Most galaxies has a giant black hole in the center. As the black hole sucks the surrounding matter in, radiation and energy is given off which makes the area glow. The Milky Way is believed to host a supermassive black hole in its core but the surrounding dust and gas may be blocking the light for Earth instruments to detect.
There are also a class of galaxies called Green Pea galaxies. They are characterized as very small luminous galaxies and has no relation to the newly classified Green Bean galaxies except for their size.
Green Bean Galaxies are entire galaxies that glow under the intense radiation from the region around its core where the central black hole lies.
