introduction to the universe - wordpress.com

Introduction to the Universe

What makes up the Universe?

Objects in the Universe

•  Astrophysics is the science that tries to make sense of the universe by - describing the Universe (Astronomy) - understanding its structure and origin (Cosmology)

•  Main objects are Galaxies, Quasars and Nebulae

© cgrahamphysics.com 2015

Galaxies

•  Fast collection of stars •  3 types of galaxies

Quasars

•  Extremely bright objects •  Very distant objects


Nebulae

•  Misty pattern in night sky •  Some are galaxies •  Others are debris of

supernovas


Stars and Galaxies This table gives some idea of the vast distances between objects in the universe.


Our Galaxy, the Milky Way

These two drawings show what our galaxy would look like from the outside; the photograph was taken in the infrared.


The Solar System

Definition: •  A planet is a celestial body that

a) orbits around the Sun b) has sufficient mass to reach hydrostatic (nearly round) shape c) has cleared the neighborhood around its orbit

The Sun and the 8 planets •  Inner Planets - solid

Mercury, Venus, Earth and Mars •  Outer planets – gas giants

Jupiter, Saturn, Uranus, Neptune •  Pluto is not a planet. It is called

dwarf planet


New Horizons


Asteroid belt

•  Between Mars and Jupiter


Asteroids

•  Rocky bodies •  Large, up to 300km across •  Irregular shape

Comets

•  Frozen gas, ice and dust •  Smaller, just a few km

across •  Follow highly elliptical path •  Tail points away from Sun •  Found in

- Kuiper belt - Oort Cloud


Comets are found here


Planet Facts


The Universe


Stellar cluster •  Stars held together by gravitational

attraction •  All stars were created about the same

time •  Many thousands of stars in a cluster


Constellation •  A group of stars that

form a recognizable pattern as viewed from Earth

•  Stars are not related •  They are very bright •  When moving away

from Earth, the pattern is no longer recognizable

•  Example: Big dipper, the Great Bear


Galaxies The next nearest galaxy, Andromeda, is some 2 million light-years away.

It is estimated that there are about as many galaxies in the universe as there are stars in our own galaxy – 100 billion or so.

Many galaxies occur in gravitationally bound clusters, some of which have only a few galaxies and others of which have thousands.

10↑6 ly

10↑5 ly © cgrahamphysics.com 2015

•  Nearest galactic object is the Magellanic Cloud


Local group of galaxies


Cluster and Super cluster Cluster - open •  Group of stars held together

by gravity •  All formed around same

time from same nebulae •  Contain younger stars

< 10 billion years •  Virgo nearest cluster to our

galaxy

Super cluster - globular •  100s of thousands of older

stars •  Very little gas and dust •  Over 11 billion years old •  Milky Way and Virgo are

part of a super cluster

Stars in a galaxy are not uniformly distributed, their separation of average is 10↑17 m. The separation of the galaxies in clusters is of the order of 10↑17 m and the separation of the clusters is of the order of 10↑24 m.


Our Universe


Apparent motion of the Stars •  Stars rise in the East and set in the West •  Their position appears to be fixed to the

giant celestial sphere – they are referred to as fixed stars

•  Certain celestial objects do not move in circles, but wander back and forth


Explanation for the observation


The nature of Stars •  Lighter elements such as hydrogen fuse to form

helium •  Main source of energy for stars •  Very high temperatures and pressure needed in order

to overcome Coulomb repulsion •  Stars are formed by interstellar dust coming together

through gravitational attraction


The birth of a star


Hydrostatic EQLB

•  The loss in PE can, if mass is high enough, produce the high temperature necessary for fusion

•  Equilibrium between radiation pressure outward and gravitational pressure inward – a stable star

If initial mass is about 80% of mass of Sun, temperature reached is not high enough for fusion to take place. A hydrogen rich object called brown dwarf forms


Different types of stars Dwarfs •  White Dwarf Much smaller than the Sun Much higher surface temperature Sirius B: T = 20 000K Do not produce energy, just radiate energy

Brown Dwarfs Just enough mass for fusion to produce own light, but not enough to sustain fusion Relatively cool, about Jupiter’s size


Red Giants •  Considerably larger than Sun •  Much lower SA temperature than Sun •  Betelgeuse a super red giant has diameter

equal to that of the distance from Jupiter to the Sun and T = 3000K


Neutron Stars

•  Completely made up of neutrons •  Remnants of a supernova


Supernovae •  An enormous shock wave caused by the outer layers

of a star falling rapidly inwards •  Much of the surface of the star will be torn away in a

massive explosion •  In 1987 the star SK69202 in the large Magellanic

Cloud went supernova – its brilliance was greater than that of the whole Universe by a factor of 100


Stephen Hawking: Supernovae


Pulsar •  Rotating neutron stars •  They emit beams of EM

radiation in range of radio frequencies from the poles of the star

•  Each time a pole lines up with Earth, a pulse of radiation will be detected


Black Holes •  After gravitational collapse stars reach a density and radius

that the gravitational field at the surface of the star will be strong enough to prevent EM radiation to escape

•  The star will not emit any light and has become a black hole


Travel into Black holes

Homer travels into a Black hole Interstellar Black hole entry


A short documentary: Black holes


Binary Stars •  Many stars appear to be a single point of light to the

naked eye •  Viewed through a telescope or by other means they

are actually two stars orbiting each other •  Sirius, the brightest star as seen from Earth consists

of Sirius A and Sirius B •  Sirius A is a main sequence star and Sirius B is a

white dwarf


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