October 16, 2013
ALMA Observatory Reveals Black Hole’s Eating Habits
[ Watch the Video: Zooming In On Active Galaxy NGC 1433 ]
Brett Smith for redOrbit.com - Your Universe Online
New observations from the Atacama Large Millimeter/submillimeter Array (ALMA) in the high-altitude Atacama Desert of Chile have revealed new details about the powerful molecular-gas jets that stream out of supermassive black holes, according to two new studies published on Wednesday in the journal Astronomy & Astrophysics.
The two studies describe the unique behaviors and properties seen by a team of international astronomers using ALMA at a nearby and relatively quiet black hole in the galaxy NGC 1433 and a very distant and active entity called PKS 1830-211.
During the early years of the universe, supermassive black holes were highly active, sucking in vast quantities of matter from their neighbors, shining with astounding intensity and firing out some of the ensnared matter via extremely powerful jets. While most supermassive black holes are relatively less active these days, the interaction between the jets and their surroundings is still affecting galaxy evolution.
"ALMA has revealed a surprising spiral structure in the molecular gas close to the centre of NGC 1433," said study author Françoise Combes from the Observatoire de Paris in France. "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."
In PKS 1830-211, the researchers also examined a supermassive black hole with a much brighter and more active jet. Because of its distance from Earth, 11 billion light years, the astronomers were essentially looking back in time at the object’s appearance when the universe was just 20 percent of its current age. The research team noted that a massive intervening galaxy between PKS 1830-211 and Earth splits our view of the object in two images through a phenomenon known as gravitational lensing.
Occasionally, a supermassive black hole will gulp down a large amount of mass, increasing the power of the jet and boosting the emitted radiation up to very high energies. According to one of the new reports, ALMA has caught one of these events as it happened in PKS 1830-211.
"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," said study author Sebastien Muller, an astronomer at the Onsala Space Observatory in Sweden. “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.”
To cross-reference their findings, the team looked to see if the event was detected by other telescopes and was able to find gamma ray evidence with NASA's Fermi Gamma-ray Space Telescope.
"This is the first time that such a clear connection between gamma rays and submillimetre radio waves has been established as coming from the real base of a black hole's jet," Muller added.
"There is still a lot to be learned about how black holes can create these huge energetic jets of matter and radiation," said study author Ivan Martí-Vidal, another astronomer at Onsala. “But the new results, obtained even before ALMA was completed, show that it is a uniquely powerful tool for probing these jets — and the discoveries are just beginning!"
The two studies are: "Probing the jet base of the blazar PKS1830−211from the chromatic variability of its lensed images" and "ALMA observations of feeding and feedback in nearby Seyfert galaxies: an AGN-driven outflow in NGC 1433."