Galactic findings

Chile’s ALMA gets up close and personal with black hole jets

Atacama based observatory gets best ever view of molecular clouds interacting with a black hole, cluing us in to the inner workings of galaxies.

Monday, December 09, 2013  
No artist’s impression — this stunning image is a composite view from ALMA and Hubble showing the NG No artist’s impression — this stunning image is a composite view from ALMA and Hubble showing the NGC 1433 galaxy in the Dorado constellation. Photo via ESO

When it comes to human achievement, the capability to peer into the depths of a black hole millions of lights years from Earth is up there. Taking that a step further, scientists at the Atacama Large Millimeter/submillimeter Array (ALMA) in Northern Chile were able to study a supermassive black hole with such detail that they managed to observe tiny — by astronomical standards — jet outflows with the highest clarity ever recorded.

The black hole in question sits at the center of galaxy NG 1433 of the Dorado constellation. Most galaxies have supermassive black holes at their center that have masses several billion times that of our sun. Scientists have long wondered why the “bulges” that surround these black holes have low star density.

These jets of matter offer clues, as they are theorized to disrupt star formation, helping to explain the mysterious relationship between the mass of a black hole at the center of a galaxy and the mass of the surrounding bulge.

The research team put the detail of the findings, in part, down to ALMA’s unrivalled sensitivity and advanced technology.

"ALMA has revealed a surprising spiral structure in the molecular gas close to the center of NGC 1433," Françoise Combes of the Observatoire de Paris and head of the new study said. "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."

As well as observing NGC 1433 and its “relatively quiet” black hole, another group of ALMA astronomers also looked at very distant and active object known as PKS 1830-211. The object displays light from the early universe and revealed a much more active black hole.
Astronomers were particularly excited by the PKS 1830-211 observation because they caught the black hole at the exact moment in time it swallowed an unusual amount of matter — perhaps a star — creating jets that reach up to the highest energies recorded in the universe.

"The ALMA observation of this case of black hole indigestion has been completely serendipitous,” Sebastien Muller of the Onsala Space Observatory and co-leader of the second study, said. “We were observing PKS 1830-211 for another purpose, and then we spotted subtle changes of colour and intensity among the images of the gravitational lens. A very careful look at this unexpected behaviour 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."

The study’s team leader Ivan Martí-Vidal said our understanding of black holes is in its infancy, though instruments such as ALMA — which at the time was not even operating at full capacity — are taking astronomical research to the next level.

"There is still a lot to be learned about how black holes can create these huge energetic jets of matter and radiation," Martí-Vidal said. “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!"

Due to its almost non-existent humidity and clear skies, Northern Chile is the world’s premier location for astronomy. Chile is home to almost half the world’s telescope infrastructure, and this is set to increase to over two thirds in the next decade.