Note4Students
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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