Transcript PRESENTATION NAME

THE UNIVERSE
10th Grade – Physics
10th - Physics
INTRODUCTION
What is the universe?
The universe is commonly defined as the totality of everything that exists including planets, stars,
galaxies, the contents of intergalactic space, and all matter and energy Definitions and usage vary
and similar terms include the cosmos, the world and nature
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GALAXIES
Galaxy Origins
 Most astronomers suggest that galaxies
formed shortly after a cosmic "big bang"
that began the universe some 10 billion to
20 billion years ago.
 In the milliseconds following this explosion,
clouds of gases began to coalesce, collapse,
and compress under gravity to form the
building blocks of galaxies.
 Galaxies are sprawling space systems
composed of dust, gas, and countless stars
 Most of the galaxies in the Universe are
probably tiny dwarf galaxies. For example, in
our Local Group of galaxies there are only 3
large spiral galaxies: the Milky Way,
Andromeda, and the Triangulum Galaxy. The
rest are dwarf and irregular galaxies
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Types of Galaxies
Spiral galaxies, such as the Milky Way,
consist of a flat disk with a bulging center
and surrounding spiral arms. The galaxy's
disk includes stars, planets, dust, and gas—
all of which rotate around the galactic center
in a regular manner.
Elliptical galaxies are shaped as their name
suggests. They are generally round but
stretch longer along one axis than along the
other. They may be nearly circular or so
elongated that they take on a cigar like
appearance
Galaxies that are not spiral or elliptical are
called irregular galaxies. Irregular galaxies
appear misshapen and lack a distinct form,
often because they are within the
gravitational influence of other galaxies
close by.
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THE SOLAR SYSTEM
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Our solar system consists of an average
star we call the Sun, the planets
Mercury, Venus, Earth, Mars, Jupiter,
Saturn, Uranus, and Neptune,.
It includes: the satellites of the planets;
numerous comets, asteroids, and
meteoroids; and the interplanetary
medium.
The Sun is the richest source of
electromagnetic energy (mostly in the
form of heat and light) in the solar
system.
Note: Pluto no longer belongs to the
category of planet because it does not
confirm to the recognized ellitical path
around the Sun. Out of the 3 moos
Pluto has, Charon is almost equal in its
size.
THE SUN
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The Sun is the most prominent feature in our
solar system. It is the largest object and
contains approximately 98% of the total solar
system mass.
One hundred and nine Earths would be
required to fit across the Sun's disk, and its
interior could hold over 1.3 million Earths.
The Sun's outer visible layer is called the
photosphere and has a temperature of 6,000°C
(11,000°F). This layer has a mottled appearance
due to the turbulent eruptions of energy at the
surface.
The Sun is the closest star to Earth and is the
center of our solar system. A giant, spinning
ball of very hot gas, the Sun is fueled by nuclear
fusion reactions.
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THE SUN
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The light from the Sun heats our planet
and makes life possible. The Sun is also
an active star that displays sunspots,
solar flares, erupting prominences, and
coronal mass ejections.
• The distance of the Sun from the earth is
nearly 1.5 x 108 km
• Light takes about 8 minutes to travel
from the sun to the earth, hence sun is
about 8 minutes light away from earth
• The mass of the sun can be calculated by
Kepler’s law, the mass of the sun is 2 x
1030 kg.
the mass of the sun is
represented by (M-Sun)
Prominences and Solar Flares
• When you look at the sun through a
telescope (with special filters so you eyes
don't get damaged!), at the sides of the
photosphere there appear to be large
eruptions of gases like it was from a
volcano. Each of these is called a
prominence.
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THE SUN
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The amount of energy radiated per
second by the sun in all direction is
called solar luminosity, it is equal to 3.9
x 1026 Watt
The solar telescope in India is situated
in Kodaikanal and Udaipur
The sun rotates from west to east with
a period about 26 days
Spectroscopes have shown the
existence of dark lines called
Fraunhofer lines in the solar spectrum,
these lines show the existence of
elements like sodium, calcium in
addition to hydrogen in the sun.
THE SUN
Granulation pattern:
The "surface" of the Sun (the photosphere) is
covered with a "granulation pattern" caused by
the convective flow of heat rising to the
photosphere from the Sun's interior.
Sunspots : are the dark irregular patches
present on the sun, they don't look that big
when you see them on the Sun The energy
from the interior is prevented from reaching
the photosphere in the regions of the sun
spots. This is due to magnetic activities below
the photosphere. The charges particles ejected
at great speeds from the sun, ionize the air
molecules which results in spectacular colour
display. These are seen from polar regions and
are called aurora or polar lights.
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THE STRUCTURE OF THE SUN
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The Core: or the center of the Sun, is the region
where the energy of the Sun is produced The
energy travels first through the radiative zone,
The Sun's core has a tremendously high
temperature and pressure.
The Radiative Zone (or radiation zone): The next
layer out from the core is this zone which emits
radiation. This radiation diffuses outwards..
