MILKY WAY

In the universe, matter is not homogeneously distributed, but on the contrary,

it’s concentrated in certain areas forming GALAXIES, which form large groups called

GALAXY CLUSTERS. Among these areas there are huge VOIDS OR EMPTY

SPACES.

THE UNIVERSE

EMPTY SPACE GALAXIES

GALAXY CLUSTER

A galaxy is a large group of stars, between 100 000 and

500 millions. Towards the center of the Galaxy, the stars

are close together. An enormous cloud of gas and dust,

called nebula, surrounds the stars

Portion of the Carina Nebula

The Rosette Nebula

STARS are made up mainly of hydrogen and helium, the two

most abundant gases in the Universe. Inside them there are

nuclear reactions which produce huge amounts of energy.

They are so hot inside that they emit heat and light.

GALAXIES

Within a galaxy we can find groups of

stars relatively close to each other. They

are open clusters.

STARS

STRUCTURE OF GALAXIES

Inside galaxies we can find the following structures:

STAR CLUSTERS:

They are

groupings of

stars held together

by gravity

NEBULAE: They consist of clouds of

gas (mainly H and He) and interstellar

dust. These are the places where stars

are born, also they can be the remains

of a star that died. Ex.: Pillars of

Creation in the Eagle Nebula, 7000

light years away

MULTIPLE STELLAR SYSTEMS: They are two or

more stars held together by gravity that revolve

around a common center. They are often apparently

seen as a single star. They are commonly double or

binary systems. Ex.: Alpha Centauri, the nearest star

to our Sun is a binary system.

BILLIONS OF

STARS

Many stars have planets that revolve around them forming planetary systems, like

our Solar System

PLANETS are bodies which orbit some

stars. They do not emit light; they receive

light from the star and reflects it (that’s why

we can see them).

Some planets have SATELLITES

or moons, They are small bodies

that orbit a planet. The Earth’s

natural satellite is the Moon

PLANETAY

SYSTEMS:

They consist of a

central star which

have other bodies

orbiting around it

1) ELLIPTICAL GALAXIES: These

galaxies have little to no structure They

are rich in old stars and have little

gas and dust. They are the most

common type of galaxy. It is believed

that large ones come from collision and

merging of other galaxies.

3) SPIRAL GALAXIES:

These galaxies are disk-

shaped either a round

central hub (unbarred) or a

hub shaped like a bar

(barred). Gas clouds and

young stars are

arranged in the spiral

arms and old stars form

the halo surrounding the

central disk.

4) BARRED SPIRAL GALAXIES: In the

central disk there is an axis or

longitudinal bar

2) IRREGULAR GALAXIES:

They look chaotic. They have

no nucleus. They are

considered to be the result of

collision of galaxies. So, they

contains a mixture of

interstellar gas and dust,

old stars and young stars

TYPES OF GALAXIES

Our galaxy is an spiral shaped galaxy called the Milky Way. The Milky Way belongs

to a galaxy cluster called the Local Group. The Local group is made up of about 33

galaxies. The closest galaxy to us is Andromeda

STARS (theSun), gas and dust clouds,

dark matter and dark energy

GALAXIES

(Milky Way)

GALAXYCLUSTERS

(Local Group and Virgo)

SUPERCLUSTERS(Local supercluster)

GALAXIES, GALAXY CLUSTERS AND SUPERCLUSTERS

Galaxies are made up of billions of stars, gas and dust clouds and dark

matter, gravitationally bound. There are over one hundred billion (1011) galaxies

in the observable universe. They are flattened ellipsoid shape, with a thicker area

in the core. Our galaxy, the Milky Way, is about 10,000 light years in diameter. The

nearest star to our Sun is Alpha-Centauri.

Galaxies move in the space and usually are grouped to form

the so-called galaxy clusters, which, in turn, may form larger

aggregates called SUPERCLUSTERS that may contain

thousands of galaxies. For example, the Milky Way is part of

the Local Group (a galaxy cluster comprising 30 galaxies, of

which Andromeda is the nearest galaxy to us). The Local

Group, in turn, orbits around the large cluster of galaxies

called Virgo. The Virgo cluster, along with the Local Group

and other clusters form the LOCAL SUPERCLUSTER. All

these clusters are moving in the same direction, although the

reason is not yet known.

THE MILKY WAY TRANSIT MAP

MILKY WAY GALAXY NEIGHBOUR

WHERE DO WE LIVE IN THE UNIVERSE?

GALACTIC FILAMENTS Observations of galaxies show that on large

scales, they are not randomly distributed in

the Universe. Most are found in groups and

clusters which are themselves part of large-

scale structures such as sheets and

filaments. These structures contain millions of

galaxies and are separated by large voids in

which very few galaxies are found.

With lengths of hundreds

of millions of light

years (but thicknesses of

only ~20 million light

years), galactic

filaments are some of the

largest known structures

in the Universe, and are

partially responsible for

the ‘honey-comb’

appearance evident in the

image

Each individual do represents a

single galaxy, and long filaments

made up of thousands of

galaxies are clearly visible. The

bright regions at the intersections

of filaments are POTENTIAL

GALAXY SUPERCLUSTERS.

GALACTIVC FILAMENTS, LARGE-SCALE STRUCTURES IN THE UNIVERSE

1) ORDINARY MATTER or baryonic matter (4%) Which can be:

- VISIBLE (stars, planets, intergalactic hot gas) (0.4%)

- INVISIBLE (black holes, intergalactic gas) (3.6%)

2) DARK MATTER (21%)

3) DARK ENERGY (75%)

ORDINARY MATTER DARK MATTER DARK ENERGY

It’s made up of ATOMS, the

chemical elements of the periodic

table consisting of protons,

neutrons and electrons. Around

70 -75% of this matter is

hydrogen (the simplest element),

about 25% is helium, and there

are small amounts of the other

108 elements of the periodic

table.

