Scientists using the Atacama Large Millimeter/submillimeter Array in the Atacama Desert, Chile, have observed jets from giant black holes in the nearby galaxy NGC 1433 and a distant blazar called PKS 1830-211.
This composite image shows the central parts of the nearby active galaxy NGC 1433. Image credit: ALMA / ESO / NAOJ / NRAO / NASA / ESA / F. Combes.
Supermassive black holes are a million to a billion times more massive than our Sun and are found in the centers of almost all galaxies in the Universe, including our Milky Way Galaxy.
In the remote past, these objects were very active, swallowing enormous quantities of matter from their surroundings, shining with dazzling brilliance, and expelling tiny fractions of this matter through extremely powerful jets.
In the current Universe, supermassive black holes are much less active than they were in their youth, but the interplay between jets and their surroundings is still shaping galaxy evolution.
A group of astronomers led by Dr Françoise Combes from Observatoire de Paris, France, used the Atacama Large Millimeter/submillimeter Array (ALMA) to study such object at the heart of a galaxy called NGC 1433.
Dr Combes, who is a lead author of a paper on NGC 1433 in the journal Astronomy & Astrophysics, said: “ALMA has revealed a surprising spiral structure in the molecular gas close to the centre of NGC 1433.”
“This explains how the material is flowing in to fuel the black hole. With the sharp new observations from ALMA, we have discovered a jet of material flowing away from the black hole, extending for only 150 light-years. This is the smallest such molecular outflow ever observed in an external galaxy.”
The discovery of this outflow shows how such jets can stop star formation and regulate the growth of the central bulges of galaxies.
Another team of scientists, led by Dr Ivan Martí-Vidal from Chalmers University of Technology in Sweden, observed a much brighter and more active jet from an enormous black hole at the center of the very distant blazar PKS 1830-211. The blazar’s brilliant light passes a massive intervening galaxy on its way to Earth, and is split into two images by gravitational lensing.
From time to time, supermassive black holes suddenly swallow a huge amount of mass, which increases the power of the jet and boosts the radiation up to the very highest energies. And now Dr Martí-Vidal’s team has caught one of these events as it happens in PKS 1830-211.
This image shows the blazar PKG 1830-211. Image credit: ALMA / ESO / NAOJ / NRAO / NASA / ESA /I. Martí-Vidal.
“The ALMA observation of this case of black hole indigestion has been completely serendipitous. We were observing PKS 1830-211 for another purpose, and then we spotted subtle changes of color and intensity among the images of the gravitational lens. A very careful look at this unexpected behavior led us to the conclusion that we were observing, just by a very lucky chance, right at the time when fresh new matter entered into the jet base of the black hole,” explained Dr Sebastien Muller from Chalmers University of Technology, who is a co-author of the study on PKS 1830-211 appearing in the journal Astronomy & Astrophysics.
Dr Martí-Vidal’s team also looked to see whether this violent event had been picked up with other telescopes and were surprised to find a very clear signal in gamma rays, thanks to observations with NASA’s Fermi Gamma-ray Space Telescope.
The process that caused the increase of radiation at ALMA’s long wavelengths was also responsible of boosting the light in the jet dramatically, up to the highest energies in the Universe.
“This is the first time that such a clear connection between gamma rays and submillimeter radio waves has been established as coming from the real base of a black hole’s jet,” Dr Muller said.
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Bibliographic information: F. Combes et al. ALMA observations of feeding and feedback in nearby Seyfert galaxies: an AGN-driven outflow in NGC 1433. Astronomy & Astrophysics, accepted for publication September 17, 2013; doi: 10.1051/0004-6361/201322288
I. Marti-Vidal et al. Probing the jet base of the blazar PKS1830-211 from the chromatic variability of its lensed images. Astronomy & Astrophysics, accepted for publication September 03, 2013; doi: 10.1051/0004-6361/201322131
