Three exceptional objects discovered in nearby galaxy
An international team of scientists, including Dr Jacco Vink of the University of Amsterdam, has discovered three exceptional objects in one of the neighbouring galaxies of our Milky Way. They found a superbubble, a pulsar wind nebula and the remnants of a supernova in the Large Magellanic Cloud. The team published their findings on 23 January in Science.
Superbubble 30 Dor C
The superbubble is the biggest surprise of the three discoveries. It is a vast area in which many stars are formed and explode. Stellar winds and explosions blow away the gas that is present, creating a void, known as a bubble. Team member Dr Jacco Vink of the Anton Pannekoek Institute (API) and the GRAPPA research priority area at the Faculty of Science: ‘Some theories suggest that this is an ideal environment for particles to accelerate to extremely high energies. The fact that we have now observed high-energy gamma radiation from such a bubble for the first time seems to confirm these theories.’
Each new exploding star in the bubble creates a shock wave which travels at thousands of kilometres per second and continues for thousands of years. In 30 Dor C, the name of the superbubble, the shock wave has already expanded over an area as big as 150 light years across. Vink: ‘The high speed and long duration of this shock wave is ideal for driving particles to higher energies than we can create here on Earth in the LHC particle accelerator at CERN.’
Pulsar wind nebula N 157B
The newly discovered pulsar wind nebula N 157B seems in many respects like a twin sister to the Crab Nebula in our own Milky Way. A big difference is that the new nebula emits about ten times more gamma radiation. This is probably because about a thousand stars have formed close to the new nebula in the past four million years which give off a lot of light. The particles in the pulsar wind nebula convert this light into gamma radiation.
Remnants of supernova N132D
The third discovery, the remnants of supernova N 132D, presents the researchers with a new puzzle. The star exploded thousands of years ago but is still emitting high-energy gamma radiation. This goes against the trend whereby old supernova remnants cease to emit high-energy gamma rays. Vink: ‘It seems likely that this supernova remnant is not too old to still be producing gamma radiation, but only just. That makes it an interesting object to watch, as it allows us to study when supernova remnants stop producing gamma rays.’
HESS Collaboration
The astronomers had their telescopes pointed on the Large Magellanic Cloud, an irregular galaxy that is visible from the southern hemisphere. They used the High Energy Stereoscopic System for their observations (the acronym HESS was chosen as a tribute to Viktor Hess, the German physicist who discovered cosmic radiation). The five telescopes in the array are located in the Namibian desert and have been linked together since 2012. In the foreseeable future, astronomers hope to build and connect 120 telescopes worldwide. The Netherlands is a participant in this project, the Cherenkov Telescope Array.
Publication details
'The exceptionally powerful TeV γ-ray emitters in the Large Magellanic Cloud', H.E.S.S. Collaboration (incl Dr Jacco Vink), Science 347, p. 406-412, Jan 23, 2015.