The Convective Zone: In this next layer, photons
continue to make their way outwards via
convection. The energy is transferred more
rapidly. This time it is the motion of the gases in
the Sun that transfers the energy outwards. The
gas at this layer mixes and bubbles
The Photosphere: This is the lower atmosphere
of the Sun and the part that we see (since it
emits light at visible wavelengths). This layer is
about 300 miles (500km) thick. The temperature
is
about
5,500
°C.
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THE STRUCTURE OF THE SUN
The Chromosphere: This reddish layer is an
area of rising temperatures. The
temperature ranges from 6,000 °C (at lower
altitudes) to 50,000 °C (at higher altitudes).
The Chromosphere is visible during solar
eclipses (when the moon blocks the
Photosphere).
The Corona: This is the outer layer of the
Sun's atmosphere. The corona extends for
millions of miles and the temperatures are
tremendous, reaching one million °C.
Holes in the corona occur where the Sun's
magnetic field loops out into space. These
coronal holes may be the source of the
solar wind, a stream of energetic particles
that permeate the Solar System.
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THE SUN – Solar Activity
The Sun is not a quiet place, but one that exhibits
sudden releases of energy. One of the most
frequently observed events are solar flares:
sudden, localized, transient increases in
brightness that occur in active regions near
sunspots
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THE STAR
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A star is a massive, luminous sphere of plasma held
together by gravity
The night sky is sprinkled with an enormous number
of stars that appear like bright points.
Stars are cosmic energy engines that produce heat,
light, ultraviolet rays, x-rays, and other forms of
radiation. They are composed largely of gas and
plasma, a superheated state of matter composed of
subatomic particles.
Though the most familiar star, our own sun, stands
alone, about three of every four stars exist as part of
a binary system containing two mutually orbiting
stars
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THE STAR : Appearance
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Hot stars are white or blue, whereas cooler stars appear to have orange or red
hues.
Stars may occur in many sizes, which are classified in a range from dwarfs to super
giants. Super giants may have radii a thousand times larger than that of our own
sun.
Hydrogen is the primary building block of stars. The gas circles through space in
cosmic dust clouds called nebulae.
Building pressures cause rising temperatures inside such a nascent star, and
nuclear fusion begins when a developing young star's core temperature climbs to
about 27 million degrees Fahrenheit (15 million degrees Celsius).
Stellar distances : The stars are so far away from us that they appear to be fixed.
Stellar distance being very large, a unit called ‘parsec’ is used in addition to the
unit light year (ly), to measure stellar distances. 1 parsec (pc) = 3.26ly = 3 x 1013
km.
Brightness and luminosity : Some stars are bright and some are dim; some stars
look white while some may look blue and some red. The difference in colour is due
to different temperatures.
Some stars have always stood out from the rest. Their brightness is a factor of how
much energy they put out, which is called their luminosity, and also how far away
from Earth they are.
The brightness of stars is represented by a system called magnitude scale
Stellar Spectra : The spectrum of a star like that of the sun, is a continuous
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THE STAR
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Sizes of stars : they appear as pin points even through the most
powerful telescopes. However the radius of a star can be deduced from
its luminosity and temperature. Majority of stars have radii in the range
of a tenth to twenty times solar radius.
Masses of stars : When two stars form a gravitationally bound system,
and go round in circles around their common centre of mass, their
individual masses can be determined by observing their motion. Such a
star system is called a binary star.
Sirius is a binary star system; its components have masses 1.4 MO and
2.4 MO. It is found in general that the luminosity of stars increases with
mass. Stars about forty times heavier than the sun are roughly million
times luminous than the sun.
Stellar Interiors : Mean densities of the stars can be calculated, knowing
their sizes and masses. The densities vary from 5 x 104 kg m-3 in the
case of the coolest star to around 10 kg m-3 for the hot stars. The
central temperature ranges from 10 to 30 million degrees as we go from
the coolest to the hot stars.
Strange stars : Among stars, there are strange types of stars known as
binary stars, red giants, white dwarfs, black dwarfs, neutron stars,
black holes and events called novae and supernovae. In addition, there
are quasars which are galaxies thousands times brighter than ordinary
galaxies, and pulsars which are stars that emit radiation in pulses
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MILKY WAY
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We can see, on a clear night, a hazy luminous band stretched
across the sky among the stars. This is known as the Milky
way. (Akasha ganga).
It was Galileo, who first observed (about 1610) that the
Milky way is comprised of countless number of individual
stars.
Careful examination has shown that the Milky Way viewed
from an edge, looks like a flat disc with a central bulge and
the thickness tapers off towards the edges.
Milky Way is a conglomeration of stars (Such a huge group
of stars is called a galaxy).
The diameter of the Milky Way is about one lakh light years,
and the central thickness is about 6000 ly. Our sun is located
more than halfway (about 28,000 ly) from the centre. As we
belong to this Galaxy, it is called Our galaxy.
Our Galaxy is a spiral galaxy. Milky way is rotating about its
centre. Our sun along with the planetary system is revolving
around the centre of our galaxy with a speed of 250 km/s
and takes about 250 million years, to go round once. Our
galaxy contains about 1011 stars and the total mass of all
stars in our Galaxy is about 3 x 1041 kg.
