High-speed molecular cloudlets around the Galactic center's supermassive black hole

Area of Science:

• Astronomy and Astrophysics
• High-resolution observations of galactic centers
• Molecular cloud dynamics

Background:

• The environment around Sagittarius A* (Sgr A*) is complex, with a circumnuclear disk (CND) and ionized gas streamers.
• Previous studies have modeled the kinematics of gas around Sgr A* using spiral and elliptical orbit models.
• The presence and behavior of molecular gas within the central parsec of the Milky Way require further investigation.

Purpose of the Study:

• To investigate the molecular gas structures and kinematics within the circumnuclear disk (CND) and the interstellar environment around Sgr A*.
• To test existing models of gas motion against new observational data.
• To understand the origin and fate of molecular cloudlets near Sgr A*.

Main Methods:

• Utilized Atacama Large Millimeter/submillimeter Array (ALMA) observations with 1″ resolution.
• Analyzed ¹²CO (J=3-2) emission to map molecular cloudlets and their velocities.
• Used ¹²CO absorption spectra and H¹³CN (J=4-3) emission to study diffuse gas and CND structure.

Main Results:

• Discovered small (≲20,000 AU) ¹²CO molecular cloudlets moving at high speeds (up to 300 km s^-1) within the CND cavity.
• Observed intricate morphologies of ¹²CO structures, varying with velocity.
• Found evidence for diffuse molecular gas at extreme negative velocities via ¹²CO absorption.
• The CND exhibits a clumpy distribution with molecular cores of ~10⁵ cm^-3, below the Roche limit.
• ¹²CO cloudlet kinematics are inconsistent with spiral models and mostly inconsistent with Keplerian ellipse models.

Conclusions:

• Molecular cloudlets exist within the Sgr A* cavity, with a total mass of several 10 M_⊙.
• These cloudlets are likely transient, with short lifetimes (≲10⁴ yr) due to photoevaporation, stellar winds, or gravitational disruption.
• The observed cloudlet motions challenge current models of gas dynamics around Sgr A*.
• Cloudlets may originate from tidally disrupted massive clouds or instabilities within the CND.