This Hubble image shows the barred spiral galaxy Messier 77; the streaks of red and blue in the image highlight pockets of star formation along the pinwheeling arms, with dark dust lanes stretching across the galaxy’s starry center; the galaxy belongs to a class of galaxies known as Seyfert galaxies, which have highly ionized gas surrounding an intensely active center. Image credit: NASA / ESA / A. van der Hoeven.
Many of supermassive black holes are hidden within a doughnut-shape ring of dust and gas known as a torus. Previous observations suggest these structures are formed from the native material found near the center of a galaxy.
However, new data from the Atacama Large Millimeter/submillimeter Array (ALMA) reveal that the central black hole of the galaxy Messier 77 is actually the source of its dusty torus, forged from material flung out of the black hole’s accretion disk.
This cosmic fountain of cold gas and dust could reshape our understanding of how black holes impact their host galaxy and potentially the intergalactic medium.
The research has been accepted for publication the Astrophysical Journal Letters (arXiv.org preprint).
“Think of a black hole as an engine. It’s fueled by material falling in on it from a flattened disk of dust and gas,” said lead author Dr. Jack Gallimore, of Bucknell University.
“But like any engine, a black hole can also emit exhaust. That exhaust is the likely source of the torus of material that effectively obscures the region around the galaxy’s supermassive black hole from optical telescopes.”
ALMA image of the central region of Messier 77; the torus of material harboring the supermassive black hole is highlighted in the pullout box; this region, which is approximately 40 light-years across, is the result of material flung out of the black hole’s accretion disk; the colors in this image represent the motion of the gas: blue is material moving toward us, red moving away; the areas in green are low velocity and consistent with rotation around a black hole; the white in the central region means the gas is moving both toward and away at very high speed; the outer ring area is unrelated to the black hole and is more tied to the structure of the central 1,000 light-years of the host galaxy. Image credit: ALMA / ESO / NAOJ / NRAO / B. Saxton / AUI / NSF / Gallimore et al.
Messier 77 is a barred spiral galaxy in the constellation of Cetus, approximately 45 million light-years away from our Solar System. Also known as NGC 1068, it is one of the most famous and well-studied galaxies.
It is also the closest and brightest example of a particular class of galaxies known as Seyfert galaxies.
At the center of Messier 77 is an active galactic nucleus, a supermassive black hole that is being fed by a thin, rotating disk of gas and dust known as an accretion disk.
As material in the disk spirals toward the central black hole, which is around 15 million times the mass of our Sun, it becomes superheated and blazes bright with UV radiation.
The outer reaches of the disk, however, are considerably cooler and glow more appreciably in IR light and the millimeter-wavelength light that ALMA can detect.
Using ALMA, Dr. Gallimore and co-authors discovered a sprinkling of cool clouds of carbon monoxide lifting off the outer portion of the accretion disk.
The energy from the hot inner disk partially ionizes these clouds, enabling them to adhere to powerful magnetic field lines that wrap around the disk.
Like water being flung out of a rapidly rotating garden sprinkler, the clouds rising above the accretion disk get accelerated centrifugally along the magnetic field lines to very high speeds – from 900,000 mph to 1.8 million mph (400-800 km per second). This is up to nearly three times faster than the rotational speed of the outer accretion disk, fast enough to send the clouds hurtling further out into the galaxy.
“These clouds are traveling so fast that they reach ‘escape velocity’ and are jettisoned in a cone-like spray from both sides of the disk,” Dr. Gallimore said.
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Jack F. Gallimore et al. 2016. High-Velocity Bipolar Molecular Emission from an AGN Torus. ApJL, accepted for publication; arXiv: 1608.02210
This article is based on a press-release from the National Radio Astronomy Observatory.
