After that supernova explosion and collapse has happened, the object that remains-star heavy, asteroid sized-is a 'neutron star.' It has been crushed together so violently by its own immense gravitation that the electrons of its atoms are driven into its protons, creating the chargeless particles called neutrons. Its substance is so dense that a cubic inch of it weighs two million tons or so; it is like compressing the hugest of Earth's old supertankers into something the size of a coin. Things do not leave a neutron star easily; with that immense, concentrated mass pulling things down to its surface, escape velocity becomes something like 120,000 miles a second. More than that: its rotational energy has been 'compressed,' too. The blue-white giant star that used to turn on its axis once a week is now a superheavy asteroid-sized thing that whirls around many times a second.
Chou knew there were observations that he had to make-magnetic, X-ray, infrared, and many others. The magnetometer readings were the most important. Neutron stars have superfluid cores and so, as they rotate, they generate intense magnetic fields-just like the Earth. Not really just like the Earth, though, because the neutro1 star's magnetic field, too, is compressed. It is one trillion times stronger than the Earth's. And as it spins it generates radiation. The radiation can't simply flow out from all parts of the star at once-the lines of magnetic force confine it. It can only escape at the neutron star's north and south magnetic poles.
The magnetic poles of any object aren't necessarily in the same place as its poles of rotation. (The Earth's north magnetic pole is hundreds of miles away from the point where the meridians of longitude meet.) So all the neutron star's radiated energy pours out in a beam, around and around, pointing a little, or sometimes a lot, away from its true rotational poles.
So that was the explanation of the thing Chou was seeing. The cones were the two polar beams from the star that lay between them, north and south, fanning out from its poles. Of course, Chou couldn't see the beams themselves. What he saw were the places
where they illuminated tenuous clouds of gas and dust as they spread out.
The important thing to Chou was that no Earthly astronomer had ever seen them that way. The only way anyone on Earth ever could see the beam from a neutron star was by the chance of being somewhere along the rim of the conical shape the beams described as they rotated. And then what they saw was a high-speed flicker, so fast and regular that the first observer to spot one thought it was the signal from an alien intelligence. They called the signal an 'LGM' (for Little Green Men) until they figured out what was causing that sort of stellar behavior.
Then they called the things 'pulsars.'
Chou got a four-hundred-thousand-dollar science bonus for what he had discovered. He wasn't greedy. He took it and returned to Earth, where he found a new career lecturing to women's clubs and college audiences on what it was like to be a Heechee prospector. He was a great success, because he was one of the first of the breed to return to Earth. alive.
Later returnees were less fortunate. For instance, there was-MISSION HALO
In some ways Mission Halo was the saddest and most beautiful of all. The mission had been written off as lost, but that turned out to be wrong. The ship wasn't lost. Only its crew was.
The ship was an unarmored Three. When it came back its arrival was a surprise to everyone. The ship had been gone over three years. It was a certainty that nobody could have survived so long a trip. In fact, no one had. When the hatch crews on Gateway got the ports open, recoiling from the stench inside, they discovered that Jan Mariekiewicz, Rolph Stret, and Lech Szelikowjtz had left a record of their experiences. It was read with compassion by the other prospectors, and with rejoicing by astronomers.
'When we reached two hundred days without turnaround,' Stret had written in his diary, 'we knew we were out of luck. We drew straws. I won. Maybe I should say I lost, but, anyway, Jan and Lech took their little suicide pills, and I put their bodies in the freezer.
'Turnaround came finally at 271 days. I knew for sure that I wasn't going to make it either, not even with only me alive in the ship. So I've tried rigging everything on automatic. I hope it works. If the ship gets back, please pass on our messages.'
As it happened, the messages the crew left never got delivered. There was no one to deliver them to. The messages were all ddressed to other Gateway prospectors who had been part of the same shipment up from Central Europe, and that batch wasn't one of the lucky ones. Every one of them had been lost in their own ships.
But the pictures the ship brought back belonged to the whole world.
Stret's jury-rigging had worked. The ship had stopped at its destination. The instruments had thoroughly mapped everything in sight. Then the ship's return had been triggered automatically, while Stret's corpse lay bloating under the controls.
The record showed that their ship had been outside the Milky Way galaxy entirely.
It brought back the first pictures ever seen of our galaxy from outside. It showed a couple of fairly nearby stars and one great, distant globular cluster-the stars and clusters of the spherical halo that surrounds our galaxy-but most of all it showed our Milky Way galaxy itself, from core to farthest spiral wisp, with its great, familiar octopus arms: the Perseus arm, the Cygnus arm, the Sagittarius-Carina arm (with our own little Orion arm, the small spur that held the Earth, nearby), as well as the large, distant arm that Earthly astronomers had never seen before. They called it simply 'Far Arm' at first, but then it was renamed the StretMariekiewicz-Szelikowitz arm to honor the dead discoverers. And in the center of it all was the great bellying octopus-body mass of core stars, laced with gas
