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Contents Overview and History Interstellar Medium Spectral Characteristics DIB Theories & Importance to Astrophysics Conclusion

As has already been mentioned, recent work suggests DIBs are caused by polycyclic aromatic hydrocarbons, or, most likely, their cations.¹¹ But recently a radically different mechanism - doubly excited atoms embedded in the condensed phase called Rydberg matter (RM) - was proposed for the formation of DIBs.¹²

Holmid's RM model, which accurately calculates 120 intense bands in a consistent manner, is of interest for its direct bearing on the DIB conundrum, but it's also a good illustration of the scientific process in general and specifically of how that process can be misinterpreted through modern media. For instance, even though Holmid's paper is the work of a single author and has but a single independent journal citation to date, Wikipedia's entry for "Diffuse Interstellar Bands" begins by overstating that "no agreement of the bands could be found with laboratory measurements or with theoretical calculations. This situation has recently changed." Wikipedia then follows this misleading statement with a more reasonable, qualified assessment of Holmid's work.¹³

The Milky Way Galaxy

A large collaboration of astronomers has been conducting a survey of unprecedented extent, with the aim of definitive spectral atlases of the DIBs and to search for correlations that will yield some observational constraints on the nature of their carriers. The hope is that these studies will pull out the spectra of individual molecules from the complex set of DIBs, which could greatly aid laboratory studies.

Some recent observations also show a robust dependence of DIB strength on the local environment in terms of cloud density and exposure to the interstellar radiation field.¹⁴ This leads to an additional goal of exploring the link between the physical and chemical conditions in the ISM as an angle of approach to uncovering the carrier or carriers.

To date, this intriguing puzzle remains largely characterized by the explanations that have been ruled out. There is no compelling evidence that DIBs are a solid-state phenomenon or are produced by some material trapped in interstellar grains. They aren't formed by reactions involving H2, and their widespread presence indicates they are not formed in stars, but in the diffuse interstellar clouds themselves.¹⁵

When and if the DIB carriers, the mechanisms for their formation, and the reasons for their correlation with other observables (such as how they manage to survive the extremes of interstellar space in such profusion) are finally and fully understood, that knowledge will be the result of countless observations, laboratory measurements, models and calculations.

List of Visuals

1. The Milky Way Galaxy
   http://www.nasa.gov/mission_pages/spitzer/multimedia/20080603a.html
   NASA/JPL-Caltech
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1. Sarre, Peter. Organic compounds as carriers of the diffuse interstellar bands. Organic Matter in Space: Proceedings IAU Symposium No. 251, 2008.

2. Ryden, Barbara. Interstellar Medium, Astronomy 162, 2003. http://www.astronomy.ohio-state.edu/~ryden/ast162_3/notes11.html Accessed November, 2009

3. Schneider, Steven & Thomas Arny. Pathways to Astronomy, New York: McGraw-Hill, 2006. http://abyss.uoregon.edu/~js/ast122/lectures/lec22.html Accessed November, 2009

4. Ehrenfreund, P. The Diffuse Interstellar Bands as evidence for polyatomic molecules in the diffuse interstellar medium. AAS Meeting #194 - Chicago, Illinois, 1999. http://aas.org/archives/BAAS/v31n3/aas194/116.htm Accessed November, 2009

5. Wszoleka, B. & M. Wszolekc. Diffuse Interstellar Bands. Astronomical and Astrophysical Transactions 22: 6, 2003, pp. 821-825.

6. Wszoleka, B. & M. Wszo?ekc. Diffuse Interstellar Bands. Astronomical and Astrophysical Transactions 22: 6, 2003, pp. 821-825.

7. Snow, Theodore. Comments on two-photon absorption by H2 molecules as a source of diffuse interstellar bands. Chemical Physics Letters 245:6, 1995, pp. 639-642.

8. Cataldo, Franco, Yeghis Keheyan & Dieter Heymann. A new model for the interpretation of the unidentied infrared bands (UIBS) of the diffuse interstellar medium and of the protoplanetary nebulae, International Journal of Astrobiology 1:2, 2002, pp. 79-86.

9. Possible Connections Between Interstellar Chemistry and the Origin of Life on the Earth. Ames Research Center. http://www.astrochem.org/LifeImplications.html Accessed November, 2009

10. Farnsworth, Martha, Maclovio Fernandez & Luca Sabbatini. Buckyballs: Their history and discovery, Connexions http://cnx.org/content/m14355/latest/ Accessed November, 2009

11. Diffuse Interstellar Bands (DIBs), The Internet Encyclopedia of Science. http://www.daviddarling.info/encyclopedia/D/DIB.html Accessed November, 2009

12. Holmid, Leif. The diffuse interstellar band carriers in interstellar space: all intense bands calculated from He doubly excited states embedded in Rydberg Matter, Monthly Notices of the Royal Astronomical Society 384, 2008, pp. 764-774

    Munari, U., L. Tomasella, M. Fiorucci, O. Bienaymé, J. Binney, J. Bland-Hawthorn, C. Boeche, R. Campbel6, K. C. Freeman, B. Gibson, G. Gilmore, E. K. Grebel, A. Helmi, J. F. Navarro, Q. A. Parker, G. M. Seabroke, A. Siebert, A. Siviero, M. Steinmetz, F. G. Watson14, M. Williams, R. F. G. Wyse & T. Zwitter. Diffuse interstellar bands in RAVE survey sp. Astronomy & Astrophysics 488, 2008, pp. 969-973

13. Wikipedia can be a good place to begin researching a topic and is often an excellent source of links and relevant resources. However, since articles can be edited by anyone without any authority, errors or biases do arise. Although other editors look out for such problems, in general, Wikipedia is not a credible source in research or scholarly work.

14. Cox, N. L. J. & Cordiner, M. A. Diffuse interstellar bands in the Local Group: From the Milky Way, the Magellanic Clouds to the Andromeda galaxy. Organic Matter in Space: Proceedings IAU Symposium No. 251, 2008.

15. Wszoleka, B. & M. Wszo?ekc. Diffuse Interstellar Bands. Astronomical and Astrophysical Transactions, 22: 6, 2003, pp. 821-825.