Red Flags Most galaxies contain a supermassive black hole at their heart. In the Milky Way and others, the black hole is relatively quiet, sporadically consuming stars and dust. In others, material is constantly flowing into the black hole, and the resulting radiation produces a bright glow that can be seen across the universe. The strength of the signal can vary as the supply of material changes over time.
For Williams and his colleagues, the constant glow from the proposed source galaxy raised a red flag.
NEWS: Mysterious 'Fast Radio Burst' Pinpointed for First Time
"I think that Keane et al glossed over the steady radio emission after the first six days," Berger said. "It was bright enough that only an AGN origin makes sense. This was what alerted us to a problem with their paper as soon as we read it."
Williams' team used the Very Large Array, run by the National Radio Astronomy Observatory, to observe the galaxy and found that the glow had not only remained steady but had brightened since the original observations, a finding Berger said supported the idea of an AGN source.
No current models suggest that an AGN could produce the fast radio bursts. Berger deemed them unlikely sources, because events that occur on such short timescales are difficult to produce near black holes. Williams also thinks it unlikely but not necessarily unreasonable.
"We know little enough about the physics of FRBs that I wouldn't want to say it's impossible," Williams said. "In fact, I wouldn't be shocked if an enterprising theorist gets inspired to cook up just such a model based on the past week's events."
Williams' team posted an informal paper online, which alerted other scientists of their conclusions.
NEWS: Mystery Cosmic Radio Pulse Leaves Magnetic Clue
"It looks like it comes from an AGN because of its spectrum and persistence," astronomer Avi Loeb, referring to the afterglow, told Space.com. Loeb serves as chairman of the Astronomy department and Direct of the Institute for Theory & Computation at Harvard University, and was not involved in either study.
Keane's team used the proposed source to "weigh" the material in the space it passed through. Their calculations matched models of the distribution of normal and dark matter through space. But according to Berger, those results could be a coincidence. The FRB could lie at approximately the same distance as the proposed source galaxy, which would give similar numbers even if it isn't in the same direction.
Loeb agreed that it was likely a coincidence.
"Given the error bars on the measurement, such a coincidence would not be unusual," he said.
Space.com reached out to the authors of the original research to ask for their thoughts on the idea of an AGN as the source of the glow.
"We are, of course, aware of work, and indeed are performing our own ongoing studies," Keane told Space.com.
PHOTOS: Cosmic Hotshots from Keck Observatory
He said that once the studies were complete, they would be reported in peer-reviewed scientific literature, "which is where scientific debate happens." He declined to comment on the informally published results posted by Williams.
"We really can't rush the scientific process," Keane said. "I'd have said the same to you if, a couple months ago, you had asked me about last week's or this week's Nature papers, when they were still in the peer-review process."
Williams and his colleagues intend to continue observing the proposed source galaxy, monitoring it for activity that might further support or deny the idea that the glow spotted by Keane's team came from an AGN rather than an FRB. Still, without more detailed observations, definitively pinpointing the source may prove impossible.
"We may never find out where this FRB came from, or even be able to conclusively prove that it did not come from the proposed galaxy," Williams said. "But I think we are well on our way to showing that there is a compelling alternative hypothesis that explains the galaxy observations without requiring that the FRB originated from the galaxy."
Originally published on Space.com. Copyright 2016 SPACE.com, a Purch company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.