What Would Happen If a Star Spun So Fast It Reached the Speed of Light?

Can stars spin faster than the speed of light? According to the laws of physics, particularly Einstein's theory of special relativity, the answer is no.

Physics Limits: Why No Stars Can Exceed the Speed of Light

No object with mass can travel faster than the speed of light. This fundamental limit derived from special relativity means that no matter how fast a star spins, it cannot exceed light speed. Any attempt to do so would lead to extreme gravitational and centrifugal forces that would tear the star apart or even create a black hole.

Consider a neutron star, one of the densest objects in the universe. Despite its incredibly high density and gravitational forces, even these astronomical phenomena cannot surpass the cosmic speed limit. Studying such celestial bodies can offer insights into the extreme physics near the speed of light, but they cannot achieve or surpass this threshold themselves.

The Ehrenfest Paradox: A Preview of What Happens

The Ehrenfest paradox, a famous thought experiment, addresses what happens when an object is subjected to extreme rotation. The paradox arises from the apparent contradiction in the application of length contraction and time dilation in the context of rotating objects. Despite its fascinating nature, the Ehrenfest paradox does not offer a solution to spinning a star faster than light. In reality, the paradox and other relativistic effects would prevent such a scenario from occurring.

Centrifugal Forces and Stellar Destruction

As a star spins faster, its rotational velocity exerts a significant centrifugal force on its matter. At a certain critical point, this force surpasses the force of gravity. When this happens, the star's matter starts to fly apart. For a star, this can happen either before it reaches light speed or during a violent rotational process that breaks the star's structure.

Even neutron stars, which are incredibly dense, can only achieve maximum rotational speeds. These speeds are limited by the balance between centripetal and gravitational forces. Any attempt to increase the spin further would result in the ejection of matter, altering the star's composition and potentially leading to the formation of a black hole or other exotic objects.

Black Holes and Rotational Limits

Rotating black holes present a unique set of challenges. Due to their intense gravitational fields and event horizons, the behavior of a spinning black hole is markedly different from a non-rotating one. Studies have shown that there is an upper limit to the angular momentum-to-mass ratio for black holes. Any excess rotational energy is radiated away in the form of gravitational waves, ensuring that the black hole does not exceed the speed of light.

Ethan Siegel, an expert in astrophysics, explains in his blog that rotating black holes, known as Kerr black holes, have two event horizons and a region known as the ergosphere. The ergosphere is where spacetime itself gets dragged along, like swirling paint. This effect, combined with the inevitable radiation of rotational energy, prevents a black hole from reaching or surpassing light speed.

Conclusion: The Speed of Light as an Unbreakable Barrier

In summary, a star cannot spin faster than the speed of light. Any attempt to do so would result in catastrophic physical phenomena, leading to the star's destruction or transformation into a black hole. The laws of physics and the limits imposed by special relativity ensure that even the most extreme celestial phenomena cannot surpass this cosmic speed limit.