These spectra show ultraviolet starlight broken down into its component wavelengths or colors, in the same way that visible light is spread into its colors in a rainbow. With spectra like this, astronomers can investigate the chemical composition, temperature, density and motion of the stars.
The spectra of two stars in the cluster R136 are shown here, each in two different formats. First (top), the spectrum appears in 'rainbow' format. Bright vertical columns are particular wavelengths where emission is strong ('emission lines'). An absorption line, where certain atoms cut off or reduce the light at particular wavelengths, appears as a dark column. The second format presents the information as a graph with wavelength as the horizontal axis and the strength of radiation as the vertical axis. In this format, an emission line appears like a narrow hill and an absorption line appears as a dip or valley.
A strong emission line is visible in the spectra of both stars at a wavelength of 1645 Å (164.5 nm). It is identified as emission from singly ionized helium in the winds of gas blowing off the stars. These emission lines are telltale clues to the amount of matter blowing out of the stars. From this evidence, the star R136a5 appears to be blowing off a mass equal to the mass of the Sun in just 50,000 to 100,000 years. Such a rapid rate of mass loss greatly affects the future fate of the star.
Instrument: Goddard High Resolution Spectrograph
(GHRS) with COSTAR
Credit: S. Heap/NASA
