As Black Holes Eat Stars, They Shoot Death Rays of Plasma Into Space

An artist’s depiction of a black hole and its plasma jet. NASA/JPL-Caltech

When astronomers caught sight of a massive burst of X-rays that had traveled almost 8,000 light-years to reach their telescopes, they realized it came from a celestial pair known as V404 Cygni, a relatively small black hole that is methodically eating a star about the size of our sun. Usually, that's uneventful, but every decade or two there's a consequence to all that gluttony, and the black hole vomits a geyser of highly energized matter called plasma out into space. When it did so in 2015, astronomers were watching with every type of telescope they could find.

Now, deep in the data those telescopes collected, they've pinpointed a tiny difference in when different types of light are produced by these plasma jets. And as a team of astronomers explains in a new article published in the journal Nature Astronomy, that tiny lag—it's just a tenth of a second—may explain how the jets are created.

Lead author Poshak Gandhi, an astronomer at the University of Southampton in the U.K., has long been intrigued by combining data from NuSTAR, a space telescope studying black holes and collapsed stars with X-ray vision, with data from a telescope in Spain that can take a snapshot every 35.94 milliseconds to study black holes, he told Newsweek in an email. "We weren't really sure what we would find, but ended up discovering these time lags which tell us something important about how nature is able to accelerate particle to high speeds," he said.

In the new study, Gandhi and his colleagues used measurements of V404 Cygni and another black hole–star pair to pinpoint precisely when different types of light emissions occurred. In both cases, they found that X-rays preceded visible light by about a tenth of a second. "There is no reason for two black hole jets in different systems to be behaving identically, so this may be telling us something fundamental about the underlying physics," Gandhi wrote Newsweek.

Essentially, astronomers can see the plasma jets themselves, but they haven't been sure how they formed—the astronomical equivalent of seeing headlights, but not seeing the car or the light bulb at their origin. A tenth of a second may not seem like that big a deal, but it turns out that time lag can give astronomers a much better picture of precisely what's happening at the black hole, the bulbs behind the beams of light, so to speak.

They think what's going on is that the X-rays are coming from near the black hole itself. But as the magnetic field around the black hole directs plasma into the jet shape, they start banging together, producing visible light. Given the speed at which these particles are moving and the tenth-of-a-second delay, scientists think that light is produced about 19,000 miles out from the black hole.

Seeing the same phenomenon twice raised the scientists' eyebrows, but they'll need a bunch more observations of more black holes before they can be sure the same thing happens in all different kinds of black holes. Gandhi also hopes to work with astronomers studying the theory behind the large black holes that hide at the center of galaxies to determine whether they could be producing plasma jets in the same way.