An array of telescopes that have spent years staring into deep space has finally provided some of the most gloriously detailed images we’ve ever seen of other galaxies.
Not only are these images spectacularly beautiful, but they reveal in unprecedented detail the inner workings of these giant cosmic objects, giving us new insight into how galaxies work in general. The results obtained so far have been published in a special issue of Astronomy & Astrophysics.
The observations were made using the Low Frequency Array (LOFAR), the largest array of low frequency radio telescopes currently in service on Earth. It can combine observations from around 70,000 antennas spread across Europe using a technique called radio interferometry to take some of the most sensitive radio observations possible of the night sky.
This has given us incredible new information about the Universe, but the new observations go even further, with a resolution 20 times higher than usual. Indeed, standard LOFAR operations are conducted only using the antennas in the Netherlands, where the collaboration is based.
Above: Radio imagery reveals a huge wind blowing from the merging galaxies. (N. Ramírez-Olivencia et al.; NASA, ESA, Hubble Heritage Team (STScI / AURA) -ESA / Hubble Collaboration and A. Evans (UVA Charlottesville / NRAO / Stony Brook University); R. Cumming)
Since these antennas are spread over an area of 120 kilometers (75 miles), this means that the “aperture” of the telescope is, in fact, about 120 kilometers in size. For the new observations, an international collaboration used the entire network from across Europe – in fact, a 2,000 kilometer (1,243 mile) radio telescope.
“Our goal is for this to enable the scientific community to use the entire European LOFAR telescope network for its own science, without having to spend years becoming an expert,” said astronomer Leah Morabito of the Durham University in the UK.
Nine articles in the special issue of Astronomy & Astrophysics are devoted to one of the most astonishing phenomena associated with galactic behavior – relativistic jets of particles projected into intergalactic space by supermassive black holes active in the centers of galaxies.
These are invisible in optical wavelengths, but in radio wavelengths they glow – meaning that radio images can give us insight into how jets form and propagate.
It is common knowledge that once something crosses the critical threshold called the event horizon, nothing can escape the gravitational pull of a black hole. But the region around an active black hole is extremely dynamic. The material is spun in a disc that surrounds the black hole, coiling in it like water in a sewer.
From the inner edge of this accretion disk, a small amount of swirling material is somehow channeled around the outside of the event horizon towards the poles, where it is launched at speeds that represent a large percentage of the speed of light. Scientists believe that the magnetic field lines around the black hole act like a synchrotron, accelerating these particles to produce relativistic speeds.
However, there is a lot that we don’t understand about this process, and the new LOFAR data is helping to fill in the missing pieces.
“These high-resolution images allow us to zoom in to see what actually happens when supermassive black holes launch radio jets, which was not previously possible at frequencies close to the FM radio band,” the astronomer explained. Neal Jackson of the University of Manchester in Great Britain.
The galaxies analyzed include 3C 293, a galaxy with particular huge radio lobes that suggest an interrupted jet stream. The researchers concluded that the galaxy underwent multiple spells of activity due to jet disruptions and intermittent refueling, suggesting that its supermassive black hole experienced at least a period of dormancy.
Another article analyzed light from a galaxy that had traveled more than 11 billion light years – usually quite difficult to observe in detail at low frequencies.
This observation made it possible to determine why such distant radiogalaxies present specific signatures; Ultimately, no conclusive answer could be found, but the observation paves the way for more in the future.
And a probe in the spectacular Hercules A radiogalaxy examined the ring structures of its radio lobes. These, the researchers concluded, were the result of intermittent strengthening and weakening of the jets, producing the structures observed.
These clues can help us understand the processes that produce and shape radio jets, but the work collected has much deeper implications. The papers also represent a milestone in radio astronomy, demonstrating the capabilities of a network like LOFAR to understand the mysteries of the Universe.
The series of articles was published in Astronomy & Astrophysics.