Unit 5

1. Unit 5 Stars *Basic Star Information *Electromagnetic Spectrum *Spectral Analysis *Energy Production in Stars *Life Cycle of a Star *HR Diagrams

2. Basic Star Info. • Vocab Words for “Basic Star Info”… • Star • Spectral Class • Luminosity • Absolute Magnitude • Apparent Magnitude • Parallax • Binary Star

3. Basic Star Info. • A Star is a burning ball of gas and dust, producing its own energy. • Each star has different and unique characteristics • Different luminosities, sizes, colors, temperatures, brightness, etc.

4. Basic Star Info. • Most stars behave as binary stars. • Binary Stars are two stars that orbit a center of mass and behave as one star. • Sirius A and Sirius B are the most common example of a binary star.

5. Basic Star Info. • A star’s spectral class, temperature and color are directly related to each other. • Spectral Class is a one letter description that scientists use to tell us the color and temperature of a star. • Each star is either an “O” type, “B” type, “A” type, “F” type, “G” type, “K” type or “M” type star. • This is the order of spectral classes from hottest stars to coldest stars! • O type stars are blue • B type stars are blueish-white • A type stars are white • F type stars are yellowish-white • G type stars are yellow • K type stars are orange • M type stars are red

6. Basic Star Info. • A stars luminosity and absolute magnitude are directly related to each other. • Luminosity is the amount of energy coming out of a star. • Luminosity is measured relative to the sun. • The sun is given a luminosity of 1. Each star with more energy has luminosity greater than 1, while each star with less energy has luminosity less than 1. • Absolute Magnitude is the actual brightness of a star, from a short distance away. • The lower the number is, the brighter the star is! • The sun has absolute magnitude of 4.8, so it is not a very bright star!

7. Basic Star Info. • Absolute Magnitude and Apparent Magnitude are very different! • Absolute Magnitude was the brightness of a star from a close distance. • Apparent Magnitude is how a bright a star appears from earth! • This is dependent upon distance because if a star is close to the earth, it is going to appear brighter, even if that star might not be that bright! • The smaller the number is, the brighter the star! • The sun has an apparent magnitude of -26.7.

8. Basic Star Info. • Parallax is the apparent shift of an object due to a change in the viewers position. • We have already demonstrated parallax using our fingers and in a lab! • Further stars have a smaller parallax than closer stars. • We can use a stars apparent vs. absolute magnitude to determine whether a star is close or far. • A close star will have an apparent magnitude that is brighter than its absolute magnitude. • A far star will have an apparent magnitude that is dimmer than its absolute magnitude. • REMEMBER…the smaller the number, the brighter it actually is!

9. Electromagnetic Spectrum • Vocab word for “Electromagnetic Spectrum”… • Electromagnetic Spectrum

10. Electromagnetic Spectrum • The Electromagnetic Spectrum is the chart of all the radiation coming off a star plotted by wavelength, frequency and energy. • The radiation is sorted into 7 different categories on the spectrum…. • Radio Waves • Microwaves • Infrared Radiation • Visible Light • Ultraviolet Radiation • X-Rays • Gamma Rays • It is relative to the earth, because this is the radiation coming off the sun and eventually traveling to earth. • Other stars produce the same radiation, that just doesn’t effect us because we are too far away from them!

11. Electromagnetic Spectrum • Wavelength is decreasing left to right. • Frequency is increasing left to right • Energy is increasing left to right.

12. Electromagnetic Spectrum • On the spectrum, the only types of radiation that penetrate earth’s atmosphere are radio waves and visible light. • There is not a significant amount of infrared and ultraviolet radiation that penetrate earth’s atmosphere. • The small section of visible light, is the only type of radiation our human eyes can actually see. • It is seen as a variation of seven different colors. • In order of decreasing wavelength, increasing frequency and increasing energy, the colors are… • Red, Orange, Yellow, Green, Blue, Indigo and Violet

13. Spectral Analysis • Vocab Word for “Spectral Analysis”… • Spectral Analysis

14. Spectral Analysis • Spectral Analysis is a practice used to learn about the composition of stars. • Scientists have studied the “spectra” of different elements. • They then look at the “spectra” of a star and compare it to the “spectra” of the different elements to determine what elements a star is made of.

