Short answers, pulled from the story.
Sagittarius A* is a compact radio source and supermassive black hole located at the Galactic Center of the Milky Way. Its mass is estimated at approximately 4 million solar masses, and it serves as the gravitational anchor for the entire galaxy. Accretion of gas onto the black hole powers the bright radio emission that makes Sagittarius A detectable from Earth.
Estimates since the year 2000 have placed the Galactic Center between approximately 24,000 and 28,400 light years from Earth. The most recent geometric measurements put the distance at roughly 8.178 kiloparsecs, or about 26,670 light years.
Interstellar dust along the line of sight absorbs visible light, ultraviolet radiation, and soft X-rays before they reach Earth. Astronomers study the Galactic Center using gamma rays, hard X-rays, infrared, submillimetre, and radio wavelengths, which penetrate the dust. Walter Baade identified a partial gap in the dust called Baade's Window in the early 1940s, enabling limited optical observation.
The Fermi bubbles are two large elliptical lobes of energetic plasma that extend roughly 25,000 light years above and below the Galactic Center. Announced in November 2010, they emit gamma rays and X-rays. Computer simulations confirmed by 2022 that the bubbles were produced by activity from the Sagittarius A* black hole, and their discovery earned the 2014 Bruno Rossi Prize for Tracy Slatyer, Douglas Finkbeiner, and Meng Su.
More than 100 massive OB and Wolf-Rayet stars exist within the central parsec around Sagittarius A*, apparently formed in a single burst of star formation a few million years ago. This is surprising because the tidal forces from the black hole should inhibit star formation. Current evidence favors the explanation that these stars formed within a massive, compact gas accretion disk around the black hole itself.
In 1958 the International Astronomical Union adopted the position of Sagittarius A as the zero coordinate point for the system of galactic latitude and longitude. This decision followed the 1954 detection of Sagittarius A by the CSIRO radio astronomy team in Australia, led by Joseph Lade Pawsey.