It emits or reflects light, so that

we can detect radiation coming

from it (with exceptions).

It has gravitational effects

Its composition is

unknown. It’s assumed that

dark matter is composed of a

type of particle that has not

been found in a laboratory

yet.

It does not emit or reflect

light, so we do not receive

any radiation from it.

Its existence is inferred from

their gravitational effects on

rotational speed of galaxies

and inside the galaxy

clusters, and also from

mathematical predictions of

the total mass of the universe

It’s nature is unknown.

It is homogeneously

distributed throughout

the universe and has

opposite effects to

gravity, so it’s thought to

be probably causing the

universal expansion to

accelerate

UNIVERSE COMPOSITION

Dark matter was proposed by astrophysicists, due to discrepancies between the mass of large

astronomical objects determined from their gravitational effects and the mass calculated from

the "luminous matter" they contain: stars, gas and dust.

HOW DO WE KNOW THAT THERE MUST BE DARK MATTER IN THE UNIVERSE ?

Stars in galaxies rotate too fast according to the

visible mass enclosed in its orbit. They should be

thrown out unless galaxies had more mass (dark

matter) that attracted them.

Calculated mass from visible

matter is not enough to hold

together the galaxies that form the

cluster. They should move away

unless there were more mass (dark

matter) in the cluster to keep them

together

METHODS TO STUDY THE UNIVERSE

1) Analysis of the matter that

comes from outer space

(meteorites, comets remnants,

etc..)

2) Analysis of the radiation

that comes to us: light and

radiation (radio waves,

infrared radiation, etc..)

detected by telescopes and

radiotelescopes both

terrestrial and space ones.

3) Analysis of the images

and data obtained by

satellites and space

probes (devices that are

sent into space to do

research work and do not

return)

Hubble Telescope Cassini Probe

LOOKING BACK

Light travels at an enormous but finite speed, (300,000 km/s), therefore when we see, for

example sunlight, that light has taken a long time to come (8 min. 18 sec.), So we are

actually seeing what the sun was like 8 minutes ago. Thus, when we see a star which is

4 light years away, it means that the light from it has taken four years to reach us. So, looking

at that star, what we're seeing (what reaches our eyes), is not what currently occurs there,

but what happened in that star four years ago. We are seeing the past!

Considering this, if we observe a star that is a million

light years away, we are seeing what the universe was

like a million years ago! Hence the interest of

astronomers on looking so far. This technique is

completely necessary, especially to look into the

origin of the universe and what its first steps were

What about the record? Hubble space telescope can

see what happened 13,200 million years ago! And COBE

and WMAP probes almost the origin of the Universe.

THE

FURTHER

WE CAN

SEE, THE

MORE TO

THE PAST

ARE WE

LOOKING AT

WHAT IS LIGHT?

• Light is a form of radiated energy which travels as elementary PARTICLES called

photons. These photons travel through the universe at a speed of 300,000 km/s. The

mass of a photon is zero, and they can travel even through empty space.

• Light is transmitted as a WAVE also. A wave is a form of energy transmission from one

point to another in space, which doesn’t involve displacement of matter. The series of

“peaks and valleys” or “ups and downs” are called wave.

• Thus, LIGHT HAS A DUAL BEHAVIOUR: like a wave and a particle

• Waves are defined by their FREQUENCY (photon number of oscillations per second),

which is proportional to its energy: the higher frequency, the higher energy; and by its

WAVELENGTH (distance between crests), which is inversely proportional to its energy: the

longer wavelength, the lower energy

• .

• Not all photons/waves contain the same amount of energy. According to the energy

containing at photons/waves, is defined the electromagnetic radiation spectrum:

ELECTROMAGNETIC RADIATION SPECTRUM

Violet 380-450 nm

Blue 450-495 nm

Green 495-570 nm

Yellow 570-590 nm

Orange 590-620 nm

Red 620-750 nm

THE HUMAN EYE

The human eye is only capable of capturing

photons whose wavelength ranges from 750 nm

(red) to 380 nm (violet). In this range of

values are, in descending order, the

wavelengths corresponding to the Rainbow

colours. That’s what we call visible light:

However, current telescopes, radio telescopes

and other devices are capable of detecting

radiation of any wavelength. Thus, analysing

the light/radiation that comes from any point

in space we know their composition,

distance, movement and even its history. For

example, the beginning of the universe in a big

explosion (Big Bang).

Doppler effect is the apparent change in the

frequency of a wave produced by the relative

motion of the source with reference to the

observer.

In the case of sound waves the pitch of a sound

emitted by a source approaching the observer is

higher than if the source moves away. The same

phenomenon occurs in the case of

electromagnetic waves.

In the case of the visible spectrum of

electromagnetic radiation:

- If the object moves away, its light is shifted to

longer wavelengths, moving towards red.

- If the object is approaching, the light has a

shorter wavelength, moving toward blue.

As it approaches, the sound waves are compressed

and you hear a higher sound (A). Moving away, the

sound waves are stretched and you hear a lower

sound (B).

The light coming from distant stars and galaxies is REDSHIFTED (stretched waves) when

they move away from us and it SHIFTED TO BLUE-VIOLET (compressed waves) when

they approach us.

DOPPLER EFFECT, THE EXPANDING UNIVERSE AND THE BIG BANG

THE EXPANDING UNIVERSE AND THE BIG BANG

Studying the light coming from galaxies it was found out that light from

distant galaxies is shifted toward red due to the Doppler effect. This

means that most galaxies are moving away from the Milky Way. The

exception were the closest galaxies (which are part of our Local Group) as

Andromeda, whose light comes blueshifted.

