A team of astronomers from Northwestern University in Illinois has just made public a strange discovery: a thousand mysterious magnetic filaments, luminous threads up to 150 light-years long and that, inexplicably, ‘hang’ in space, from the center of our galaxy.
In an unprecedented image obtained after several years of work, the filaments appear in pairs or in clusters, often arranged at the same distance, one next to the other, like the strings of a harp. To this day, astronomers do not know how they formed or why they are there.
The director of the study, Farhad Yusef-Zadeh, first observed those puzzling highly organized magnetic filaments early in the decade
in the 1980s, and even then he discovered that they contain extremely accelerated electrons, which cause the magnetic field to rotate at the speed of light. But its origin, since then, has remained unknown.
Now, the new image obtained by Farhad Yusef-Zadeh and his team has revealed a thousand filaments, ten times more than in previous research, allowing researchers to carry out, for the first time, statistical studies that could help to unravel the mystery. The study, which will be published in ‘The Astrophysical Journal Letters’, can already be consulted on the pre-publication server
“For a long time – explains Yusef-Zadeh – we have studied the filaments with a myopic vision. And now, at last, we have the big picture: a panoramic view filled with a whole host of them. Examining just a few made it difficult to draw any real conclusions about what they are and where they come from. This is a milestone in improving our understanding of these structures.”
Three years of analysis
To build the detailed new image, the team of astronomers spent three years analyzing data at the South African Radio Astronomy Observatory (SARAO) and carrying out new observations with the telescopio MeerKAT. In this way, they managed to assemble a mosaic of 20 independent observations of different sections of the sky around the center of the Milky Way, about 25,000 light-years from Earth.
Along with the filaments, the image captures radio emissions from numerous phenomena, including exploding stars, stellar nurseries, and new supernova remnants. The complete image will be published in the same magazine in a second article,
also available on arXiv and co-directed by Yusef-Zadeh himself together with Ian Heywood, an astrophysicist at the University of Oxford who is also a signatory of the first article.
“I’ve spent a lot of time looking at this image,” says Heywood, “and I never get tired of it. When I show it to people who may be new to radio astronomy, or unfamiliar with it, I always try to emphasize that radio imaging hasn’t always been this way, and that MeerKAT really is a leap forward in terms of its capabilities. It has been a real privilege to work for years with the colleagues at SARAO who built this fantastic telescope.”
While there are still many unknowns surrounding these luminous strands, Yusef-Zadeh has managed to identify new pieces of the puzzle. In their paper, he and his collaborators specifically explored the magnetic fields of the filaments, and it appears that they are most likely related to past activity of the Sagittarius A*, to the supermassive black hole of four million solar masses that resides in the center of our galaxy, and not with the explosion of nearby supernovae. Although the possibility that they have something to do with the huge radio station ‘bubbles’ that Yusef-Zadeh and his collaborators discovered in 2019 is not ruled out.
“This is the first time -explains the researcher- that we have been able to statistically study the filaments. By doing so, we can learn more about the properties of these unusual structures. If you were from another planet, for example, and you met a very tall person on the Earth, you could assume that all people are tall. But if you do statistics on a population of people, you can find the average height. That is exactly what we are doing. We can find the strength of the magnetic fields, their lengths, their orientations, and the radiation spectrum.”
What we don’t know yet
Among the remaining mysteries, Yusef-Zadeh is particularly puzzled by the structure of the filaments, many of which are spaced apart at perfectly equal distances, equivalent to about 150 million kilometers, the distance between the Earth and the Sun.
“We still don’t know why they come in groups or how they separate,” explains the astronomer, “and we don’t know how these regular spaces are produced. Every time we answer one question, many new ones come up.” The researchers also don’t know if the filaments change or move over time, or what causes the electrons to accelerate to such incredible speeds. “How do electrons manage to accelerate to almost the speed of light? Yusef-Zadeh wonders. There could be something at the end of the filaments that is accelerating these particles.”
Currently, the team of astronomers continues to identify and catalog each of the filaments. The angle, curve, magnetic field, spectrum, and intensity of each will be published in a future study. Understanding these properties may allow the scientific community to ferret out more clues about the strange and elusive nature of these structures.