From Way Out

At Volcano Ranch, 20 miles west of Albuquerque, a group of 19 small, coop-like structures covers a grassy, mile-wide plain. Inside each coop are four disks, each one meter across and wrapped in black plastic. From the disks, cables run to a central building crammed with oscilloscopes and other delicate gear. Last week the Massachusetts Institute of Technology, institutional proprietor of all this apparatus, announced that it has detected a cosmic ray (high-speed particle) that came to the earth from a foreign galaxy millions of light years away in the far depths of space. This was eye-opening scientific news.

Cosmic rays have long been a fascinating and controversial subject among scientists. It is generally agreed that most low-speed cosmic rays are particles shot out of the sun, but that those with higher energy must come from somewhere else. The late Enrico Fermi thought they came from interstellar magnetic fields which gradually speed up protons and other charged particles moving between the stars of the Milky Way galaxy (the earth itself is a smallish satellite to one of the smaller stars in this galaxy). But this theory could not account for rays whose energy is above a critical limit. The galaxy's overall magnetic field can make fairly powerful rays curve enough to stay inside it, but if the rays acquire more than about 1018 (11billion billion) electron volts, the galactic field cannot hold them. Such rays will shoot off and be lost in intergalactic space. So cosmic-ray experts reason that if rays hit the earth with more than 1018 electron volts, they must come from some unknown accelerating force that works outside the galaxy.

Counting Showers. For many years Professor Bruno Rossi of M.I.T. has hunt ed for cosmic rays above this critical limit. The original energy of a cosmic ray can be measured by counting the second--ary particles that it showers down on the earth after colliding with air molecules in the high atmosphere. If its energy is 1016 (io million billion) electron volts, it generates millions of particles, mostly electrons and mesons which spread over many acres of ground. More powerful rays give even bigger showers.

Rossi's ray catcher at-Volcano Ranch is an array of scintillation counters that gives electrical signals whenever fast-moving particles hit it. If a shower looks interesting, its record is transferred to tabulator cards and analyzed by a computer at Kirtland Air Force Base. The final answer tells the ray's energy when it hit the top of the atmosphere and caused the shower.

The detector started work last fall, and on Dec. 3 Irma Argandona, a student from Bolivia, noted by scanning the raw data that something unusual had happened at nine minutes after midnight.

She gave the record sheet (No. 026508) to Dr. John Linsley, one of her immediate superiors at the Volcano Ranch installation, but he put it aside for more pressing matters. Seven weeks ago it was processed and sent to the Kirtland com puter--thence back to Volcano Ranch for final appraisal.

Computer Gives Up. There, late one night four weeks ago. Dr. Linsley was studying a pile of computer reports from Kirtland. He came to the Dec. 3 shower. The report started like many others, but toward the end the computer wrote in effect: "I give up." Linsley said to his wife, "I see something crazy," and went to work with his slide rule. Half an hour later he telephoned his colleague, Dr. Livio Scarsi: "I think we may have something."

Next morning the shower caught by Record No. 026508 went back to the Kirtland computer for a special full-dress analysis. Next day Dr. Linsley got the exciting news. The shower peppered the ground with io billion particles, and when it hit the atmosphere, it carried 20 to 40 billion billion electron volts. This made it by far the most powerful ray ever detected. Its energy, far above the critical limit, proved that it must have come from outside the Milky Way galaxy. Very likely it had been traveling for billions of years, pushed by unknown forces from an unknown source.

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