Galaxies are moving away from each other, but those that move away

faster show their light more redshifted. Hubble noticed that the recession

speed of galaxies was greater the farther they were (Hubble’s Law).

The farther the galaxies are, the faster they move away, and no one

approaches another one. How is it possible?

Edwin Powell Hubble related the moving away of galaxies with an Expanding Universe: The Universe

increases in size (volume) in time because the space between galaxies increases. The universal

expansion is the only way we can explain that all galaxies move away from each other, without approaching

anyone.

Universal expansion is an expansion of space, while galaxies (its

own motions outside) maintain size and position.

A good model to understand it is to represent the universe with one

dimension less , like the surface of a balloon. In it, galaxies would be

paper stickers pasted on the surface. As the balloon is inflated, galaxies

move away from each other and observers of each galaxy have the

impression that all others galaxies move away from them. It is the

space between galaxies which increases while they remain more or

less stationary. Thus, galaxies lack of their own velocity rate

Explaining the redshift of the light coming from distant galaxies based

on the Doppler effect is, therefore, inaccurate. However, redshift takes

place and we use it to determine the distance at which objects are, but

it does not occur due to Doppler effect, it’s due to expansion of the

universe that "stretches" the photons, displacing its wavelength to

red one.

If we see redshift in the light

coming from distant galaxies it is

because that light has been

travelling through expanding

space long , and photons have

been "stretched" with it. It can help

us to see this image.

THE ORIGIN OF THE UNIVERSE: THE BIG BANG

The universe is expanding: That implies that if you go back in time, galaxies were getting

closer and the Universe was smaller and smaller. Finally, the conclusion is that the Universe

originated from a single point, a primeval atom, by a gigantic explosion called the Big Bang

This Big Bang happened about 15,000 million years ago.

Before the Big Bang, according to

scientists, the vastness of the

observable universe, including all

its matter and radiation, was

compressed into a hot, dense mass

just a few millimeters away. This

almost incomprehensible state has

been speculated that existed just a

fraction of the first second of time.

Massive blast allowed all known

matter and energy of the universe,

including space and time, to arise

from some type of unknown energy.

3. The microwave background

radiation. It’s detected a relic radiation in

all directions that represents the "glow" or

“switch on" of the initial explosion that

comes to us today as microwave due to

the expansion of the Universe. Later we

will see its source.

EVIDENCE CONFIRMING THE BIG BANG THEORY

2. The atomic composition of the

Universe (75% H, 25% He) which, as we

shall see, is consistent with this theory.

1. The Universal expansion itself.

Currently, from the data provided by

COBE spacecraft (Cosmic Background

Explorer) and WMAP (Wilkinson

Microwave Anisotropy Probe),

perturbations of this background

radiation have been studied and

analyzed, and the results confirmed that

the Big Bang occurred 13,700 m and the

early universe was extremely hot, from

about 1013 - 1031 K and very very dense.

They Also revealed that big bang radiation

contained fluctuations from the beginning,

which are the reason why matter is no uniformly

distributed, but it is concentrated in some areas,

leaving a lot of empty space.

The theory holds that, in an instant (one trillionth of a second) after the Big Bang, the

universe expanded at an incomprehensible speed from its origin: the size of a pebble to

reach an astronomical size (inflation phase).

Apparently, its expansion continued later but much more slowly, over the next few

billion years. Although nowadays we know it is accelerating due to dark energy.

UNIVERSE EVOLUTION

As the universe expands

over time, the size

(volume) increases, but

temperature decreases

and its density too.

Thus, as time passed the

material were getting

cooler and began to

form diverse types of

atoms, and these

eventually condensed

into stars and galaxies

of our present universe.

ELEMENTARY PARTICLES

(electrons, positrons, neutrinos quarks and

photons)

HOMOGENEUS COSMIC SOUP

Protons, neutrons, electrons, positrons,

neutrinos and photons

(“caught” by particles)

PRIMARY

NUCLEOSYNTHESIS

(75% nuclei of H and 25% nuclei of He)

FIRST LIGHT

ATOMS FORMATION

(75% H y 25% He)

STAGES IN THE UNIVERSE EVOLUTION

A) OPAQUE OR DARK AGE OF THE UNIVERSE (Up to 300,000 years after the Big Bang)

1. Inflation phase

2. Stages of matter formation:

- As temperature drops, elementary particles begin to interact with each other to form stably particles of

increasing size as protons and neutrons.

- About 3 minutes after the Big Bang temperature had dropped enough and protons and neutrons joined

and gave rise to the first light nuclei. This process is called primary nuceosynthesis, and lasted only a

few minutes. Nuclei formed almost the current composition of the Universe: 75% hydrogen and 25% helium.

(In form of “plasma”, in which nuclei and electrons are separated from each other)

- From atomic nuclei, when the temperature dropped below 3000 K (300,000 years after the Big Bang) atoms

formed the first chemical elements: 75% H and 25% He

- One hundredth of a second after the Big Bang the universe began to cool (1013 K)

due to expansion and the first elementary particles of matter appeared : electrons,

positrons, neutrinos, quarks and photons. Matter and radiation (photons) interact

and are coupled to form a hot, gaseous phase called homogeneous cosmic

soup or elementary particles soup. Temperature was so high that particle

interactions were very unstable.

B) LIGHTINING ON THE UNIVERSE and TRANSPARENT UNIVERSE (300,000 years after BB)

- 300,000 years after the Big Bang, temperature

dropped below 3000 K and atomic nuclei and

electrons joined to form electrically neutral ATOMS: H

(75%), and He (25%). As a result, photons broke away

from matter and breakup, disengagement or

decoupling of matter and radiation took place.

