The Contrarian

This week’s StR is all about distant stars… looking at them and traveling to them…

Recently, some creative science types have been eating their Wheaties and have cooked up a couple of really nifty interstellar propulsion schemes.

Physicist Jia Liu at New York University suggested a spacecraft propulsion system powered by dark matter.

His plan is to drive the rocket using the energy released when dark matter particles annihilate each other. Here’s where Liu’s idea depends on more speculative physics. No one knows what dark matter is actually made of, though there are numerous theories of the subatomic world that contain potential dark matter candidates. One of the frontrunners posits that dark matter is made of neutralinos, particles which have no electric charge. Neutralinos are curious in that they are their own antiparticles: two neutralinos colliding under the right circumstances will annihilate each other.

If dark matter particles do annihilate in this way, they will convert all their mass into energy. A kilogram of the stuff will give out about 10¹⁷ joules, more than 10 billion times as much energy as a kilogram of dynamite, and plenty to propel the rocket forwards.

The design calls for a large scoop to precede the crew cabin of the spacecraft, gathering up dark matter particles en masse and then shrinking their container, thereby increasing the frequency of collisions and annihilations. The energy from the collisions could then be directed behind the craft, propelling it forward. Such a design could theoretically accelerate the spacecraft to relativistic speeds, yielding interstellar travel within the span of human lifetimes (for the passengers — not for those of us waiting back on Earth — darn that Einstein).

Meanwhile, mathematicians Louis Crane and Shawn Westmoreland at Kansas State University in Manhattan want to power their interstellar craft with energy provided by an artificial black hole.

Again, the trick is to capitalize on the energy output of matter/antimatter particle collisions, but this time the secret is Hawking radiation — various types of particles and anti-particles that materialize and annihilate each other very close to the  event horizon of a black hole. The problem is, you need a black hole that’s small enough to generate the needed amount of energy (small black holes emit Hawking radiation at a greater rate than large ones), but large enough to not just evaporate after a few microseconds. It turns out that there’s a “sweet spot” when it comes to the size of a black hole.

Crane has calculated that a black hole weighing about 1 million tonnes would make a perfect energy source: it is small enough to generate enough Hawking radiation to power the starship, yet large enough to survive without radiating away all its mass during a typical interstellar journey about 100 years long.

Of course, creating an artificial black hole isn’t something we can just do (despite the best efforts of those wackos at CERN).

To create a black hole, says Crane, you need to concentrate a tremendous amount of energy into a tiny volume. He envisages a giant gamma ray laser “charged up” by solar energy. The energy would be collected by solar panels 250 kilometres across, orbiting just a few million kilometres away from the sun and soaking up sunlight for about a year. “It would be a huge, industrial effort,” Crane admits.

The resulting million-tonne black hole would be about the size of an atomic nucleus. The next step would be to manoeuvre it into the focal range of a parabolic mirror attached to the back of the crew quarters of a starship. Hawking radiation consists of all sorts of species of subatomic particles, but the most common will be gamma ray photons. Collimated into a parallel beam by the parabolic mirror, these would be the starship’s exhaust and would push it forward.

As with the dark matter drive above, a black hole-powered propulsion system is still a “sub-light” form of space travel and travel times would be anywhere from years to generations from the perspective of the crew (and many millions of years for those of us watching from Earth), depending on destination and speed.

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And an enormous 120 feet-across image of the Milky Way, compiled from images taken by the Spitzer Space Telescope, is on display in Chicago.

The panorama represents the combined effort of two Spitzer survey teams, who used two of the telescope’s onboard instruments, the Infrared Array Camera (IRAC) and the Multiband Imaging Photometer.

The large image was made from stitching together 800,000 individual pictures taken by Spitzer, for a total of 2.5 billion infrared pixels. It covers an area of the sky about as wide as a pointer finger and as long as the length of arms outstretched, which might sound small, but covers about half of the entire galaxy, says Robert Hurt, of the Spitzer Science centre at Caltech.

The Hubble Space Telescope would like to remind us all down here on Earth that size isn’t everything.