Westerhout 49
A giant HII region hosting some of the most massive stars known.
Last updated
Westerhout 49 (W49) is a strong galactic thermal radio source characteristic of an HII region, discovered by Gart Westerhout in 1958. It lies in the galactic plane at an estimated distance of about 11.1 kiloparsecs (36,000 light-years), roughly the same distance from the Galactic Center as the Sun. The region is notable for containing some of the most luminous and massive stars known, including a star with an initial mass of 250 solar masses.
Lore & Background
Westerhout 49 was identified as a strong thermal radio source in 1958 during a survey of galactic continuum radiation. It is an HII region, a cloud of ionized gas surrounding young, hot stars. Its distance is estimated at 11.1 kiloparsecs, placing it in the galactic plane at a similar distance from the Galactic Center as the Sun. The region has been compared to the giant HII region NGC 3603, which is about half as distant.
Non-thermal radiation has been detected, believed to originate from an old supernova remnant. Gaseous molecular outflows and H2O (water) masers have also been observed. No optical counterpart has been discovered, partly due to interstellar absorption; any tight clustering of stars at such a great distance in the galactic plane would be scarcely distinguishable from the general background.
Reader's Guide
Westerhout 49 is significant as a powerful radio source and a site of active star formation, hosting some of the most massive and luminous stars known. A study using the VLT and other instruments revealed the presence of a very massive star in its central cluster, W49nr1, with a luminosity several million times that of the Sun and an initial mass between 100 and 180 solar masses, possibly even higher. Another star, [WBB2016] 2, has a mass of 250 solar masses, placing both among the most massive stars known.
The region also exhibits non-thermal radiation from an old supernova remnant, molecular outflows, and water masers, indicating ongoing complex processes. Despite its prominence at radio and infrared wavelengths, no optical counterpart has been identified, underscoring the heavy interstellar absorption along the line of sight. Its legacy lies in providing a laboratory for studying extreme stellar masses and the early stages of massive star formation in the galactic plane.
Frequently Asked Questions
What is Westerhout 49?
Westerhout 49 is a powerful galactic HII region that appears as a strong thermal radio source. It is best known for containing some of the most massive and luminous stars ever catalogued.
What makes Westerhout 49 notable among HII regions?
The region hosts stars of staggering mass, including one with an initial mass of roughly 250 solar masses and another at 100–180 solar masses shining at several million times the Sun's luminosity. These make W49 a premier site for studying the upper mass limit of stars.
More in Emission, Dark and Reflection Nebulae
Sources
Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.
- Wikipedia: Westerhout 49 (CC BY-SA 4.0).
- Word definitions: the Codexery glossary, each quoted from its Wikipedia article.
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