- This initial radiation of light travelling through space is

what today is recorded as microwave background

radiation. That initial glow of light has become

microwave because the expansion of the universe has

"stretched" their wavelength.

- Data obtained by COBE probe when the Universe

was only 300,000 years old indicate that this glow was

not completely uniform but had regions of higher

density material. These denser regions, in which the

gravity was increased, attracted the matter to itself,

and while it was added, matter was fusing together in

small units. That’s how it began to form dense

objects: So first stars were made, and by meeting

these, first galaxies (approx. 5,000 m y ago). Later

first supernovae appeared and heavier atoms began

to appear.

- Photons, now free from interactions with particles,

began to travel freely through space: light began to

travel through space and Universe became

transparent to light.

STAGES OF UNIVERSE EVOLUTION

THE HISTORY OF THE UNIVERSE

Arno Penzias and Robert Wilson with

6-m antenna to detect microwave in the

Milky Way

"THE ECHO OF THE BIG BANG"

COSMIC BACKGROUND RADIATION

In 1965 two young astronomers, Arno Penzias and Robert Wilson, built a

strange 6m antenna to catch possible microwave from the Milky Way. They

didn’t find it, however, they detected a mysterious radiation observable in

all directions of the sky that remained omnipresent day and night all the

year long. First, they thought it might be "noise" caused by the abundant

droppings left by the pigeons on their big antenna. But, in spite of a careful

cleaning of the antenna, the situation didn’t change . It was a highly uniform

sign that seemed not to come from our galaxy. They mentioned the strange

discovery to some colleagues who quickly identified the radiation as the

one predicted by the proponents of the theory of the Big Bang two

decades earlier. Thus, the discovery became to be an evidence of the big

bang as the origin of the Universe.

We can capture this

radiation in our homes

with old analogy TVs:

When any channel isn’t

tuned, 1% of the "snow"

that can be seen on the

screen is that background

radiation captured by the

antenna device ....

"Picture" of the cosmic

microwave background by the

WMAP probe obtained in 2003.

This radiation was generated

when the atoms began to form

about 300,000 years after the

Big Bang. In the picture, the

different colours represent

density differences in the

Early Universe, which led to

the formation of galaxies

THE FUTURE OF THE UNIVERSE

THE FUTURE OF THE UNIVERSE

Nowadays we know that when the universe was between 5,000 –

6,000 m.y. old and was half the size it is today, dark energy

already existed. By that time the rate of expansion of the universe

began to accelerate. Other data that reinforce this accelerated

expansion is that when the universe was about 1,000 m.y. old,

mergers between galaxies were very common, and this

process has been decreasing increasingly, until about 6,000 m.y.

after the Big Bang, when these mergers were almost nonexistent,

as at present time. Also at this time stars formation decreased

too. We know that most stars we can see now were born in the

first half of the life of our universe.

Before the existence of dark energy was discovered, astronomers had proposed two possible futures for the

Universe. Following this discovery a third theory appeared :

1) If the Universe density were greater than a critical value, there would come a time when mutual gravity

would exceed the expansion. The Universe would reach a maximum size and then begin to collapse. It

would be getting smaller, denser and hotter until becoming in a similar state to its beginning. The process is

called the “Big Crunch”, and we would be talking about a cyclic universe.

2) If the Universe density were equal or less than the critical value, the expansion would never stop. Star

formation would cease and the Universe would become less dense and cooler. When the temperature

reached almost absolute zero, we would be talking about the “thermal death of the Universe”.

3) Predominance of dark energy would move galaxies away from each other at an accelerated pace and

they`d end up as islands in a vast emptiness. Dark energy would end up separating all objects joined by

gravity: It would disintegrate galaxy clusters and galaxies, planets would separate from their stars, they would

be disintegrated, and even atoms would be destroyed. It Is the theory of the “Big Rip”.

A strong radiation emitted from cores of many galaxies was found, that

would mean that there probably exists a black hole inside them.

BLACK HOLES

Black holes are high density material concentrations. As a result, its

gravitational field is so huge that not even light with its extraordinary

speed can escape from it. So, we can’t see it, and we say it’s “black”

Almost all galaxies that have been deeply studied

contain a black hole in its center . The one

occupying the center of the Milky Way is called

Sagittarius A *. Its mass is 3 million suns and its

current event horizon is 7.7 million km away

It has such a gravity power that it absorbs anything that is too close to it.

How close? For each black hole there is a no return distance or “event

horizon” so that anything that will trespass it will be absorbed hopelessly.

But fortunately, gravitational attraction decreases very rapidly with distance,

so that, out of this safety limit gravitational pull is zero and bodies are not

attracted to it. The paradox is that the more bodies fall on it, the greater

its mass is and therefore its gravitational attraction increase and its

event horizon is extended.

Black hole devouring a star

So, if it do not emit light, How do we know about their existence?

- We know about it from radiation (especially X-rays) released by accelerating matter just before falling into

the large gravity well.

- Also because sometimes we see stars rotating around an "empty" to which depends gravitationally. There

must be a black hole.

Black holes are formed when a very very massive star runs out of fuel

and dies, with a big explosion called supernova. The remaining residue can

be a black hole.

Theories about

black holes

BLACK HOLES INTO GENERAL RELATIVITY

We could imagine space as a sheet gripped by the extreme to remain stretched. If

we throw a bowling ball on top, it will bend. Something similar, according to the

theory of general relativity, makes a star into space, The greater the mass of the

ball, or star, is, the steeper the curve generated is. In a black hole curvature acquires

such an intensity that space is "broken“, it’s made a "hole". This hole, more properly

called singularity, is a real challenge, the laws of physics as we know them today,

including general relativity, lack there of validity.

