Question

Decide whether the statement makes sense (or is clearly true) or does not make sense (or is clearly false). Explain clearly; not all these have definitive answers, so your explanation is more important than your chosen answer. Most white dwarf stars have masses close to that of our Sun, but a few white dwarf stars are up to three times as massive as the Sun.

Short answer

The statement is clearly false due to the Chandrasekhar limit.

Step-by-step solution

Understanding White Dwarf Stars

White dwarf stars are remnants of stars that have exhausted their nuclear fuel. They are very dense and have masses that are generally comparable to that of the Sun. Typically, white dwarfs do not exceed about 1.44 times the mass of the Sun due to the Chandrasekhar limit.

Introducing the Chandrasekhar Limit

The Chandrasekhar limit is approximately 1.44 solar masses. It represents the maximum mass that a white dwarf star can have before it must collapse further, often into a neutron star or a black hole. This limit is determined by the balance between electron degeneracy pressure and gravitational forces.

Analyzing the Statement

The statement claims that some white dwarf stars can be up to three times as massive as the Sun. Based on the Chandrasekhar limit, this is not possible for a white dwarf. Those exceeding the limit would collapse into a different type of stellar remnant.

Drawing a Conclusion

Considering the physical limitations posed by the Chandrasekhar limit, the statement is clearly false. No white dwarf can have a mass three times that of our Sun while remaining a white dwarf.

Key concepts

Chandrasekhar Limit

The Chandrasekhar Limit is a fundamental concept in astrophysics, and it's key to understanding the nature of white dwarf stars. It defines the maximum mass a white dwarf star can have while still supporting itself against gravitational collapse. This limit is about 1.44 times the mass of our Sun.

• If a white dwarf's mass exceeds this limit, it can no longer sustain itself as a white dwarf and will undergo further collapse.
• The name 'Chandrasekhar Limit' honors the astrophysicist Subrahmanyan Chandrasekhar, who determined this boundary in 1930.

The significance of this limit comes from the underlying physical processes. White dwarf stars are supported by a special force known as electron degeneracy pressure. When the mass of a white dwarf approaches 1.44 solar masses, even this powerful force is unable to prevent gravitational collapse, leading to the formation of a neutron star or black hole.

Electron Degeneracy Pressure

Electron Degeneracy Pressure plays a crucial role in the existence of white dwarf stars. This pressure arises from the principles of quantum mechanics, which restrict how closely electrons can be packed together.

• In a white dwarf, the core's gravitational contraction is opposed by electron degeneracy pressure.
• It comes from the Pauli Exclusion Principle, stating that no two electrons can occupy the same quantum state simultaneously.

This pressure is extremely strong, allowing white dwarfs to resist collapse under their gravity despite being so dense. The electrons in the star are crushed close to one another, creating a supportive force independent of the temperature.
This means that unlike normal stars where heat and nuclear pressure balance gravity, a white dwarf relies solely on electron degeneracy pressure for its stability. Yet, it is only effective up to the mass limit defined by the Chandrasekhar Limit.

Stellar Remnants

When stars exhaust their nuclear fuel, they leave behind stellar remnants. These relics of past stars come in various forms, with white dwarfs being just one type.

• White dwarfs form from stars that were not massive enough to explode as supernovae.
• They are common end-states for stars with masses up to about eight times that of our Sun.

Stellar remnants showcase different forms:

• White dwarfs continue cooling and fading over time.
• If they gain enough mass beyond the Chandrasekhar Limit, they can become neutron stars, or even black holes.

Neutron stars are significantly more compact, and black holes, which arise from even more massive stars, have a gravitational pull so strong that not even light can escape. Understanding white dwarfs and their limits helps illuminate the broader lifecycle of stars, from their main-sequence life to the residual end-stages that dot the cosmos with these extraordinary remnants.