Intergalactic space, the space between galaxies, can be filled with a hot gas that emits X-rays, but this is only found within clusters of galaxies.
Sensitive searches have been made for a variety of forms of hot and cold gas in the intergalactic space outside clusters of galaxies. Some indications are that, long ago, there once were vast clouds of hydrogen gas, but we do not know where these clouds went because they can no longer be detected except as 'absorption features' in the light from very distant quasars. It is believed that many if not all of these clouds were ultimately 'eaten' by galaxies.
THE INTERGALACTIC MEDIUM (IGM) MAY HAVE BEEN DETECTED , at least that part of it consisting of singly ionized helium. Using the Hubble Space Telescope (HST), a Dutch- British-French-US team of astronomers have sampled the light coming from the quasar Q0302- 003 (redshift of 3.286). They notice that ultraviolet light at a wavelength of 304 angstroms is being absorbed along the way, supposedly by the singly ionized helium making up part of the IGM. (Another presumed IGM component, singly ionized hydrogen, cannot be observed since, consisting of bare protons, it exhibits no atomic transitions.) Using the quasar approach to inferring the presence of the IGM is difficult because the quasar must be far away, so that the ultraviolet radiation can be redshifted into a range that can be detected by HST, and because it is rare for such a quasar not to lie behind several foreground neutral-hydrogen clouds, which could also absorb the ultraviolet. (P. Jakobsen et al., Nature, 7 July 1994.)
Some stars can get stripped from galaxies during collisions between galaxies and these could end up in intergalactic space as renegade stars. The Hubble Space Telescope has detected these intergalactic wanders too. The above artist rendering shows what the sky would look like from a planet orbiting such a star.
NASA's Hubble Space Telescope has found a long sought population of "stellar outcasts" -- stars tossed out of their home galaxy into the dark emptiness of intergalactic space. This is the first time stars have been found more than 300,000 light-years (three Milky Way diameters) from the nearest big galaxy. The isolated stars dwell in the Virgo cluster of galaxies, about 60 million light-years away. The results suggest this population of "lone stars" accounts for 10 percent of the Virgo cluster's mass, or 1 trillion Sun-like stars adrift among the 2,500 galaxies in Virgo. Astronomers are trying to determine just how many of these stars might be present, but it seems from the level of optical background light, that their numbers are rather low.
Copyright 1997 Dr. Sten Odenwald
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