A jet of particles emitted by two merging stars appears to be travelling at seven times the speed of light, but astronomers attribute this to a cosmic illusion known as superluminal motion.
Astronomers have detected a gargantuan blast of energy from space that appears to be doing the impossible: Traveling seven times faster than the speed of light.
This is, of course, an optical illusion — a rare and mind-boggling phenomenon called superluminal motion, which occurs when particles come very close to moving at the speed of light. In this case, scientists detected a jet of energy blasting out of a stellar collision site at a staggering 99.97% of the speed of light — about 670 million mph (1.07 billion km/h).
A jet of particles blasts out of a black hole at near-light-speed. A similar jet was just detected from a pair of colliding neutron stars, seemingly breaking the laws of physics. (Image credit: NASA Goddard)
The jet in question is the result of a cosmic cataclysm that first made waves in the scientific community in 2017. That year, scientists detected a violent collision between two neutron stars — ultra-dense, collapsed star cores that pack a sun’s-worth of mass into a ball no wider than a city — located roughly 140 million light-years from Earth. The collision was so powerful it created ripples in the fabric of space-time; such disturbances are known as gravitational waves.
Albert Einstein predicted the existence of these space-time ripples in 1916, and it took scientists 100 years to find the evidence to prove it, following a collision between two black holes that was detected in 2016. The gravitational waves released by the colliding neutron stars in 2017 — a signal named GW17081 — were the first to be detected from a source other than black holes, proving that more than one type of cosmic catastrophe is capable of creating them.
Gravitational waves are invisible to the naked eye, but can be detected with equipment such as the Pasadena-based Large Interferometer Gravitational Wave Observatory (LIGO). As a result, after LIGO detected the initial explosion of waves from merging stars in 2017, astronomers all over the world focused their telescopes on the merger to learn everything they could about it. Soon after, astronomers noticed a high-speed jet of particles shooting out of the collision location and lighting up globs of matter blasted by the stars.
Astronomers examined the jet using NASA’s Hubble Satellite Telescope, the European Space Agency’s Gaia space observatory, and six other radio telescopes on Earth in their new paper. Using these measurements, the scientists determined the true speed of the jet as well as the imagined physics-defying speed.
The disparity in speed between the particles in the jet and the light particles (or photons) that they release causes the beyond-light-speed illusion. Because the particles in the jet move nearly as quickly as the light they emit, it can appear that particles in the early stages of the jet arrive at Earth approximately at the same time as photons in the later stages of the jet, giving the impression that the jet is moving faster than the speed of light.
This illusion has already been witnessed in several other cosmic objects, including a near-light-speed jet blasting out of the Messier 87 galaxy in the Virgo constellation. So far, all examples of superluminal travel can be described mathematically in a fashion that does not violate existing physical principles.