Photons that a distant observer could see increase in

wavelength and "redden" to "fall" into the black hole

STARS

Stars are spherical bodies that generate energy as a result of special

reactions that take place inside them: They are high temperature nuclear

fusion reactions or thermonuclear reactions. This energy is released into

space as all types of electromagnetic radiation (Light, heat, x-rays, gamma-

rays, UV-rays, etc.) neutrinos and solar wind (jets of tiny electrically charged

subatomic particles)

In the universe there are stars of very different ages and stages of development. It is calculated first stars were formed about

13,200 m.y. ago, shortly after the beginning of the universe. Large number of stars were formed about 5,000 m.y. ago.

Stars form (are born), evolve in a series of stages from youth, maturity and old age, and eventually die

off after a time more or less long. The larger a star (more massive) is, the faster its evolution and the shorter

its life is.

STAR BIRTH

Stars are formed in dense regions of a nebulae, when the dust and gas that

it contains is compressed (pushed by the shock wave from the explosion of a

nearby supernova or the collision of galaxies), and its density increases. When

the nebula contracts, gas and dust begins to spin and focus on the center

(process of gravitational collapse). This increasingly density raises the

temperature progressively and forms a very hot core called protostar.

Around it, in the equatorial plane of the core, remains a flat disc with the

leftover material, from which planets will be formed (protoplanetary disc)

When temperature reaches millions of Kelvin degrees, nuclear fusion

reactions start and therefore the core begins to emit radiation and a star

is born.

STAR AND PLANETARY SYSTEM FORMATION

Energy emitted by stars comes from thermonuclear fusion reactions

that take place in the core, where a temperature of about 107 ºC is

reached. In these reactions light nuclei merge to form new nuclei of

heavier atoms. At first, main reaction is fusing two hydrogen nuclei

to form a helium nucleus. This process releases large amounts of

energy in form of all types of radiation (light, heat, X-rays, Gamma-rays,

UV-rays. etc.) and stellar wind (particles and ionized gas)

- In a 1st phase the hydrogen is transformed successively in

increasingly heavier elements of the periodic table, up to

iron: H > He > C > O > Ne > Mg > Si > Fe.

Stars do this at various stages of their life. The biggest

stars move more in the series of chemical elements formed

than medium or smaller stars that fail to complete the series.

- A 2nd phase, takes place only at the end of giant stars

life, when they explode in supernovas and temperature

rises further to form the heavier than iron atoms of the

periodic table.

STARS AND CHEMICAL ELEMENTS FORMATION

STARS ARE THE FACTORIES WHERE ALL CHEMICAL

ELEMENTS OF THE PERIODIC TABLE ARE MADE

STARTING FROM HIDROGEN

It starts with the lightest atom of all, the hydrogen, to form

increasingly heavy atoms, at different stages of the life of a

star:

1) MAIN STAGE: YOUTH AND MATURITY OF THE STAR

- At the beginning of its life stars are BRIGHT BLUE STAR and their main

component is hydrogen, which by nuclear fusion reactions is transformed

into helium nuclei. These heavier than hydrogen nuclei , are placed at the

center of the star.

- Over time, its temperature and luminosity increases, and becomes a

YELLOW STAR (like our Sun currently), but basically the same reaction takes

place.

STAGES OF A STAR LIFE

2) OLD AGE AND DEATH

From the helium formed, stars formed now, by nuclear reactions, carbon,

which is placed again in the center of the star. When enough carbon is formed,

it’s originated successively, by the same process, oxygen, neon, magnesium,

silicon and iron. The result is a RED GIANT STAR with an onion layered

structure, with heavier chemical elements in the center and progressively more

light toward the surface. The star evolves increasing heavy elements content

and decreasing hydrogen

From this point, the evolution of a star is different depending on its size:

Small and medium stars (M <9 MSun): When fuel is exhausted (He) the star dies

expelling outer layers as a planetary nebula, while the core (rich in C and O) shrinks

forming a WHITE DWARF. This one will cool slowly to burn out in a BLACK DWARF.

The cooling time is so long that there is still none.

PHASE OF HEAVY ELEMENTS

FORMING IN A SUPERNOVA

(EXPLOSION)

Stellar

Evolution

Giant stars (Red supergiants) (m> 9 Msun): When fuel runs out, they suffer an intense gravitational

collapse: The nuclear stove stops and gravity acts to fall toward the center trillion tons. An instant nuclear

fusion produces chemical elements heavier than iron (gold, silver, uranium, etc.). The energy released

causes a big explosion of the star named SUPERNOVA.

- Outer layers, with the chemical elements formed, are ejected forming a remaining nebula (from which stars of

2nd or 3rd generation may form again).

- The core forms a heavy residue which can be a NEUTRON STAR (very dense) or in cases of supermassive

stars (M> 30 Msun) one BLACK HOLE may be formed.

Our Sun is an average star, nowadays a yellow star that was formed about 4,600 m.y. ago. It is in the middle

of its life, so it still has many millions of years ahead. But when it passes to the phase of Red Giant it will

expand greatly and will occupy the orbits of Mercury, Venus and probably the Earth. Then, it will expel its outer

layers into a planetary nebula and the core will remain as a white dwarf, which slowly will turn into a black

dwarf.

The Solar System comprises the Sun and a large

number of bodies attached to it by gravity:

8 Planets, their moons, 3 dwarf planets (Ceres in

the asteroid belt and Pluto and Eris, on the Kuiper

belt) comets, asteroids and meteorites

SOLAR SYSTEM

It was formed about 4,600 m.y. ago, from gas and

cosmic dust of a nebula located in one of the spiral

arms (Orion arm) of the Milky Way. When the

nebula became a rotating disk originated, in the

center, the star, and from the rest of the disc material

all planetary bodies in the system.

