If there's one thing we know about the universe, is that there are huge swathes of it that we don't understand -- in fact, most of it we can't even see.
We already knew about Dark Matter and Dark Energy, two despairingly complex and confusingly named pillars of the invisible cosmological infrastructure that has so far evaded detection.
Now to their ranks we can add "dark light", after a team at CU Boulder found using data from Hubble that up to 80% of light in the universe is "missing".
Using the Cosmic Origins Spectrograph, a $70 million instrument on Hubble to study the "tendrils" of hydrogen that connect galaxies across the vast wastes of space, the team found an inconsistency that -- currently -- makes no sense.
The experiment looked for charged ions in those massive tendrils, which are created when the hydrogen is struck by UV light. What they found were far more charged ions that could be explained by the known UV light in the universe -- in fact up to 400% more than expected.
And oddly this effect is only obvious when observing the nearby sky.
"Strangely, this mismatch only appears in the nearby, relatively well-studied cosmos. When telescopes focus on galaxies billions of light years away—which shows astronomers what was happening when the universe was young—everything seems to add up."
The UV light that turns neutral hydrogen into hydrogen ions comes from only two sources - quasars, which are powered by hot gas pouring into black holes, and the very hottest young stars. The results indicate that there are five times fewer quasars or young stars than we need -- meaning something else could be producing UV light that we don't currently know about.
“If we count up the known sources of ultraviolet ionizing photons, we come up five times too short,” said Benjamin Oppenheimer at CU Boulder. “We are missing 80 percent of the ionizing photons, and the question is where are they coming from? The most fascinating possibility is that an exotic new source, not quasars or galaxies, is responsible for the missing photons.”