Origin of the Universe, Galaxies, Stars & Planets

Early Theories

• One of the earlier theory about origin of the Universe was by German philosopher Immanuel Kant.
• Mathematician Laplace revised it in 1796.
• It is known as Nebular Hypothesis.
• The hypothesis considered that the planets were formed out of a cloud of material associated with a youthful sun

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Modern Theories of Origin of the Universe

Big Bang Theory

• The most popular argument regarding the origin of the universe is the Big Bang Theory.
• It is also called expanding universe hypothesis.
• In the beginning, all matter forming the universe existed in one place in the form of a “tiny ball”
• At the Big Bang the “tiny ball” exploded violently.
• It is now generally accepted that the event of big bang took place 13.7 billion years before.
• The expansion continues even to the present day.
• As it grew, some energy was converted into matter
• As time passes, galaxies move further and further apart.
• Edwin Hubble, in 1920, provided evidence that the universe is expanding.

Steady State Theory

• The steady state theory was governed by Hermann Boudi and Thomas Gold.
• It is also known as theory of continuous creation.
• According to this theory universe has always existed and will always exist and will always look essentially the same
• So there is no overall evolution thus balancing the average density despite the expansion.
• As old galaxies move apart the new galaxies are being formed.

Oscillating Universe Theory

• This theory was advocated by Dr. Alan Sandage.
• This theory postulates that the universe not only expands but it also contracts.
• The time interval between the two phases is presumed to be billions of years.
• It is a mixture of both Big Bang a Big Crunch theory.

Galaxies

• A galaxy is a huge mass of stars nebulae, and inter-stellar material
• Galaxies are the major building blocks of the universe.

Regular Galaxies

• The regular galaxies may be of either spiral or elliptical bi shape.

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Spiral Galaxies

• It is disc-shaped with greater concentration of stars near their centers.
• The Milky Way and the Great Galaxy in Andromeda are examples of large spiral galaxies

 Elliptical Galaxies

• These are generally smaller than the spiral galaxies.
• They are generally symmetrical or spheroidal shape with no obvious structure.
• Most of their member stars are very old and no new star forming in them.
• Sonic of them are so small that the term ‘dwarf has been applied.

Irregular Galaxies

• Irregular galaxies get their odd shapes in many ways.
• One way irregular galaxies are formed is when galaxies collide or come close to one another, and their gravitational forces interact.
• Another source of irregular galaxies may be very young galaxies that have not yet reached a symmetrical state.

Famous Galaxies

Milky Way

• Milky Way is the galaxy that contains our Solar System.
• Solar System is located within the disk, 26,490 light-years from the Galactic Center, on the inner edge of the Orion Arm, one of the spiral-shaped concentrations of gas and dust
• The Milky Way as a whole is moving at a velocity of approximately 600 km per second with respect to extragalactic frames of reference.
• The rotational period is about 240 million years at the position of the Sun
• Milky Way has several satellite galaxies and is part of the Local Group of galaxies, which form part of the Virgo Super cluster, which is itself a component of the Laniakea Supercluster.
• Milky Way contains between 200 and 400 billion stars

Canis Majo

• The Closest galaxy is the recently discovered Canis Major dwarf galaxy, which is 25,000 light-years away.

Andromeda Galaxy

• Andromeda galaxy is the nearest galaxy to the Earth apart from smaller companion galaxies.
• It is at a distance of about 2.5 million light years.

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IC 1101

• IC 1101 is the single largest galaxy that has ever been found in the observable universe.
• It has a mass of about 100 trillion stars.

NebuIa

• A nebula is a cloud of dust and gas inside a galaxy.
• Stars are born from nebula cloud
• Nebulae become visible if the gas glows or if the cloud reflects straight or obscures light from distant objects.

