Supermassive black holes sit at the core of most galaxies. Some are quasars, actively emitting powerful jets, while others are quiet and idle. Then there are some active ones that get shrouded by huge clouds of gas, possibly indicating the early stages of a supermassive black hole growing and entering its full quasar phase.
Astronomers have now discovered what they think is the farthest "cloaked" supermassive black hole. Since looking into the cosmos is like looking back in time, the light from this object comes from when the universe was 830 million years old (just 6 percent of its current age). The discovery is accepted for publication in the journal Astronomy & Astrophysics.
The object in question, called PSO167-13, was part of a group of quasars previously identified three years ago. The team followed up by conducting routine investigations on this and another nine quasars using the Chandra X-ray observatory. They assumed that the quasars were all unobscured having been already detected in visible light, but the X-rays told another story.
After 16 hours of observations, researchers could only detect three X-ray photons for PSO167-13 and these were all relatively high energy. X-ray astronomers are used to a low number of photons, but the characteristics of this detection suggested something else was happening. The low-energy X-ray emissions, which should be present in a quasar, were missing. For this reason, the team thinks the quasar is cloaked.
"It's extraordinarily challenging to find quasars in this cloaked phase because so much of their radiation is absorbed and cannot be detected by current instruments," lead author Fabio Vito, from the Pontificia Universidad Católica de Chile, said in a statement. "Thanks to Chandra and the ability of X-rays to pierce through the obscuring cloud, we think we've finally succeeded."
So how can a quasar go from visible to cloaked in just three years? The team has two ideas: either the black hole just received a large amount of gas or its possible that the researchers are spotting a nearby black hole. The galaxy that hosts PSO167-13 has a companion, so either explanation might fit the bill.
"With a longer Chandra observation we'll be able to get a better estimate of how obscured this black hole is," added co-author Franz Bauer, also from the Pontificia Universidad Católica de Chile, "and make a confident identification of the X-ray source with either the known quasar or the companion galaxy."
If it turns out to be from the companion, this would be the furthest quasar pair ever identified. The team plans to search for more examples of these types of black holes. It is likely that cloaked supermassive black holes are common in the early universe. Studying them might help us understand how they grew so exponentially fast during the first billion years of the cosmos.
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