It was long thought that these stars lived mostly solitary lives, or formed a very wide binary system. The modern studies suggest that these stars were not only very massive, but also fast rotating.
Clark et al (2011), however, provided numerical simulations that show that these stars could be members of tight multiple systems. Their results show that the massive gaseous disks formed around the first rapidly rotating stars were unstable to gravitational fragmentation and could possibly fall into small binary and higher-order systems.
All the elements heavier than helium found in later stars were formed by the first stars and recycled in later generations of stars. And however there are no first generation stars left in the nearby Universe to study, we can still reconstruct the chemical composition and masses of first stars using data from the very old stars observable now.
Here low mass stars become very handy. Low mass stars (1Msun- 0.5 Msun), live very long lives and contain elements produced by the first generation of stars. They are observable now, gathering in globular clusters, and can be used to provide insights into the lives of the first stars.
Chiappini of the Institute for Astrophysics in Potsdam and collaborators used the European Southern Observatory's Very Large Telescope in Chile to study the chemical composition of some of 8 oldest stars from an ancient globular cluster NGC-6522 to figure out what the first stars were like. These stars are old enough to have formed out of the original chemicals produced by the first generation.
They found extraordinarily high levels of the heavy elements strontium (Sr) and yttrium (Y) in the surfaces of stars in NGC6522, which suggest that the first stars were both massive and very rapidly rotated to achieve the degree of mixing needed to produce these elements.
Fast stellar rotation makes possible to mix the He-buring core and outer nuclear burning layers, which don’t normally mix in slow rotating stars. The nuclear reactions in the overlapping region leads to an enhanced production of radioactive neon, which emit neutrons that are subsequently captured by Fe and other heavy elements to produce Sr and Y.
Chiappini et al. (2011) suggest that, given the abundance of Sr and Y, the first generation of stars could have been rotating as fast as 500 km/s. The typical values for massive stars in the Milky Way are about 100 km/s, and our Sun rotates at 2 km/s.
Note that the rapidly rotating stars are more likely to result in gamma-ray bursts, which, in turn, would impact on the ionizing power of the first stars and impact early Universe.
References:
Clark, P., Glover, S., Smith, R., Greif, T., Klessen, R., & Bromm, V. (2011). The Formation and Fragmentation of Disks Around Primordial Protostars Science, 331 (6020), 1040-1042 DOI: 10.1126/science.1198027
Clark, P., Glover, S., Smith, R., Greif, T., Klessen, R., & Bromm, V. (2011). The Formation and Fragmentation of Disks Around Primordial Protostars Science, 331 (6020), 1040-1042 DOI: 10.1126/science.1198027
Chiappini, C., Frischknecht, U., Meynet, G., Hirschi, R., Barbuy, B., Pignatari, M., Decressin, T., & Maeder, A. (2011). Imprints of fast-rotating massive stars in the Galactic Bulge Nature, 472 (7344), 454-457 DOI: 10.1038/nature10000
Chiappini, C., Frischknecht, U., Meynet, G., Hirschi, R., Barbuy, B., Pignatari, M., Decressin, T., & Maeder, A. (2011). Imprints of fast-rotating massive stars in the Galactic Bulge Nature, 472 (7344), 454-457 DOI: 10.1038/nature10000
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