Star Formation

• Starts to form by accumulation of hydrogen gas in the form Nebula cloud.
• Cloud slowly shrinks and then starts to collapse onto a number of points (or cores) within the cloud, due to the pull of gravity.
• Right in the middle of these cores, it can get very hot and dense.
• When this happens, nuclear fusion can start and a star is born.
• This is called stellar ignition.
• Lifetime of a star depends very much on its size.
• Massive stars burn their fuel much faster
• Smaller stars, like Sun burn their fuel slowly and last billions of years
• Small stars will undergo a relatively peaceful death
• It will go through a planetary nebula phase to become a white dwarf
• Then it cools down over time leaving a brown dwarf.
• Massive stars, will experience a violent end called a supernova.
• Once the dust clears, the only thing remaining will be a very dense star known as a neutron star, these can often be rapidly spinning and are known as pulsars.
• If the star which explodes is larger than 4 solar masses, it can form a black hole.

Dwarfs

• Small stars less than 1.4 solar masses became Dwarf stars.
• It became extremely small in size like planet with very high densities
• Their densities may be a million times that of water.
• The matter in this state is called ‘degenerate matter’.

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Chandrashekhar Limit

• Chandrasekhar Limit of 1.4 solar masses, is the theoretical maximum mass for a stable white dwarf star can have
• Stars with mass higher than the Chandrasekhar limit ultimately collapse under their own weight and become neutron stars or black holes.

Supernova

• The point of light is the explosion of a star that has reached the end of its life, known as a supernova.
• Supernovae can briefly outshine entire galaxies and radiate more energy than our sun will in its entire lifetime.
• They’re also the primary source of heavy elements in the universe

Neutron Star

• Massive stars with 1.4 to 3 solar masses became Neutron star after supernova.
• Its hyper dense, composed almost entirely of neutrons.
• A sub-class of neutron stars is called pulsars.
• Pulsars emit regular pulses of electromagnetic radiations.
• Pulsars spin very rapidly.

Black Hole

• Massive stars with more than 3 solar masses became black hole after supernova.
• It is a region of space-time exhibiting such strong gravitational effects that nothing – not even particles and electromagnetic radiation such as light – can escape from inside it.
• The term “black hole” coined in the mid-60s by US physicist John Archibald Wheeler
• 1st photo of a black hole taken from ‘Messier 87’ supergiant elliptical galaxy in the constellation Virgo
• Photos taken by ‘Event Horizon Telescope’
• The boundary of a black hole is called Event Horizon.

Quasar

• A Quasi-Stellar Radio Source is a very energetic and distant active galactic nucleus.
• Quasars are extremely luminous.
• Most large galaxies contain a supermassive central black hole.
• Quasars contain massive black holes and may represent a stage in the evolution of some galaxies

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Famous Stars

Sirius A

• It also known as the Dog Star, is the brightest star in Earth’s night sky.

Proxima Centauri

• It is the nearest from earth about 4.22 light-years.
• Sun’s nearest neighbor, Alpha Centauri, is actually a triple-star system —three stars bound together by gravity.
• Alpha Centauri A and B are two bright, closely orbiting stars with a distant, dim companion, Proxima Centauri.

Units of Measurement

Astronomical Unit (AU)

• It is the average distance between Earth and the Sun, which is about 93 million miles or 150 million kilometers.
• Astronomical units are usually used to measure distances within our Solar System.

Light Year

• It is a measure of distance.
• Light travels at a speed of 300,000 km/second.
• Considering this, the distances the light will travel in one year is taken to be one light year

Parsec

• It is a unit of length used to measure large distances to astronomical objects
• One parsec is equal to about 3.26 light-years in length.
• A parsec is defined as the distance at which one astronomical unit subtends an angle of one arcsecond

Arc-seconds

• Angular measure of an object is usually expressed in degrees, arc-minutes or arc-seconds.
• A degree is divided into 60 arc-minutes and an arc-minute is divided into 60 arc-seconds.

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Formation of Planets

• The stars are localized lumps of gas within a nebula.
• The  gravitational force within the lumps leads to the formation of a core to the gas cloud and a huge rotating disc of gas and dust develops around the gas core.
• In the next stage, the gas cloud starts getting condensed
• Matters around the core develops into small-rounded objects.
• It develop into planetesimals.
• Planetesimals are a large number of smaller bodies.
• Larger bodies start forming by collision, and gravitational attraction causes the material to stick together.
• In the final stage, these large number of small planetesimals accrete to form a fewer large bodies in the form of planets