stars, gas, dust, and dark matter held together.
Normal Galaxy
The galaxy that has inactive super massive black holes at the center that governs all the stars, and their respective planetary system, gas and dust by the force of gravity in association of dark matter. It may be lenticular, Elliptical Spiral or Irregular on the basis of appearance.
Examples: Andromeda Galaxy, Milky Way Galaxy, Messier 87 Galaxy
Milky way galaxy
Milky way galaxy is the galaxy that we and our solar system is located. It is the type of spiral galaxy. It extends millions of light years in girth and thousands of light years in its thickness. It has many extended arms like Orion arms that may have millions of stars and planetary system like our sun and solar system. There is a super massive black hole at the center of our milky way galaxy named Sagittarius A*. Milky way has the mass of trillions of suns.
Radio Galaxy:
The galaxies these emits the radio waves signal from its core is called radio galaxy. These waves may be strong enough to displace the planets from its position in the space. Their core may contain heavenly bodies like Pulsars and Blazars.
Pulsars: A pulsar is a highly magnetized rotating compact star that emits beams of electromagnetic radiation out of its magnetic poles. This radiation can be observed only when a beam of emission is pointing toward Earth, and is responsible for the pulsed appearance of emission.
Quasar: A quasar is an extremely luminous active galactic nucleus, in which a supermassive black hole with mass ranging from millions to billions of times the mass of the Sun is surrounded by a gaseous accretion disk.
Blazars: A blazar is an active galactic nucleus with a relativistic jet directed very nearly towards an observer.
Stars
Stars are the illuminating heavenly bodies of universe. The visible part of universe is dominated by the stars. The intense gravity of star causes the fusion reaction at the core of star. This is the source of energy for stars. Stars like our sun behave as perfect black body radiators which emits the thermal radiation that follows the Stefan’s law. It means the intensity of radiation highly increases in the increase in surface temperature of the star. The electromagnetic radiation follows the Wien’s displacement law it means the wavelength of light emitted by stars is directly proportional to the surface temperature. Surface temperature of stars increases when it gets old. So the younger stars are bluish and older star are reddish. Some examples of stars are Sun, Antares, Canopus, Betelgeuse, Aldebaran, Rigel etc.
The radii of the vary quite significantly ranging from 220 solar radius to ¹∕₅₀ fraction of solar radius. Stars having girth of 220 solar radius are called supergiant. Betelgeuse is best example of supergiant. Similarly the stars having girth of 50 solar radius are giants. Capella is suitable example of giant stars. Star such as our sun are medium sized, main sequence, dwarf star. Much more smaller stars that have girth of ¹∕₅₀ times solar radius are white dwarf. White dwarf is distinguished from dwarf stars according to its size.
Sun
Sun is the main source of energy and the reason why life exist in Earth. The source of solar energy is nuclear fusion and in nuclear fusion reaction, lighter nuclei fuse together to form heavy nucleus along with the release of tremendous amount of energy. In the core of sun 4 protium nuclei fuse to give helium nucleus.
₁H¹+₁H¹→₁H²+ ₊₁e⁰+ ν +γ
₁H²+₁H¹→ ₂He³ + γ
₂He³+₂He³ → ₂He⁴+ ₁H¹+₁H¹+γ
This reaction emits the energy equal to 26.7 MeV energy. Such billions of reaction occurs in the second, giving rise to high amount of energy for billions of year. As the result sun shines persistently.
When we photograph the sun many spots are seen in its disc which are often called as solar spot and are darker in comparison to its surroundings due to low temperature. Its numbers vary with time and maximum number of sun spots in every 11 years. During the time of maximum sun spots, unusual, highly bright activities can be noticed in certain region which is often called as solar flares. Such solar flares carries high number of γ,α particles and ₋₁e⁰ are expelled with X-rays, R- rays, and UV rays. It disturbs terrestrial radio communication by interacting Earth’s ionosphere. This disturbance in radio communication due to solar flares are called black out. Solar flares can even effect the growth of plants.
Planetary system
Planetary system is the structural organization of star, planets, dwarf planets, comets, asteroids, meteors and comets. The planetary system that we live in is solar system. Sun is the core of solar system that governs all other heavenly bodies with the force of gravity. Mercury, Venus, Earth are Mars are rocky planet that lies before asteroid belt and Jupiter, Saturn, Uranus, and Neptune lie after the asteroid belt. Pluto and Ceres are some famous dwarf planets. Each planet revolves around sun and their respective natural satellites revolve around the planets. Moon is the natural satellite of our planet Earth.
Asteroid: The mass of rocky bodies that lie between mars and Jupiter and revolve round the sun. There are 1000s of asteroids in our solar system, of which some comes very near to earth and make an approach. Their size may differ from a small grain to large rocks. They may be the potentially hazardous also. The extinction of dinosaurs in late cretaceous period became extinct due to collision of Asteroid and Earth. It is believed that the asteroids are the minute fragments of heavenly body which once existed between mars and Jupiter due to unequal gravity of jupiter and mars.
Meteor: The pieces of rocks that creates the fireworks in the sky by burning due to friction and has a very high speed. They get burnt in atmosphere completely before reaching Earth’s surface giving huge amount of heat. So they appears glowing and they are often called shooting stars. It may be the ejected part of Asteroid or may be an space debris coming from other parts of milky way. In specific month the meteor coming from direction of different constellation causes the meteor shower in night sky. Perseid meteor shower is the king of the meteor shower. Some remnant of the meteor that is able to reach the ground is called meteorite.
Comets: Fast moving rocks covered by icy bodies and ammonia that periodically comes near the sun and follows the same elongated elliptical path. It is noticed by its distinguishing head and tail. Head may extends to thousands of kilometers and the tail can extends upto millions. Shoemaker levy, Halley and Neowise are example of comets.
