How does gas form an accretion disk around Sagittarius A*?

An accretion disk forms around Sagittarius A* when matter, such as gas pulled into the black hole from the surrounding nuclear region, possesses sufficient rotational or angular momentum to prevent it from falling directly inward in a straight line.123

As this gas approaches the black hole, the intense gravitational force squeezes the material into a rapidly rotating disk. Because the gas has rotational momentum, it tends to flatten into a disk shape perpendicular to the rotation axis, while contracting toward the central plane in directions parallel to that axis until thermal pressure balances the gravitational force.31

To move inward and accrete onto the black hole, the gas must lose energy and angular momentum. This process is driven by turbulence and viscosity, which act as a form of friction that allows the material to spiral inward. As the gas loses energy, it becomes extremely hot, emitting radiation across infrared and X-ray wavelengths.123