A Natural Particle Accelerator with a Quadrillion Kilometer Length

manatee nebula xmmnewton
X-rays (shown in yellow, magenta, and cyan) superimposed on visible light (green) and radio wave (red) observations of the Manatee Nebula show that particles are bubbles of matter accelerated to incredible speeds, creating high-energy X-rays. . Photograph: S. Safi-Harb et al (2022)

A Manatee Nebula, 650 light-years across, emits incredibly fast subatomic particles, and we don't know why, but we know where they came from.

A massive gas cloud located in space about 18.000 light-years away is known as Westerhout 50. This is the remnant of a supernova, which is gas that has expanded since a star exploded long ago. But strange. For starters, it's elongated and forms a rough oval measuring 350 x 650 light years or 3,3 x 6,2 quadrillion kilometers, much larger than most other remnants!

manateenebula wise
Also called the Manatee Nebula, Westerhout 50 is seen by the WISE spacecraft in infrared (red) as well as at radio wavelengths (green) versus stars. Photograph: NRAO/AUI/NSF, K. Golap, M. Goss; NASA's Wide Field Survey Explorer (WISE)

In fact, it looks like a sea cow swimming past us when seen on radio waves, giving rise to this nickname.

The Manatee Nebula got its name because when seen on radio waves, it looks slender and structured and actually resembles a sea cow swimming past us.

It has a strange black hole at its center. What remains of the star that exploded to form the nebula is known as SS 433. The star's outer layers were blown up, and its enormous core collapsed to form a black hole. It orbits a star in a binary system so close to the black hole that the star is torn apart by the black hole's strong gravity. As the material sinks towards the black hole, it creates a heated disk that spins around it.

The disk is filled with powerful magnetic fields that twist like twin tornadoes centered above and below the black hole. This magnetic field causes material to be dragged up and away from the disk and then accelerated to about 1/4 the speed of light. Astronomers call these "jets," which are twin rays that look like searchlights for lighthouses.

Strangely enough, they don't come out of the black hole right away. The disk of matter is pulled and torqued by the gravity of the companion star, causing the disk to become nutty and begin to wobble slightly. As a result of this gradual change of direction, known as precession, the jets actually form huge spirals like a corkscrew.

ss vla
The corkscrew beams of matter shoot away from SS 433, apparently spiraling as the disk of matter orbiting the black hole twists and changes the direction the beams are aimed at. Photograph: B. Saxton from data provided by RM. Hjellming, KJ Johnston, NRAO/AUI/NSF

Surprisingly, Manatee emitted high-energy X-rays produced when electrons were accelerated to truly mind-blowing energies of 300 to 450 tera-electonVolts. It has the same energy as a small raindrop falling from the sky.

This may seem trivial, but an electron has this much energy. Given that there are sextillions of electrons in a drop of water, whatever energizes the electrons in the Manatee nebula gives them a billion trillion times more energy than they would normally have when they lay there. Therefore, it is many.

Since X-rays in the nebula are the physical manifestation of particle acceleration, it would be helpful to know where they came from. Early observations failed to answer this question, but more recent observations with the help of the space-based XMM-Newton and the Chandra X-ray Observatory have made significant progress in understanding this physical process.

Surprisingly, they show that X-rays are not emitted, at least not directly, from black hole SS433. Instead, the X-rays originate from a diffuse, splashing-looking structure resembling a fountain that begins about 100 light-years east of the black hole.

manatee nebula xmmnewton
X-rays superimposed on visible light (green) and radio wave (red) observations of the Manatee Nebula (shown in yellow, magenta, and cyan) show that particles are bubbles of matter accelerated to wild speeds, creating high-energy X-rays. . Photograph: S. Safi-Harb et al (2022)

This is actually quite interesting right now. Note that most supernova remnants are roughly round, whereas Manatee is elliptical. The elongation of the gas turned out to coincide with the orientations of the black hole's jets, and it is quite possible that the material ejected from SS433 is what gives the much larger nebula its elliptical shape by expanding it along an axis.

We know that gas expands at varying rates in supernova remnants, and that occasionally a faster-moving gas cloud will collide with a slower-moving cloud.

As a result, both are compressed and form the wonderful leaves and filaments we observe in the Manatee Nebula.

However, large shock waves are also produced. Subatomic particles such as electrons can become trapped in the magnetic fields of gas clouds due to complex physics, and particles can be pushed to extremely high velocities as the clouds collide. This type of electron collides with a photon of light (we call this inverse Compton scattering), which is then pumped into extremely high energies such as X-rays or even gamma rays.

This might help explain what's going on; When the black hole jet collides with pre-existing supernova gas, it produces incredibly powerful shock waves. When electrons are caught in these shock waves, they are greatly excited, producing the X-rays observed by XMM-Newton.

It's a fascinating story, but it leaves out a lot of information, especially how the particles got to such high energy. Models show that this is difficult, so there could be much more here. However, it's a good place to start.

I can still see the excitement in the astronomy community when SS433 was first found and later attributed to the jets that followed its strange behavior. Decades later, we're still learning unusual behavior from this beast. But isn't that what makes it all so enjoyable? There is always more to learn about the enormous space manatees sculpted by active black holes emitting radiation and particles.

source: syfy


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