When it comes to high-speed collisions, nobody here on Earth has anything on black holes. Astronomers have witnessed a new first: two high-speed knots of matter colliding in a sort of rear-end impact. They saw this after creating a time-lapse video of a super-speed jet of plasma as it shot out of a supermassive black hole. The knots of matter were inside the black hole until it blasted them out-and into each other.
The collision may help astronomers explain the incredible speeds at which these jets can move. This "superluminal" motion astronomers witness as the energized jets escape the black hole appear to exceed the speed of light, but this is an optical illusion caused by their high speeds and angle relative to our line of sight.
This "faster than light speed" sighting far away from the source of a black hole is the second one in history. Astronomers hope that they'll be able to use the data from extragalactic jets like these to better understand the evolution of galaxies. Jets like these seem to send confined beams of energized plasma away from the host galaxy's active nucleus.
"Something like this has never been seen before in an extragalactic jet," says Eileen Meyer of the Space Telescope Science Institute (STScI) in Baltimore, Maryland. "This will allow us a very rare opportunity to see how the kinetic energy of the collision is dissipated into radiation."
The jet which is the subject of the video was first seen in 1992. Meyers was matching archived images of the jet from Hubble with new Hubble images to analyze jet motions. This led to the sighting of the superluminal collision, which caused them to emit even more light.
The way this supermassive black hole ejected the knots is not so unusual. What is less common is the fact that they were sighted so far from the black hole's nucleus using an optical telescope. Newly formed stars also eject streams of gas which resemble knotty structures. When the material expelled originates from a choppy influx, the expelled knots look like a string of pearls.
The source of these jets moving at almost light speed-relativistic jets-is a topic of discussion for astrophysicists. The black hole's spinning accretion disc may be producing the relativistic energy.
The BBC reports that Martin Hardcastle, a professor of astrophysics at the University of Hertfordshire in the UK, said, "These chunks of stuff follow each other up the jet and you would expect fast ones to run into slow ones."
"When that happens what you get is a hydrodynamic shock, which means that energy is transferred from blob number two, to material that used to make up blob number one. As a result, you increase the energy of the particles in the fluid... so you see a brightening effect."
"There's a lot of interpretation going into this, because even Hubble can't see this as sharply as you would like. But it's perfectly plausible that's what they're seeing."
Meyer published her results in the May 28 issue of the journal Nature. Her next step will be to compile more time-lapse videos of black hole jets in nearby galaxies in the hope of seeing similar events.
