Wobbling Fast

This Black Hole’s Jets Are Wobbling Fast Because It’s Dragging Space-Time

BY GENEVIEVE SCARANO

Astronomers have spotted wobbly jets of particles shooting out from a black hole, and they believe that this strange motion could be happening because the black hole’s strong gravitational pull is dragging space around it.

Artist rendering

Named V404 Cygni, this black hole is nine times more massive than the sun and located almost 8,000 light-years from Earth, said a National Radio Astronomy Observatory (NRAO) press release. The black hole belongs to a binary system where it and a star that’s similar to a sun orbit one another, Space.com reported. V404 Cygni draws in material from its companion star, and as the material streams toward the black hole, it develops a rotating disk, also known as an accretion disk, that surrounds the black hole.

“We’ve never seen this effect happening on such short timescales,” James Miller-Jones, of the Curtin University node of the International Centre for Radio Astronomy Research (ICRAR), who led a team using the National Science Foundation’s (NSF) Very Long Baseline Array (VLBA), said in the press release.

This strange phenomenon causes some of the particles that fall into the black hole to escape through relativistic jets, which are long energetic plasma beams that flow from the black hole’s axis of rotation at a rate of more than half the speed of light. According to astronomers, V404 Cygni’s jet material moves as fast as 60 percent of the speed of light.

The rapid wobble, also known as precession, has not been spotted before in other similar systems. Explaining this mysterious occurrence requires using an effect of Albert Einstein’s general theory of relativity. According to the theory, massive objects, such as black holes, distort space and time, and when they spin, their gravitational influence pulls space and time around with it, also known as frame-dragging.

Particularly in V404 Cygni, the black hole’s spin axis is misaligned from the plane of its orbit with its starry companion, which causes the frame-dragging effect to “warp” the inner area of the disk and then pull the warped portion around with it. The jets originate from either the black hole or the inner disk, causing a change in jet orientation and producing the “wobbling” effect similar to a spinning top toy.

“This is the only mechanism we can think of that can explain the rapid precession we see in V404 Cygni,” Miller-Jones said in the press release. “You can think of it like the wobble of a spinning top as it slows down, only in this case, the wobble is caused by Einstein’s general theory of relativity.”

Miller-Jones and his team observed the black hole using the VLBA, a network of 10 radio telescopes located around the world that are monitored and owned by the NSF. Since 1938, this black hole has been a hot topic for many observations, and in 2015, which was the year of its most recent outburst, Miller-Jones and his team started making observations of V404 Cygni.

The group of astronomers, which studied the black hole’s jet activity, published their findings in the journal Nature on April 29. The black hole’s accretion disk is roughly 10 million kilometers (about 6.2 million miles) wide, and Miller-Jones noted that only the inner few thousand miles is warped and puffed up by strong radiation pressure that yields a doughnut-like shape. The jets’ rapid direction changes led the team to alter their observation strategy.

Typically, astronomers will generate a single image using data collected over the course of many hours, similar to how a long time exposure works. This time though, the astronomers made 103 individual images that were each approximately 70 seconds long, and then combined them to make a movie in order to show the jets’ rapid motion.

“We were gobsmacked by what we saw in this system — it was completely unexpected,” Greg Sivakoff, of the University of Alberta, said in the press release. “Finding this astronomical first has deepened our understanding of how black holes and galaxy formation can work. It tells us a little more about that big question: ‘How did we get here?’”