Presentation on theme: "The Life Cycles of Stars"— Presentation transcript:
1 The Life Cycles of Stars THE HR DIAGRAMThe Life Cycles of Stars
2 Stands for the Hertzsprung-Russell Diagram HR-Diagram- What is it?Stands for the Hertzsprung-Russell DiagramGraphs surface temperature (color) vs. Absolute BrightnessHorizontal Axis- Surface Temp/ColorVertical Axis- Absolute BrightnessMass can also be estimated when Stars are placed on the HR Diagram. Typically the higher the star is on the diagram the larger the mass with a couple of exceptions.
3 Main Sequence starsThis is the diagonal band of stars that start with the bright hot stars in the upper left and the cool, dim stars in the lower right corner90% of the stars in the universe lie on the main sequenceThe sun is located in the middle
4 Giants VS. DwarfsThe HR diagram can estimate size and mass of the starIf you compare two stars of the same temperature the brighter star must be largerIf you compare two stars of the mass/size the hotter stars are brighter than the cooler stars.ray.org/labs/star_life/hr_interactive.html
5 Super Giants And White Dwarfs GIANTS- large bright stars a bit smaller and fainter than Super giantsSuper giantsIn the Red temp range tend to be in their last stages of life. They run out of hydrogen and are now fusing Helium into Carbon.In the Blue temp range they are hot bright main sequence stars.White Dwarfs- are the small, dense remains of low or medium mass stars.They are very hot, but dimmer then the main sequence stars of the same temperature.They are no longer producing energy or light, they are lit because of the remaining energy from the collapse of the original star. They will eventually cool to a black dwarf.Most stars fall on the main sequenceClose to 9% are White DwarfsLess than 1% are Giants or Super giants
6 Lifecycle of a star-BIRTH and Formation FORMATION- Space contains gas and dust and stars are formed in nurseries called Nebulas or a contracting cloud of dust and gasSome Nebulas glow while others are darkStars are created from Gravity pulling the nebula together and making a dense ball of gasPROTOSTAR- enough gas and dust to form a star is available, but it is not an actual star until it gets hot enough to start nuclear (hydrogen) fusion
7 Adult starWhen a star is on the main sequence it is considered an adult star. It will spend approx. 90% of its life span on as an adult star on the main sequence.This begins the moment Hydrogen fusion beginsThe more massive the star, the more nuclear fusion takes place to produce energyThe mass of the star determines the place it lies on the main sequence.Larger stars die quicker than smaller stars because it uses its fuel quickerLarge- live a few million yearsMedium- 10 billion (like our Sun)Small- 100 billion or more
8 DEATHAt some point the star runs out of fuel. Now remember the star is stable because of its balance between inward and outward forces.The outward force- Thermal PressureThe inward force- GravityThe star now begins to lose thermalpressure and gravity squeezes the corewhich starts hydrogen fusion in the shell of the star. Thiscauses the outer layers of the star to expand.The star cools down and turns redThe core continues to shrink causing helium fusion. For a moment ( few million years) the star stabilizes in the red giant region of the HR diagram.
9 Death of a LOW or MEDIUM mass star As the Helium supplies dwindle, the outward pressure is not enough to balance the inward pressure of gravityThe star collapsesThe hot core remains with all of the gas around it. We call this a Planetary NebulaEventually the gas surrounding the core blows off and we are left with a hot core called a White DwarfThis will cool off after 20 billion years leaving a cold core called a Black dwarf
10 High Mass Star- more than 8x the Sun The star runs out of energy and turns into a Red Super Giant the same way a low mass star does.The Star CollapsesThis time there is so much energy because of the large mass of the outer star that the collapse causes a Super Nova Explosion.NOW…if the CORE of the star has a mass of 3x or less the size of the sun ( but has a much smaller diameter than the sun) it creates a Neutron Star which spins and emits a steady beam of radiation and light out of its poles.*Neutron stars are so Dense that a teaspoon of a neutron star on EARTH would weigh a billion tons.* If the neutron star is spinning it will appear to pulse giving it the name PULSARFINALLY…if the CORE of the star is more than 3x the mass of the Sun ( and still a much smaller diameter than the Sun) the star collapses with so much energy and as the star get smaller, the gravity gets much larger. In Fact it is too large even for light to escape the gravity. This is a BLACK HOLE!