Young, Very Hot Stars May Be A New Source Of Gamma Rays

The release of a catalog of more than 70 galactic gamma-ray sources has been accompanied by a flurry of papers. One proposes a young, very hot star might be a powerful gamma-ray emitter, which would force a rethink of ideas about the conditions around one of the rarest categories of stars.

Gamma rays are the highest-energy part of the electromagnetic spectrum, which has radio waves at the opposite end and visible light towards the middle. As such, their astronomical sources include the most powerful objects in the universe, such as neutron stars and the births of black holes. For the last 15 years, the High Energy Stereoscopic System (HESS) has been surveying the Milky Way at extreme gamma-ray frequencies from Namibia.

The results have been reported in Astronomy and Astrophysics, along with 14 papers discussing some of the most interesting new finds. One paper deals with a strong gamma-ray source in a cluster of stars that includes LBV 1806-20, a blue giant star some 20-30 times the mass of the Sun, one of only a dozen luminous blue variable stars in the entire galaxy.

“The cluster of stars also harbors a rare, extremely magnetic, neutron star known as a magnetar,” Dr Gavin Rowell of the University of Adelaide said in a statement. Magnetars are major gamma-ray sources; “but we think the gamma-ray emission could be linked to the luminous blue variable star. 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.”

Rowell explained to IFLScience that the distribution of gamma-ray intensity HESS found closely matches the distribution of radio waves, where LBV 1806-20 is known to be the dominant local source. This makes it, rather than the magnetar, the most likely source. Rowell added that stars similar to LBV 1806-20 have been seen associated with gamma-ray emissions before, but since these stars usually exist in clusters with other extreme objects, such as supernova remnants, astronomers have attributed the emissions to known sources. This case could shake that belief.

LBV 1806-20 has a stellar wind 10,000 times as powerful as the Sun’s. Rowell told IFLScience there was speculation decades ago such winds could accelerate particles to the speeds needed to release gamma rays when they collide. Since then attention has shifted to other possible sources, but Rowell thinks it might be time to revive that work.

Among the associated papers, Rowell highlights one describing three new circular features that are invisible to telescopes operating at other wavelengths. Rowell described these as a mystery, but said they might reflect the energy from supernova remnant shockwaves, possibly indicating a previously unknown stage in the evolution of supernova remnants.

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