International Space Agencies – Missions and Discoveries

What is White Dwarf?


From UPSC perspective, the following things are important :

Prelims level : White dwarf

Mains level : Not Much

Using the Hubble Space telescope and Transiting Exoplanet Survey Satellite (TESS), astronomers have identified several white dwarfs over the years.

Where is this white dwarf?

  • A white dwarf is what stars like the Sun become after they have exhausted their nuclear fuel.
  • Near the end of its nuclear burning stage, this type of star expels most of its outer material, creating a planetary nebula.
  • Only the hot core of the star remains. This core becomes a very hot white dwarf, with a temperature exceeding 100,000 Kelvin.
  • Unless it is accreting matter from a nearby star, the white dwarf cools down over the next billion years or so.

Limits for white dwarf

  • White Dwarf is half the size of our Sun and has a surface gravity 100,000 times that of Earth.
  • There is a limit on the amount of mass a white dwarf can have.
  • Subrahmanyan Chandrasekhar discovered this limit to be 4 times the mass of the Sun. This is appropriately known as the “Chandrasekhar Limit.”

Observing white dwarf

  • Many nearby, young white dwarfs have been detected as sources of soft, or lower-energy, X-rays.
  • Recently, soft X-ray and extreme ultraviolet observations have become a powerful tool in the study the composition and structure of the thin atmosphere of these stars.

What is TESS?

  • The researchers observed this phenomenon using Transiting Exoplanet Survey Satellite (TESS).
  • TESS is a space telescope in NASA’s Explorer program, designed to search for extrasolar planets using the transit method.
  • The primary mission objective for TESS is to survey the brightest stars near the Earth for transiting exoplanets over a two-year period.
  • The TESS project will use an array of wide-field cameras to perform an all-sky survey. It will scan nearby stars for exoplanets.

How does white dwarf ‘switch on and off’?

  • In these types of systems, the donor star orbit around the white dwarf keeps feeding the accretion disk.
  • As the accretion disk material slowly sinks closer towards the white dwarf it generally becomes brighter.
  • It is known that in some systems the donor stars stop feeding the disk.


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