Planets revolve around the Sun describing

elliptical orbits (the Sun located at one focus), all

located in the same plane, called plane of the

ecliptic. The direction of translation is

counterclockwise. The axis of rotation of planets

is almost perpendicular to the ecliptic, except

Uranus, which is almost parallel to it. They all rotate

counterclockwise, except Venus, which makes it

clockwise.

Pluto stopped being a planet in 2006. Its orbit crosses

the Kuiper belt asteroid (beyond Neptune)

Dwarf planets orbit around the Sun, but its gravity

is insufficient to clear its orbit of neighboring bodies.

Its orbit is located or through any of the two belts of

asteroids (main belt and Kuiper)

SMALL ROCKY PLANETS AND GAS GIANT PLANETS

INNER, TERRESTRIAL OR ROCKY PLANETS:

They are Mercury, Venus, Earth and Mars.

• They occupy the inner orbits of the solar

system (within the main asteroid belt)

• They are small compared to the rest

• Their surface is rocky (crust and mantle),

but they have a metallic core and they have

little or no atmosphere

• They have few or no satellite (Earth has

one, the Moon, and Mars have 2, Deimos

and Phobos)

The eight planets are divided into two groups:

OUTER, JOVINS OR GAS GIANT PLANETS: They

are Jupiter, Saturn, Uranus and Neptune

• They occupy the outer orbits of the solar system

(outside the main asteroid belt)

• They are of enormous size (Jupiter is the largest

of the Solar System)

• They consist mainly of gases (thick

atmospheres), except a small rocky core

• They have great number of satellites (Jupiter

63, Saturn 60 and its famous ring, Uranus 27 and

Neptune 10)

MAIN BELT ASTEROID

KUIPER BELT ASTEROID

ASTEROIDS

They are small rock

fragments, grouped in a

narrow strip, although they

orbit independently of each

other around the Sun

There 2 large asteroid belts:

- The Main belt between Mars and Jupiter (therein lies the dwarf

planet Ceres)

- The Kuiper belt located beyond Neptune (in it are the dwarf

planets Pluto and Eris)

Most meteorites that fall to Earth are

fragments of Main-Belt asteroids

Beyond the Kuiper belt is the Oort

Cloud: A set of bodies formed by ice,

methane and ammonia.

While the Oort Cloud, has not been

observed directly (a body at those

distances is impossible to detect even

with X-ray), astronomers believe it is the

source of all comets like Halley.

COMET HALLEY: It is a short-period

comet because it passes near Earth

every 76 years. The last time It passed

near the Earth was in 1986 (it will pass

again in 2062)

HALEY COMET ORBIT

COMETS

These celestial bodies are very rare since they have a highly

eccentric orbit and are only visible when they approach the Sun,

which they do every so many years because they come from the

limits of the Solar System (the Oort Cloud). When they are away

from the sun, the comet’s nucleus is formed by ice, dust, methane

and ammonia in solid due to low temperatures. As they approach the

Sun the temperature rises and their components begin to melt and

evaporate, leaving a trail dust along its path forming the tail of the

comet. Each time they pass near the Sun they lose a fraction of its

mass

The comet's

tail is always

oriented away

from the Sun

because the

Solar wind

pushes it out.

The last comet seen from Earth

was the Hale-Bob in 1997. It could

be seen for several nights in the

sky, but its return period is 2,500

years, so that we will not see it

again until 4497. It’s a long-period

comet.

Hale-Bob

A shooting star is a small dust or small rock (called also meteoroid) of

about a few millimeters that as entering the upper layers of Earth's

atmosphere, produce a luminous phenomenon by ionization of the air

in its path and by light emission after suffering a sudden high heat.

SHOOTING STARS AND TEARS OF SAN LORENZO

NIGHT

The tears of San Lorenzo night: The story tells that after crucifying Pope Sixtus II,

the Romans wanted to obtain the treasures of the Church. But when the emperor

demanded Lorenzo, responsible for managing and maintaining the property of the

Church in the time of Pope Sixtus II, to deliver the treasures to them, he gathered a

large group of blind, lame and needy people and presented them saying that those

were the property of the Church. The emperor's response was immediate. According

to legend, St. Lawrence was roasted in a kind of grill by Emperor Valerian.

There are dates on which the activity

of shooting stars increases, as is the

case of the Tears of San Lorenzo

night. This is due to the Earth

crossing the orbit of a comet,

where the density of interplanetary

dust is greater.

The comet causing the Perseid is

Swift-Tuttle comet, which visit us

every 134 years.

The saint endured his

martyrdom on 10 August

of 258 year, and for

subsequent nights the

Romans saw hundreds

of shooting stars drawn

in the sky : they were his

burning tears.

Thereafter, the night of

the year with more

shooting stars become

to be called the tears of

San Lorenzo night

(always in mid-August).

METEORITES

They are fragments of asteroids or comets that remain travelling

through space at a high speed. They revolve around the sun until they are

attracted by Earth's gravity (or other planets gravity). When they enter the

atmosphere, its temperature increases to incandesce and we see them

as shooting stars. If they are small in size, they disintegrates as they

pass through the atmosphere, but if they are large in size they fall on the

surface forming large impact craters (as such filling the Moon or Mercury)

Depending on their composition are

classified: lititos (rocky, coming from the

asteroid's surface layers) and siderite

(metallic, consisting in iron and nickel from

the core of the asteroid)

THE DISAPPEARANCE OF THE DINOSAURS

One of the most popular theories is that the dinosaurs disappeared 65 m.y. ago by the impact of a large

meteorite on the Earth. The strong impact pulverized the meteorite and part of the Earth's surface where it fell,

causing a thick layer of atmospheric dust that covered sunlight for several years. The Earth's temperature

dropped sharply and plants and vegetables disappeared. With it, large herbivores and also carnivores

disappeared, so that only small scavengers and detritivores animals survived, like a rodent like a shrew, from

which all mammals evolved since that time. Finally the atmospheric dust deposited on the ground, sunlight

came to the surface of the Earth again and seeds that were dormant germinated. New organisms appeared and

the Age of Mammals began, replacing the empty niches left by the large reptiles.

