HST Images of Bipolar Nuclear Shells From the Active Galaxy NGC 4438

Jeffrey Kenney

False color image from Hubble Space Telescope of bubbles of hot gas blown by jets from an active nucleus in the peculiar galaxy NGC 4438. The bubbles form because jets of gas, not directly visible, are probably outflowing from an accretion disk around a supermassive black hole. When the jets from the accretion disk, which is the brightest source in the image, run into the galaxy's gas, they form expanding bubbles which shine. The 2 jets shot out in opposite directions, and therefore 2 bubbles. The second bubble is faint and located further from the nucleus, and is barely visible in the image. There is more gas on one side of the nucleus than the other, so the collision is more violent and the bubble is much brighter on that side. The darker bands arise from dust which blocks much of the light from the galaxy center. This is a nearby weak example of an active galactic nucleus, which is the phenomenon responsible for powerful quasars and radio galaxies. This galaxy is located in the Virgo Cluster, which is 50 million light years from earth. The bright bubble is 800 light-years in diameter.