Halo Google Drive Download

[Autumn Pitz]

Back in 2016, the physicist Stephen Hawking and the billionaire Yuri Milner unveiled a plan to travel to the stars. The so-called Breakthrough Starshot project is a $100 million program to develop and demonstrate the technologies necessary to visit a nearby star system. Potential targets include Proxima Centauri, a system some four light-years away with several exoplanets, including one Earth-like body orbiting in the habitable zone.

Laser propulsion has various advantages. The most significant is that the spacecraft need not carry any fuel, vastly reducing their mass. It should also be capable of accelerating the light sails to a velocity of up to 20% the speed of light. At that rate, a starchip would arrive at Proxima Centauri in less than 30 years.

The fantastically powerful lasers required for such a mission will be particularly difficult and expensive to develop. And that raises an obvious question: is there any other way to reach relativistic speeds?

Today, we get an answer of sorts thanks to the work of David Kipping, an astronomer at Columbia University in New York. Kipping has come up with a novel form of gravitational slingshot, the same technique that NASA has used, for example, to send the Galileo spacecraft to Jupiter. The idea is to accelerate a spacecraft by sending it skimming past a massive object such as a planet. In this way, the spacecraft steals some velocity from the movement of the planet, propelling it on its journey.

Gravitational slingshots work best around hugely massive bodies. In the 1960s, the physicist Freeman Dyson calculated that a black hole could accelerate a spacecraft to relativistic speeds. But the forces on the spacecraft as it approached such an object would be likely to destroy it.

Since the halo drive exploits the movement of a black hole, it is best applied to binary systems in which a black hole is orbiting another object. The photons then gain energy from the movement of the black hole at appropriate points in its orbit.

The Milky Way contains around 10 billion binary black-hole systems. But Kipping points out that there are likely to be just a limited number of trajectories that link them together, so these interstellar highways are likely to be valuable regions.

A new study envisions firing laser beams that would curve around a black hole and come back with added energy to help propel a spacecraft to near the speed of light. Astronomers could look for signs that alien civilizations are using such a "halo drive," as the study dubs it, by seeing if pairs of black holes are merging more often than expected.

"Sometimes, in a computer game you find an 'exploit,' a hack which allows you to do something overpowered that would otherwise be forbidden by the rules of the game," Kipping told Space.com. "In this case, the game is the physical world, and I tried to think about exploits that would allow a civilization to achieve relativistic flight back and forth across the galaxy without the vast energy expense that one might naively assume."

A key challenge to using rockets to fly through space is that the propellant they carry with them has mass. Long trips need a lot of propellant, which makes the rockets heavy, which in turn requires more propellant, making the rockets even heavier, and so on. That problem gets exponentially worse the bigger the rocket gets.

Instead of carrying propellant for propulsion, however, spacecraft equipped with mirror-like sails could rely on lasers to push them outward. The $100 million Breakthrough Starshot initiative, announced in 2016, plans to use powerful lasers to propel swarms of spacecraft to Alpha Centauri, the closest star system to our own, at up to 20 percent the speed of light.

Spacecraft now regularly use "slingshot maneuvers," in which the gravity of a body, such as a planet or moon, hurls the vessels across space and boosts their speed. In 1963, famed physicist Freeman Dyson suggested that spaceships of any given size could rely on slingshot maneuvers around compact pairs of white dwarfs or neutron stars to fly at relativistic speeds. (Dyson came up with the notion of what became known as a Dyson sphere, a megastructure that encapsulates a star to capture as much of its energy as possible to power an advanced civilization.)

However, a "Dyson slingshot" runs the risk of damaging a spacecraft through extreme gravitational forces and hazardous radiation from those pairs of dead stars. Instead, Kipping suggests that gravity might assist spaceships by increasing the energy of laser beams fired at the edges of black holes.

Black holes possess gravitational fields so powerful that nothing can escape them once it gets close enough, not even light. Their gravitational fields can also distort the paths of photons of light that do not fall into the holes.

In 1993, physicist Mark Stuckey suggested that a black hole could, in principle, act like a "gravitational mirror," in that the black hole's gravity could slingshot a photon around so that it flew back at its source. Kipping calculated that if a black hole was moving toward a photon's source, the "boomerang photon" would siphon away some of the black hole's energy.