An evidence supporting this theory is the crater found in Yucatan

Peninsula (crater Chicxulub), which agrees in size and age with

the one expected according to the theory. Another evidence is the

fact that a thin sediment layer rich in a rare metal, iridium, (rare

on Earth and abundant in meteorites) had been found . This

layer is 65 m.y. old and is distributed homogeneously throughout

the planet's surface.

ORIGIN OF THE SOLAR SYSTEM (Theory of planetesimals)

5000 m.y. ago, the materials of a nebula located on the outskirts of

the Milky Way, began to stir and concentrate probably due to the

push of a shock wave produced by the explosion of a nearby

supernova. (figures 1 to 5)

Consequently most of the matter in the nebula, attracted by its own

gravity, condensed and began to concentrate in the central part of

the future planetary system that will be formed. The huge gravitational

force in the central mass compressed and heated the material until the

core temperature reached enough to initiate thermonuclear reactions

that make stars emit large amounts of energy. It was the birth of the

Sun.

The intense solar emissions "blown" into space much of the matter. The

rest remained revolving around the young star because of gravity, to

eventually form an equatorial flattened disk around the Sun

In the equatorial flattened disk, denser materials were

placed closer to the center (innermost orbits) and the

lighter ones also did outwards. Subsequently, within the

disk concentrations of matter called planetesimals,

which were arranged in different orbits around the sun,

were shown They began to collide into each other,

destroying and gathering in larger bodies, with more

gravity, that attracted the planetesimals in their

environment. So in each area of the ring, a planet began

to "grow" from planetesimals that met and merged.

The gaseous outer planets were formed first and they

were formed with the lighter elements of the nebula. On

inner zones of the disk were the rocky inner planets

formed with heavier materials. In these rocky planets,

collisions of planetesimals melted down the outside of

these protoplanets generating magma oceans up to 1000

km depth.

Then the planets cooled and created an atmosphere

with the gases released, that were retained only on the

planets which had enough gravity.

Satellites were formed with the remaining material of

planets construction, except for the Moon, which is a

particular case. Far from planets, there are also billions of

comets, icy debris of initial nebula.

EARTH AND OTHER PLANETS OF THE SOLAR SYSTEM FORMATION

It is believed that the asteroid belts are planetesimals remnants of a planet that failed to form for unknown

reasons.

SOLAR SYSTEM PLANETS

MERCURY

The smallest planet in the

Solar system (its radius is

1/3 of the Earth's radius). It

lacks satellites and

atmosphere.

Its outdoor temperature

undergoes extreme

variations, between 425 ºC

at day to -170 °C at night.

Its surface is covered with

numerous impact craters

from meteorites

VENUS

It has similar size to the Earth and

also its internal structure is

similar (Iron core, rocky mantle and

crust). It is volcanically active,

although it has not been detected

tectonic plates like on the Earth.

Its rotation is opposite to the other

planets.

Its atmosphere is mainly carbon

dioxide, so that the greenhouse

effect is very powerful and its

average surface temperature is

480 °C.

EARTH

It is the only planet that has 3/4 of

its surface covered by water. It

has a thin layer of gases that

form the atmosphere, thanks to

which the average surface

temperature is maintained at

about 15°C. This allows existence

of liquid water and life on the

planet. It has a single satellite

(the Moon). Its magnetic field is

exceptionally strong and is the

only planet that has plate

tectonics.

MARS

Olympus Mount is the largest

volcano in the solar system with 24

km altitude, the base would occupy

most of the Iberian Peninsula

The Red Planet, about half-size of the Earth. It has 2 small

satellites (Deimos and Phobos). Its light atmosphere is low in

carbon dioxid, therefore it barely possesses greenhouse effect. Its

average surface temperature is -50°C. In its atmosphere it has

detected methane gas that could be produced by organisms. At

some point, long ago it had liquid water because on its surface

there are signs of erosion produced by a watercourse. Currently

there is no water on its surface, although it is believed that there

could be water under the icy poles.

Its surface is the best known so far (it has been explored by

robots: first by the Pathfinder, then by the Spirit and the

Opportunity) and it is the target of the next manned mission. Its

surface is abundant in impact craters and large reliefs indicating

a great external and internal activity. Mount Olympus, the largest

volcano in the Solar System is on it .

Elongated marks on its surface led to

believe in fantastic "channels" built by alien

beings and the existence of Martians and

potential invasions of the Earth. Ex.: The

War of the Worlds by Orson Wells

JUPITERThis is the largest planet in the Solar System (Its radius is eleven

times the Earth's radius). It has an intense magnetic field.

Although it has some solid or liquid material inside, it is a purely

gaseous planet. Like the stars, it is made of hydrogen and helium,

but it does not meet the conditions to have nuclear fusion reactions.

On its surface there are huge meteorological formations. The Great

Red Spot is a powerful anticyclone twice the size of our planet.

It has 63 satellites, four major (Io, Europa, Ganymede and Callisto)

were discovered by Galileo in 1610

SATURN

The most characteristic feature of Saturn is that it has over 60

satellites and a peculiar system of rings visible from the Earth,

formed by dust and rock fragments orbiting at its equatorial plane.

