v.-2.-Physical-Science-SHS-1.2-Stellar-Evolution-and-the-Formation-of-Heavier-Elements_073931.pptx

study on how star created

1. Lesson 1.2 Stellar Evolution and the Formation of Heavier Elements

2. give evidence for and explain the formation of heavier elements during star formation and evolution. 1 At the end of the lesson, you should be able to:

3. Stars , which are giant balls mostly made up of hydrogen and helium , act as sites for nuclear reactions in the universe. Through the process, they are able to fuse light elements to form heavier elements. These reactions also involve light emission , which is the reason why stars are so bright.

4. The BBN did not give rise to elements heavier than beryllium. Drop in temperature resulted in insufficient energy levels for fusion reactions to push through. Nucleosynthesis continued with the expansion of the universe. Big Bang Nucleosynthesis

5. What’s the reason why no elements heavier than Beryllium were formed during BBN? NOTE: Nucleosynthesis/nuclear fusion is different from BBN/primordial nucleosynthesis. Big Bang Nucleosynthesis

6.   Nuclear fusion- the process by which two light atomic nuclei combine to form a single heavier one while releasing massive amounts of energy. Nucleosynthesis/Nuclear Fusion Nucleosynthesis the  process that creates new atomic nuclei from pre-existing nucleons (protons and neutrons) and  nuclei.  

7. Big bang nucleosynthesis (BBN) is  the creation of the light nuclei, such as deuterium , T, 3He , 4He and  7 Li during the first few minutes of  the universe . Let us recall: What is the time frame for the beginning of BBN in relation to Big Bang? BBN/primordial nucleosynthesis.

8. The star formation theory states that stars formed when gravity acted on the particles expanding with the universe . Stellar Formation

9. Molecular Clouds Stars form in large clouds of gas and dust called molecular clouds . Molecular clouds range from 1,000 to 10 million times the mass of the Sun and can span as much as hundreds of light-years . Molecular clouds are cold which causes gas to clump , creating high-density pockets . Some of these clumps can collide with each other or collect more matter , strengthening their gravitational force as their mass grows. How are stars formed?

10. Astronomy a unit of  astronomical distance equivalent to the distance that light travels in one year , which is 9.4607 × 10 12  km (nearly 6 trillion miles). informal a long distance or great amount. " the new range puts them  light years ahead of  the competition" Light Years

11. Eventually , gravity causes some of these clumps to collapse. When this happens, friction causes the material to heat up, which eventually leads to the development of a protostar – a baby star . Batches of stars that have recently formed from molecular clouds are often called stellar clusters , and molecular clouds full of stellar clusters  are called stellar nurseries. Protostars , Stellar Clusters, & Stellar Nurseries.

12. The W51 ( Westerhout 52) nebula in Aquila (constellation) is one of the largest star factories in the Milky Way .

13. The edge of a nearby stellar nursery called NGC 3324 , found at the northwest corner of the Carina Nebula , forms the “mountains” and “valleys” spanning this image captured by the James Webb Space Telescope.

14. Describe what is a molecular cloud.

15. Describe the process of how protostars are formed from molecular clouds.

16. Elements associated with both living and non-living things mostly originated from stars. Processes that occurred inside stars were responsible for the formation of these elements Stellar Nucleosynthesis

17. In astrophysics, stellar nucleosynthesis is the creation of chemical elements by nuclear fusion reactions within stars . Stellar nucleosynthesis has occurred since the original creation of hydrogen, helium and lithium during the Big Bang. Stellar Nucleosynthesis

18. Elements heavier than beryllium were formed through stellar nucleosynthesis. H and He produced from lighter elements produced by BBN started to combine in nuclear fusion reactions . Very high amounts of energy were released in the form of light, heat and radiation . Stellar Nucleosynthesis

19. What is Stellar Nucleosynthesis?

20. What is produced during this process and in what form?

21. Stellar evolution refers to t he process in which a star changes through its lifetime. The abundances of elements a star contains change as it evolves. The course of evolution is determined by its mass. Stellar Evolution

22. All stars are formed from stellar nurseries called nebulae or molecular clouds. A nebula breaks into smaller fragments as it further collapses before contracting into a protostar , or a very hot stellar core that continues to gather gas and dust as it contracts and increases in temperature. Stellar Evolution

