Laser Physicist Gets No Respect From Astronomers

Peter Sorokin is a world-class laser physicist. But when it comes to astronomy, he admits he's a rank amateur. That has given him a unique perspective on a 75-year-old astronomical mystery - along with a bruising intellectual experience.

Something is absorbing light from many bright young stars in such a way that certain colors in their spectra are less intense than expected. Astronomers know that interstellar material is absorbing this light. They don't know what it is. They called the missing-light spectra "diffuse interstellar bands" (DIBs) and have puzzled over them for decades.

Dr. Sorokin thinks he's cracked the DIBs mystery by taking a new look at the most abundant material in the universe - hydrogen. This new perspective involves physical principles familiar in laser research which astronomers haven't considered. However, when Sorokin and his colleague James Glownia offered their solution, astronomers rejected their presentation because it contained naive astronomical errors.

This was a humbling experience for Sorokin, a co-discoverer of the second and third types of lasers ever made and a widely acclaimed prizewinning scientist. He says it has made him cautious about claiming a definitive solution to the DIBs mystery. But he is sticking to his claim that he and Dr. Glownia are on the right track.

As Sorokin explained during the recent New Horizons in Science seminar held in Baltimore by the Council for the Advancement of Science Writing, astronomers have tried vainly to match the DIBs absorption to a variety of substances, including alien bacteria. They didn't consider hydrogen molecules because they don't absorb visible light. Photons of visible light don't have the right energy or frequency to kick a hydrogen molecule into a higher energy state and thus to be absorbed. Laser physicists know that isn't the whole story.

Sorokin, an IBM Fellow at the company's Almaden Research Center in San Jose, Calif., and Glownia, a senior scientist at IBM's T.J. Watson Research Center in Yorktown Heights, N.Y., knew that nature can get around this absorption problem by pairing visible light photons with ultraviolet (UV) photons of the right frequency. The two together excite the hydrogen molecule and are absorbed. Sorokin says conditions within the interstellar hydrogen clouds envisioned by their theory "favor exactly this process."

These clouds would be very cold and close to a hot, bright star. They would also be so thin that their hydrogen molecules would collide with one another only about once in two years. Under these circumstances, most of the stars' radiation would zip through the cloud as though it were not there. But the hydrogen molecules would scatter UV photons of certain frequencies so that, instead of passing through the cloud, they are trapped within it. These are the same kinds of uv photons that can pair with certain visible light photons in Sorokin's absorption process.

Thus, as starlight passes through the hydrogen cloud there is always an ample supply of the right kind of uv photons to allow hydrogen to absorb certain colors of visible light. According to Sorokin's and Glownia's calculations, many of these theoretical absorption patterns match those of many of the known diffuse interstellar bands. To "prove" this theory means refining it to account more precisely for DIBs features. That, in turn, requires more precise measurements of the DIBs, which planned new satellites could provide.

So far, the theory has failed to impress astronomers partly because its designers originally included unrealistic features in their theoretical hydrogen clouds. They are working to correct this failing. Sorokin says they know "we're at odds with the established astronomical literature ... but we see no alternative."

Whether they turn out to be right or wrong, they at least have shown that novices who are seasoned scientists in another field can bring new insight to an old astronomical mystery.