2019 October 3
Explanation:
Gorgeous spiral galaxy M33 seems to have more than its fair share of
glowing hydrogen gas.
A prominent member of the local group of galaxies, M33 is also
known as the Triangulum Galaxy and
lies a mere 3 million light-years away.
The galaxy's inner 30,000 light-years or so are shown in this
magnificent 25 panel telescopic mosaic.
Based on image data from space and ground-based telescopes,
the portrait of M33 shows off the galaxy's reddish ionized hydrogen
clouds or HII
regions.
Sprawling along loose spiral arms that wind toward the core,
M33's
giant HII regions are some of the largest known
stellar nurseries, sites of the formation of short-lived
but very massive stars.
Intense ultraviolet radiation from the luminous, massive stars ionizes
the surrounding hydrogen gas and ultimately produces the
characteristic red glow.
To enhance this image, broadband data was used to produce a color view
of the galaxy and combined with narrowband data recorded through a
hydrogen-alpha filter.
That filter transmits the light of the strongest visible hydrogen
emission
line.