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The simulated radio images in this artist-scale illustration show ultra-fast jets drawn from the black hole created by the merger of two neutron stars, a dramatic event observed in August 2017. In the 155 days between two sightings, the jet seemed to move 2 light-years away, a distance that would require traveling four times faster than light. This "superluminal movement" is an illusion created when the jet almost points towards the Earth; it travels at about 97% of the speed of light.
Credit: D. Berry, O. Gottlieb, K. Mooley, Hallinan G., NRAO / AUI / NSF
According to a new study, the spectacular fusion of neutron stars that astronomers noticed last year generated a jet of material that seemed to move at a speed four times faster than light.
"Like" is the key word here, of course; the laws of physics tell us that nothing can travel faster in space than light. So, the superluminal movement was an illusion, which was caused by the speed (still very fast) of the jet and the fact that it exploded almost directly on us, according to the researchers.
"Based on our analysis, this jet is probably very narrow, at most 5 degrees wide, and was oriented at only 20 degrees from Earth," said Adam Deller, co-author of Swinburne University of Technology. in Australia. in a statement from the National Radio Astronomy Observatory (NRAO), a facility of the National Science Foundation (NSF) of the United States. [Gravitational Waves from Neutron Stars: The Discovery Explained]
"But to match our observations, the material in the jet must also explode at more than 97% of the speed of light," he added.
Deller and his colleagues – led by Kunal Mooley of NRAO and the California Institute of Technology in Pasadena – have used various radio telescopes to study the consequences of the star-neutron collision, a historical event known as GW170817.
GW170817 was the first documented collision of two neutron stars, the superdense remains of massive stars dead in supernova explosions. GW170817, which occurred about 130 million light-years from Earth, also opened the era of multimessaging astronomy: it was the first event detected by both gravitational waves (spatio-temporal undulations predicted by Albert Einstein a century ago) and electromagnetic radiation.
By the way, the name GW170817 is a nod to these gravitational waves, as well as to the dates at which astronomers observed the event – August 17, 2017.
Scientists believe that the fusion generated a powerful explosion that ejected a shell of matter far into space. Inside this shell, the fused neutron stars created a single black hole, which began to suck up a lot of gas and dust. This material formed a rapidly rotating disk around the black hole; Before long, the twinned jets began to explode from the poles of this disc, the members of the research team said.
It was unclear whether these jets had crossed the debris shell created by the initial explosion. But the observations of Mooley and his team – 75 days and 230 days after the initial detection of GW170817 – indicate that this actually happened.
At first, the jets interacted with the debris expelled to form a kind of cocoon that moved much more slowly than the jets themselves. But the jets finally broke loose in the interstellar space.
"Our interpretation is that the cocoon dominated the radio show until about 60 days after the merger, and later the show was dominated by the planes," said the co-author of The study Ore Gottlieb, a theorist from the Tel Aviv University in Israel. same statement.
This illustration shows the consequences of star-neutron fusion. The ejectas of a first explosion formed a shell around the black hole formed by the fusion. A jet of material propelled by a disk surrounding the black hole first interacted with the ejection material to form a large "cocoon". Later, the jet went through to emerge in interstellar space, where its extremely fast motion became apparent.
Credit: Sophia Dagnello, NRAO / AUI / NSF
Now, for the faster part than the light: In the 155 days between the two sightings, the Earth-facing jet seemed to jump 2 light-years away, a distance that suggests that it was moving four times faster than light. But again, it was just an illusion.
The new findings suggest that neutron star mergers are important sources of short-lived gamma-ray bursts, the study team members said. The jets generated by the fusion must be almost aligned with the Earth so that these eruptions of high energy light are detected, they added.
"The merger event was important for a number of reasons, and it continues to surprise astronomers with more information," said Joe Pesce, director of the NSF program for NRAO, in the same release. "Jets are enigmatic phenomena observed in many environments, and now, these exquisite observations in the radio part of the electromagnetic spectrum provide a fascinating glimpse of these observations, helping us to understand how they work."
The new study was published online today (Sept. 5) in the journal Nature.
Follow Mike Wall on Twitter @ michaeldwall and Google+. follow us @Spacedotcom, Facebook or Google+. Originally published on Space.com.
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