A Cosmic Mystery: Diffuse Interstellar Bands
Diffuse Interstellar Bands. (DIBS) What are they? No one knows. Where are they? In deep space. Were they the inspiration for Pink Floyd? I seriously doubt it. What am I talking about? Diffuse Interstellar Bands. Sheesh, pay attention.
OK, let’s start at the beginning, the early 20th century to be exact. Scientists by then were studying the light of stars. A spectrum is the light emitted by a star or bright object passed through a prism. Molecules in and near a star will block some of the spectrum, making dark stripes as seen above, these are called absorption or spectral lines. Thus scientists can tell what a star is made of. It even works with reflected light, this is how they tell what planets and asteroids are made of. This is all of course terribly simplified, because I have a very dim grasp of it all myself. All well and good until 1922, scientists happily studied what stars were made of. However, in 1922 astronomer Mary Lea Heger discovered some absorption lines that were much more diffuse than the typical lines in a star’s spectrum. She also found that the lines were associated with the galactic interstellar medium, not stars.
This was a head scratcher. People commonly think that space is a perfect vacuum. It isn’t, it varies widely, but one atom per cubic centimetre is the “average” density of interstellar space. It was thought this matter was so diffuse that while it might dim an entire spectrum slightly, it wouldn’t make lines. Well, sciencists were wrong, some molecules in interstellar space were apparently common enough to cause absorption lines. Mary discovered a few such lines, and by 1975 about 25 had been discovered. By 1994 when the first conference on DIBs was held, about 50 were known. Today about 300 have been discovered, illustrated above. The reason it’s a head scratcher is because no one knows exactly what molecules are creating these lines. Despite scientist’s best efforts, they have not been able to replicate the lines experimentally, or even come up with a theoretical calculation that explains the lines.
This is a major scientific mystery and has been for decades. For reasons I don’t understand, let alone can explain, it does seem pretty certain that the lines are caused by molecules, not single atoms. And it also is clear that numerous different molecules are involved, a single type of molecule couldn’t produce over 300 DIBs. The best guess is that they are being caused by long chain molecules. Polycyclic aromatic hydrocarbons, long carbon-chain molecules, and fullerenes are all strong suspects. And that’s that. Somehow our galaxy contains dust or gas of unknown origin or composition, what it is and how it is created is still a complete mystery.
Is this important? In a practical sense, no, figuring this out isn’t going to change our lives. Not figuring it out will have the same effect. It’s important though to understand that there are plenty of complete mysteries in our scientific understanding of the Universe. A lot of people, especially certain religious types, don’t seem to understand that. Science can’t currently explain everything, and there doesn’t appear to be any chance that it will ever explain everything. This isn’t a failure of science, th0ough it is oft presented as such by science-deniers, it is one of science’s greatest strengths. So whenever I stumble across an unsolved scientific mystery, I am impressed by the mystery itself, and I’m impressed by the fact that science even uncovered the mystery. Is there any chance that the solution to DIBs will force a re-examination of other aspects of science? Possibly, but I don’t know how possible. When it comes right down to it, our understanding of the cosmos is still in its infancy.
One last little observation is that I am always curious that science deniers miss things like this. If one was going to construct logical sounding attacks on science, mysteries like this would be a great place to start. Instead, the science deniers seem to make very little effort to find new arguments, and simply recycle old arguments. Some of the “objections” raised about evolution date from the nineteenth century for God’s sake. And while some of them were valid concerns then, a hundred years later they have long been laid to rest. I suppose it’s further evidence that science deniers are in actual denial about science, since few of them seem to take the time to even understand it well enough to construct modern arguments against it. Or it could mean that when people study science hard enough they realize its true, they are converted to science and reason?
Pause for laughter. Beats me. The older I get the more I find people and their motivations both painfully predictable … and painfully puzzling. It’s a conundrum it is.
(The above image is claimed as Fair Use under US copyright law. I got it off of Wikipedia so it’s safe to say that non-commercial use of the image is OK. And I left the copyright information on the image itself. Next a furniture history post, or a post about the recent discovery that the Universe is flat.)