Mysteries of Jets from Giant Black Holes
Two international teams of astronomers have used the power of the Atacama Large Millimeter/submillimeter Array (ALMA) to focus on jets from the huge black holes at the centres of galaxies and observe how they affect their surroundings. They have respectively obtained the best view yet of the molecular gas around a nearby, quiet black hole and caught an unexpected glimpse of the base of a powerful jet close to a distant black hole.
There are supermassive black holes â€” with masses up to several billion solar masses â€” at the hearts of almost all galaxies in the Universe, including our own galaxy, the Milky Way. In the remote past, these bizarre 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, most 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.
Two new studies, both published today in the journal Astronomy & Astrophysics, used ALMA to probe black hole jets at very different scales: a nearby and relatively quiet black hole in the galaxy NGC 1433 and a very distant and active object called PKS 1830-211.
â€œALMA has revealed a surprising spiral structure in the molecular gas close to the centre of NGC 1433,â€ says FranÃ§oise Combes (Observatoire de Paris, France), who is the lead author of the first paper. â€œThis 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, which is being dragged along by the jet from the central black hole, shows how such jets can stop star formation and regulate the growth of the central bulges of galaxies .
In PKS 1830-211, Ivan MartÃ-Vidal (Chalmers University of Technology, Onsala Space Observatory, Onsala, Sweden) and his team also observed a supermassive black hole with a jet, but a much brighter and more active one in the early Universe . It is unusual because its brilliant light passes a massive intervening galaxy on its way to Earth, and is split into two images by gravitational lensing .
The two new observations are just the start of ALMAâ€™s investigations into the workings of jets from supermassive black holes, near and far. Combesâ€™s team is already studying other nearby active galaxies with ALMA and the unique object PKS 1830-211 is expected to be the focus of much future research with ALMA and other telescopes.
This wide-field image shows the patch of sky around the galaxy NGC 1433. This view was created from photographs forming part of the Digitized Sky Survey 2. The prominent red star to the left of the galaxy is HD 23719, which is just bright enough to be seen with the naked eye on a dark night.
â€œThere is still a lot to be learned about how black holes can create these huge energetic jets of matter and radiation,â€ concludes Ivan MartÃ-Vidal. â€œBut the new results, obtained even before ALMA was completed, show that it is a uniquely powerful tool for probing these jets â€” and the discoveries are just beginning