White Dwarfs

Why in news?

• As per the recent study, a bright explosion born out of the cosmic dance of a white dwarf and its companion star resulting in thick dust around an   could unravel mysteries behind the start of life.

What is Novae?

• A nova is an astronomical event in which a strong explosion occurs temporarily, thus increasing the brightness and then slowly darkening over weeks or months.
• It generally occurs in a binary system (two stars orbiting around a common centre of mass) consisting of a white dwarf and a main sequence star.

About White Dwarfs:

• White dwarfs are stars that have burned up all of the hydrogen they once used as nuclear fuel.
• Such stars have very high density.
• A typical white dwarf is half the size of our Sun and has a surface gravity 1,00,000 times that of Earth.
• Stars like our sun fuse hydrogen in their cores into helium through nuclear fusion reactions.
• Fusion in a star's core produces heat and outward pressure (they bloat up as enormous red giants), but this pressure is kept in balance by the inward push of gravity generated by a star's mass.
• When the hydrogen, used as fuel, vanishes and fusion slows, gravity causes the star to collapse in on itself into white dwarfs.

Black Dwarfs:

• Eventually - over tens or even hundreds of billions of years - a white dwarf cools until it becomes a black dwarf, which emits no energy. Because the universe's oldest stars are only 10 billion to 20 billion years old there are no known black dwarfs.
• It must be noted that not all white dwarfs cool and transform into black dwarfs.

Chandrasekhar Limit:

• Those white dwarfs which have enough mass reach a level called the Chandrasekhar Limit.
• At this point the pressure at its center becomes so great that the star will detonate in a thermonuclear supernova (explosion).
• Chandrasekhar Limit is the maximum mass theoretically possible for a stable white dwarf star.
• A limit which mandates that no white dwarf (a collapsed, degenerate star) can be more massive than about 1.4 times the mass of the Sun.
• Any degenerate object more massive must inevitably collapse into a neutron star or black hole.
• The limit is named after the Nobel laureate Subrahmanyan Chandrasekhar, who first proposed the idea in 1931.
• He was awarded the Nobel Prize in Physics in 1983 for his work on the physical processes involved in the structure and evolution of stars.

PRACTICE QUESTION:

Consider the following statements:

1. White dwarfs are stars that have burned up all of the hydrogen they once used as nuclear fuel.

2. Chandrasekhar Limit is the maximum mass theoretically possible for a stable white dwarf star

Which of the statements given above is/are correct?

(a) 1 only

(b) 2 only

(c) Both 1 and 2

(d) Neither 1 nor 2

Answer