The Haunting of HDF 130

July 08, 2009

Some 10 billion light years away is a mysterious "X ray source" that dates back to a mere 3 billion years after the Big Bang -- right when lots of galaxies and blacks were forming. It seems to be a kind of "cosmic ghost" lurking around a distant black hole, according to scientists with NASA's Chandra X-Ray Observatory mission. We're not talking "ghost" as in that 1990s Patrick Swayze movie; this is lingering evidence of a huge eruption from a black hole.

That's what Cambridge University's Andy Fabian thinks, anyway. "We'd seen this fuzzy object a few years ago but didn't realize until now that we were seeing a ghost," he says. "It's not out there to haunt us, rather it's telling us something -- in this case, what was happening in this galaxy billions of years ago."

Sounds kind of like an "actual" (and I use that term loosely) ghost to me -- they're always trying to solve their own murders or reveal secrets of the past. In this case, the "ghost" is the X-ray remnant "afterglow" of a power explosion from the central black hole -- so big, it would have been the equivalent of a billion supernovae. That is one violent event.

This kind of outburst produces a huge amount of radio and X-ray radiation that usually dies down after a few million years. So why are we seeing this ghostly X-ray remnant? Fabian explains that the cosmic microwave background is to blame -- another glowing artifact, this time from the actual Big Bang. Less energetic electrons can still produce x-rays, it seems, because they keep colliding with photons in the CMB. This gives them a boost of extra energy so they emit faintly in the X-ray regime of the spectrum. The result is a lingering X-ray source that can last as long as 30 million years after the initial radiation has died away.

That's not all: HDF 130 might not be the only object being haunted. Fabian and his co-author, Caitlin Case, figure that the night sky is actually filled with these sorts of "ghosts"; black holes apparently erupt more often than you might think. So long as they're the "good" kind of "ghost" that helps us solve the mysteries of our early universe, that's probably okay.

Image: HDF 130 as seen in the Chandra Deep Field North, one of the deepest X-ray images ever taken. NASA/Chandra X-Ray Observatory