Closing in On Gravitational Waves --"Will Be a Clear Message About How the Universe is Put Together"
Astronomers Detect a Cosmic Burst of Light from Long Before Origin of Life on Earth

Something is Amiss with Light in the Universe --"May Be Coming from Some Exotic Unknown Source" (Today's Most Popular)




The vast reaches of empty space between galaxies are bridged by tendrils of hydrogen and helium, which can be used as a precise "light meter." In a recent study published in The Astrophysical Journal Letters, a team of scientists finds that the light from known populations of galaxies and quasars is not nearly enough to explain observations of intergalactic hydrogen. The difference is a stunning 400 percent.

"The most exciting possibility is that the missing photons are coming from some exotic new source, not galaxies or quasars at all," said Neal Katz a co-author from the University of Massachusetts at Amherst. For example, the mysterious dark matter, which holds galaxies together but has never been seen directly, could itself decay and ultimately be responsible for this extra light.

"You know it's a crisis when you start seriously talking about decaying dark matter!" Katz remarked.

"The great thing about a 400% discrepancy is that you know something is really wrong," commented co-author David Weinberg of The Ohio State University. "We still don't know for sure what it is, but at least one thing we thought we knew about the present day universe isn't true."

"It's as if you're in a big, brightly-lit room, but you look around and see only a few 40-watt lightbulbs," noted Carnegie's Juna Kollmeier, lead author of the study. "Where is all that light coming from? It's missing from our census."

Strangely, this mismatch only appears in the nearby, relatively well-studied cosmos. When telescopes focus on galaxies billions of light years away (and therefore are viewing the universe billions of years in its past), everything seems to add up. The fact that this accounting works in the early universe but falls apart locally has scientists puzzled.

The light in question consists of highly energetic ultraviolet photons that are able to convert electrically neutral hydrogen atoms into electrically charged ions. The two known sources for such ionizing photons are quasars—powered by hot gas falling onto supermassive black holes over a million times the mass of the sun—and the hottest young stars.

Observations indicate that the ionizing photons from young stars are almost always absorbed by gas in their host galaxy, so they never escape to affect intergalactic hydrogen. But the number of known quasars is far lower than needed to produce the required light.

"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," Kollmeier said. "We are calling this missing light the photon underproduction crisis. But it's the astronomers who are in crisis—somehow or other, the universe is getting along just fine."

The mismatch emerged from comparing supercomputer simulations of intergalactic gas to the most recent analysis of observations from 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," explained Ben Oppenheimer a co-author from 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 image at the top of the page shows a type Ia supernovae that are brighter than whole galaxies and visible billions of light-years away. The Supernova Cosmology Project devised ways of finding Type Ia supernovae “on demand,” then measured the expansion of the universe with a precision that led to the discovery of dark energy.

The Daily Galaxy via the Carnegie Institution

Image credit:


Is there a connection between this, and the previous article?
"Sources Unknown for Hotspot of Cosmic Rays Near the Supergalactic Plane"

Fiat Lux,

Could light ever suffer from terminal gravity? Obviously it is affected by black holds so despite lights intense nature gravity can still affect it. If light reached the edge of the known universe before blazing out into the unknown could it be that the collective weight of the universe sends the light back into the universe to forever bounce around inside itself. This could explain the “light barrier” as light could only exist within the confines of the universe that created it.

ATK, wonderful idea! Why didn't they ask you!?

I believe the universe is massively larger in terms of light-years across than it is years old. Also, the universe undergoes inflation at a rate faster than the speed of light.

The light barrier is due to special relativity and increasing mass whereby you can get to 99% the speed of light; but the closer you get to 100% light speed your mass approaches infinity.

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