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COSMOLOGY
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Cosmology is the study of the universe. It deals especially with
the search for suitable theories to understand the observed
universe, its origin and its future.
Birth and death of stars (Stellar evolution): The process from
the birth to the death of a star is called stellar evolution.
Huge gaseous clouds mostly hydrogen exist in space. It is
believed that the birth of a star begins when such a gaseous
cloud contracts due to gravity. There will be increase in density
which leads to increase in pressure. Gradually the cloud settles
with a spherical mass at the centre of the cloud.
The central portion has a mass of about 99% of the mass of the
cloud. The sphere formed at the centre is called a protostar.
This represents the cocoon stage of a star. A protostar has a
hydrogen core formed at its central portion.
When the temperature is high enough, fusion of hydrogen
begins. The energy released during nuclear fusion tries to
expand the matter.
The energy released during nuclear fusion tries to expand the
matter. Eventually the outward pressure due to the radiation
generated balances the inward gravitational pull. This gives the
star a stable state. A protostar thus reaches steady state.
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Birth and Death of Stars
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The star is now in the youth stage and it is said to be in the main sequence.
The youth stage of a star may last for several billions of years depending on its mass. Less massive
stars stay longer in the main sequence.
The sun has remained in the youth stage for about five billion years. It will continue in the same
stage for another five billion years. For massive stars.
Evolution of Sun - like star
• As hydrogen continues to fuse forming helium a helium core forms at the centre. This is
surrounded by hydrogen in the outer shell and hydrogen fuses at a rapid rate. The resulting
radiation causes the star’s envelope to expand and cool. The colour of the star changes to red and
the star is now called red giant.
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The sun in its red giant stage, will swallow up mercury and venus and the earth will be burnt in the
heat.
• As a star’s envelope expands, its core contracts and heats up. When the temperature reaches 108
K, helium is converted into carbon in the core.
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Once the fusion of helium in the core is complete the core can not contract further.
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Evolution of Sun - like star
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Outer envelop of red giant gets detached and thrown into space.
It forms a cloud of hydrogen gas called planatary nebula.
As the temperature increases, the core develops pressure which
prevents further collapse; the star becomes what is called White
dwarf.
White dwarfs shine due to their high temperature. When further
nuclear reactions stop, a white dwarf gradually cools losing its
internal energy resulting in decrease of temperature. It becomes
dimmer and dimmer until it emits no light. It has then become a
black dwarf a dark cold chunk of mass. This corresponds to the
death of a sun like star.
Stars which are 5 times or still more massive than the sun, evolve
differently
The carbon nuclei produced during the fusion of helium form a
carbon core.
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Evolution of massive stars
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This will get ignited to produce a core of oxygen. The chain
continues leading to the production of heavier elements.
Thus cores of oxygen, magnesium, silicon, etc are formed and the
cores lie one inside the other like the layers of an onion. Iron is
formed at the inner most core. At this stage, the star explodes and
the event is called supernova .
The supernova of 1054 is today recognisable as a nebula, located in
the constellation of Taurus. It is called crab nebula.
The supernova of 1572 (called Tycho’s star) and 1604 (called
Kepler’s star) have been studied using radiotelescope.
A sphere of neutrons remains at the centre and this is called
neutron star.
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Evolution of massive stars
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In the case of stars with masses about 30 times that of
sun, the remnant at the end of supernova, has huge
amount of matter compressed into a very small region.
This is a region of intense gravitational field and is
called a black hole.
The sun would become a black hole, if compressed to a
radius of 3 km. The only recognizable property of a
black hole is its mass
Thus there can be three end states in stellar evolution
namely - white dwarf, neutron star and black hole. This
is decided by the stellar mass. Their presence can be
inferred indirectly.
The star clusters are of two types - open and globular
clusters based on their appearance.
In open type, stars appear to be loosely bound where
as in globular type, stars appear to be tightly bound.
The open clusters have many blue stars which are
young. The older globular clusters have mostly red
stars.
The study of star clusters can verify theories of stellar
evolution.
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ORIGIN OF THE UNIVERSE
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Study of galaxies shows that the galaxies in space are uniformly distributed.
The galaxies are the building blocks of our vast universe. Since the time of Aristotle, it was believed
that the universe was static and unchanging.
This was shown to be false in the 1920s leading to the realization of a dynamic evolving universe.
The spectral lines of all galaxies show red shift. Spectral lines of a given galaxy show equal red
shifts. However it varies from galaxy to galaxy.
The red shifts of galaxies show that they are moving away from us with enormous speeds.
This demonstrates that the universe is expanding.
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ORIGIN OF THE UNIVERSE
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The velocity of recession of a celestial body is proportional to its distance from us. This is
known as Hubble’s law.
The age of the universe is estimated to be 10 to 20 billion years.
At the beginning of the universe, all matter comprising galaxies and star
and radiation were compressed into a fiery region, with extremely high
temperature and enormous density. This is known as the “primordial fireball”
The fireball exploded with a bang. There was an awesome explosion which
launched the expansion of the universe. This is called the “Big Bang”. As matter
and radiation cooled, stars and galaxies formed. Planets came into existence.
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