Posted: 27 November, 2008
Two of our Galaxy's most massive stars have been scrutinised by the Hubble Space Telescope to reveal a third component of the system.
The pair of mammoth stars, WR 25 and Tr16-244, are located within the open cluster Trumpler 16, which itself is embedded within the Carina Nebula around 7,500 light years from Earth. Many stars in the Carina Nebula, including the highest luminosity star known, Eta Carinae, are ultra bright, hot stars, emitting most of their radiation in the ultraviolet and appearing blue in colour. They burn so ferociously that they power through their hydrogen fuel source faster than any other type of star.
WR 25 is situated near the centre of the image in the bottom third. Tr16-244 is located to the upper left of WR 25. The star to the left of WR 25 is a low mass star located much closer to the Earth. The massive stars are thought to be responsible for the radiation that is creating a giant gas bubble, and controlling the globule's interesting shape, which includes a finger-like shape pointing towards WR 25 and Tr16-244. Image: NASA, ESA, and J. Maíz Apellániz (Instituto de Astrofísica de Andalucía, Spain).
WR 25 and Tr16-244 interest astronomers because they are associated with star-forming nebulae, and influence the structure and evolution of galaxies. Such massive stars are usually formed in compact clusters, and combined with their extreme brightness, makes the study of any individual star very difficult. New Hubble observations have come to the rescue. Obtained by a team of scientists from US, Chilean, Spanish, and Argentine institutions and led by Jesus Maiz Apellaniz from the Instituto de Astrofisica de Andalucia in Spain, astronomers have been given an even finer look at the system, revealing that the pair is actually a triple star system. The third star takes tens or even hundreds of thousands of years to orbit the other two stars.
The true nature of WR 25 was revealed two years ago when astronomers discovered that it was actually composed of two stars. WR 25 is the more massive Wolf-Rayet star and may weigh more than 50 times the mass of our Sun. It is losing mass rapidly through powerful stellar winds that have ejected the majority of its outermost hydrogen-rich shells, while its more commonplace binary companion is roughly half as massive, orbiting around it once every 208 days.
Two of the stars are so close to each other that they look like a single object, but Hubble's Advanced Camera for Surveys reveals them as two. Image: NASA, ESA, and J. Maíz Apellániz (Instituto de Astrofísica de Andalucía, Spain).
Astronomers believe that WR 25 and Tr16-244 are the likely sources of radiation that is causing a giant gas globule within the Carina Nebula to slowly evaporate away into space, while possibly inducing the formation of new stars within it.
The research team are using Hubble as well as ground-based observatories in Spain, Chile, and Argentina to build a comprehensive catalogue of observations of all the massive stars in the Galaxy that are detectable at visible wavelengths.