Hubble Video Shows Shock Collision

By Rob Garner
NASA

When you’re blasting though space at more than 98 percent of the speed of light, you may need driver’s insurance. For the first time, astronomers have discovered a rear-end collision between two high-speed knots of ejected matter. This discovery was made while piecing together a time-lapse movie of a plasma jet blasted from a supermassive black hole inside a galaxy located 260 million light-years from earth.

In the central region of galaxy NGC 3862, an extragalactic jet of material can be seen at the 3 o'clock position (left). Hubble images (right) of knots (outlined in red, green and blue) shows them moving along the jet over 20 years. The "X" is the black hole. (Photos: NASA, ESA, and E. Meyer STScI/Released)

In the central region of galaxy NGC 3862, an extragalactic jet of material can be seen at the 3 o’clock position (left). Hubble images (right) of knots (outlined in red, green and blue) shows them moving along the jet over 20 years. The “X” is the black hole.
(Photos: NASA, ESA, and E. Meyer STScI/Released)

The finding offers new insights into the behavior of “light saber-like” jets that are so energized that they appear to zoom out of black hole at speeds several times the speed of light. This “superluminal” motion is an optical illusion due to their being pointed very close to our line of sight and very fast speeds.

Such extragalactic jets are not well understood. They appear to transport energetic plasma in a confined beam from the active nucleus of the host galaxy. The new analysis suggests that shocks produced by collisions within the jet further accelerate particles and brighten the regions of colliding material.

The video of the jet was assembled with two decades’ worth of NASA Hubble Space Telescope images of the elliptical galaxy NGC 3862, the sixth brightest galaxy and one of only a few active galaxies with jets seen in visible light. The jet was discovered in optical light by Hubble in 1992. NGC 3862 is in a rich cluster of galaxies known as Abell 1367, located in the constellation Leo.

The jet from NGC 3862 has a string-of-pearls structure of glowing knots of material. Taking advantage of Hubble’s sharp resolution and long-term optical stability, Eileen Meyer of the Space Telescope Science Institute (STScI) in Baltimore, Maryland assembled a video from archival data to better understand jet motions. Meyer was surprised to see a fast knot with an apparent speed of seven times the speed of light catch up with the end of a slower moving, but still superluminal, knot along the string.

The resulting “shock collision” caused the merging blobs to brighten significantly.

“Something like this has never been seen before in an extragalactic jet,” said Meyer. As the knots continue merging they will brighten further in the coming decades. “This will allow us a very rare opportunity to see how the energy of the collision is dissipated into radiation.”

It’s not uncommon to see knots of material in jets ejected from gravitationally compact objects, but it is rare that motions have been observed with optical telescopes, and so far out from the black hole, thousands of light-years away.

Beyond the collision, which will play out over the next few decades, this discovery marks only the second case of superluminal motion measured at hundreds to thousands of light-years from the black hole where the jet was launched. This indicates that the jets are still very, very close to the speed of light even on distances that start to rival the scale of the host galaxy.

Meyer’s results were reported in the May 28 issue of the journal Nature.

Watch the video of the collision below.

Story and information provided by NASA
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