A cool accretion disk around the Galactic Centre black hole.

Area of Science:

• Astrophysics and Astronomy
• Black Hole Research
• Gas Dynamics in Galactic Centers

Background:

• The Milky Way's central supermassive black hole, Sagittarius A*, has a mass of 4 × 10^6 solar masses.
• A reservoir of hot and cool gas surrounds Sagittarius A*, but the mass of cool gas in the black hole's accretion zone remains unconstrained.
• Hydrogen recombination spectral lines offer a potential method for detecting this cooler gas.

Purpose of the Study:

• To image and characterize the cool, ionized gas disk surrounding Sagittarius A*.
• To constrain the mass and density of this gas component.
• To investigate the physical processes governing gas in the immediate vicinity of the supermassive black hole.

Main Methods:

• Utilized 1.3-millimeter radio astronomy to observe the H30α hydrogen recombination line.
• Imaged the gas disk within 2 × 10^4 Schwarzschild radii of Sagittarius A*.
• Analyzed the double-peaked emission line profile and spatial distribution to infer gas properties.

Main Results:

• Successfully imaged a 10^4 Kelvin ionized gas disk rotating around Sagittarius A*.
• The disk exhibits a double-peaked H30α emission line with a full velocity linewidth of ~2,200 km/s.
• The observed emission is stronger than anticipated, suggesting maser enhancement of the H30α transition.

Conclusions:

• The observations reveal a rotating gas disk with an estimated mass of 10^-5 to 10^-4 solar masses and a hydrogen density of 10^5 to 10^6 cm^-3.
• The spatial displacement of redshifted and blueshifted emission components indicates rotation within the disk.
• The enhanced H30α emission suggests maser amplification, a significant finding for understanding gas physics near black holes.