Gas blasts from black holes show surprising alignment
Fountains of gas from a handful of remote galaxies all seem to be pointing in roughly the same direction, a new study reports. If the result holds up, it puts a new twist on how galaxies and black holes arise from the larger cosmic web, though some researchers worry that the alignment might just be a chance occurrence.
Out of a group of 64 galaxies that are blasting out radio waves, about a dozen are spewing jets of gas that are roughly aligned with one another, astronomers report in the June 11 Monthly Notices of the Royal Astronomical Society Letters. The galactic geysers are powered by supermassive black holes whose magnetic fields launch some infalling debris into intergalactic space. If the geysers are aligned, that means the black holes are all spinning in the same direction. And that means these galaxies, which are spread over roughly a hundred million light-years, might all have been influenced by the larger scaffolding from which they formed.
“Naively we expect that shouldn’t happen,” says Ryan Hickox, an astrophysicist at Dartmouth College who was not involved with this study. Black holes, even supermassive ones, are minuscule compared with filaments of galaxies that can span hundreds of millions of light-years. These filaments are the threads along which most matter in the universe congregates, branching through space like a cosmic spider web. Though galaxies live there, they are thought to form and develop independently of what the filaments are doing. A twisting filament should have no influence over what’s happening around one of its resident black holes.
And yet that’s the explanation favored by study lead Russ Taylor, an astrophysicist at the University of Cape Town in South Africa. “What we’re seeing is the result of a very large region in the early universe spinning coherently in the same direction,” he says. If that’s true, it adds a “new wrinkle to explain how large-scale structure formed.”
Taylor and colleagues found the apparent alignment while probing a patch of sky in the constellation Draco with the Giant Metrewave Radio Telescope in India. They don’t know the distances to the galaxies, but all seem to sit near a galactic supercluster whose light takes about 7.4 billion years to reach Earth — just over half the age of the universe.
Other researchers using different techniques have previously reported similar alignments among another set of galaxies (SN: 12/27/14, p. 6). Both studies, though, relied on a small number of galaxies, which means the alignment might not be statistically significant.
“If an alignment like this exists, it’s very interesting,” says astrophysicist Michael DiPompeo, also at Dartmouth. “But I’m not super convinced that it’s really there.” While Taylor and colleagues argue that the alignment is not a statistical fluke, DiPompeo did his own calculations that suggest otherwise. He simulated observations of 64 randomly oriented galaxy jets — the computer equivalent of repeatedly dropping a bunch of toothpicks on a table and noting where each was pointed. “I could pretty regularly get patterns that look like this,” he says.
It’s also hard to imagine how such an alignment, if it was present as the galaxies formed, could persist for billion of years, he says. “It’s not like [galaxies] form in the early universe and then just sit there blasting these jets.” Galaxies grow by colliding with other galaxies, which can change how the galaxies and their central black holes rotate.
Both DiPompeo and Hickox say it’s worth probing other galactic gatherings, though, before dismissing these alignments as a coincidence. If similar orientations appear in many galaxy clusters, then the researchers could be on to something. Hickox would also like to see distances to these galaxies. If it turns out the galaxies sit at wildly varying distances from Earth, he says, then the alignment is less likely to be real.
Taylor hopes to do just that. Colleagues are planning observations at other telescopes that will let them determine how far away these galaxies are. And Taylor is gearing up for a more thorough investigation over a much larger patch of sky with a new radio observatory in South Africa called MeerKAT, which should be ready for operation later this year.