Close-up Views of Triangulum Galaxy (M33)

Details in the Triangulum galaxy

While the Triangulum galaxy (M33) has led a quiet life compared to other massive galaxies, it still contains evidence of a rich "inner life." This collage zooms into several areas of the larger mosaic, highlighting the amazing details that NASA's Hubble Space Telescope reveals. Almost every dot of light is a star, with occasional dense clusters of stars, or even rare background galaxies shining through.

The top image is a close-up of NGC 604, a glowing nebula of hot, ionized hydrogen gas that cocoons bright young stars, found in the upper left corner of the larger mosaic image. The high density of star formation throughout the galaxy is one of Triangulum’s most striking features, leading to many bright nebulae like NGC 604.

Dense knots of many thousands of ancient stars gravitationally bound together, called globular star clusters, can also be seen in the galaxy. The image also includes foreground stars that are within our own Milky Way galaxy and lie along the line-of-sight to M33. These bright nearby stars show characteristic “diffraction spikes” (lines that appear to be radiating from a bright star) that are optical artifacts caused by the mirror support structure in most reflector telescopes.

Some of the more extended features in the image are not nebulae like NGC 604, but instead are distant galaxies shining through from the far side of Triangulum. They are distinguishable from stars only due to Hubble’s exceptional sensitivity and resolution.

Even though Triangulum is one of our closest galactic neighbors, Hubble still puts the vastness of space in perspective. Beyond the awe-inspiring display of Triangulum's nearly 25 million stars and 19,400 light-year span, other — perhaps even larger — galaxies lie waiting to be explored.

The mosaic was created from images taken by Hubble's Advanced Camera for Surveys between February 2017 and February 2018.