Though they're the universe's most sought-after celebrities, some black holes aren't fans of the limelight.
In a paper published Wednesday in the journal Nature, researchers announced that a supermassive black hole, about 15 million times the mass of our sun and 47 million light-years from Earth, prefers its privacy. Right in the center of galaxy Messier 77, this introverted abyss is shielded by a thick halo of cosmic dust that serves as a sort of enormous blackout curtain. This ring hides the dangerous void while it does what dangerous voids do: gobble up nearby particles, then spit them out in the form of gleaming jets at nearly the speed of light.
The concealed chasm is a spectacle in itself, but most importantly, it may help solve a long-standing puzzle in astronomy.
For years, astronomers have theorized that energetic black holes at the center of galaxies like Messier 77's, aka active galactic nuclei, or AGNs, have the same general architecture. These galactic control centers are thought to be surrounded by accretion disks, or donuts of particles slowly falling into the void, and emanate iconic jets like those seen on Messier 77's leviathan. Outlined by what's called the Unified AGN Model, the structure also includes a massive dust ring around the whole AGN, like the one hiding Messier 77's gigantic abyss.
But backing up a little to AGN jets – if such violent streams are present on all AGNs, scientists say, every AGN should flood the sky with incredible luminescence. However, experts have discovered that some AGNs that aren't aggressively bright. A few are surprisingly more subdued, like Messier 77's, emitting a duller light despite their huge, speedy torrents. The difference is so noticeable, in fact, that the powerful galaxy centers are classified into separate types based on varying brightness.
That's where AGN dust rings come in. Scientists believe the cosmic clouds can affect how luminescent the phenomena appear to us Earthlings while we view it from our planet. Basically, depending on a telescope's angle of sight, an AGN enclosure could block portions of jet-based light.
Still, the Unified Model hadn't been totally proven, and a jarring question remained: Would such a ring be dense enough to fully obscure black hole jets, offering a supermassive void complete solitude?
The team behind the new research says, yes. Offering concrete evidence for the Unified Model, their observed AGN within Messier 77 even has a dust curtain so thick it conceals the galaxy's entire monstrous void, dimming its luminescence.
"The real nature of the dust clouds and their role in both feeding the black hole and determining how it looks when viewed from Earth have been central questions in AGN studies over the last three decades," Violeta Gámez Rosas, an astronomer from Leiden University in the Netherlands and lead author of the study, said in a statement. "Whilst no single result will settle all the questions we have, we have taken a major step in understanding how AGNs work."
To observe the sneaky black hole lurking within Messier 77, Gámez Rosas and team tapped high-tech equipment such as the European Southern Observatory's Multi AperTure mid-Infrared SpectroScopic Experiment, a device mounted atop the organization's Very Large Telescope Interferometer.
"MATISSE can see a broad range of infrared wavelengths, which lets us see through the dust and accurately measure temperatures," co-author Walter Jaffe, a professor at Leiden University said in a statement, adding, "because the VLTI is, in fact, a very large interferometer, we have the resolution to see what's going on even in galaxies as far away as Messier 77."
After combining temperature data with light absorption maps of the dust around Messier 77's central black hole, the researchers painted a very detailed picture of the halo obscuring the void.
Added Gámez Rosas, "Our results should lead to a better understanding of the inner workings of AGNs. They could also help us better understand the history of the Milky Way, which harbors a supermassive black hole at its center that may have been active in the past."