“Halo-engine” could propel a spacecraft to nearly the speed of light

In 2016, physicist Stephen Hawking and billionaire Yuri Milner revealed a plan to travel to the stars. The so-called project Breakthrough Starshot is a program worth $ 100 million to develop and prove the technologies needed to visit the nearest star system. Potential targets include Proxima Centauri system, at a distance of about four light-years, with multiple exoplanets, one of which is similar to Earth.

Project Breakthrough Starshot

The plan of Hawking and Milner was to build thousands of tiny spaceships the size of a microchip and use the light to disperse them up to relativistic speeds — that is, close to the speed of light. Big fleet increases the chances that at least one of them will safely arrive. Each “star chip” is attached to the light sail the size of a badminton court, and then is irradiated with extremely powerful ground-based lasers.

The laser has many advantages. The most important thing that space ships do not need any fuel, and not have to carry extra weight. Also using acceleration light sail to accelerate the boat up to 20% of the speed of light. In this scenario the fleet will arrive to Proxima Centauri in less than 30 years.

Fantastically powerful lasers needed for such a mission will be particularly difficult and expensive to develop. Born to an obvious question: is there any other way to reach relativistic speeds?

Today we have a kind of answer, thanks to the work of David Kipping, an astronomer from Columbia University in new York. Kipping has invented a new form of the gravitational slingshot, the same technology used by NASA to send, such as, the spacecraft Galileo on Jupiter. The idea is to accelerate a space ship, sending it close to a huge object like a planet. Thus, the spacecraft will take some of the velocity of the planet, overclocking with it.

Gravitational slingshots work well in the massive telephone In the 1960-ies of the physicist Freeman Dyson calculated that a black hole can accelerate the spacecraft to relativistic speeds. But the forces on a space ship approaching such an object is likely to destroy it.

So Kipping suggested a cleverHis idea is to send photons around the black hole, and then use added energy which they receive, to disperse the light sails. “The kinetic energy of a black hole is passed to the ray of light in blue offset, and return the photons are dispersed not only spacecraft, but also add to his energy,” says Kipping.

This process depends on an extremely powerful gravitational field around the black hole. Since photons have a small rest mass, this field is able to hold the light in a circular orbit.

The work of Kipping is based on a slightly different orbit, directing the photons emitted by a space ship around a black hole and back — a kind of orbit like a boomerang. While traveling photons on the boomerang will get kinetic energy from the motion of the black hole.

It is this energy could accelerate a space ship, equipped with light sail. Kipping calls his idea “halo-engine”. Halo-the engine transfers the kinetic energy of the moving black hole a spaceship using the gravity. If the spacecraft does not consume any of its own fuel in the process.

Because halo-the engine uses the motion of the black hole, it is best to apply to dual systems in which the black hole is rotating around another object. Then the photons receive energy from the motion of the black hole at the corresponding point in its orbit.

And this engine should work with any mass, which is smaller than the mass of the black hole. Kipping says that it possible mechanisms the size of a planet. Thus, a sufficiently advanced civilization can travel with relativistic velocities from one part of galaxy to another, jumping from one binary system of black holes in another. “Advanced civilization could use the concept of light sails to do relativistic speeds and an extremely effective motion,” he says.

This same mechanism can also slow down the spacecraft. So this advanced civilization will probably look for pairs of binary systems with black holes that will act as accelerators and retarders.

In the milky Way has about 10 billion binary systems of black holes. But Kipping notes that is likely to be only a limited number of trajectories that link them together, so these interstellar highway will probably be very valuable.

Of course, the technology required to use this concept, are now beyond the capabilities of civilization. But astronomers should be able to figure out where the best star highway, and look for thesignature civilizations that are unable to exploit them.