23. When the core temperature reaches about 10 million K in a protostar , nuclear fusions and other nuclear reactions begin. Hydrogen will start combining with one another in a series of proton-proton fusion reactions . (to be discussed in the next lesson). Stellar Evolution

24. Nuclear reactions (specifically, PPFR/PPCR) inside protostars form subatomic particles called neutrinos and positrons. An increase in pressure brought about by positrons and neutrinos halt the contraction of the protostar . The increase in pressure halts the contraction of a protostar and the protostar reaches gravitational equilibrium. Upon reaching gravitational equilibrium, a protostar has evolved and becomes a main sequence star. Protostar  Main Sequence Star

25. How can we say that the protostar has reached gravitational equilibrium? Stellar Evolution

26. When does nuclear fusions and reactions occur in a protostar ?

27. How does the contraction of a protostar halts?

28. Main sequence stars fuse hydrogen atoms to form helium atoms in their cores. About 90 percent of the stars in the universe, including the sun, are main sequence stars. These stars can range from about a tenth of the mass of the sun to up to 200 times as massive. The sun is believed to be in the middle of the main sequence phase of stellar evolution . It will remain as such for at least five billion years Stellar Evolution :Main sequence star

29. Most  main sequence stars are dwarf stars. A  dwarf star  is a star of relatively small size and low  luminosity.   Some examples of dwarf stars are the following: Red Dwarf Red dwarfs are the smallest main sequence stars – just a fraction of the Sun’s size and mass. They’re also the coolest, and appear more orange in color than red. Stellar Evolution :Main sequence star

30. When a red dwarf produces helium via fusion in its core , the released energy brings materia l to the star’s surface, where it cools and sinks back down , taking along a fresh supply of hydrogen to the core . Red dwarf stars stay on the main sequence phase for at least 100 billion years due to the slow rate of hydrogen fusion.

31. Red dwarfs are also born in much greater numbers than more massive stars. Because of that, and because they live so long, red dwarfs make up around 75% of the Milky Way galaxy’s stellar population . Our closest stellar neighbor, shown here in this Hubble image, is the red dwarf Proxima Centauri. It’s just over 4 light-years away in the southern constellation Centaurus.

32. Yellow Dwarf A yellow dwarf has a mass almost like the mass of the sun, 1.989 × 10^30 kg . Its color ranges from white to a lighter yellow. Among the stars in the galaxy, yellow dwarf stars are bigger than most of the stars although giant stars are the biggest of all . The life span of a yellow dwarf is said to be ten billion years and it glows brighter as years go by. Its hydrogen fuses into helium which makes its core hotter. Its energy eventually surmounts its gravity while it grows bigger and turns into a  red giant . 

33. An example of a yellow dwarf would be the sun . The sun is made of hydrogen, helium, oxygen, iron, and carbon. However, its main component is hydrogen at 75%.

34. Not all protostars become main sequence stars

35. Brown Dwarfs Brown dwarfs aren’t technically stars . They’re more massive than planets but not quite as massive as stars . Generally, they have between 13 and 80 times the mass of Jupiter . They emit almost no visible light , but scientists have seen a few in infrared light. Some brown dwarfs form the same way as main sequence stars, from gas and dust clumps in nebulae, but they never gain enough mass to do fusion on the scale of a main sequence star. Others may form like planets, from disks of gas and dust around stars

36. Brown dwarf stars are only able to fuel deuterium fusion reactions. They cool gradually and have an average lifespan of less than a billion years Brown dwarfs are invisible to both the unaided eye and backyard telescope. The image beside is the Brown dwarf LSRJ1835+3259 , it resides 20 light-years away in the northern constellation Lyra.

37. What atoms are fused in main sequence stars and what do they produce?

38. Why are brown stars aren’t considered as a star?

39. Sooner , the proton-proton chain reactions will exhaust all hydrogen in the core of a main sequence star. Helium , which is the product of these nuclear fusion reactions, will become the major component of the core. Hydrogen fusion becomes significant on the outer shell, while some of it is also fused to the core’s surface. Stellar Evolution- Main Sequence Stars to Red Giant.

40. Main sequence stars evolve into red giant stars when all hydrogen atoms in their cores get depleted Helium becomes the major component of the core . Proton-proton chain reactions use hydrogen to produce helium Hydrogen fusion moves to the outer shell and the core's surface SHORT SUMMARY Stellar Evolution- Main Sequence Stars to Red Giant.

