The center of our Milky Way galaxy,approximately twenty-five thousand light years from Earth, is invisible to us in optical light because of the extensive amounts of absorbing, and intervening dust. Radiation at many other wavelengths,however, including the infrared, or radio,and energetic X-rays, can penetrate the veiling fabric. At the heart of the galactic center is a supermassive black hole, or SagA*,with approximately four million solar-masses of fabric. It is a relatively dim thing, and shows some slight flickering that is thought to be the result of small blobs of fabric randomly accreting onto a disk around it. Its general passivity distinguishes SagA* from many other supermassive black holes in other galactic centers that actively accrete and heat large amounts of fabric, and then eject powerful bipolar jets of snappily-moving charged particles.
Source: phys.org