Stellar Death

The inexorable grip of gravity

Rohan Gharate
3 min readFeb 5, 2021


Introduction figure

This is the summary of the 2nd chapter of the book ‘Cosmic Catastrophe’ by Craig Wheeler. This chapter is going to be in ‘point format’ so that the audience could grab the information easily and in less time.

  1. The sun is burning its Hydrogen into Helium.
  2. A star shrinks and swells when the Hydrogen is fully transformed.
  3. At this stage, the inner part is full of Helium and the outer of Hydrogen. These parts are called ‘Core’ and ‘Envelope’ respectively.
  4. The repulsion, due to charge, among particles is overcome by providing heat. This ends up causing a nuclear reaction in the core of the star.
  5. As the lower elements get converted into higher more heat is required to continue the reaction.
  6. Thus, the star contracts and drives heat continuously.
  7. The excess heat is released into the envelope.
  8. Therefore, the core contracts and heats, while the envelope expands and cools.
  9. This type of star is called the ‘Red giant’.
  10. A ‘SuperGiant’ is much smaller and hotter than a giant.
  11. The Sun will leave as a red giant for 10% of its life.
  12. A star- more massive than the Sun- burns the Helium into Carbon and Oxygen.
  13. The mass of the star defines how many elements are going to form in the core. It even goes up to Neon, magnesium, Silicon, Sulphur, Argon, Calcium, Titanium, and Radioactive elements (Fig- 1).
  14. Some stars, including the Sun, release the breeze of particles into space, as the result tails of comets face away from the Sun (Fig- 2).
  15. Power- emitted in the form of radiation- from a star is known as its luminosity. Mass of a star = the cube of its luminosity.
  16. A star may lose its mass in the red giant phase.
  17. Wolf-Rayet Stars’ end up as supernovae or black holes.
  18. The ‘Eddington limit’ of a star is proportional to the mass of the star.
  19. The rate of infalling mass that just provides the Eddington luminosity to the star is known as the ‘Eddington mass accretion rate’.
  20. The burning phase of a star is halted, when the cold gets too dense.
  21. At this stage, the quantum pressure deregulates and the thermostat of the star breaks.
  22. Now, unlike the former condition, if the star loses net energy the pressure remains unchanged.
  23. Here, the envelope of a red giant is as big as the orbit of the earth, but the core is comparable with the size of the Earth. Density equals millions to billions of grams per cubic centimeter. Mass equals to 60% of a solar mass. The pressure of the radiation blows the envelope. Finally, only the shell remains and is called planetary nebulae. Though they have nothing to do with planets.
  24. Next, the core cools off and is known as ‘White dwarf’.
  25. White dwarfs possess low luminosity.
  26. From here, only potentially massive star continues to build the core of advanced elements and lives further.
  27. When the Iron converts into heavier elements, the energy is released in the form of light.
  28. Consequently, the process of nuclear fission commences. Iron absorbs heat and provides thermal pressure.
  29. Here, particles lose their energy and begin collapsing into the nucleus, and gravity, then, compresses the star.
  30. In the massive star, the iron core terminates the thermonuclear reaction and the core collapses. Electrons and protons combine to convert all into neutrons and neutrinos.
  31. Neutrinos escape in space taking a large amount of energy.
  32. Thus, it all ends with a formation of the neutron core called a neutron star.
  33. Here, density equals 10¹⁴ gram per cubic centimeter and Mass equals 1.5 to 2 solar masses.
  34. Gradually, that star becomes a ‘Blackhole’.

Here, you may have noticed that the fate of a star depends on its mass.

Figure- 1
Figure- 2



Rohan Gharate

I am a high school student and an excellent astrophysics enthusiast