Munich, June 26 With help of a unique "ballistic study" that combines data from ESO's Very Large Telescope and NASA's Chandra X-ray Observatory, astronomers have now solved a long-standing mystery of the Milky Way's particle accelerators.
The study shows that cosmic rays from our galaxy are very efficiently accelerated in the remnants of exploded stars.
Galactic cosmic rays come from sources inside our home galaxy, the Milky Way, and consist mostly of protons moving at close to the speed of light, the "ultimate speed limit" in the Universe.
"It has long been thought that the super-accelerators that produce these cosmic rays in the Milky Way are the expanding envelopes created by exploded stars, but our observations reveal the smoking gun that proves it," said Eveline Helder from the Astronomical Institute Utrecht of Utrecht University in the Netherlands, the first author of the new study.
"You could even say that we have now confirmed the caliber of the gun used to accelerate cosmic rays to their tremendous energies," said collaborator Jacco Vink, also from the Astronomical Institute Utrecht.
"When a star explodes in what we call a supernova a large part of the explosion energy is used for accelerating some particles up to extremely high energies," said Helder.
"The energy that is used for particle acceleration is at the expense of heating the gas, which is therefore much colder than theory predicts," she added.
The researchers looked at the remnant of a star that exploded in AD 185, as recorded by Chinese astronomers.
The remnant, called RCW 86, is located about 8200 light-years away towards the constellation of Circinus (the Drawing Compass). It is probably the oldest record of the explosion of a star.
Using ESO's Very Large Telescope, the team measured the temperature of the gas right behind the shock wave created by the stellar explosion.
They measured the speed of the shock wave as well, using images taken with NASA's X-ray Observatory Chandra three years apart.
They found it to be moving at between 10 and 30 million km/h, between 1 and 3 percent the speed of light.
The temperature of the gas turned out to be 30 million degrees Celsius.
This is quite hot compared to everyday standards, but much lower than expected, given the measured shock wave's velocity. This should have heated the gas up to at least half a billion degrees.
"The missing energy is what drives the cosmic rays," concluded Vink. (ANI)
