The gravitational collapse of a massive star is a natural process that can produce a black hole. But, have you ever thought, that a massive star can also gravitationally collapse into a wormhole. Yeah, thats what Chakrabarti and Kar considered in their recent paper. They proposed a non-singular model of gravitational collapse and explored a possibility of the formation of wormhole. They showed that a time-dependent/Lorentzian wormhole geometry can arise in gravitational collapse and this wormhole structure is very similar to the recently proposed Simpson-Visser vacuum solution. Their study recently appeared in Arxiv.
Simpson-visser solution is a modification of the standard Schwarzschild spacetime, with an additional parameter ‘a’ being introduced in the metric, which controls the interpolation of the metric between a standard Schwarzschild black hole and a Morris-Thorne traversable wormhole.
In other words, for different values of the parameter ‘a’, the metric can yield different geometric structure such as:
- When a = 0, you will get the standard Schwarzschild geometry.
- When a ≠ 0, you will get a regular black hole.
- If a > 2m, you will get a two-way traversable wormhole geometry.
- If a = 2m, you will get a one-way wormhole with an extremal null throat.
Chakrabarti and Kar studied the time evolution of the collapsing wormhole geometry, which is very similar to the Simpson-Visser vacuum solution.
They investigated the behavior of geodesic congruences and confirmed that no zero proper volume singularity is reached at any time.
From a suitable boundary matching condition, they have also given an exact collapsing solution, which slowly evolves into a spherical wormhole geometry at a non-zero minimum radius.
“The term responsible for a wormhole structure comes from the g11 component of the metric”
Finally, they discussed that this singularity-free nature of the spacetime lies within its wormhole-like structure (called collapsing sphere), which also leads to a violation of the Null Convergence Condition.
Reference: Soumya Chakrabarti, Sayan Kar, “A wormhole geometry from gravitational collapse”, Arxiv, pp. 1-14, 2021. https://arxiv.org/abs/2106.14761
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