Study sheds light on origins of mysterious space ribbon
Scientists in Poland and the US have put forward a novel explanation for the mysterious ribbon-like structure running around our Solar System. Writing in the Astrophysical Journal Letters, they explain that the ribbon could mark the boundary between the cooler Local Cloud of interstellar gas and another cloud of extremely hot gas known as the Local Bubble. Furthermore, if the scientists are correct, the Sun will enter the Local Bubble in around 100 years. This comes as a surprise, as researchers had previously thought that the boundary between the Local Cloud and the Local Bubble was further away. 'We observe the ribbon because the Sun is approaching a boundary between our Local Cloud of interstellar gas and another cloud of very hot and turbulent gas,' explained Professor Stan Grzedzielski of the Space Research Centre at the Polish Academy of Sciences, who led the research. According to Professor Grzedzielski, this is nothing unusual, as the Sun regularly moves through different clouds of interstellar gas. As the Sun moves into the hotter cloud, the heliosphere will most likely shrink a little, causing levels of cosmic radiation to rise slightly. The heliosphere is a kind of 'bubble' in which the solar wind offers protection against damaging cosmic rays. 'Perhaps future generations will have to learn how to better harden their space hardware against stronger radiation,' Professor Grzedzielski commented. The peculiar space ribbon under investigation in this study was discovered by NASA's IBEX (Interstellar Boundary Explorer) spacecraft last year. IBEX was launched in 2008 with the mission of exploring the boundary between the heliosphere and interstellar space. Its first task was to create a full-sky map of emissions of energetic neutral atoms (ENAs). This revealed the mysterious ribbon of ENAs surrounding the Solar System. Since then, many researchers have put forward theories on the origin of ENAs. These theories tend to focus on interactions between the heliosphere and interstellar space. However, the latest study proposes that the ENAs are created at the boundary between the cool Local Cloud and the hotter Local Bubble. The Local Bubble is an extremely hot and turbulent region of space that is suspected to be the remnant of a series of supernova explosions that took place millions of years ago. According to the researchers, the ENAs are created when protons in the hot Local Bubble snatch electrons from neutral atoms at the edge of the cooler Local Cloud. The ENAs then whiz off in all directions, some of them reaching the IBEX detectors. 'If our hypothesis is correct, then we are catching atoms that originate from an interstellar cloud that is different from ours,' exclaimed Dr Maciej Bzowski, head of the Polish IBEX team and an author on the paper. Meanwhile Professor Grzedzielski explains that the ribbon is a kind of optical illusion, as in fact ENAs are being created across the entire boundary between the Local Cloud and the Local Bubble. 'It's a purely geometrical effect, which we observe because the Sun is presently just in the right place, within a thousand of astronomical units from the cloud boundary,' he noted. 'If the cloud-cloud boundary is flat, or better slightly extruded towards the Sun, then it appears the thinnest towards the centre of the ribbon and thicker at the sides, right where we see the edge of the ribbon. If we were farther away from the boundary, we would see no ribbon, because all the ENAs would be re-ionised and dispersed in the intervening gas of the Local Cloud.'
Countries
Poland, United States