Rear-end Collisions Between High-speed Knots in Relativistic Jet

Produces shocks that accelerate particles, illuminating the colliding material 

The Hubble Space Telescope took this image of the core region of galaxy NGC 3862 with relativistic jet of material visible as line of light in the 3 o'clock position. Images to the right show knots of material outlined in blue, red and green moving along the jet over two decades. X marks the supermassive black hole. Credits: NASA/ESA/Hubble
The Hubble Space Telescope took this image of the core region of galaxy NGC 3862 with relativistic jet of material visible as line of light in the 3 o’clock position. Images to the right show knots of material outlined in blue, red and green moving along the jet over two decades. X marks the supermassive black hole.
Credits: NASA/ESA/Hubble

Space news (astrophysics: relativistic jets; shock collisions inside particle jets) – Observing plasma jet blasting from supermassive black hole in core of galaxy NGC 3862, 260 million light-years from Earth toward the constellation Leo in the rich galaxy cluster Abell 1367 –

Astronomers recently made an interesting discovery while studying data collected by the Hubble Space Telescope over two decades of observing the core of elliptical galaxy NGC 3862.  They were originally looking to create a time-lapse video of a relativistic jet blasting from the supermassive black hole thought to reside within its core. Instead, they discovered a rear-end collision between two separate high-speed waves of material ejected by a monster black hole whose mass astronomers have yet to measure. In this case, scientists believe the rear-end collision accelerated and heated particles which illuminated the colliding material for Hubble to see.

The relativistic jet erupting from the accretion disk of the supermassive black hole thought to reside at the core of galaxy NGC 3862 is one of the most studied and therefore best understood. It’s also one of the few active galaxies with jets observed in visible light. It appears to stream out of the accretion disk at speeds several times the speed of light, but this is just a visual illusion referred to as superluminal motion created by the combination of insanely fast velocities and our line of sight being almost on point. It forms a narrow beam hundreds of light-years in length that eventually begins to spread out like a cone, before forming clumps at around 1,000 light-years. Clumps scientists study looking for clues pointing to facts they can use to learn more about these plasma jets and the cosmos.

Astronomers have observed knots of material being ejected from dense stellar objects previously during the human journey to the beginning of space and time. This is one of the few times they have detected knots with an optical telescope thousands of light-years from a supermassive black hole. It’s the certainly the first time we have detected a rear-end collision between separately ejected knots in a relativistic jet. 

“Something like this has never been seen before in an extragalactic jet,” said Eileen Meyer of NASA’s Space Telescope Science Institute (STScI). “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.”

What would cause successive jets of material to achieve varying speeds? One theory involves the idea of material falling onto the supermassive black hole being superheated and ejected along its spin axis. Ejected material is constrained by the powerful magnetic fields surrounding the monster black hole into a narrow beam. If the flow of falling material isn’t perfectly smooth, knots are ejected in a string, rather than a continuous beam or steady hose.

It’s possible knots ejected later travel through a less dense interstellar medium, which would result in varying speeds. In this scenario, a knot launched after another knot would eventually catch up and rear-end it. 

Beyond learning knots of material ejected in plasma jets erupting from the accretion disk of a supermassive black hole sometimes rear-end each other, astronomers are interested in this second case of superluminal motion observed in jets hundreds, thousands of light-years from the source supermassive black hole. This indicates the jets are still moving at nearly the speed of light at distances rivaling the scale of the host galaxy and still contain tremendous energy. Understanding this could help astronomers determine more about the evolution of galaxies as the cosmos ages, including our own Milky Way.

Astronomers are also trying to figure out why galaxy NGC 3862 is one of the few they have detected jets in optical wavelengths? They haven’t been able to come up with any good theories on why some jets are detected in visible light and others aren’t. 

Work goes on

Work at the institute continues. Meyer is currently working on additional videos using Hubble images of other relativistic jets in nearby galaxies to try to detect superluminal motion. This is only possible due to the longevity of the Hubble Space Telescope and ingenuity of engineers and scientists from NASA and the ESA. Hopefully, they could discover more clues to answer these questions and other mysteries gnawing at the corner of my mind.

Watch this video made by Eileen Meyer of the Space Telescope Science Institute (STScI) in Baltimore, Maryland using archival data from two decades of Hubble Space Telescope observations of galaxy NGC 3862.

Read about magnetic lines of force NASA astronomers viewed emanating from a supermassive black hole 900 million light-years from Earth.

Read and learn more about how astronomers study the formation of stars in the Milky Way.

Read about a runaway star discovered traveling across the Tarantula Nebula.

Take the space voyage of NASA.

Read and learn more about relativistic jets here.

Learn more about the discoveries made by the ESA.

Learn more about galaxy NGC 3862 here.

Learn what astronomers have discovered about supermassive black holes.

Discover and learn more about superluminal motion here.

Discover NASA’s Space Telescope Science Institute (STScI).

Take the space journey of the Hubble Space Telescope here.

 

 

 

 

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