Stars form from gas and dust floating in interstellar space. But, astronomers do not yet fully understand how it is possible to form the massive stars seen in space. One key issue is gas rotation. The parent cloud rotates slowly in the initial stage and the rotation becomes faster as the cloud shrinks due to self-gravity. Stars formed in such a process should have very rapid rotation, but this is not the case. The stars observed in the Universe rotate more slowly.
By analyzing the level of a carbon isotope in tree rings from a specimen of an ancient bristlecone pine, a team led by Nagoya University researchers has revealed that the sun exhibited a unique pattern of activity in 5480 BC.