Astronomers could look for signs that alien civilizations are exploiting pairs of black holes for travel with such an engine. For example, halo drives would effectively steal energy from such binary black hole systems, increasing the rates at which pairs of black holes merge above what one would expect to see naturally, Kipping said.

His findings were based on boosts from pairs of black holes orbiting each other at relativistic speeds. Although there are an estimated 10 million pairs of black holes in the Milky Way, Kipping noted that few of those likely orbited at relativistic speeds for long, since they would merge rather quickly.

Still, he noted that isolated, spinning black holes could also launch halo drives at relativistic speeds, "and we already know of numerous examples of relativistic, spinning supermassive black holes."

The major drawback of a halo drive would be that "one has to travel to the nearest black hole," Kipping said. "It's akin to paying a one-time toll fee to ride the highway system. You have to pay some energy to reach the nearest access point, but after that, you can ride for free as a long as you like."

The halo drive works only in close proximity to a black hole, at a distance of about five to 50 times the black hole's diameter. "This is why you have to travel to the nearest black hole first and [why you] can't simply do this across light-years of space," Kipping said. "We still first require a means to travel to nearby stars to ride the highway system.

"If we want to achieve relativistic flight, it takes immense energy levels no matter what propulsion system you use," he added. "One way to get around this is to use astronomical objects as your power source, since they possess literally astronomical levels of energy within them. In this case, the black-hole binary is essentially a giant battery waiting for us to tap it. The idea is to work with nature and not against it."

Kipping is now investigating ways to exploit other astronomical systems for relativistic flight. Such techniques "may not be quite as efficient or fast as the halo-drive approach, but these systems possess the deep energy reserves needed for these journeys," Kipping said.

Charles Q. Choi is a contributing writer for Space.com and Live Science. He covers all things human origins and astronomy as well as physics, animals and general science topics. Charles has a Master of Arts degree from the University of Missouri-Columbia, School of Journalism and a Bachelor of Arts degree from the University of South Florida. Charles has visited every continent on Earth, drinking rancid yak butter tea in Lhasa, snorkeling with sea lions in the Galapagos and even climbing an iceberg in Antarctica. Visit him at http:\/\/www.sciwriter.us"}), " -0-10/js/authorBio.js"); } else console.error('%c FTE ','background: #9306F9; color: #ffffff','no lazy slice hydration function available'); Charles Q. ChoiSocial Links NavigationContributing WriterCharles Q. Choi is a contributing writer for Space.com and Live Science. He covers all things human origins and astronomy as well as physics, animals and general science topics. Charles has a Master of Arts degree from the University of Missouri-Columbia, School of Journalism and a Bachelor of Arts degree from the University of South Florida. Charles has visited every continent on Earth, drinking rancid yak butter tea in Lhasa, snorkeling with sea lions in the Galapagos and even climbing an iceberg in Antarctica. Visit him at

A lot of hopes currently hinge on the use of directed energy and lightsails to push tiny spacecraft to relativistic speeds. But what if there was a way to make larger spacecraft fast enough to conduct interstellar voyages? According to Prof. David Kipping, the leader of Columbia University's Cool Worlds lab, future spacecraft could rely on a halo drive, which uses the gravitational force of a black hole to reach incredible speeds.

Prof. Kipping described this concept in a recent study that appeared online (the preprint is also available on the Cool Worlds website). In it, Kipping addressed one of the greatest challenges posed by space exploration, which is the sheer amount of time and energy it would take to send a spacecraft on a mission to explore beyond our solar system.

As Kipping put it, relativistic propulsion (or accelerating to a fraction of the speed of light) is very expensive in terms of energy. Existing spacecraft simply don't have the fuel capacity to get up to those kinds of speeds, and short of detonating nukes to generate thrust la Project Orion, or building a fusion ramjet la Project Daedalus, there are not a lot of options available.

"But even here, you are talking about several terra-joules of energy for the most minimalist (a gram-mass) spacecraft conceivable," said Kipping. "That's the cumulative energy output of nuclear power stations running for weeks on end... so this is why it's hard."

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