41. When most of the hydrogen in the core is fused into helium, f usion stops and the pressure in the core decreases. Gravity squeezes the star to a point that helium-burning occurs . Helium is converted to carbon in the core via alpha processes , increasing the star’s core density. These processes involves helium atoms (also called alpha particles. Stellar Evolution

42. Main sequence stars evolve into red giant stars when all hydrogen atoms in their cores get depleted Fusion stops when all hydrogen atoms in the core are used up Pressure in the core decreases Helium atoms or alpha particles are converted to carbon via the alpha fusion processes SHORT SUMMARY Stellar Evolution

43. Meanwhile , hydrogen is converted to helium in the shell surrounding the core , increasing the temperature up to 10 million kelvins. This increase in temperature is accompanied by an increase in pressure that pushes inert hydrogen away from the core, depleting the core of hydrogen atoms , making the star, at this point, a red giant. Fusion of elements in a red giant

44. When the majority of the helium in the core has been converted to carbon , the rate of alpha fusion processes decreases . Gravity again squeezes the star . The star’s fuel is depleted and over time , the outer material of the star is blown off into space as planetary nebula . Stellar Evolution: Low Mass Stars(Red Giant to White Dwarf.

45. The only thing that remains is the hot and inert carbon core. The star becomes a white dwarf. Stellar Evolution: Low Mass Stars ( Red Giant) to White Dwarf.

46. Low mass stars turn into white dwarf stars when the majority of helium in their cores are consumed Hot and inert carbon core eventually becomes the white dwarf Lower amounts of helium in the core decrease the rate of the alpha processes Outer shell expands into space, forming a planetary nebula SHORT SUMMARY Stellar Evolution: Low M ass Stars (Red Dwraf ) to White Dwarf.

47. The composition of a white dwarf depends on how much mass is in it before it becomes such . The white dwarf discussed previously is assumed to have come from the main sequence low mass stars . White dwarf from stars with a size similar to most main sequence stars such as that of the sun does not contain enough energy to fuse carbon , and is thereby composed of inert carbon and oxygen atoms. On the other hand, a star of less than half the mass of the sun will produce a white dwarf that is mainly made up of helium and some unfused hydrogen. Composition of White Dwarf Based on their Mass

48. The composition of a white dwarf depends on how much mass is in it before it becomes such . The white dwarf discussed previously is assumed to have come from the main sequence low mass stars . A sun-sized main sequence star lacks energy to fuse carbon and the white dwarf would mostly contain inert carbon and some oxygen A smaller star with l ess than half the mass of the sun will produce a white dwarf mostly composed of helium and a bit of hydrogen Composition of White Dwarf Based on their Mass

49. Low mass stars turn into white dwarf stars when the majority of helium in their cores are consumed A white dwarf’s composition depends on its predecessor’s mass. A sun-sized main sequence star lacks energy to fuse carbon and the white dwarf would mostly contain inert carbon and some oxygen A smaller star with l ess than half the mass of the sun will produce a white dwarf mostly composed of helium and a bit of hydrogen SHORT SUMMARY Stellar Evolution

50. Unlike low mass stars, the fate of a massive star (or high mass star) is different. A massive star has enough mass such that temperature and pressure increase to a point where carbon fusion can occur . The star goes through a series of stages where heavier elements are fused in the core and in the shells around the core. Stellar Evolution: Massive Stars to Multiple Shell Red Giant Stars

51. The element oxygen is formed from carbon fusion . Neon from oxygen fusion. Silicon from neon fusion.

52. Lastly, iron from silicon fusion . The star then becomes a multiple-shell red giant. .

53. Massive stars evolve into multiple-shell red giant stars A high mass star can reach pressure and temperature levels favorable for carbon fusion It evolves through several stages where heavier elements are fused in the core and in the shells around it eventually forming multiple shells Multiple elements formed in a series of reactions in the following order: carbon → oxygen → neon → silicon → iron SHORT SUMMARY: Stellar Evolution

54. Elements lighter than iron can be fused because when two of these elements combine, they produce a nucleus with a mass lower than the sum of their masses. The missing mass is released as energy . The fusion of two elements lighter than iron therefore releases energy. Stellar Evolution: Fusion of Elements Lighter than Iron vs. Elements Heavier than Iron

