Astronomers have found a distant quasar illuminating a vast nebula of diffuse gas, revealing for the first time part of the network of filaments believed to connect galaxies in a cosmic web.
Using the 10-meter Keck I telescope at the W. M. Keck Observatory in Hawaii, the researchers detected a very large, luminous nebula of gas extending about 2 million light-years across intergalactic space.
In this study, the researchers detected the fluorescent glow of hydrogen gas resulting from its illumination by intense radiation from the quasar.
The hydrogen gas illuminated by the quasar emits ultraviolet light known as Lyman alpha radiation. The distance to the quasar is so great (about 10 billion light-years) that the emitted light is “stretched” by the expansion of the universe from an invisible ultraviolet wavelength to a visible shade of violet by the time it reaches the Keck telescope and the LRIS spectrometer used for this discovery.
Knowing the distance to the quasar, the researchers calculated the wavelength for Lyman alpha radiation from that distance and built a special filter for LRIS to get an image at that wavelength.
Sebastiano Cantalupo, first author of the paper and a postdoctoral fellow at UC Santa Cruz, said that they think this is part of a filament that may be even more extended than this, but they only see the part of the filament that is illuminated by the beamed emission from the quasar.
The study has been published in the journal Nature.