Probing the Shadow Image of the Sagittarius A* with Event Horizon Telescope

TL;DR

This paper investigates whether the supermassive object at the Milky Way's center, Sgr A*, is a black hole or a naked singularity by simulating its shadow images using EHT data and models of alternative spacetime geometries.

Contribution

It introduces a method to distinguish black holes from naked singularities at Sgr A* using simulated EHT images based on specific naked singularity models.

Findings

Simulated images show distinguishable features between black holes and naked singularities.

The study demonstrates the potential of EHT to identify the true nature of Sgr A*.

Different array configurations improve the resolution of shadow images.

Abstract

Recent observations of the Milky-way galactic center at various frequencies suggest a supermassive compact object. Generally, that supermassive compact object is assumed to be a `Black Hole', having more than four million solar masses. In this work, we study the observational appearance at $230$ GHz and probe the nature of Sagittarius-A* (Sgr A*) as the naked singularity. Here, we consider the first type of Joshi-Malafarina-Narayan (JMN-1) and Janis-Newman-Winicour (JNW) naked singularity spacetimes which are anisotropic fluid solutions of the Einstein field equations. Motivated by radiatively inefficient accretion flows (RIAF), we use an analytical model for emission and absorption coefficients to solve the general relativistic radiative transfer equation. The resulting emission is then utilized to generate images to predict the nature of the Sgr A* with synthetic Very Long Baseline Interferometry (VLBI) images from current and future Event Horizon Telescope (EHT) arrays. Three different EHT array configurations are being used to simulate the models of naked singularities and a black hole. This may have little effect on the baseline, but it would increase the u-v plane gridding, making it feasible to capture a better-resolved image. Therefore, it is quite interesting and useful for the upcoming shadow image of the Sgr A* to predict whether it is a supermassive black hole or a naked singularity.