What Happens to a Star's Core When It Becomes a White Dwarf or Neutron Star

When a star with a mass in the range of 3.4 Solar masses and up collapses, its fate can vary significantly depending on its mass. For massive stars, the result is a black hole, while less massive stars may end their lives as either white dwarfs or neutron stars. This article explores the transformation of a star's core into these stellar remnants, providing insights into their formation and characteristics.

The Fate of Massive Stars

When a star with a mass greater than 3.4 Solar masses collapses, it undergoes a catastrophic event known as a supernova. This collapse results in a black hole. Unlike lower mass stars, which can transform into white dwarfs or neutron stars, black holes do not revert to more ordinary stellar states.

The Evolution of Less Massive Stars

In contrast to massive stars, less massive stars, such as our Sun, will end their lives as white dwarfs. This transformation begins with the star evolving through a red giant phase, during which the core compresses, and the outer layers expand and are eventually ejected. The core remains as a white dwarf, which is the collapsed remnant of the star.

Formation of Neutron Stars

Larger stars, which are more massive than the Sun, can transform into neutron stars. This process involves the core collapsing under gravity, causing the outer layers to be ejected in a massive explosion known as a supernova. In a neutron star, the core is made up almost entirely of neutrons, which are the byproduct of proton-electron mergers. Neutron stars are incredibly dense, with masses comparable to that of a typical star but occupying a much smaller volume.

Understanding the Star's Core

The core of a star is the fundamental component that determines its fate. In the case of a white dwarf, the core remains relatively unchanged until the outer layers are ejected. The core is the remnant of the star after the red giant phase, once the fusion reactions cease and gravity overcomes the nuclear forces.

For a neutron star, the process is more extreme. As the outer layers are blown away in a supernova, the core is compressed to an incredible density. The neutrons in the core are produced by the merging of protons and electrons, resulting in an extremely dense, compact body.

Collapsing to a Neutron Star or White Dwarf

When a star collapses to form a white dwarf, the core essentially becomes the white dwarf itself. The star's outer layers are gradually stripped away, leaving the core as a white dwarf. This process can take billions of years, as the star slowly sheds its mass and exposes its core.

Neutron stars, on the other hand, are formed in much more rapid and catastrophic events. When a giant star collapses under the immense gravity, the core undergoes a violent collapse, ejecting the outer layers in a supernova. The remaining core, now a neutron star, is a highly dense remnant of the original star, with a diameter roughly 69,000 times smaller than the Sun's diameter and a mass equivalent to 1.5 Solar masses.

Conclusion

The transformation of a star's core into a white dwarf or neutron star is a fascinating process. While white dwarfs represent a gradual and long-term transformation, neutron stars result from more dramatic and immediate events. Understanding these stellar remnants provides insight into the lifecycle of stars and the physical processes that govern their behavior.