Electron acceleration in laboratory bow shock
Description: Laboratory bow shock generated in magnetized plasma-obstacle interaction excites plasma waves, leading to electron acceleration.
Credits: F. Cruz and L. O. Silva, IST Lisbon, Portugal
Scientists from 15 institutes, led by the University of Oxford in the U.K., announced today (March 20, 2018) that they’ve solved the mystery of why comets emit x-rays. Very hot objects like the sun emit x-rays, but comets aren’t hot. In fact, they’re sometimes described as dirty snowballs and are among our solar system’s coldest objects. So what’s the mechanism for x-rays from comets?
The answer comes from experiments performed at the LULI laser facility in Paris, where, these scientists say, they were able to replicate the interaction of comets with the solar wind. The new study is published in the peer-reviewed journal Nature Physics. These scientists’ statement explained:
When comets travel through the solar system they interact with solar radiation, the solar wind and the solar magnetic field. This produces a visible atmosphere or ‘coma’ as well as the observed cometary tail, and in some cases, X-rays. These are generated on the sunward side of the comet where the solar wind impacts the cometary atmosphere, forming a bow shock.
Alexandra Rigby, an Oxford University student who is doing her doctoral research on the project, led the experiment. She explained:
The laser beams are fired onto a plastic foil which explodes, causing a stream of electrons and ions to be expelled forming a high speed flow of ionized gas (plasma) like the solar wind.
To replicate a ‘comet’ in the lab, the researchers placed a solid sphere of material about 1 centimeter (0.4 inches) away from the plastic foil. They fired the laser toward this “comet.” The result, they said, mimicked conditions comets encounter while traveling through our solar system. The researchers found the plasma turbulence heated the electrons in the up-stream region to about a million degrees Celsius (~1.8 million degrees Fahrenheit). They said these hot electrons are responsible for emitting the X-rays from comets, in the presence of a magnetic field.
Gianluca Gregori of Oxford – who led the scientific team – commented:
These experimental results provide direct laboratory evidence that objects moving through magnetized plasmas can be sites of electron heating. This process is common in astrophysics and can take place not only in comets, but also in planetary magnetospheres (as of our own Earth), or even in supernova remnants where the ejected material sends a shock wave into the interstellar gas.
The scientists said it is now, indeed, possible to sensibly replicate astrophysical phenomena in the laboratory and to thereby solve mysteries like this one.
Bottom line: X-rays come from very hot objects, and comets are cold. Yet comets emit x-rays. Researchers used lasers to solve the mystery of x-rays from comets.
Source: Electron acceleration by wave turbulence in a magnetized plasma
from EarthSky http://ift.tt/2HPJo8r
Electron acceleration in laboratory bow shock
Description: Laboratory bow shock generated in magnetized plasma-obstacle interaction excites plasma waves, leading to electron acceleration.
Credits: F. Cruz and L. O. Silva, IST Lisbon, Portugal
Scientists from 15 institutes, led by the University of Oxford in the U.K., announced today (March 20, 2018) that they’ve solved the mystery of why comets emit x-rays. Very hot objects like the sun emit x-rays, but comets aren’t hot. In fact, they’re sometimes described as dirty snowballs and are among our solar system’s coldest objects. So what’s the mechanism for x-rays from comets?
The answer comes from experiments performed at the LULI laser facility in Paris, where, these scientists say, they were able to replicate the interaction of comets with the solar wind. The new study is published in the peer-reviewed journal Nature Physics. These scientists’ statement explained:
When comets travel through the solar system they interact with solar radiation, the solar wind and the solar magnetic field. This produces a visible atmosphere or ‘coma’ as well as the observed cometary tail, and in some cases, X-rays. These are generated on the sunward side of the comet where the solar wind impacts the cometary atmosphere, forming a bow shock.
Alexandra Rigby, an Oxford University student who is doing her doctoral research on the project, led the experiment. She explained:
The laser beams are fired onto a plastic foil which explodes, causing a stream of electrons and ions to be expelled forming a high speed flow of ionized gas (plasma) like the solar wind.
To replicate a ‘comet’ in the lab, the researchers placed a solid sphere of material about 1 centimeter (0.4 inches) away from the plastic foil. They fired the laser toward this “comet.” The result, they said, mimicked conditions comets encounter while traveling through our solar system. The researchers found the plasma turbulence heated the electrons in the up-stream region to about a million degrees Celsius (~1.8 million degrees Fahrenheit). They said these hot electrons are responsible for emitting the X-rays from comets, in the presence of a magnetic field.
Gianluca Gregori of Oxford – who led the scientific team – commented:
These experimental results provide direct laboratory evidence that objects moving through magnetized plasmas can be sites of electron heating. This process is common in astrophysics and can take place not only in comets, but also in planetary magnetospheres (as of our own Earth), or even in supernova remnants where the ejected material sends a shock wave into the interstellar gas.
The scientists said it is now, indeed, possible to sensibly replicate astrophysical phenomena in the laboratory and to thereby solve mysteries like this one.
Bottom line: X-rays come from very hot objects, and comets are cold. Yet comets emit x-rays. Researchers used lasers to solve the mystery of x-rays from comets.
Source: Electron acceleration by wave turbulence in a magnetized plasma
from EarthSky http://ift.tt/2HPJo8r
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