Caldwell 77

Better known as Centaurus A, Caldwell 77 is the closest active galaxy to Earth.

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11 million light-years

Apparent Magnitude




object type

Elliptical Galaxy

NASA, ESA, and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration; Acknowledgment: R. O’Connell (University of Virginia) and the WFC3 Scientific Oversight Committee

Caldwell 77, also cataloged as NGC 5128 and commonly called Centaurus A, is a peculiar elliptical galaxy. Centaurus A is apparently the result of a collision between two otherwise normal galaxies, which led to a fantastic jumble of star clusters and dark, imposing dust lanes. Near the galaxy's center, leftover cosmic debris is steadily being consumed by a central supermassive black hole, making Centaurus A something astronomers call an active galaxy. As in other active galaxies, the black hole’s feeding process generates bursts of radio, X-ray, and gamma-ray light.

The Hubble image (on the right), showing dust and stars near the center of Centaurus A, is a combination of visible-light observations taken by the Wide Field and Planetary Camera 2 in 1997 and 1998. The green outline in the ground-based National Optical Astronomy Observatory (NOAO) image (upper left) shows the area covered by the Hubble image.
Ground-based image: NOAO; Hubble image: E.J. Schreier (STScI) and NASA; Team members: E.J. Schreier, A. Marconi, D. Axon, N. Caon, and D. Macchetto (STScI)

“Only” about 11 million light-years away (not far in cosmic terms), Centaurus A is the closest active galaxy to Earth. The galaxy is about 60,000 light-years wide, but this Hubble image zooms in on a region that is about 8,500 light-years wide. The image combines observations taken in visible, infrared, and ultraviolet light using Hubble’s Wide Field Camera 3 in 2010. Hubble’s observations of Centaurus A have provided insights into star formation in the galaxy, peering into regions typically obscured by dust and revealing the vibrant glow of young, blue star clusters. Using its infrared vision, Hubble also discovered that a tilted disk of hot gas 130 light-years across is encircling the black hole at the heart of Centaurus A, which is likely supplying material to a smaller, inner accretion disk that feeds the black hole. In addition, astronomers have used Hubble to probe the galaxy’s outskirts, finding that Centaurus A’s vast halo of stars extends much farther out than previously imagined.

In 1986, Centaurus A got the world’s attention when amateur astronomer Robert Evans discovered a Type Ia supernova in the bizarre galaxy. Supernovae like this one erupt after a compact star called a white dwarf siphons material off of a companion star, resulting in an uncontrolled fusion reaction that ultimately detonates the white dwarf. Since then, Centaurus A has produced just one more known supernova, observed in 2016.

Centaurus A was discovered by astronomer James Dunlop in 1826. It is the fifth brightest galaxy in the sky, making it an ideal target for amateur astronomers. It is best spotted from the Southern Hemisphere in autumn and can be found in the Centaurus constellation. Northern Hemisphere observers will need to be as far south as possible and look for the galaxy low in the southern sky during late spring. With a magnitude of 6.7, it’s visible in binoculars, but a telescope is recommended for ideal viewing. Through a telescope the galaxy will appear nearly circular, with its prominent, dark dust lane crossing the center.

The infrared image in the lower right, taken by Hubble’s Near Infrared Camera and Multi-Object Spectrometer (NICMOS), shows the bright core of Centaurus A (bright white region) with an apparent disk of glowing hot gas (red patches immediately to the upper left and lower right of the core). On the left, a white square in the Wide Field and Planetary Camera 2 (WFPC2) image of the center of Centaurus A shows the area covered by the NICMOS image.
E.J. Schreier (STScI) and NASA; Team members: Ethan J. Schreier, Alessandro Marconi, David J. Axon, Nicola Caon, Duccio Macchetto (STScI), Alessandro Capetti (Osservatorio Astronomico di Torino, Italy), James H. Hough, Stuart Young (University of Hertfordshire, UK), and Chris Packham (Isaac Newton Group, Islas Canarias, Spain)
This star chart for Caldwell 77 represents the view from mid-southern latitudes for the given month and time.
Image courtesy of Stellarium


Elliptical Galaxy - A nearly featureless, spherical or football-shaped galaxy, typically lacking new star formation and often containing much older stars than those in spiral galaxies.

Galactic Halo - A roughly spherical collection of old stars and globular clusters surrounding a spiral galaxy.

Magnitude - The brightness of an astronomical object, represented by a number; bright objects have low numbers on the magnitude scale, while dim objects have high numbers.

Supermassive Black Hole - A black hole millions or billions of times more massive than the Sun, typically residing at the center of a large galaxy.

Supernova - The explosion of a massive star at the end its life, which ejects material into space and causes the star to temporarily brighten in our sky.

White Dwarf - The core of a dead Sun-like star whose outer layers have been expelled into space.

Explore Hubble's Caldwell Catalog

The following pages contain some of Hubble’s best images of Caldwell objects.

Caldwell 1

Also known as NGC 188, this group of stars formed from a large cloud of gas making the stars roughly…

Caldwell 2

This shell of gas is expanding outward, away from the dying star within.

Caldwell 3

This barred spiral galaxy was first spotted by British astronomer William Herschel in April 1793 in the constellation Draco.