15. Spectral Analysis • Scientists use spectrometers or spectroscopes to study the “spectra” of the stars and different elements. • A spectroscope has special lenses that allow scientists to see the different properties of light waves coming off a star or an element. • A spectrometer is just a spectroscope that has scales on it to measure wavelength.

16. Spectral Analysis • Example of the spectra of an entirely black object and the spectra of a few different elements!

17. Energy Production • Vocab words for “Energy Production”… • Hydrogen Fusion • Photon

18. Energy Production • Energy in a star is produced in the same manner as energy in the sun is produced because THE SUN IS A STAR!!! • It is produced by constant Hydrogen Fusion reactions occurring in the core of a star. • This is when two hydrogen atoms bond together under an extreme amount of heat and pressure to produce helium and energy.

19. Energy Production • The energy is given off in the form of a Photon. • A Photon is a particle of energy traveling through a star. • Each photon takes a totally random and different path through a star, just like they did through the sun!

20. Life Cycle of a Star • Vocab Words for “Life Cycle of a Star”… • Nebula • Protostar • Brown Dwarf • Main Sequence • Giant • Planetary Nebula • White Dwarf • Black Dwarf • Supergiant • Supernova • Neutron Star • Black Hole

21. Life Cycle of a Star • An average star lives for about 10 billion years. • During this 10 billion years a star goes through distinct phases in its life. • A star will spend most of its life in the “Main Sequence” phase because that is where it is most stable.

22. Life Cycle of a Star • The final product of star’s life is determined when the star is first formed. • The size or mass of a star determines which path it will take during its life cycle. • Stars are classified as… • Sun-like Stars – up to 1.5 times the mass of the sun • Huge Stars – from 1.5 to 3 times the mass of the sun • Massive Stars – more than 3 times the mass of the sun • A star will end it’s life as either a black dwarf, a neutron star or a black hole depending on how large the star is.

23. Life Cycle of a Star • Every star begins its life in the nebula. • A Nebula is a “stellar nursery” or a collapsing cloud of gas, dust, A LOT of hydrogen and a little bit of helium. • The Nebula develops a gravitational center called a protostar. • A protostar is the gravitational center of a nebula, which may form into a star. • Some protostars never get hot enough or are not large enough for hydrogen fusion to begin. If this is the case, that protostar never becomes an actual star and instead becomes a brown dwarf.

24. Life Cycle of a Star • The following animation will show you how a protostar forms out of nebula Nebula forming a Protostar

25. The following animation will show you how a protostar may not ever reach “star” phase and become a brown dwarf. Protostar forming a Brown Dwarf

26. Life Cycle of a Star • Relative size of a Brown Dwarf.

27. Life Cycle of a Star • If the protostar is hot enough and large enough for fusion to begin the star goes into the Main Sequence of its life. • At this stage, the star is going to remain here and fuse hydrogen into helium and energy until it begins to run out of hydrogen. • Main Sequence is the group of stars with a direct relationship between their temperature and luminosity. • Stars spend the majority of their lives in the main sequence because they are stable. • Our sun is currently a Main Sequence star!

28. Life Cycle of a Star • The following animation will show a star going from a protostar in a nebula into Main Sequence phase. The star will remain in Main sequence phase fusing hydrogen for most of its life. Forming of a Main Sequence Star

29. Life Cycle of a Star • When stars begin to run out of hydrogen to fuse, they are going to reach the ending stages of their lives. • The ending stages of a stars life is dependent upon the size or mass of the star. • We classified the stars in a previous slide.

30. Life Cycle of a Star • Sun-Sized Star (up to 1.5 times the mass of the sun). • As a sun-sized star runs out of hydrogen is left with only helium in its core. • The star will move into Giant phase and begin fusing the left over helium. • Giant is the group of stars that is cool, but bright. • Helium is a heavier element to fuse and in order to compensate for this, the outer layers of the star’s atmosphere begin expanding. • This causes the star to come less and less stable.

31. Life Cycle of a Star • Sun-Sized Star (up to 1.5 times the mass of the sun) • Eventually the star will become so unstable and begin to run out of helium. • This point all of those outer, expanded layers will be shed in a stellar wind burst called a planetary nebula.

32. Life Cycle of a Star • Sun-Sized Star (up to 1.5 times the mass of the sun) • Once the outer layers have been shed, we are left with just the remnants of the core of the star. • This core is composed mainly of carbon at this point because it has run out of helium to fuse. • The star is now in White Dwarf phase. This is the group of stars that is hot, but not very bright.

