Cold fronts in Earth's atmosphere can be annoying, bringing frosty weather and postponing spring. However, at least here, they are seasonal. In the Perseus cluster, astronomers have seen a cold front that is 2 million light-years long and has managed to persist for 5 billion years, more than a third of the age of the Universe.
The cold front was observed by NASA’s Chandra X-ray Observatory, and the researchers estimate that the gas moves at 500,000 kilometers (310,000 miles) per hour. The gas is not “conventionally cold” as it has a temperature of around 16 million degrees Celsius (30 million degrees Fahrenheit), but it's significantly colder than the surrounding gas, which can reach a temperature of around 50 million degrees Celsius (90 million degrees Fahrenheit).
Another team saw the first hints of the cold front in 2012, analyzing X-ray data from a variety of space telescopes. The new work, published in Nature Astronomy, adds a heap of detail to the first observations. The material inside and outside the cold front is not at all dense, so it is expected to change slowly. Still, its persistence is extraordinary.
By combining sophisticated simulations with the Chandra observations, the team worked out some interesting properties of this space weather. The reason why the cold front is not being eroded by the surrounding material or blurred out on the edges is a strong magnetic field. The field protects the cold front, and for this reason, it appears sharper than previously thought.
While it's not exactly clear what gives rise to these intriguing peculiarities, its origin is connected to the rest of the spiraling gas seen in the cluster. The Perseus cluster is huge, with the central region – weighing hundreds of times the mass of the Milky Way – pulling in close-by galaxies. These objects make close passes of the core, creating ripples in the gas. One of these passes was responsible for the creation of a gas tsunami twice the length of the Milky Way.
This gas sloshing is actually a note. The Perseus cluster is playing a B flat, although its period is so long, it corresponds to 57 octaves below middle C. The cluster is located 240 million light-years from Earth.