A fugitive on the lam in the heavens for years has finally been nailed. In tomorrow's issue of Nature, scientists announce that they have glimpsed an unusual three-proton hydrogen ion, H3+, floating in interstellar clouds. The sighting bolsters theories suggesting that H3+ is a key catalyst for star formation.
Because an H3+ ion is shaped like an equilateral triangle, it does not absorb radio- or microwaves well and is practically invisible in absorption bands that astronomers use to study the stars. The best way to detect these ions is to look in the infrared range, where molecular vibrations absorb infrared light in distinctive patterns.
After a 16-year search, Takeshi Oka of the University of Chicago and Thomas Geballe of the Joint Astronomy Center in Hilo, Hawaii, espied the very faint signature of H3+ in two molecular clouds. Using an infrared telescope, they spotted two gentle dips in the strong infrared spectrum of two young stars about 1000 light-years away from Earth. "It's remarkable that they saw it," says Harvard University chemist William Klemperer, who thinks the observation is "very real."
Scientists suspect that H3+ ions are formed as cosmic rays pass through cold interstellar clouds, altering hydrogen atoms. H3+ is a strong proton donor, so it may react with other molecules in an interstellar cloud (even when temperatures are so low that normal hydrogen is inert) to trigger a cascade of hundreds of new compounds.
The cascade may even explain how these clouds of plasma--consisting initially of gas in atomic form--coalesce into stars. The plasma cannot condense without shedding a lot of heat. And, as Klemperer says, molecules, as opposed to lone atoms, "are extremely good heat dissipaters." But the molecules might never form without the elusive H3+ ion to bring them together.