Megan Garmes Betsy Nichols

1. Megan Garmes Betsy Nichols Stages of Stars

2. What is a star? • Stars are hot bodies of glowing gas that start their life in Nebulae. • Career of a star depends mostly on its mass. • The more massive the star, the more pressure is built up inside. • Stars radiate energy in all directions into space, allowing us to unravel the secrets of our universe.

3. Different Types of Stars • Giants D. Supergiants • White Dwarfs E. Sun • Main Sequence

4. Hertzsrung Russell Diagram It shows that the temperature coincides with the luminosity, the hotter the star the higher the luminosity the star has. You can also tell the size of each star from the graph as the higher the radius the higher the temperature and luminosity.

5. Facts about stars • Vary in size, mass, and temperature • The color of a star is determined by its temperature • Hottest stars are blue and the coolest are red • Nuclear fusion in the stars core produces the star’s energy • Brightness is measured in magnitude (the brighter the star, the lower the magnitude) • There are two types of magnitude: • Apparent magnitude-brightness seen from Earth • Absolute magnitude-brightness seen from a standard distance of 36.2 light years

6. Life of a small star • Stage 1: • Stars are born in a region of high density Nebula, and condenses into a huge globule of gas and dust and contracts under its own gravity. Stage 2: • A region of condensing matter will begin to heat up and start to glow forming Protostars. If a protostar contains enough matter the central temperature reaches 15 million degrees centigrade. Stage 3: • At this temperature, nuclear reactions in which hydrogen fuses to form helium can start.

7. Image of the outflow and protostar Outflow=red Protstar=green

8. Stage 4: • The star begins to release energy, stopping it from contracting even more and causes it to shine. It is now a Main Sequence Star. Stage 5: • A star of one solar mass remains in main sequence for about 10 billion years, until all of the hydrogen has fused to form helium. Stage 6: • The helium core now starts to contract further and reactions begin to occur in a shell around the core.

9. Stage 7: • The core is hot enough for the helium to fuse to form carbon. The outer layers begin to expand, cool and shine less brightly. The expanding star is now called a Red Giant. Stage 8: • The helium core runs out, and the outer layers drift of away from the core as a gaseous shell, this gas that surrounds the core is called a Planetary Nebula. Stage 9: • The remaining core ( 80% of the original star) is now in its final stages. The core becomes a White Dwarf the star eventually cools and dims. When it stops shining, the now dead star is called a Black Dwarf.

10. Red Giant Is an expanded small star, this happens because the helium is hot enough to convert into carbon, and the outer layers of the core begin to expand and shine less brightly.

11. Life of a massive star (10 solar masses) • Stage 1: • Massive stars evolve in a similar way to a small stars until it reaches its main sequence stage. The stars shine steadily until the hydrogen has fused to form helium ( it takes billions of years in a small star, but only millions in a massive star). Stage 2: • The massive star then becomes a Red Supergiant and starts of with a helium core surrounded by a shell of cooling, expanding gas.

12. Red Super Giant Just like in the process of a small star, a massive star expands into a large mass called a red super giant

13. Stage 3: • In the next million years a series of nuclear reactions occur forming different elements in shells around the iron core. Stage 4: • The core collapses in less than a second, causing an explosion called a Supernova, in which a shock wave blows of the outer layers of the star. (The actual supernova shines brighter than the entire galaxy for a short time). The star going into a stage called Supernova and contracting to become a neutron star

14. Final Stage • Stage 5: • Sometimes the core survives the explosion. If the surviving core is between 1.5 - 3 solar masses it contracts to become a a tiny, very dense Neutron Star. If the core is much greater than 3 solar masses, the core contracts to become a Black Hole.

15. Sky above 39°6'6"N 84°30'34"W at Mon 2004 Apr 5 19:37 UTC Explain symbols in the map.

16. Burnout and Death of Stars Death of Low Mass Stars: >May remain on main sequence for up to 100 billion years >Never evolve to become bloated red giants >Remain as stable main sequence stars until they consume their hydrogen fuel and collapse into white dwarfs Death of Massive Stars: >Have relatively short life spans >Terminate in an explosion known as a supernova >During this event, a star becomes millions of times brighter when it consumes most of its nuclear fuel >Predictions say that stars condense into very hot bodies known as neutron stars

17. White Dwarfs • -Extremely small stars with densities greater than any known terrestrial material Remnants of Stars • Neutron Stars • -remnants thought to be of supernova events • Black Holes • -massive star that has collapsed to such a small volume that its gravity prevents the escape of all radiation