[Paper Review] An Approach Detecting the Event Horizon of Sgr A*

Makoto Miyoshi, Seiji Kameno+4 more|ArXiv.org|Sep 21, 2008

Astrophysical Phenomena and Observations2 references4 citations

TL;DR

This paper proposes using submillimeter very long baseline interferometry (VLBI) to image the event horizon of Sgr A*, the supermassive black hole at the Galactic center. Simulations show that arrays with over 10 southern hemisphere stations can produce high-fidelity images, while even small arrays enable accurate shadow size and black hole mass estimation via visibility analysis, marking a critical step toward direct black hole horizon imaging.

ABSTRACT

Imaging the vicinity of a black hole is one of the ultimate goals of VLBI astronomy. The closest massive black hole, Sgr A*, located at the Galactic center, is the leading candidate for such observations. Combined with recent VLBI recording technique and submillimeter radio engineering, we now have sufficient sensitivity for the observations. Here we show performance simulations of submillimeter VLBI arrays for imaging Sgr A*. Good images are obtained from submillimeter VLBI arrays in the southern hemisphere composed of more than 10 stations. We also note that even with a small array, we can estimate the shadow size and then the mass of the black hole from visibility analysis. Now, all we need is to construct a submillimeter VLBI array in the southern hemisphere if we wish to unveil the black hole environment of Sgr A*. Key words: black hole, event horizon, Sgr A*, submillimeter

Motivation & Objective

• To develop a practical approach for imaging the event horizon of S. A*, the nearest supermassive black hole.
• To assess the feasibility of submillimeter VLBI for resolving the black hole environment at the Galactic center.
• To determine the minimum array configuration required for reliable detection of the black hole shadow and mass estimation.
• To evaluate the performance of southern hemisphere VLBI arrays in achieving high dynamic range and angular resolution.

Proposed method

• Simulating submillimeter VLBI observations of Sgr A* using realistic instrument configurations and source models.
• Employing visibility-based imaging techniques to reconstruct the black hole shadow and surrounding emission structures.
• Analyzing the visibility amplitude and closure phase data to estimate the black hole shadow size and mass.
• Evaluating array performance across different configurations, including small arrays with limited stations.
• Using sensitivity and dynamic range metrics to assess image fidelity and reliability of the reconstructed source structure.
• Focusing on southern hemisphere arrays to optimize baseline distribution and visibility coverage for Sgr A*.

Experimental results

Research questions

• RQ1 Can submillimeter VLBI arrays image the event horizon of Sgr A* with sufficient resolution and dynamic range?
• RQ2 What is the minimum number of stations required in a southern hemisphere VLBI array to reliably detect the black hole shadow?
• RQ3 Can the shadow size and black hole mass be accurately estimated from visibility data using small arrays?
• RQ4 How does array configuration affect the fidelity and dynamic range of images reconstructed from submillimeter VLBI data?
• RQ5 What sensitivity and angular resolution are required to resolve the emission structure around Sgr A*’s event horizon?

Key findings

• Submillimeter VLBI arrays with more than 10 southern hemisphere stations can produce high-fidelity images of Sgr A*’s environment.
• Even small VLBI arrays can estimate the black hole shadow size and mass through visibility analysis with sufficient accuracy.
• The simulations demonstrate that current submillimeter VLBI recording and engineering capabilities are sufficient for such observations.
• The dynamic range and image fidelity improve significantly with increased station count and optimized baseline distribution.
• Visibility-based analysis enables robust mass estimation independent of full image reconstruction.
• The study confirms that constructing a southern hemisphere submillimeter VLBI array is the key remaining step toward imaging Sgr A*’s event horizon.