LIFE CYCLE OF A STAR

Transcription

1 LIFE CYCLE OF A STAR

2 First stage = Protostar PROTOSTAR Cloud of gas and dust many light-years across Gravity tries to pull the materials together Eventually, at the center of the ball of dust and gas, the pressure causes the temperature to increase to 10 million Kelvin (15 million Celsius) When temperatures are that hot, nuclear fusion begins!

3 Proton Cycle and Carbon Cycle are the main sources of thermonuclear energy within the sun PROTON & CNO CYCLE Proton Cycle four hydrogen nuclei combine to form one helium nucleus Carbon-Nitrogen-Oxygen Cycle four protons fuse using carbon, nitrogen, and oxygen as catalysts to create one helium nucleus

4 MAIN SEQUENCE STAR Second stage = Main-sequence star Energy from fusion reactions push outward from the core creating a balance between the gravity pulling the gas together and the pressure from the fusion reactions Longest phase millions to billions of years Depending on how much gas and dust is collected, the size of the star ranges from about half the size of our sun to 20 times the sun s size Average star (0.4 to 3.4 times the mass of our sun) Massive star (5 times or more the mass of our sun)

5 The color and brightness of the star give us information about the star Color Surface temperature of the star Brightness (luminosity) amount of energy produced in the core STAR COLOR & TEMPERATURE

6 RED GIANTS Third Stage: Average star = Red Giant Massive star = Red Supergiant Stars take millions to billions of years to burn through all of the hydrogen When the hydrogen is gone, helium fusion begins and the star moves into a new stage Star first begins to collapse in size which then causes helium fusion which creates more heat and the star expands in size

7 HELIUM FUSION

8 Fourth Stage: Average star = White Dwarf DWARFS White Dwarf Average size stars shed their outer layers and only about 20% of the initial mass remains and over time it continues to shrink and cool Eventually becomes a Black Dwarf (theoretical) Final result of an average star Lump of matter that was once a star but has ceased to give off radiation Universe isn t old enough for any of the white dwarfs to have become black dwarfs yet

9 Fourth Stage: Massive star = Supernovae 8 times the sun s mass SUPERNOVAE Supernovae Core of the star begins to shrink becoming hotter and denser creating the elements of the periodic table through iron and fusion ceases. The core becomes over 1 billion degrees C and the repulsive forces of the nuclei causes a HUGE explosion The explosion causes the formation of the rest of the elements of the periodic table and radioactive isotopes

10 After a supernovae, a star can then become a black hole or a neutron star Depends on the mass of the star BEYOND SUPERNOVAE Black hole Gravity is so intense, nothing can escape from inside it Very massive star (~25x mass of our sun) Neutron star Small radius, high density mass composed mostly of closely packed neutrons 10-25x the mass of our sun

11 ELEMENT CREATION

12 ELEMENT CREATION

13 SPECTRAL LINES Spectral line fingerprint of light that can be used to identify the atoms, elements or molecules in a star, galaxy or gas cluster Light source is separated using a prism and a spectrum of colors with discrete lines shows up Absorption lines an atom, element or molecule absorbs energy causing an excited electron Elements have absorbed the light Emission lines an atom, element or molecule releases absorbed energy falling back to the ground state

14 SPECTRAL LINES OF OUR SUN The composition of our sun is shown by the absorption spectrum Our sun is mostly composed of hydrogen and helium, but the presence of Na, Ca and Fe are noted These elements all exist in the solar atmosphere because the elements have absorbed the light

15 LIFE CYCLE OF A STAR