Messier 77, a huge spiral galaxy in Cetus

 
Messier 77, a huge spiral galaxy in Cetus

Messier 77 (also designated NGC 1068 and Arp 37) is a very bright barred spiral galaxy of about 170,000 light-years in diameter and an estimated mass of nearly 1 billion sunmasses, what makes it one of the biggest galaxies of Messier’s catalog. The galaxy lies some 47 million light-years away in the constellation Cetus, and is receding from us at a speed of about 1137 kilometers per second.

Messier 77 is among the brightest and most nearby active galaxies. It looks like a rather normal, barred spiral galaxy, but its core, however, is very luminous, not only in optical, but also in ultraviolet and X-ray light. It is an example of a Seyfert II galaxy with an active galactic nucleus (AGN) — one with an expanding core of starbirth. It is obscured from view by astronomical dust at visible wavelengths.

Messier 77 has broad structured spiral arms with, besides obscuring lanes of gas and dust, lots of regions with massive star formation. There are also many evolved yellow stars like our own Sun in the outer regions. The galaxy has very broad emission lines, indicating that giant gas clouds are rapidly moving out of this galaxy’s core, at several hundreds of kilometers per second.

At the center of Messier 77 astronomers found an infrared source of less than 12 light-years in diameter what appears to be a supermassive black hole with a mass equivalent to about 100 million times the mass of our Sun, which accounts for the nuclear activity in this galaxy.

Messier 77’s nucleus has an innermost, comparatively “hot” cloud of dust, heated to about 500°C and with a diameter of about 3 light-years. It is surrounded by a cooler, dusty region, with a temperature of about 50°C, measuring 11 light-years across and about 7 light-years thick. This is most likely the predicted central, disk-shaped cloud that rotates around the black hole.

This image was taken using the Advanced Camera for Surveys on the Hubble Space Telescope and processed by André van der Hoeven.

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