In a paper published in the May 10 online issue of the esteemed journal Science Express, astronomers reveal that the Sun has no bow shock. The discovery was made using the Interstellar Boundary Explorer (IBEX), a probe developed by NASA specifically to investigate such a potential structure.
Our understanding of basic physics currently suggests that the Sun is surrounded by the heliosphere, which is a very large bubble of gas containing magnetic fields generated by our parent star. This structure moves through space with the solar system.
According to solar physicists, the bubble creates three boundary layers, of which the outermost is referred to as the bow shock. Most stars astronomers observed thus far have such formations, as do planets. Earth has a bow shock as it moves around the Sun.
Scientists say that the bow shock also develops as supersonic aircraft pass the sound barrier. In the industry, this is called the sonic boom. IBEX and the twin Voyager spacecraft found no evidence that our star produces such a structure.
Computer models of the heliosphere suggest that the magnetized bubble simply isn't spinning fast enough to allow for a bow shock to develop. The solar system is currently traveling through a part of the galaxy that is highly magnetized and tenuous, so this may explain the weird occurrence.
“IBEX gives a global view. It shows the whole of this region. At the same time the Voyager spacecraft are actually there, in situ, measuring its environment at two locations,” expert Eric Christian explains.
“The combination of IBEX and Voyager gives you great science and now the new IBEX results strongly indicate that there is no bow shock,” he adds. Christian holds an appointment as an IBEX mission scientist at the NASA
Goddard Space Flight Center (GSFC), in Greenbelt, Maryland.
The expert was also a program scientist for the Voyager mission. He explains that physicists used to think that the heliosphere was made up of three different layers – the termination shock, the heliopause and the bow shock.
“We recently analyzed two years’ worth of IBEX data, and they showed that the speed of the heliosphere – with respect to the local cloud of material – is only 52,000 miles per hour, instead of the previously believed 59,000,” David McComas explains.
“That might not seem like a huge difference, but it translates to a quarter less pressure exerted on the boundaries of the heliosphere. This means there's a very different interaction, a much weaker interaction, than previously thought,” he adds.
The expert was the first author of the Science Express paper. He is the principal investigator of the IBEX mission, and is based at the Southwest Research Institute in San Antonio, Texas.