SALT astronomers make an exciting discovery

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Cape Town – The Southern African Large Telescope (SALT) in Sutherland has discovered a binary star system in the Hourglass Nebula, one of the most famous nebulae captured by the Hubble Space Telescope.

“A total of 26 SALT measurements were taken that detected the small movements of the central star towards or away from us caused by the gravity of a second companion star,” said SALT astronomer Dr Brent Miszalski from the South African Astronomical Observatory (SAAO).

“This Doppler or “wobble” method, that can also be used to find planets around other stars, revealed a hidden companion orbiting the central star every 18.15 days.”

Dr Miszalski led an international team of astronomers, who used SALT to peer into the “sparkle” of the eye of the Hourglass Nebula.

The Hourglass Nebula consists of two hourglass-shaped lobes of gas and what appears to be an eye staring right back at us. Shells of gas form the eye surrounding the hot central star that illuminates the nebula like a neon sign.

According to SAAO, astronomers have long suspected the peculiar nebula to be formed by two interacting stars in a binary system, but until now no one could prove it. The SALT discovery of two stars orbiting each other every 18.15 days in the Hourglass Nebula firmly settles the debate and gives new insights into how a wide variety of close binary stars and hourglass-shaped nebulae may form.

“The combination of SALT’s enormous 11-metre mirror, highly sensitive instrumentation and flexible queue-scheduled operations was fundamental to making this difficult, cutting-edge discovery,” said Dr Miszalski, who added that they will continue searching other nebulae for new binary systems to gain more insights into their complex origins.

While astronomers still do not quite understand how hourglass-shaped nebulae form, the discovery of a binary in the Hourglass Nebula considerably strengthens the long suspected, but difficult to prove, connection between binary stars and hourglass-shaped nebulae.

The study, titled “SALT HRS discovery of the binary nucleus of the Etched Hourglass Nebula MyCn 18”, was recently accepted for publication in the Publications of the Astronomical Society of Australia (PASA) journal and is available from https://arxiv.org/abs/1805.07602.

The work was the result of a collaboration between astronomers at SAAO and SALT in South Africa, the Nicolaus Copernicus Astronomical Center in Poland, and the Katholieke Universiteit Leuven in Belgium.

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