Blue supergiant stars are hot luminous stars, referred to scientifically as OB supergiants. Maser emission is common from the circumstellar material around red supergiants. Stars still more luminous than giants are referred to as supergiants and hypergiants. These are red giants or supergiants with little or no detectable periodicity. There is a strong upper limit to the luminosity of red supergiants at around . Rigel's spectral type is a defining point of the classification sequence for supergiants. Higher-mass stars never cool sufficiently to become red supergiants. It is also one of the most luminous and massive red supergiants. During the 2014 expedition, several new species were filmed including huge crustaceans known as supergiants. Lower mass blue supergiants continue to expand until they become red supergiants. In IPL 2016 he became the coach of Rising Pune Supergiants. While many red supergiants will not experience a blue loop, some can have several. Mumbai went onto the finals to beat Rising Pune Supergiants to claim their third championship. In "Supergiants", BBC One 2013, he sought to explain why species grow very large. This matches the expected parameters of lower mass red supergiants.