Cluster of Stars Harbors a Massive Mystery Source of Cosmic Rays


"This particular source of gamma rays was found towards an unusual cluster of stars which harbors one of the Milky Way's most massive and energetic young stars, a luminous blue variable star called LBV1806-20," says Associate Professor Gavin Rowell, from the University of Adelaide's High Energy Astrophysics Group and leader of Australia's participation in HESS -the High Energy Stereoscopic System (HESS) gamma ray telescopes in Namibia. "The cluster of stars also harbors a rare, extremely magnetic, neutron star known as a magnetar, but we think the gamma ray emission could be linked to the luminous blue variable star.

The multinational team of astronomers involving the University of Adelaide has catalogued over 70 sources of very high energy gamma rays, including 16 previously undiscovered ones, in a survey of the Milky Way using gamma ray telescopes. Gamma rays are the highest energy form of light. They are studied by astronomers and astrophysicists around the world because they can be used to trace the origins of cosmic rays, elusive charged particles which are an important ingredient in the evolution of the Universe.


The results have been published in 14 scientific papers in a special edition of the journal Astronomy and Astrophysics, including details of a particularly intriguing new source of gamma rays.

"If the source is the luminous blue variable star, it is the first time that gamma ray emission has been linked to such a massive star. Many of the other gamma ray emission sources, in this very high energy band, have so far been linked to pulsars or supernova remnants (the remains of an exploding star). This would mean a new kind of gamma ray source, the first discovery of its kind. We haven't, however, completely ruled out an association with the magnetar or the other stars of the cluster yet.

But to be absolutely sure, we'll probably have to wait for far more sensitive gamma ray observations with the Cherenkov Telescope Array, the next gamma ray observatory now under construction in Chile."

Other discoveries in the Milky Way detailed in the special edition include the sharpest image yet of a gamma ray source – a nearby supernova remnant – which will enable researchers to study this object at finer scale than before – and three new 'gamma ray shells' that are possibly examples of a new type of supernova remnant.

"Interestingly, about half the catalogued sources still remain unidentified, an aspect which will inspire astronomers to search for answers using different kinds of telescopes, operating in the radio to the X-ray bands," says Associate Professor Rowell.

The HESS team consists of scientists from Germany, France, the United Kingdom, Namibia, South Africa, Ireland, Armenia, Poland, Australia, the Netherlands, Austria and Sweden.

HESS is a system of four 13-meter diameter and one 28m diameter telescopes sensitive to gamma rays that have 100 billion times more energy than optical light.

The image at the top of the page shows NGC 3603 is an open star cluster and starburst region, surrounded by an H II region (a massive cloud of gas and plasma in which stars are continuously being born), situated in the Carina spiral arm of the Milky Way, about 20,000 light-years away in the constellation Carina.

It is one of the most luminous and impressive young star clusters in the Milky Way, and the densest concentration of massive stars known in the galaxy. Bathed in gas and dust the cluster formed in a huge rush of star formation thought to have occurred around a million years ago. The hot blue stars at the core are responsible for strong ultraviolet radiation and stellar winds, carving out a huge cavity in the gas.

NGC 3603 also harbors  Several blue supergiant stars crowd into a volume of less than a cubic light-year, along with three so-called Wolf-Rayet stars (extremely bright and massive stars that are ejecting vast amounts of material before finishing off in glorious supernovae).

The Daily Galaxy via University of Adelaide

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