Gamma Ray Mystery Reestablished By Fermi Telescope

eldavojohn writes "New observations from NASA's Fermi Gamma-ray Space Telescope reveal that our assumptions about the 'fog' of gamma rays in our universe are not entirely explained by black hole-powered jets emanating from active galaxies — as we previously hypothesized. For now, the researchers are representing the source of unaccounted gamma rays with a dragon (as in 'here be') symbol. A researcher explained that they are certain about this, given Fermi's observations: 'Active galaxies can explain less than 30 percent of the extragalactic gamma-ray background Fermi sees. That leaves a lot of room for scientific discovery as we puzzle out what else may be responsible.' And so we reopen the chapter on background gamma-rays in the science textbooks and hope this eventually sheds even more light on other mysteries of space — like star formation and dark matter."

Re:Black

[OldSoldier]

So I'll say this: what's with all the black in outer space anyway. Black holes, black energy, black matter, even the nothing part is black. Black black black. It's depressing.

I know you meant this in jest, but it's a surprising legitimate question [wikipedia.org]. (or at least it was.)

I don't think that's really the answer, though

[sean.peters]

Let's run through these:

• Absorption by dust: doesn't really solve the problem, as over an infinite period of time, the dust would heat up to the same temperature as the stars behind it, and begin radiating itself.
• The universe "that we see" is not infinite: this seems to beg the question. Why don't we see all of it? (but with this one you're getting somewhere... see below)
• Stars not evenly distributed. It's true that at distance scales of up to the size of galaxy superclusters, stars are not evenly distributed. But over larger scales, this lumpiness goes away. If you trace it out far enough, every point should still trace out to the surface of a star.

As usual, Wikipedia knows all [wikipedia.org], but in a nutshell, there are a couple of possible explanations for the "paradox". Among them: 1) star formation has not been in progress for an infinite period of time, so it would seem to be the case that in fact, not every point in the sky can be traced back to the surface of a star. And 2) the universe is expanding at an inflationary pace - that means some stars are receding beyond our ability to see them, because the space between us and them is expanding faster than the light can go through it. Another way to look at this is that the light has become so red-shifted that it's not detectable any more. Either way, the second bullet above hints at the answer - we really DON'T see the whole universe.

Re:Why is it a mystery?

[VoiceInTheDesert]

It just seems to me that there could be black holes that we simply are unable to detect. In the end, it doesn't matter, because the end result is "we don't know." I just get picky when scientists say "we know this," because current science is just our best theory at the moment. Good theories? Absolutely. But I think saying things like "we know" discourage full exploration of a mystery because you're already eliminating one possibility without considering that your initial assumption about that fact may be wrong.