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Stellar evolution ppt

Journey of the star from its birth to death

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Stellar evolution ppt

  3. 3. STAR FORMATION • Star formation is the process by which dense regions within molecular clouds in interstellar space, sometimes referred to as "stellar nurseries" or "star-forming regions", collapse and form stars. • These stellar nurseries or the star-forming regions are inside a dust cloud termed as Nebula.
  4. 4. NEBULA
  5. 5. NEBULA • A nebula, which means “cloud” or “mist” in Latin, is an interstellar cloud of dust, hydrogen, helium and other ionized gases. • Originally, the term was used to describe any diffuse astronomical object, including galaxies beyond the Milky Way. The Andromeda Galaxy, for instance, was once referred to as the Andromeda Nebula (and spiral galaxies in general as "spiral nebulae") before the true nature of galaxies was confirmed in the early 20th century by Vesto Slipher, Edwin Hubble and others. • Although denser than the space surrounding them, most nebulae are far less dense than any vacuum created on Earth – a nebular cloud the size of the Earth would have a total mass of only a few kilograms.
  6. 6. TYPES OF NEBULA Nebula are classified into 4 major groups: • Planetary Nebula • Supernova Remnant • H II regions, large diffused nebula containing ionised hydrogen. • Dark Nebula
  8. 8. TYPES OF NEBULA Nebula are classified into 4 major groups: • Planetary Nebula • Supernova Remnant • H II regions, large diffused nebula containing ionised hydrogen. • Dark Nebula
  10. 10. TYPES OF NEBULA Nebula are classified into 4 major groups: • Planetary Nebula • Supernova Remnant • H II regions, large diffused nebula containing ionised hydrogen. • Dark Nebula
  11. 11. DIFFUSE NEBULA • Most nebulae can be described as diffuse nebulae, which means that they are extended and contain no well-defined boundaries. • Diffuse nebula can be further classified into 3 sub groups, as in: A.Emission Nebula B.Reflection Nebula C.Dark Nebula • Emission Nebula is the one that emits spectral line radiation from excited or ionised gas, mainly ionised hydrogen, they are often called H II regions.
  13. 13. STAR FORMATION • Stars form inside relatively dense concentrations of interstellar gas and dust known as molecular clouds. These regions are extremely cold (temperature about 10 to 20K, just above absolute zero). At these temperatures, gases become molecular meaning that atoms bind together. • CO and H2 are the most common molecules in interstellar gas clouds. • The deep cold also causes the gas to clump to high densities. When the density reaches a certain point, stars form.
  14. 14. • Star formation begins when the denser parts of the cloud core collapse under their own weight/gravity. • These cores typically have masses around 104 solar masses in the form of gas and dust. The cores are denser than the outer cloud, so they collapse first. • As the cores collapse they fragment into clumps around 0.1 parsecs in size and 10 to 50 solar masses in mass. • These clumps then form into protostars and the whole process takes about 10 millions years. STAR FORMATION
  15. 15. PROTOSTARS
  16. 16. T-TAURI STARS
  17. 17. T-TAURI STAR • The T-Tauri phase is when a star has: vigorous surface activity (flares, eruptions) strong stellar winds variable and irregular light curves. • A typical T-Tauri star can lose upto 50% of its mass before settling as a main sequence star. Hence, it’s also called pre-main sequence star.
  19. 19. WHY DO STARS DIE?
  20. 20. WHY DO STARS DIE? • Stars die because they end their nuclear fuel. • The events at the end of a star’s life depend on its mass.
  22. 22. Really massive stars use up their hydrogen fuel quickly ,but are hot enough to fuse heavier elements such as helium and carbon. Once their is no fuel left, the star collapses and the outer layers explode as a 'supernova'. What's left over after a supernova explosion is a ‘neutron star' - the collapsed core of the star - or, if there's sufficient mass , a black hole. MASSIV E STAR Average - sized stars will die less dramatically. As their hydrogen is used up, they swell to become red giants , fusing helium in their cores , before shedding their outer layers , often forming a 'planetary nebula'. The star's core remains as a 'white dwarf' , which cools off over billions of years. AVERAG E STAR The tiniest stars , known as 'red dwarfs', burn their nuclear fuel so slowly that they might live to be 100 billion years old - much older than the current age of the universe. TINIEST STAR
  23. 23. SUPERNOVA
  24. 24. SUPERNOVA • A supernova happens where there is a change in the core, or centre of a star. A change can occur in two different ways, with both resulting in a supernova. • The first type of supernova happens in binary star systems. Binary stars are two stars that orbit the same point. One of the stars, a carbon-oxygen white dwarf, steals matter from its companion star. Eventually, the white dwarf accumulates too much matter. Having too much matter causes the star to explode, resulting in a supernova. • The second type of supernova occurs at the end of a single star’s lifetime. As the star runs out of nuclear fuel, some of its mass flows into its core. Eventually, the core is so heavy that it cannot withstand its own gravitational force. The core collapses, which results in the giant explosion of a supernova. The sun is a single star, but it does not have enough mass to become a supernova.
