SALT helps to unveil a record-breaking cosmic blast

January 20th, 2016, Published in Articles: EE Publishers, Articles: EngineerIT

 

A collaboration of telescopes, including a major contribution by the Southern African Large Telescope (SALT) in Sutherland, Africa’s giant eye on the universe, has unveiled a cosmic explosion about 200 times more powerful than a typical supernova, events which already rank amongst the mightiest outbursts in the universe. It was more than twice as luminous as the previous record-holding supernova.

SALT is the largest single optical telescope in the southern hemisphere and among the largest in the world. It has a hexagonal primary mirror array 11 metres across, comprising 91 individual 1 m hexagonal mirrors. With the Square Kilometre Array (SKA) so much in focus, SALT tends to be in the back ground yet it makes major contributions to astronomy.

An artist's impression of the record-breaking powerful, superluminous supernova ASASSN-15lh as it would appear from a planet located 10,000 light years away in the host galaxy of the supernova. (Credit: Beijing Planetarium / Jin Ma)

An artist’s impression of the record-breaking powerful, superluminous supernova ASASSN-15lh as it would appear from a planet located 10,000 light years away in the host galaxy of the supernova. (Credit: Beijing Planetarium / Jin Ma)

To prove the record breaking nature of this supernova explosion its distance had to be established. This was achieved with spectroscopic observations taken by SALT. “Upon seeing the spectral signatures from SALT and realising that we had discovered the most powerful supernova yet, I was too excited to sleep the rest of the night,” said Subo Dong, an astronomer and a Youth Qianren Research Professor at the Kavli Institute for Astronomy and Astrophysics (KIAA) at Peking University.

At its peak intensity, the explosion, called ASASSN-15lh, shone with 570 billion times the brightness of the sun. This is approximately 20 times the entire output of the 100 billion stars comprising our Milky Way galaxy.

ASASSN-15lh is amongst the closest superluminous supernovae ever found, at around 3,8-billion light years away. Given its exceptional brightness and closeness, ASASSN-15lh might offer key clues in unlocking the secrets of this baffling class of celestial detonations.

ASASSN-15lh is the most powerful supernova discovered in human history. “The explosion’s mechanism and power source remain shrouded in mystery because all known theories meet serious challenges in explaining the immense amount of energy ASASSN-15lh has radiated”’ Dong said.

ASASSN-15lh was first glimpsed in June 2015 by twin telescopes with 14 cm diameter lenses in Cerro Tololo, Chile, conducting the All Sky Automated Survey for SuperNovas (ASAS-SN), an international collaboration headquartered at the Ohio State University. These two tiny telescopes sweep the skies to detect suddenly appearing objects like ASASSN-15lh that are intrinsically very bright, but are too far away for human observers to notice

To know for sure how luminous ASASSN-15lh was, a measurement of its distance was required. This was determined with spectroscopic observations by Dong’s colleague Saurabh Jha of Rutgers University using the Southern African Large Telescope (SALT). “SALT and its queue schedule observing are ideal for rapidly following up transient events like ASASSN-15lh,” explained Jha.

To clear up where exactly ASASSN-15lh is located, as well as numerous other mysteries regarding it and its hyper-kinetic ilk, the research team has been granted valuable time this year on the Hubble Space Telescope. With Hubble, Dong and colleagues will obtain the most detailed views yet of the aftermath of ASASSN-15lh’s stunning explosion. In concert, Jha has continued to use SALT to obtain spectroscopic follow-up observations to analyse the composition and structure of the explosion as it progresses, including making use of special “Director’s Discretionary Time” awarded to study this unique event.

One of the best hypotheses is that superluminous supernovae’s stupendous energy comes from highly magnetised, rapidly spinning neutron stars called magnetars, which are the leftover, hyper-compressed cores of massive, exploded stars. But ASASSN-15lh is so luminous that this compelling magnetar scenario falls short of the required energies. “The honest answer is at this point that we do not know what could be the power source for Ah,” said Dong. “ASASSN-15lh may lead to new thinking and new observations of the whole class of superluminous supernova.”

The Southern African Large Telescope (SALT) in Sutherland. (Credit: SALT / Janus Brink)

The Southern African Large Telescope (SALT) in Sutherland. (Credit: SALT / Janus Brink)

SALT is situated at the South African Astronomical Observatory (SAAO) field station near Sutherland, in the Northern Cape province, about 400 km from Cape Town. SALT is funded by a consortium of international partners from South Africa, the United States, Germany, Poland, India, the United Kingdom and New Zealand. The construction phase was completed at the end of 2005 and from 2006 to 2009 it entered a period of commissioning and performance verification. Observing has been in full swing since September 2011 and the telescope is finally realising its huge potential as Africa’s Giant Eye on the Universe.

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