"X" Structure at Core of Whirlpool Galaxy (M51)
Hubble Space Telescope provides a detailed look at the core of the giant spiral galaxy M51. These images, taken at different wavelengths of light, reveal complex structure and detail in the galaxy's core, which is thought to hide a massive black hole.
[upper left] – A ground telescopic image of M51, the Whirlpool Galaxy, taken with Kitt Peak National Observatory's 4-meter telescope. M51 is spectacular because it is one of the nearest and brightest galaxies and is tilted nearly face-on to Earth, allowing an unobstructed view of the bright nucleus. The image is 14,000 light-years across.
[upper right] – A NASA Hubble Space Telescope image of the center of M51, taken in visible light with the Wide Field Planetary camera (in PC mode). This image provides the first direct view of what may be an immense ring of dust which fuels a massive black hole at the heart of M51. This "donut-ring" or torus appears as the darkest bar in the striking "X" silhouetted across the bright nucleus. The 'X" marks the exact position of the black hole. Because the giant ring is tilted edge-on as viewed from Earth, it hides the black hole from direct view. The second bar of the "X" could be second disk seen edge on, or possibly rotating gas and dust in M51 interacting with the jets and ionization cones. The image is 1100 light-years across.
[bottom right] – An HST image of the same region, filtered in the light of ionized oxygen shows an hour-glass or double ionization cone structure bisected by the widest bar of the X. The black hole's hot accretion disk, buried deep inside the torus, is presumably the source of the ionizing radiation. The dusty ring confines the radiation from the accretion disk so that it can only escape through the "donut hole' of the torus as a pair of oppositely-directed cones of light.
[bottom left] – An HST image of the same region, filtered in the light of ionized hydrogen, shows a double-lobed hour-glass structure across the nucleus. The dust ring determines the axis of a jet of material being accelerated away from the black hole. The high-speed jet lies in the galaxy's plane and plows into the interstellar medium. The interaction of the nuclear jet with the interstellar medium is analogous to a fire hose directed against a large pile of sand. The jet inflates a cavity of ionized gas which expands and advances into the gas and dust in the M51's disk.