Two of the Milky Way's gigantic spiral arms appear to be much farther away than we realized, scientists have discovered after listening to the echoes of distant cosmic explosions. The findings could potentially force us to reconsider our galaxy's mass and maybe even its shape, researchers say.
The Milky Way is a barred spiral galaxy made up of a dense central region containing a supermassive black hole (dubbed Sagittarius A*), orbited by four major arms — the Sagitarrius arm, the Scutum-Centaurus arm, the Perseus arm and the Outer arm — that curve and stretch outward like a giant pinwheel. Most of our galaxy's stars and gas are tightly packed together in these cosmic limbs, although some stars, including the sun, exist in the gaps between them or within other smaller structures.