  25. 25. RED GIANT
  26. 26. RED GIANT • Red giants are stars that have exhausted the supply of hydrogen in their cores and have begun thermonuclear fusion of hydrogen in a shell surrounding the core. They have radii tens to hundreds of times larger than that of the Sun. However, their outer envelope is lower in temperature, giving them a reddish-orange hue. • A red giant star is a dying star in the last stages of stellar evolution. In only a few billion years, our own sun will turn into a red giant star, expand and engulf the inner planets, possibly even Earth. • The outer layers of the star starts to grow, cool and turn red again as it enters its second red giant phase. Small sun-like stars move into a planetary nebula phase, whilst stars greater than about 8 times the mass of the Sun are likely to end their days as a supernova.
  27. 27. HOW LONG DO STARS LIVE? • A star’s life expectancy depends on its mass. • Generally, the more massive the star, the faster it burns up its fuel supply, and the shorter its life. The most massive stars can burn out and explode in a supernova after only a few million years of fusion. • A star with a mass like the Sun, on the other hand, can continue fusing hydrogen for about 10 billion years. • And if the star is very small, with a mass only a tenth that of the Sun, it can keep fusing hydrogen for up to a trillion years, longer than the current age of the universe.
  28. 28. STARS EXPLODE! •Mild Explosions: A.Planetary Nebula. B.Ejection of outer layers of a red giant. •Strong Explosions: A.Nova B.Eruptions in binary systems. •Catastrophic Explosions: A.Supernova. B.Blasting away of the outer parts of a star.
  29. 29. WHITE DWARF
  30. 30. WHITE DWARF • A white dwarf, also called a degenerate dwarf, is a stellar core remnant composed mostly of electron-degenerate matter. • A white dwarf is very dense: its mass is comparable to that of the Sun, while its volume is comparable to that of Earth. • Very low mass stars cannot fuse helium and so leave behind their helium cores. • Intermediate mass stars may progress beyond carbon burning but not all the way to iron – they leave can leave cores of oxygen or heavier elements. • The material in a white dwarf no longer undergoes fusion reactions, so the star has no source of energy. As a result, it cannot support itself by the heat generated by fusion against gravitational collapse, but is supported only by electron degeneracy pressure, causing it to be extremely dense.
  31. 31. THE CHANDRASHEKHAR LIMIT • For masses larger than 1.4 Msun, electron degeneracy pressure cannot support the mass because electrons would have to move faster than the speed of light. • Therefore it was predicted that white dwarfs with masses larger than this limit cannot exist.
  32. 32. LIFETIME OF A WHITE DWARF • The length of time it takes for a white dwarf to reach this state is calculated to be longer than the current age of the universe (approximately 13.8 billion years), it is thought that no black dwarfs yet exist. • The oldest white dwarfs still radiate at temperatures of a few thousand kelvins.
  33. 33. SOME FACTS ABOUT WHITE DWARF • They can go supernova . • Their gravity is 350,000 times that of earth. • Many will become black dwarfs. • A teaspoon of white dwarf matter weighs 5.5 tons. • They have radius that’s typically around 100 times smaller around smaller that our earth but have the mass. • About 97% of all milky way stars will become white dwarfs. • Almost all white dwarf star have a same mass. • White dwarf star have atmosphere.
  34. 34. SIRIUS-B • The first white dwarf ever observed is called "Sirius B" and was discovered by Alvan Clark (a telescope maker) in 1862.
  35. 35. NEUTRON STAR
  36. 36. NEUTRON STAR • A neutron star is the collapsed core of a giant star which before collapse had a total mass of between 10 to 29 solar masses. • Discovered in 1967 by Jocelyn Bell and Antony Hewish by regular radio pulses from PSR B1919+21 • Mass : 1.4 times mass of sun • Density: 10^17 kg/m^3 • Temperature: 600000 kelvin
  37. 37. FORMATION OF A NEUTRON STAR • Neutron stars are created when giant stars die in supernova and their cores collapse, with protons and electrons essentially melting into each other to form neutrons. • Neutron stars are city-size stellar objects with a mass about 1.4 times that of the sun.
  38. 38. HOW DANGEROUS IS A NEUTRON STAR? • It is dangerous because of their strong fields. If a neutron star enters our solar system , it could cause chaos , throwing off the orbits of the planets and if it got closed enough , even raising tides that would rip the planet apart. But the closest known neutron star is about 500 light-years away.
  41. 41. PULSAR
  42. 42. PULSAR- A FLASHING NEUTRON STAR • Pulsar are spinning neutron star that emits a narrow radiation beam . the beam is offset from pulsar’s spin axis , sweeping across space like a lighthouse. • As the pulsar rotates , the beam may sweep across the earth, appearing to astronomers as a flashing object. If the beam does not point in the direction of earth, it cannot be seen. • All pulsars are neutron stars , but not all neutron stars are pulsars
