Massive stars, by which we mean to say stars that are about thirty times the mass of the Sun or even more massive, are distinguished from their less massive brethren in several ways.
These blue luminaries shine brighter, have shorter lives, create many different elements of the periodic table, end their lives famously as supernovae, and are extremely rare. A new study reported in this month’s issue of Science magazine asks us to revisit the notion that massive stars are such a minority.
Massive stars, and in fact all stars, tend to form in large families in which there can be hundreds of “siblings.”
In this study, 800 massive stars were observed in a large and nearby star forming nursery called the Tarantula Nebula. This is star forming region that got its name because some regions which correspond roughly to the stellar “incubation” centers trace out spindly shapes that resemble the legs of a spider.
Stars in this nursery are in various stages of development. Some stars have in fact left the incubation center and emerged in the “delivery wing.” These newborn stars are remarkably numerous – it turns out that there are about 30 percent more ultra-massive stars showing up than the number expected by the theory.
This comes as a surprise. This is because just as doctors know how common each birth-weight for a baby is, astronomers know how common each stellar birth-weight is, also called the Initial Mass Function (IMF). The stellar IMF is fairly well established.
If the IMF allows more high mass stars to be formed than expected, then such an excess would result in the production of more light, and in their brief “lifetime” also more metals that ultimately enrich their surroundings and get incorporated into the formation of new stars and planets. It would also mean that there would be an 180 percent greater rate of the production black holes!
Note the authors do leave open the possibility that the Tarantula nebula may be anomalous in that the stellar nursery is “constructed” with fewer metals than other examples, an attribute which is correlated with an increased likelihood to form massive stars.
Another possibility is that this nebula may have been primed especially to have a more productive massive stellar production rate than other nebulae.