intergalactic hydrogen
July 9, 2014

Astronomers Discover Enormous Amount Of Missing Ultraviolet Light

redOrbit Staff & Wire Reports - Your Universe Online

The amount of light originating from known populations of galaxies and quasars is far less than the amount required to explain the amount of hydrogen that helps bridge empty spaces between galaxies, according to research appearing in a recent edition of The Astrophysical Journal Letters.

In fact, as lead author Juna Kollmeier of the Carnegie Institution for Science and her colleagues explained in a statement Tuesday, the difference between the ultraviolet light and observed intergalactic hydrogen is an astonishing 400 percent, equivalent to walking into “a big, brightly-lit room” and seeing “only a few 40-watt lightbulbs.”

The source of the extra light is “missing from our census,” Kollmeier added. The phenomenon only appears in the nearby cosmos, she added. When telescopes analyze galaxies located billions of years away (during the earlier universe), the figures add up – a fact which has the investigative team somewhat puzzled.

The light at the heart of this mystery is comprised of highly energetic UV photons that can convert electrically neutral hydrogen atoms into charged ions, the study authors explained. Only two sources for ionizing photons have been identified: quasars powered by hot gas falling into supermassive black holes, and extremely hot young stars.

Based on observations, scientists explained that ionizing photons which originate from young stars are typically absorbed by gas in their host galaxy which means they never escape to affect intergalactic hydrogen. In light of that, however, there simply are not enough known quasars to produce the necessary amount of light.

Keep an eye on the cosmos with Telescopes from

“Either our accounting of the light from galaxies and quasars is very far off, or there’s some other major source of ionizing photons that we’ve never recognized,” explained Kollmeier. “We are calling this missing light the photon underproduction crisis. But it’s the astronomers who are in crisis… the universe is getting along just fine.”

The discrepancy was detected when astronomers compared supercomputer simulations of intergalactic gas to a more recent analysis of observations from the Hubble Space Telescope’s Cosmic Origins Spectrograph.

“The simulations fit the data beautifully in the early universe, and they fit the local data beautifully if we’re allowed to assume that this extra light is really there,” said co-author Ben Oppenheimer of the University of Colorado. “It's possible the simulations do not reflect reality, which by itself would be a surprise, because intergalactic hydrogen is the component of the Universe that we think we understand the best.”

“The most exciting possibility is that the missing photons are coming from some exotic new source, not galaxies or quasars at all,” added co-author Neal Katz of the University of Massachusetts at Amherst. He suggested that the light source might be decaying dark matter, the mysterious and abundant substance that has never been directly observed. “You know it's a crisis when you start seriously talking about decaying dark matter!”

David Weinberg of The Ohio State University, who was also involved in the research, noted that the fact that there was a 400 percent discrepancy was proof that “something is really wrong.” While he and his colleagues are not certain exactly what that “something” is, their observations indicate that “at least one thing we thought we knew about the present day universe isn't true.”