Blog #23 - History of ISM

History of ISM

The interstellar medium, or ISM, is one of the more complicated phenomena in the universe. Interestingly, the first mention of ISM was back in 1626 quoted by English explorer Francis Bacon as he stated "The Interstellar Skie.. hath .. so much Affinity with the Starre, that there is a Rotation of that, as well as of the Starre." Later, English philosopher Robert Boyle (of Boyle's law) claimed "The inter-stellar part of heaven, which several of the modern Epicureans would have to be empty." 

These early reports showed that even with primitive technology, early philosophers and astronomers were able to deduce that the space between the stars and planets in the night sky was not mere emptiness. However, for centuries, scientists believed there was an luminiferous ether that moved light throughout the universe but did not have any quantitative data as to how electromagnetism or quantum physics operated. 

In 1904, after the advancement of absorption spectroscopy, Johannes Hartmann, a German physicist, made the first observation of cold diffuse matter. This matter, later to be described as the Interstellar Medium was found as Hartmann observed the light curves of Delta Orionis. He saw that the "k" line of calcium appeared far too faint given the observing conditions and surrounding spectra. He concluded that much of the light must have been absorbed before entering Earth's atmosphere. 

Within the next decade, research into the ISM exploded and various researchers helped categorize ISM as clouds with doppler shifts. Then the discovery of cosmic rays confirmed that with the incredibly number of stars in the Universe there could statistically not exist an absolute vacuum and some medium would need to exist to absorb and transfer the massive amounts of cosmic rays, ionized hydrogen, and other basic elements that exist throughout the universe.

Today NASA has developed much of the theory behind the ISM but still lacks the knowledge to fully develop the development, growth, and existence of ISM. We now know that ISM interacts with polycyclic aromatic hydrocarbons (PAHs) to create the earliest forms of organic matter that may help shape how the big bang developed into life as we know if today. If these connections are confirmed, ISM will truly be responsible for all life as we know it.