Across the vast swathe of interstellar space exist long streaks of organic material of uncertain origin and even less certain composition. Astronomers have been studying these “diffuse interstellar bands”, or DIBs, for decades and recent discoveries have provided new clues to what they are made of. Now, astronomers have found them all around the Solar System. And that’s quite surprising.
The Solar System is located in the so-called Local Bubble, a cavity in the interstellar medium (ISM). It’s a region 300 light-years across with a density of about one-tenth of the regular ISM. It contains a lot of hot gas, heated to millions of degrees, creating conditions too harsh for your standard interstellar molecules. As reported in Nature Astronomy, this doesn’t seem to be the case for the DIBs.
Researchers have taken some painstakingly accurate measurements of the Local Bubble, hunting for two specific DIBs described only by their wavelengths. In their 3D map of the region, they discovered that λ5,780 DIB is present suggesting that it must be more stable and made of larger molecules that thought in order to withstand the high temperatures.
“The DIBs are most easily seen in front of distant stars, but we wanted to know whether this stuff can also be found closer to home. To do this, we had to look at nearby, bright stars and get a very good signal on them,” co-author Dr Jacco van Loon, Director of Keele Observatory, said in a statement.
“We aimed to reach a precision of at least one in 1,000, while most astronomers are happy – if not ecstatic – to get a precision of one in 100. This required careful observation and processing of the data. But we succeeded, and we saw the characteristic pattern of DIBs. In short, we have found this mystery material inside the Local Bubble for the first time!”
The presence of these DIBs so close to home has important consequences. Researchers have suspected that the material in these bands and the organics found in comets have the same origin. The clouds that originally formed the Solar System could have potentially crossed DIBs billions of years ago.
“What our discovery means is that whatever this material is, it can survive in pretty harsh conditions," said van Loon. "That, or there must be small, dense structures threaded throughout the Local Bubble. When the Sun and the Earth move through this material, it is not unthinkable that some of it might rain upon Earth, so there is a possibility that it could have brought some vital ingredients for life.”
The Local Bubble is the result of supernovae that have exploded within the last 10 to 20 million years. The Sun and its planets have been traveling through it for, at most, 10 million years.
DIBs were first observed by Mary Lea Heger in 1919, when she was still a student. More recently, astronomers have found electrically charged buckminsterfullerene in some of these DIBs.