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Star’s Life and Death: Brown and Red Dwarf explained

Life and death of stars depends on

  1. The mass with which the star started
  2. If they were born with siblings nearby or not

Indicator/ Evidence of the life of star

  • Color of a star is an indicator of its temperature and temperature indicates its life.
  • The cooler stars are brown to dark red, barely warmed enough to glow, like the cooling embers in a fire. The hotter stars are blindingly blue-white, like the extreme flame of a welder’s torch.

Stages in the life of star

  1. MSS- Main Sequence Star
  2. RGS- Red Giant Star
  3. Death of star- depends on mass of stars
  • Small stars die as Dwarf star
  • Medium sized stars die as Pulsar/ Neutron Star
  • Massive stars die as Black Hole

Types of star and their life

The Sun and the bulk of the stars in the Universe are called dwarf stars. These stars range in size from brown dwarfs, which grow up to around 8% of the mass of our Sun, to yellow dwarfs, which we find up to about 120% of the mass of our Sun. There are stars those are 100 times larger than our Sun. So they die differently.

  1. Life and Death of Brown Dwarfs: Brown dwarfs are barely stars, as they only shine for about ten million years while their cores crush the rare element deuterium into helium.
    After their deuterium is gone, brown dwarfs glow in the invisible light of infrared waves for billions of years, their insides churned and warmed by the bubbling of escaping heat as they slowly collapse under their weight. Brown dwarf stars will eventually cool down and become dark balls of cold gas.
  2. Life and Death of Red, orange, and yellow dwarf stars: Red, orange, and yellow dwarf stars can keep up the tug of war — gravity squeezing inward against a fusing core shining outward — for billions of years. Their insides tumble, creating powerful magnetic fields around them.

All dwarf stars do eventually change, but it takes them billions of years to do so.

  • When a dwarf star’s core finally uses up the hydrogen fuel it. needs to shine outward, its outer atmosphere begins to collapse under its own weight.
  • As it compresses onto the hot core, a thin layer of the squashed hydrogen fuses into helium. The fusion pumps energy toward the surface, boiling the star’s atmosphere.

Red Giant Star: The boiling gas cools off as it expands, and the bloating star takes on a redder color. Swelling to thousands of times its original size, this expanding dwarf star becomes a red giant. When our Sun becomes a red giant, it will swell to engulf the Earth.

  • During the two billion years of its red giant phase, its hot core becomes coated in the ashes of helium from the layer burning above it. For stars the mass of the Sun or more, this burden increases the core’s temperature until its helium is hot enough to fuse into carbon.
  • A carbon-burning red giant star gives off nearly 10 times the energy it did as a dwarf star. In only a few hundred million years, the red giant burns through its helium and collapses again.
  • This fuses a layer of helium above the hotter carbon core, which creates enough heat to boil the outer gases of the star so fiercely so as to expand beyond its ability to keep hold of itself. However, the dwarf star does not have enough mass to crush the carbon core into heavier elements, and the core stops fusing.

White Dwarf:  the hot core of carbon atoms holds together due to gravity, but it resists crushing itself, due to the pressure of the spaces inside the atoms. This delicate balancing act results in white dwarf.

  • The expanding outer gases eventually fly away, leaving the exposed white dwarf to gradually cool into a black dwarf.
  • A white dwarf is stable as long as it is no more than 1.4 times the mass of our Sun, a value called the Chandrasekhar limit.
  • However, if a white dwarf’s companion star goes through its giant phase, it will likely swell enough to spill hydrogen on to the white dwarf. This will ruin the white dwarf’s stability. If it gains enough gas to tip over the balance mass, the white dwarf will detonate, leaving behind only an ever-expanding fireworks display of exploding star matter.

Brown dwarfs

  • They are sub stellar star like objects that have just failed to become main sequence stars
  • They are not massive enough to burn the hydrogen they contain, during the first few million years of their existence, they give off energy by burning deuterium (a heavier isotope of hydrogen)
  • They have mass of approximately 13 to 75–80 Jupiter masses
  • On the basis of mass, a Brown Star lies between the Cub Brown Star or Rogue Planet and Red Dwarf.
  • They may be fully convective, with no layers or chemical differentiation by depth.
  • They are not massive enough to sustain nuclear fusion of ordinary Hydrogen to helium in their cores. They are, however, thought to fuse deuterium (2H) and to burn lithium (7Li) if their mass is above a debated threshold of 13MJ and 65 MJ, respectively.
  • Despite their name, brown dwarfs are of different colors.
  • Brown dwarfs are not very luminous at visible wavelengths.

Red Dwarfs

  • Are small and relatively cool star on the MSS.
  • Their mass range between low of 0.075 solar masses to about 0.50 M and have a surface temperature of less than 4,000 K
  • They are the most common type of star in the Milky way, at least in the neighborhood of the Sun, but because of their low luminosity, individual red dwarfs cannot be easily observed.
  • Proxima Centauri, the nearest star to the Sun, is a red dwarf
  • According to some estimates, red dwarfs make up three-quarters of the stars in the Milky Way

 

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