One of the fundamental quirks of our universe is that nothing inside of it can be “superluminal,” or faster than the speed of light. That’s one reason why an explosive jet fueled by the supermassive black hole of a faraway galaxy that appears to be traveling at up to 20 times light speed has caught the eye of scientists.
New observations of this optical illusion are also “the sharpest-ever images” of a jet powered by a supermassive black hole, according to a study published on Tuesday in Astronomy & Astrophysics. Understanding how these jets are formed is “one of the major quests in modern astrophysics,” said the authors, who were led by Jae-Young Kim, an astrophysicist at the Max Planck Institute for Radio Astronomy.
The radiant jets are erupting from a galaxy called 3C 279, located five billion light years from Earth. Even across this immense distance, 3C 279 shines like a cosmic beacon because it is a “blazar,” which means its galactic core is among the brightest and most energetic objects in the universe.
At the center of 3C 279 lies a supermassive black hole that is about one billion times as massive as the Sun. When clumps of matter fall into the hole, they become super-hot and energetic, sparking the enormous jet explosion that scientists see blasting out of the blazar’s pole.
3C 279 is so bright that astronomers have been able to observe it, and its illusory superluminal jet, since the 1970s. But Kim’s team, which consists of hundreds of co-authors, has the advantage of a new type of ultrasensitive observatory: The Event Horizon Telescope (EHT).
The EHT collaboration is best known for capturing the very first image of a black hole almost exactly one year ago. The telescope consists of a global network of radio arrays that combine to form one ultra-sensitive observatory that is the size of Earth itself. These colossal dimensions enable the EHT to image distant objects in unprecedented detail.
Kim’s team observed 3C 279 with the EHT for four nights in April 2017 at an extremely high resolution of 20 microarcseconds, which is equivalent to spotting an orange on the Moon from Earth. The observations produced “new and more detailed maps of the core region of 3C 279” including the “finest details” of the base of one of its jets.
These observations reveal something so strange as to be impossible: the black hole’s jet appeared by all indications to be traveling faster than the speed of light. As it turns out, this curiosity is due to a mega-scale optical illusion in space.
This blazar jet shoots from the galactic center with so much force that it reaches 99.5 percent the speed of light, about as close to the cosmic speed limit as possible. However, because the jet is oriented toward Earth, it looks like it is traveling 15 to 20 times faster than light speed.
“This extraordinary optical illusion arises because the material is racing toward us, chasing down the very light it is emitting and making it appear to be moving faster than it is,” said co-author Dom Pesce, a postdoctoral fellow at the Harvard–Smithsonian Center for Astrophysics, in a statement.
In other words, the blazar jet is not actually defying the laws of physics, though it does put on a pretty good show of it.
The observations also revealed that the jet appears to be twisted at the point where it emerges from the galactic center, which offers the first clear glimpse of a blazar jet’s base. The discovery suggests that the black hole somehow deforms the jet as it is emitted, perhaps into a helical structure that is distinct from the straight jet that forms further from the galactic center.
“Follow-up work combining the results from this paper with other multiwavelength data obtained close in time, will provide a more detailed understanding of the physical processes in the jet, allowing detailed tests of the potential curvature in the innermost jet, and possible jet acceleration and alternative physical scenarios,” the team said in the paper.
For decades, scientists have marveled over the ultra-luminous center of 3C 279 and puzzled over how such blinding amounts of light could be generated. The EHT collaboration has now brought the answer to that question one step closer to resolution.