Westerhout 49-2
One of the most massive and luminous stars known.
Westerhout 49-2 (W49-2) is an extremely massive and luminous star found within the H II region Westerhout 49. Located about 11.1 kiloparsecs from the Sun, it is heavily obscured by dust, suffering nearly 5 magnitudes of reddening in the K band—the highest of any star in that region. Classified as an evolved slash star with a spectral type of O2-3.5If, it has a temperature of roughly 35,500 K and a radius exceeding 55 times that of the Sun. Its luminosity places it among the most luminous stars known.
The star's properties come with considerable uncertainty. One estimate, based on mass-luminosity relations, suggests a mass between 90 and 250 solar masses, though the true value may be even higher. This mass likely surpasses the theoretical upper limit for a single star, implying that W49-2 could be a binary system if X-rays are detected. Notably, Westerhout 49-1, 49-2, and 49-12 are all bright X-ray sources, indicating they may all be binary stars, in which case their individual masses would be lower than the predicted single-star values.
Quick Facts
- Mass
- 250 solar masses (with significant uncertainty)
- Distance
- about 11.1 kiloparsecs from the Sun
- Spectral type
- O2-3.5If
- Temperature
- about 35,500 K
- Radius
- over 55 times that of the Sun
- Reddening
- nearly 5 magnitudes in the K band
Facts from the source article.
Lore & Background
Westerhout 49-2 is located within the H II region Westerhout 49, approximately 11.1 kiloparsecs from the Sun. The star is heavily reddened, by nearly 5 magnitudes in the K band, the most of any star in the region. It is classified as an evolved slash star, with a spectral type of O2-3.5If. The star has a temperature of about 35,500 K, corresponding to a radius of over 55 times that of the Sun.
There is significant uncertainty about Westerhout 49-2's properties. One estimate using mass-luminosity relations finds a mass between 90 and 250 solar masses. Its mass is likely higher than the theoretical upper limit, which means it could be a binary, if x-rays are detected. Westerhout 49-1, 49-2 and 49-12 are all bright x-ray sources, which means they could all be binary stars and their masses would be lower than the predicted mass if they were single stars.
Reader's Guide
Westerhout 49-2 is notable as one of the most massive and most luminous stars known, with a mass of 250 solar masses and a luminosity that places it among the extreme stellar population. Its location within the H II region Westerhout 49, at a distance of about 11.1 kiloparsecs, and its heavy reddening—nearly 5 magnitudes in the K band, the most of any star in the region—underscore its extreme environment. The star's classification as an evolved slash star of spectral type O2-3.5If and its temperature of about 35,500 K, corresponding to a radius over 55 times that of the Sun, further highlight its exceptional nature. However, significant uncertainty surrounds its properties: mass estimates range from 90 to 250 solar masses, and its mass likely exceeds the theoretical upper limit for single stars. The detection of x-rays from Westerhout 49-2, along with Westerhout 49-1 and 49-12, suggests these could be binary systems, which would imply lower masses than predicted for single stars. This uncertainty makes Westerhout 49-2 a key object for studying the upper limits of stellar mass and the role of binarity in massive star evolution.
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