The red arc in this infrared image from NASA's Spitzer Space Telescope is a giant shock wave, created by a speeding star known as Kappa Cassiopeiae.
Roguish runaway stars can have a big impact on their surroundings as they plunge through the Milky Way galaxy. Their high-speed encounters shock the galaxy, creating arcs, as seen in this newly released image from NASA's Spitzer Space Telescope.
In this case, the speedster star is known as Kappa Cassiopeiae, or HD 2905 to astronomers. It is a massive, hot supergiant moving at around 2.5 million mph relative to its neighbors (1,100 kilometers per second). But what really makes the star stand out in this image is the surrounding, streaky red glow of material in its path. Such structures are called bow shocks, and they can often be seen in front of the fastest, most massive stars in the galaxy.
Bow shocks form where the magnetic fields and wind of particles flowing off a star collide with the diffuse, and usually invisible, gas and dust that fill the space between stars. How these shocks light up tells astronomers about the conditions around the star and in space. Slow-moving stars like our sun have bow shocks that are nearly invisible at all wavelengths of light, but fast stars like Kappa Cassiopeiae create shocks that can be seen by Spitzer's infrared detectors.
Incredibly, this shock is created about 4 light-years ahead of Kappa Cassiopeiae, showing what a sizable impact this star has on its surroundings. (This is about the same distance that we are from Proxima Centauri, the nearest star beyond the sun.)
The Kappa Cassiopeiae bow shock shows up as a vividly red color. The faint green features in this image result from carbon molecules, called polycyclic aromatic hydrocarbons, in dust clouds along the line of sight that are illuminated by starlight.
Delicate red filaments run through this infrared nebula, crossing the bow shock. Some astronomers have suggested these filaments may be tracing out features of the magnetic field that runs throughout our galaxy. Since magnetic fields are completely invisible themselves, we rely on chance encounters like this to reveal a little of their structure as they interact with the surrounding dust and gas.
Kappa Cassiopeiae is visible to the naked eye in the Cassiopeia constellation (but its bow shock only shows up in infrared light.)
For this Spitzer image, infrared light at wavelengths of 3.6 and 4.5 microns is rendered in blue, 8.0 microns in green, and 24 microns in red.
Image credit: NASA/JPL-Caltech
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Case Study of the Runaway Star Kappa Cassiopeiae or HD 2905, an Illustration of Dark Matter Accumulation by Objects Speeding Through Space.
A claim made here is that a condensed matter entity traveling through space within or without a galaxy acquires by mutual gravity a certain amount of dark matter, quantity dependent on the mass and speed of the object. The object may be a star as in the example here. The volume of dark matter is nicely outlined in red which is also an indicator of the leading shock wave. Kappa Cassiopeiae, HD 2905, star bow shock wave, Credit NASA, JPL, Caltech
Another entity frequently launched across vast distances in space is the black hole. This may be a stellar black hole that has been expelled from a globular cluster of stars. It may be a cluster of black holes, now itself a nucleus of black holes, that has been dispatched from the central nucleus of a galaxy. Traveling through space, these stars and black holes attract dark matter which forms something like an atmosphere around the object. Rate of accumulation and amount of dark matter depends upon the speed of the body and its total mass. A bow or shock wave develops along the front where dark matter makes contact with the plasma of particles that make up inter or intra galactic space.
As noted elsewhere, it is the accruing ‘weight’ of the dark matter and some friction that slows the runaway star or black hole. In some cases the thing, depending upon its velocity, will remain in the galaxy, and in others it may escape the galaxy. Surrounding most galaxies is a halo of denser dark matter. Almost nothing gets past this barrier. The escapee nucleus of black holes will settle here and begin the construction of a satellite galaxy, making good use of the real matter and dark matter it has acquired. Those caught within the galaxy assemble clusters of new stars.
Worth noting that smaller objects like comets and asteroids can be subject to this ac-cumulation of dark matter. But, because of their smaller mass and slower speeds these are not much affected. Still, their rigidity, especially for asteroids, can work against them. A bow wave, when there is one, can transmit shock waves to the asteroid. Unevenly distributed in space, the density of dark matter can vary from point to point either a little or a lot. This impacts the bow front and this varying force is transmitted to the runaway object. In a star or black hole this doesn’t matter too much because these have a degree of resilience and give. (Should be able to detect these waves of dark matter by observing minute changes in brightness of the runaway star.) But, an asteroid traveling at a high rate of speed could get hammered by variations in the density of dark matter it encounters. For example, density increases around planets, moons, and stars; a contributing factor to the breakup of asteroids
A close watch of objects speeding through the galaxy could tell us a lot about the unseen structure of our Milky Way. K
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