  43. 43. MAGNETAR
  44. 44. MAGNETAR- A MAGNETIC MONSTER • A magnetar is a type of neutron star with an extremely powerful magnetic field. The magnetic field decay powers the emission of high-energy electromagnetic radiation, particularly X-rays and gamma rays. • Starquakes caused by fracturing of the magnetar’s surface can cause huge radiation bursts to be released , which are powerful enough to be detected on earth , tens of thousands of light years away.
  45. 45.,h_312,al_c,q_
  46. 46. SOME FACTS ABOUT NEUTRON STAR • In just the first few seconds after a star begins its transformation into a neutron star, the energy leaving in neutrinos is equal to the total amount of light emitted by all of the stars in absolute universe. • Its been speculated that if there were life on neutrinos stars , it would be 2 dimensional. • The fastest known spinning neutron star rotates about 700 times each second. • The wrong kind of neutron star would wreak havoc on earth. • Despites the extremes of neutron stars , researchers still have ways to study them.
  47. 47. DEATH OF A NEUTRON STAR Neutron star dies when pressure on its core become so great that the quarks collapse and lose their angular momentum. They turn in cluster singularities orbited by strings of energy as forming dark matter or black hole.
  48. 48. BLACK HOLE
  49. 49. WHAT IS A BLACK HOLE? • Everyone always talks about black holes and how things go in and never come out .But what is black hole exactly? Black holes are extremely massive objects with immense gravity that don’t allow anything to escape, not even light. • The strong gravity occurs because matter has been pressed into a tiny space. This compression can take place at the end of a star’s life. Black holes are a result of dying stars. • Because no light can escape, black holes are invisible. However, space telescope with special instruments can help find black holes. • They can observe the behaviour of material and stars that are very close to black holes.
  50. 50. DISCOVERY OF A BLACK HOLE • The first time the idea of a black hole was suggested was in the late 1790’s by John Michell of England and Pierre-Simon Lapace of France. • They both proposed the idea of the existence of an “ invisible star” by applying the first Newton Law. They calculate its mass and size, which is now called the “ event horizon” that an object would need in order to be faster than even the speed of light.
  51. 51. TYPES OF BLACK HOLES There are three types of Black Holes: 1. Primordial 2. Stellar 3. Supermassive
  52. 52. FORMATION OF BLACK HOLES • Primordial black holes are thought to have formed in the early universe, soon after the big bang. • Stellar black holes form when the centre of a very massive star collapses in upon itself. This collapse also causes a supernova, or an exploding star, that blasts part of the star into space. • Scientists think supermassive black holes formed at the sae time as the galaxy they are in. The size of the supermassive black hole is related to the size and mass of the galaxy it is in.
  54. 54. • There are two basic parts to a black hole: A. The singularity. B. Event Horizon. • The event horizon is the “point of no return” around the black hole. It is not a physical surface, but a sphere surrounding the black hole that marks where the escape velocity is equal to the speed of light. Its radius is the Schwarzschild radius mentioned earlier. • This point is called the singularity. It is vanishingly small, so it has essentially an infinite density. It’s likely that the laws of physics break down at the singularity. Scientists are actively engaged in research to better understand what happens at these singularities, as well as how to develop a full theory that better describes what happens at the centre of a black hole. STRUCTURE OF A BLACK HOLE
  55. 55. DEATH OF A BLACK HOLE • Yes, black holes do die, and they do so when the theories of the extremely large come together with the theories of the very small. • They do so slowly , and then all at once.
  56. 56. • Framed English physicist Stephen Hawking theorised that something different happens around a black hole. The idea is that particles and antiparticles may not be able to automatically cancel each other out because the black hole’s gravity pulls the negative antiparticle into black hole-oblivion. • This process leaves the positive particle then, are emitted from the black hole. The phenomenon is called Hawking Radiation. DEATH OF A BLACK HOLE
  57. 57. • But that’s not the end. After a long time, the black hole would lose mass due to gradual addition of antiparticles. As Hawking says, the black holes would evaporate. During evaporation, the black hole emits energy in the form of the positive particles that escape. • The more massive the black hole, the more energy would be released. Over time, the black hole would eventually lose so much mass that it would become small and unstable. This is the dramatic end. The black hole would then lose the rest of its mass in a short amount of time as abrupt explosions as gamma rays bursts. The end. DEATH OF A BLACK HOLE
  58. 58. Thank You

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Journey of the star from its birth to death


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