The “Weak” Seyfert Galaxy NGC 4639

NGC 4639 is a beautiful example of a type of galaxy known as a barred spiral. It lies over 70 million light-years away in the constellation of Virgo and is one of about 1,500 galaxies that make up the Virgo Cluster. In this image, one can clearly see the bar running through the bright, round core of the galaxy. Bars are found in about two-thirds of spiral galaxies and are thought to be a natural phase in their evolution. The galaxy’s spiral arms are sprinkled with bright regions of active star formation. Each of the small, bluish dots is actually several hundred light-years across and contains hundreds or thousands of newly formed stars. NGC 4639 is classified as a Seyfert galaxy, meaning that it has an active galactic nucleus (AGN) whose radiation is extremely luminous and characterized by X-rays. These features are evidence that a massive black hole exists at its center, radically heating the gas and dust it draws in toward itself. Indeed, most galaxies are thought to contain a massive black hole at their centers. The core of NGC 4639 is, relatively speaking, an example of a weak AGN. In contrast, distant galaxies that contain quasars can have their light completely dominated by emissions from their AGN.