Universe may have significantly higher number of massive stars than scientists thought

Presence of more 200-300 solar mass stars would have far-reaching implications for the universe.
By Laurel Kornfeld | Jan 05, 2018
A study in which scientists found the Tarantula Nebula to have a higher number of massive stars than previously predicted could indicate the universe as a whole has many more such stars as well.

Massive stars are defined as those with a minimum of 10 times the mass of the Sun. The most massive known star, R136a1, located in the Tarantula Nebula, has approximately 300 solar masses.

Because these stars have played an important role in the evolution of the universe through their emission of powerful radiation and charged particles and their deaths in supernovae, discovering that they are more numerous than thought would have significant consequences, such as an increase in neutron stars and black holes, and the release of up to three times more elements into the interstellar medium, according to University of Oxford astrophysicist Fabian Schneider, lead author of a paper on the findings published in the journal Science.

The "metals" or elements heavier than helium, necessary for the formation of planetary systems, are released in supernova explosions that occur when massive stars die.

Using the European Southern Observatory's (ESO) Very Large Telescope (VLT) in Chile, Schneider and his research team studied the ages and masses of 800 stars in the Tarantula Nebula, located in the Large Magellanic Cloud, approximately 180,000 light years away.

This area, about 1,000 light years in diameter, is the largest star-forming region close enough for scientists to study in detail.

Observations of the nebula revealed 30 percent more stars of 30 solar masses or larger than predicted by computer models. One possible reason for the discrepancy is that stars of 150 solar masses or more were viewed as incapable of forming, resulting in scientists centering their studies of massive stars on those with at most 30 to 40 solar masses.

However, Schneider's team found the Tarantula Nebula to host a large number of 200-solar mass stars.

Researchers are uncertain as to whether the higher incidence of massive stars is limited to the Tarantula Nebula. This limitation is possible since the nebula has only about 40 percent the metallicity of the Sun. Low metallicity can result in the formation of massive stars.

Additionally, the nebula is a region with a very high rate of star formation, meaning previous generations of stars may have heated up the nebular clouds, another factor that would increase massive stars' formation rates.

If the larger number of massive stars is not limited to the Tarantula Nebula, supernova explosions may be far more common than expected, resulting in many more stellar mass black holes, producing up to three times more elements and higher levels of ionizing radiation.

 

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