55. Here are the atomic mass unit for each subatomic particle. Particle Symbol Mass electron e - 0.0005486 amu proton p + 1.007276 amu neutron n o 1.008665 amu

56. For Example: Let us weigh a Helium atom. An atom of Helium nucleus weighs 4.002602. However if you weigh its components individually you will get: 2 protons x 1.007276 amu = 2.014552 2 neutrons x 1.008665 amu = 2.01733

57. For Example: Let us weigh a Helium atom. An atom of Helium nucleus weighs 4.002602. However if you weigh its components individually you will get: 2.014552 + 2.01733 = 4.031882 Which is less compared to the amu of an Helium atom. 4.031882 - 4.002602 = 0.02928

58. Which is less compared to the amu of a Helium atom. 4.031882 - 4.002602 = 0.02928 There is a missing amount of mass (0.02928) and this missing mass is converted into energy. This conversion from mass to energy and vice versa is allowed by Alberts Einstein's famous formula: E = mc 2 Where: E= energy m= mass c= speed of light ( 3.00 x 10 8 m/s)

59. However, the fusion of two iron nuclei requires an input of energy . As a consequence, no elements heavier than iron are produced in the stars . The  production of any heavier elements requires more energy than it produces.  Stellar Evolution: Fusion of Elements Lighter than Iron vs. Elements Heavier than Iron

60. Why cant we fuse elements heavier than iron? Stellar Evolution

61. Elements lighter than iron can be fused since the nucleus produced has a mass lower than the sum of their masses. Missing mass is released as energy Stellar nucleosynthesis of elements heavier than iron is NOT POSSIBLE due to its energy requirement. SHORT SUMMARY: Stellar Evolution

62. When the core can no longer produce energy to resist gravity , the star is doomed. Gravity squeezes the core until the star explodes and releases a large amount of energy . The star explosion is called a supernova . Stellar Evolution: Supernova

63. The explosion also releases massive amounts of high-energy neutrinos which, in turn, breaks nucleons ( a term used to collectively refer to the protons and neutrons ) and release neutrons. These neutrons are picked up by nearby stars and lead to the creation of elements heavier than iron . Stellar Evolution: Supernova

64. Elements HEAVIER THAN IRON ARE FORMED AFTER A SUPERNOVA An exploding multiple-shell red giant is called a supernova. Happens when its core can no longer produce energy to resist gravity It releases massive quantities of high-energy neutrinos. Neutrinos break nucleons and release neutrons The generated neutrons are picked up by nearby stars Key step in the formation of elements heavier than iron. SHORT SUMMARY: Stellar Evolution: Supernova

65. The discovery of interstellar gas and dust in the early 1900s The study of different stages of stellar evolution happening throughout the universe. Energy in the form of infrared radiation (IR) is detected from different stages of star formation . For instance, astronomers measure the IR released by a protostar and compare it to the IR from a nearby area with zero extinction. Proving Stellar Evolution and Nucleosynthesis

66. Extinction in astronomy means the absorption and scattering of electromagnetic radiation by gases and dust particles between an emitting astronomical object and an observer. Approximation of energy, temperature and pressure in the protostar is measured from the IR. Proving Stellar Evolution and Nucleosynthesis

67. Electromagnetic radiation can be defined as a form of energy that is generated when electrically charged particles move through matter or a vacuum. Electromagnetic radiation

68. Stellar nucleosynthesis is the process by which elements are formed within stars. 1 The star formation theory proposes that stars form due to the collapse of the dense regions of a molecular cloud. 2 Stellar evolution is the process by which a star changes during its lifetime. 3

69. The primary factor that determines how stars evolve is mass . 1 All stars are born from clouds of gas and dust called nebulae or molecular clouds that collapsed due to gravity . 2 As a cloud collapses, it breaks into smaller fragments which contract to form a superhot stellar core called a protostar . 3

70. The protostar continues to accumulate gas and dust from the molecular cloud and continues to contract while the temperature increases , forming a main sequence star . 1 Main sequence star transforms into red giants if hydrogen atoms successfully fuse to form the helium core. 2 When the core can no longer produce energy to resist gravity , the star undergoes an explosion , called a supernova . 3