This vibrant spiral galaxy and the subject of today’s NASA/ESA Hubble Space Telescope Picture of the Week is NGC 5042, which resides about 48 million light-years from Earth in the constellation Hydra (the water snake). The galaxy nicely fills the frame of this Hubble image, with a single Milky Way star marked by cross-shaped diffraction spikes attempting to blend in with the bright stars along the galaxy’s edge.
Hubble observed NGC 5042 in six wavelength bands from the ultraviolet to the infrared to create this multicoloured portrait. The galaxy’s cream-coloured centre is packed with ancient stars, and the galaxy’s spiral arms are decorated with patches of young blue stars. The elongated yellow-orange objects that are scattered around the image are background galaxies far more distant than NGC 5042.
Perhaps NGC 5042’s most striking feature is its collection of brilliant pink gas clouds that are studded throughout its spiral arms. These flashy clouds are called H II (pronounced “H-two”) regions, and they get their distinctive colour from hydrogen atoms that have been ionised by ultraviolet light. If you look closely at this image, you’ll see that many of these reddish clouds are associated with clumps of blue stars, often appearing to form a shell around the stars.
H II regions arise in expansive clouds of hydrogen gas, and only hot and massive stars produce enough high-energy light to create an H II region. Because the stars capable of creating H II regions only live for a few million years — just a blink of an eye in galactic terms — this image represents a fleeting snapshot of life in this galaxy.
[Image Description: A spiral galaxy. It’s noticeably bright around the central region of its disc, then dims somewhat out to the edge where there are fewer stars. Two spiral arms circle through the disc and emerge beyond its edge, around the galaxy’s sides. Many pink spots of new star formation, as well as dark reddish strands of dust, cover the galaxy. The arms contain some speckled, blue patches containing hot stars.]