Comment on "Horizon-scale tests of gravity theories and fundamental physics from the Event Horizon Telescope image of Sagittarius A*"

TL;DR

This paper critiques a previous study on the constraints of a wormhole parameter using Sagittarius A* observations, highlighting overlooked aspects that invalidate prior conclusions and emphasizing the need for joint parameter estimation.

Contribution

The authors identify critical oversights in previous work, demonstrating that the constraints on the wormhole parameter $oldsymbol{}$ are invalid and proposing a more accurate joint estimation approach.

Findings

The Damour-Solodukhin wormhole is asymptotically flat.

The wormhole's throat acts as an effective photon sphere for certain parameters.

Both the mass and the parameter $oldsymbol{}$ influence the wormhole's mass estimate.

Abstract

Vagnozzi et al. constrained the additional parameter of spacetimes with a photon sphere from the observation of the shadow of Sagittarius A* under the assumption that a distance to the Sagittarius A* and its mass parameter was estimated from other observations. They claimed that a Damour-Solodukhin wormhole with an additional parameter $\lambda$ is not an asymptotically-flat spacetime and that they gave the first robust observational constraint on the parameter $\lambda$ of the Damour-Solodukhin wormhole. However, they overlooked the fact that: (A) the Damour-Solodukhin wormhole spacetime is asymptotically flat, (B) the throat of the Damour-Solodukhin wormhole works as an effective photon sphere for $\lambda>\sqrt{2}/2$, and (C) not only a usual mass parameter but also the parameter $\lambda$ contributes the mass of the Damour-Solodukhin wormhole. Because of the overlook (C), we realize that their constraint on the parameter $\lambda$ is invalid. This is because their method corresponds to the following way: They estimated the mass parameter from the other observations under the assumption $\lambda=0$ even though the value of the parameter $\lambda$ strongly affects the determination of the mass parameter, and then, they used the value of the mass parameter to constrain $\lambda$ from the observation of the shadow. We conclude that we should constrain the mass parameter and $\lambda$ from the shadow observation and other observations without the assumption $\lambda=0$.