The stars

We are going to explain theses topics

-What is a star

-The composition of the stars

-How they are created

-How they die

-Constellations

-The sun

-Types of stars

-Curiosities

What is a star-We can define it like a celestial body made up of gas which lives in the space.

- It produces energy in its interior and this energy is transmitted to the exterior as light.

-The stars are diferenciated from the planetes because they emit their own light .

-The bright spots that we can see at night can be planetes or stars.

-The most known star for us is the sun

The composition of the stars

·External compositionThe superfcial lawyers of a tipical star, like the Sun, are composed by hydrogen and helium.

It has:

-92% of hydrogen

-7% of helium

-And 1% of other materials

The composition of the stars

·Internal composition-The stellar atmospheres are composed by a strange element called “tecnio”.

-Some cientifics had investigated that this element only can be present in the nuclear transformation of ohter elements.

-This show us that the stars are changing constantly their internal composition.

How they are created

-The formation of stars it's go through in places where there are a high density of moleculars clouds (big mass of gas), due to the gravitaional inestability their produce supernovas and galactic collisions.

-This molecular cloud starts to fall on itseft, it is compressed and it generates a very hot nucleus known as a protostar. After that it gets colapsed and it stops when the temperature increases.

-Then, when the fusion of the hydrogen gets stabilized it becomes to a star in principal sequence.

-That process is the 90% of the star's life.

How they die

Most of the stars take millions of years to die. There are two types of deaths depending on the size of the star

*A star like the sun...When it has consumed all their hydrogen fuel, expands to become a red giant. After to get rid of its superficial layers, the star is compressed and forms a very dense white dwarf. Through millions of years the white dwarf will realise and becomes invisible.

*The star heavier than eight times the mass of the Sun just his life very suddenly. When the fuel of the star just expand into red canterell. They try to stay alive using different fuels, but this just serves them for a couple of million of years. After this produced a large explosion that we called Supernova. During a week the supernova brightness shine more than all the other stras in the Galaxy.

How they die

Constellations

● -In modern astronomy, a constellation is a specific area of the celestial sphere as defined by the International Astronomical Union (IAU)

-There are 88 officially recognized constellations

● -Other cultures also have, or had, their own constellations.( such as Chinese, Hindu and Australian Aboriginal. The names of these constellations are not recognized by the IAU.)

The sun-The sun is star that we have the nearest. It gives us the biggest quantity of light and heat or electromagnetic radiation of this system.

-It is the center of the solar system and it represents a 99'86% of the mass of the system.

-The Earth and other bodies orbit around it.

-Furthermore it is our unique star, it's the brightest and it gives life to the all lifes of the Earth.

-The Sun is on the period called principal phase. It is a medium-sized star.

-It was created from gas clouds and dust from other death bodies and stars.

-It was formated 4650 millions of years ago, besides it has fuel for 7500 more.

-After that it will become a red giant.

-And Finally it will sink because of its weight and it will be a white dwarf.

Sun's layers

The life of the sun

Types of stars● There are seven different types of stars:

-Main sequence stars

● A star is said to be born once nuclear fusion commences in its core. At this point it is considered a main sequence star. This is where the majority of a star's life is lived. Our Sun has been on the main sequence for about 5 billion years, and will persist for another 5 billion years

-Red giant stars

Once a star has used up all of its hydrogen fuel in its core it transitions off the main sequence and becomes a red giant. Depending on the mass of the star it can oscillate between various states before ultimately becoming either a white dwarf, neutron star or black hole.

-White dwarfs

When low-mass stars, like our Sun, reach the end of their lives they enter the red giant phase. But the outward radiation pressure overwhelms the gravitational pressure and the star expands farther and farther out into space. Eventually, the outer envelope of the star begins to merge with interstellar space and all that is left behind is the remnant of the star's core. This core is a smoldering ball of carbon and other various elements. A white dwarf is not technically a star as it does not undergo nuclear fusion. Eventually it is this type of object that will be the sole remains of our Sun billions of years from now.

Types of stars-Neutron stars

A neutron star, like a white dwarf or black hole, is actually not a star but a stellar remnant. When a massive star reaches the end of its life it undergoes a supernova explosion, leaving behind its incredibly dense core. A soup-can full of neutron star material would have about the same mass as our Moon. There only objects known to exist in the Universe that have greater density are black holes.

-Black holes

Black holes are the result of very massive stars collapsing in on themselves due to the massive gravity they create. When the star reaches the end of its main sequence life cycle, the ensuing supernova drives the outer part of the star outward, leaving only the core behind. The core will have become so dense that not even light can escape its grasp. These objects are so exotic that the laws of physics break down.

-Brown dwarfs

Are not actually stars, but rather "failed" stars. They form in the same manner as normal stars, however they never quite accumulate enough mass to ignite nuclear fusion in their cores. Therefore they are noticeably smaller than main sequence stars. In fact those that have been detected are more similar to the planet Jupiter in size, though much more massive (and hence much denser).

Types of stars

Variable stars

Most stars we see in the night sky maintain a constant brightness (the twinkling we sometimes see is actually an atmospheric effect and not a variation of the star), but some stars actually do vary. While some stars owe their variation to their rotation (like rotating neutron stars, called pulsars) most variable stars change brightness because of their continual expansion and contraction. The period of pulsation observed is directly proportional to its intrinsic brightness. For this reason, variable stars are used to measure distances since their period and apparent brightness (how bright they appear to us on Earth) can be sued to calculate how far away they are from us.

Curiosities

- The closest observable star is Sol, or as it’s more commonly known, the Sun.

-There are approximately 400 billion stras in the Milky way.

-Many stars you look at in the night sky seem like single, distant glimmer of light. However that is not the case. Most stars you see in the night sky are actually two star systems, or binary star systems.

- There are some stars that are 100 times more massive than our Sun. These stars also can output about a million times more energy than our sun.

-Eta Carinae is one of the largest stars in the known galaxy, it is designated as a hyper-giant.

Video

● And now let's show you a video to sum up all this information:

- https://www.youtube.com/watch?v=JjvddwWaaQY :

● How a star die

That's all! Thank you for your attention!

Maria del Mar Andreu, 1Batx D

Llum Mestre, 1Batx A