Hubble observes the hidden depths of M77

The patches of red across this galaxy highlight pockets of star formation along the pinwheeling arms.
By | Published: March 29, 2013 | Last updated on May 18, 2023
Hubble image of M77 // NASA/ESA and A. van der Hoeven
The NASA/ESA Hubble Space Telescope has captured this vivid image of spiral galaxy M77, one of the most famous and well-studied galaxies in the sky. The patches of red across this image highlight pockets of star formation along the pinwheeling arms, with dark dust lanes stretching across the galaxy’s energetic center. M77 (NGC 1068) is a galaxy in the constellation Cetus, some 45 million light-years away.

Despite its current fame and striking swirling appearance, the galaxy has been a victim of mistaken identity a couple of times. When it was initially discovered in 1780, the distinction between gas clouds and galaxies was not known, causing finder Pierre Mechain to miss its true nature and label it as a nebula. It was misclassified again when it was subsequently listed in the Messier catalog as a star cluster.

Now, however, it is firmly categorized as a barred spiral galaxy with loosely wound arms and a relatively small central bulge. It is the closest and brightest example of a particular class of galaxies known as Seyfert galaxies — galaxies that are full of hot, highly ionized gas that glows brightly, emitting intense radiation.

Strong radiation like this is known to come from the heart of M77, which is caused by an active black hole that is around 15 million times the mass of our Sun. Material is dragged toward this black hole and circles around it, heating up and glowing strongly. This region of a galaxy alone, although comparatively small, can be tens of thousands of times brighter than a typical galaxy.

Although no competition for the intense center, M77’s spiral arms are also bright regions. Dotted along each arm are knotty red clumps — a signal that new stars are forming. These baby stars shine strongly, ionizing nearby gas that then glows a deep red color. The dust lanes stretching across this image appear as a rusty, brown-red color due to a phenomenon known as reddening; the dust absorbs more blue light than red light, enhancing its apparent redness.