33. Life Cycle of a Star • Sun-Sized Star (up to 1.5 times the mass of the sun) • The star is not large enough to fuse carbon so it stops producing its own energy and begins to cool down. • It cools down to a Black Dwarf, which is the cooled down remnants of a white dwarf. • This is the final stage of a Sun-Sized star’s life!

34. Life Cycle of a Star • The following animation shows a sun-sized star going from the Main Sequence to the end of its life. • This star would eventually cool down and from white dwarf phase and become a black dwarf. End of Sun-Sized Star's Life

35. Life Cycle of a Star • Huge Star (from 1.5 to 3 times the mass of the sun) • As a huge star runs out of hydrogen in its core, it begins to fuse the left over helium. • It now enters the Supergiant phase of its life. • A Supergiant is a star that is cool, but very bright. • Helium is a heavier element to fuse and in order to compensate for this, the outer layers of the star’s atmosphere begin expanding. This star is larger, so it expands more than the sun-sized star. • This causes the star to become less and less stable.

36. Life Cycle of a Star • Huge Star (from 1.5 to 3 times the mass of the sun) • Eventually the star will begin to run out of helium and become so unstable it will explode as a Supernova. • A Supernova is a large stellar explosion that causes this area of space to temporarily be brighter than its surroundings.

37. Life Cycle of a Star • Huge Star (from 1.5 to 3 times the mass of the sun) • Once the star explodes, we are left with a whirling ball of neutrons. • A Neutron Star is a whirling ball of neutrons left over from a supernova explosion. • This is the final stage of Huge Star’s life!

38. Life Cycle of a Star • Massive Star (more than 3 times the mass of the sun) • As a massive star runs out of hydrogen in its core, it begins to fuse the left over helium. • It now enters the Supergiant phase of its life. • A Supergiant is a star that is cool, but very bright. • Helium is a heavier element to fuse and in order to compensate for this, the outer layers of the star’s atmosphere begin expanding. This star is larger, so it expands more than the sun-sized star. • This causes the star to become less and less stable.

39. Life Cycle of a Star • Massive Star (more than 3 times the mass of the sun) • Eventually the star will begin to run out of helium and become so unstable it will explode as a Supernova. • A Supernova is a large stellar explosion that causes this area of space to temporarily be brighter than its surroundings.

40. Life Cycle of a Star • Massive Star (more than 3 times the mass of the sun) • Once the star explodes, a massive star is large enough that the gravity is so powerful everything is sucked into this area of space. • A Black Hole is an area of space where gravity is so intense, nothing, not even light, can escape. • This is the final stage of a Massive Star’s Life!

41. Life Cycle of a Star • The following animation will show how a massive stars goes from main sequence and ends its life. • This animation should say “Supergiant” in place of “Giant” End of Massive Star's Life

42. Life Cycle of a Star

43. HR Diagram • Vocab Words for “HR Diagram”… • HR Diagram • Supergiant • Giant • Main Sequence • White Dwarf

44. HR Diagram • Ejnar Hertzsprung and Henry Russell developed the Hertzsprung-Russell diagram (HR Diagram) • The HR Diagram is a diagram of the stars charted by their luminosity vs. color. • Hertzsprung and Russell originally did this with the thousands of stars visible to the naked eye. • Since techonology has evolved we have been able to chart more stars and link temperature, spectral class and absolute magnitude to the HR Diagram.

45. HR Diagram • Hertzsprung and Russell grouped stars on the HR Diagram that are similar to each other. • They are grouped in 5 categories • Giants • Supergiants • Main Sequence • White Dwarf • Subgiant • The categories also tell us something about where a star is in its life cycle, or the evolution of the star.

46. HR Diagram

47. HR Diagram • You can clearly see the giants, supergiants, main sequence stars and white dwarfs on the diagram. • We defined those words using the group’s brightness and temperature, and you can see how that correlates to where they are located on the diagram. • Subgiant is also on the diagram. • This group of stars is slightly brighter than Main Sequence stars, but not as bright as Giant stars.

48. HR Diagram • The HR Diagram is sometimes called an evolutionary diagram of the stars because it has the different phases of the star’s lives on it. • It does not contain ALL of the stages of ALL of the different types of star’s lives.

49. HR Diagram • This is the evolution of a sun-sized star shown on the HR Diagram