These are small-sized particles with plenty of iced water.

Its density is extremely low, even lower than that of water.

Its two main satellites are Titan and Enceladus: Titan has a

methane-rich atmosphere, similar to that of the early Earth and

Enceladus has liquid water a short distance bellow the surface.

Saturn is the

second largest

planet in the

Solar System (it

has a radius of

10 times

greater than the

Earth)

URANUS

Uranus has a radius 4 times that of the Earth. Its

main feature is that its axis of rotation is highly

leaned, almost 90° to the plane of the orbit (Its

rotation axis is nearly horizontal with reference to

an ecliptic plane). It's like it revolve lying. This

also produces a singular magnetic field (with a

corkscrew-shaped tail)

It is the coldest planet in the solar system

It has 27 satellites, known so far and a ring

system, darker than those of Jupiter. It is blue-

green due to methane in its atmosphere

NEPTUNE

Neptune has a size slightly smaller than Uranus (its radius is three

times that of the Earth). It’s the farthest planet to our Sun. It was

discovered by mathematical calculations and once given its

position, it was observed with a telescope.

It has 8 satellites and a set of 4 very faint rings. Like Uranus it has

a rocky core (consisting of rocks, ammonia and methane) and an

atmosphere of hydrogen, helium, steam water and methane,

which gives it its blue coulor.

In the atmosphere of Neptune the temperature is below -200°C and it

produces giant hurricanes. Its atmosphere is very dynamic and

changes rapidly. Its winds are the fastest in the Solar System, reaching

2.000 km/h

Double Planet is the name that scientists give to

Earth-Moon system because of the excessive size

of the satellite with reference to the planet, only

49 times smaller than the Earth (if the planet were the

size of a basketball, the moon would be like a tennis

ball). It is too large compared to the other

satellites of the Solar System and its

corresponding planets. It is also lower in density

and gravitational force. It lacks atmosphere and the

surface temperature changes from the maximum

daytime of 107°C, to night minimum -173ºC.

THE MOON

Actually, the Moon doesn’t revolve around the Earth,

but the Earth and the Moon revolve around the mass

center of both

Apollo 11 (in 1969)

was the first

manned spacecraft

that reached the

surface. They

collected lunar rocks

and soil samples.

As the Earth is a large body, the gravity that the Moon

exerts on it is different at each point: At the nearest

point it is much higher than at the center of the mass of

the Earth, and much lower at the furthest point of the

moon. So while the Earth is rotating around the center of

gravity of the Earth-Moon system, it appears a force that

attempts to deform it, giving it the appearance of an egg.

This phenomenon is called gravity gradient, which

produces the tides. As the Earth is solid, deformation

affects more in the waters and is what gives the effect of

water moving up and down twice a day (rises in the

nearest and farthest points from the Moon and descending

in both middle points). The tide changes every six hours

following the rotation of the Earth.

When the gravity of the moon and sun are added, it

produces a particularly high tides called spring tides and

therefore, an especially low water. When the Moon and

the Sun are perpendicular to each other, tides are

smaller than current, and they are called neap tides

TIDES

An associated effect is that tides slow Earth in its

rotation (there’s a lost of energy due to friction of the

oceans to the bottom of the sea), and since the Earth-

Moon system has to conserve angular momentum, Moon

makes up away 38 mm (aprox.4 cm) each year. It has

been demonstrated by laser distance measurements made

possible by the retro-reflectors that the astronauts left on

the moon.

ORIGIN OF THE MOON: THE BIG IMPACT HYPOTHESIS

When it was discovered that the Moon composition was the same as that of the

earth's surface it was assumed that its origin had to come from the earth itself. A

body so large relative to our planet could hardly have been captured, nor was likely

to have been formed near the Earth. Thus, the best explanation to the formation of

the Moon is that it was originated from fragments that remained after a

cataclysmic collision with a Mars-sized protoplanet in the early Solar System

(Giant impact hypothesis). This theory also explains the great inclination of the

Earth’s rotation axis, which was caused by the impact.

The enormous energy supplied by the collision melted the crust to complete and large amount of

incandescent debris flung into space. Eventually, it formed a rocky ring around our planet until, by

accretion, the moon was formed.

Its initial orbit was much closer

than the current one and the

Earth-day was much shorter as

the Earth rotated faster. For

hundreds of millions of years, the

Moon has been moving slowly

away from the Earth, while the

rotation speed of the Earth has

decreased. It’s due to the transfer

of angular momentum that occurs

between the two bodies. This

process continues today at a rate

of 3.8 cm per year.

In a intermediate state, the Earth had also a ring

LUNAR RELIEF

After its formation, the Moon experienced a cataclysmic period, dated around 3,800-4,000 million years ago,

in which the Moon and the other inner Solar System bodies suffered violent impacts of large asteroids. This

period, known as late heavy bombardment formed most of the craters observed on the Moon, as well as

in Mercury. The analysis of the surface of the moon provides important data about this final period in the

formation of the solar system. Later there was a period of volcanism consisting in the emission of large

amounts of lava, which filled the largest impact basins forming the lunar seas. This period finished 3,000

million years ago. Since then, little has happened on the lunar surface but the formation of new craters due to

the impact of asteroids

When Galileo Galilei turned his telescope toward the

moon in 1610 he could see two different surface

regions. Ones are dark regions called “seas“ which of

course do not have water, and have names such as Sea

of Serenity and Sea of Fertility. They are plains with few

craters. The rest of the lunar surface is brighter, and

represents higher regions with a high density of

craters, such as Tycho and Clavius. In the lunar surface

there are also mountain ranges, they have names like

Alps and Apennines, as on Earth.

Crater TychoSea of Tranquility