Magnetic loops in the galactic center
Loops in space are not uncommon structures. They usually arise when electrically charged gases come into the sphere of influence of a strong magnetic field - as with our sun. But the newly discovered loops from the center of the Milky Way are a thousand billion times larger. Do the same rules apply in these scales?
Astronomy is a natural science in its own right. Since its objects are usually "astronomically" large and many processes are "galactically" slow, it rarely offers the opportunity to research open questions in the home laboratory. Instead, it usually progresses in a dynamic interplay of unexpected observations and attempts at theoretical explanations. In other words, astronomers are always trying to find coherent reasons why they see things in their telescopes that they didn't expect.
This is also the case with the gigantic gas loops discovered by a Japanese team of astronomers led by Yasuo Fukui from the University of Nagoya using the NANTEN telescope, which works in the transition range between microwaves and infrared radiation. The gas carbon monoxide can be seen particularly well in those frequencies. One of the most common molecules in the space between stars, it is a reliable indicator of where larger amounts of volatile matter populate the galaxy.
One of the known regions with high concentrations of interstellar gases is the region around the center of the Milky Way. And so it was hardly to be expected that a slightly more open look in this direction would provide new information. But there, where experience sensed gentle gas plumes in the plane of the Milky Way stars, two huge gas loops arch up. Located just a few thousand light-years from the galaxy's core, they span almost a thousand light-years. And to top it all off, they stick out straight out of the galactic disk.
This orientation of the loops is unusual, since the gravitational pull of the stars normally pulls matter into the galactic plane with strong pulls. Now, if gases can escape the pull that far, there must be a very energetic process behind it all. Quite similar to our sun, from which material loops also protrude against gravity into space. The reason for this is the magnetic fields in our central star. And it is precisely their influence that astronomers suspect in the galactic loops.
The considerations are based on the ideal case of a smooth magnetic field that runs parallel to the plane of the stars. Like the surface of a pond with absolutely no wind, practically every location would be equally good or bad - and the gas molecules would age in their respective places.
In reality, such an untroubled picture doesn't last, of course. There is bound to be some kind of disturbance – and the water surface or the magnetic field is already throwing waves. In a hilly landscape, however, gravity immediately plays to its strengths, and so gas molecules migrate further into the galactic plane along an initially only shallow gradient in the magnetic field lines.
This migration in turn amplifies the disturbance. The magnetic valleys are deepening, the peaks higher - and what started as a smooth field has unexpectedly become a magnetic mountainous landscape, known in scientific circles as the Parker instability after its theoretical discoverer. Luckily for us, by the way, because it's only thanks to these ups and downs that the gas clouds in the galaxy cluster tightly enough that they eventually clump together into new stars. At least that's what theorists think.
Fukui and his team believe, however, that the loops in their observations are the very waves in the magnetic field caused by the Parker instability. An explanation that seems tempting and that most colleagues would be happy to get used to.
On closer inspection, however, there are some open problems: The loops and arcs of ions around our sun are indeed on the trail of magnetic fields, but on a galactic scale twelve orders of magnitude larger, such structures have never been detected before. And despite the impressive pictures from Japan, it is by no means certain that there is a correspondingly shaped magnetic field in this region of space. Even if: why haven't the molecules slipped into the troughs long ago, but instead are surfing at the top of the magnetic wave?
Neither Japanese scientists nor astronomers from other nations have been able to answer these questions. But there are already plans as to what measurements would be needed to unravel the mystery of the loops. New experiments that once again take on astronomical proportions - to measure a magnetic field that is around 25,000 light-years from Earth. Astronomy is a field on the edge of limitlessness.
