Milky Way ‘Orphans’ Visible To Indigenous Stargazers

A RADIO telescope near Geraldton has identified the remnants of a supernova which exploded about 9000 years ago when it would have been visible to indigenous people in Australia.

University of Melbourne cultural astronomer Duane Hamacher said some Aboriginal traditions described bright new stars appearing in the sky, “but we don’t know of any definitive traditions that describe this particular event”.
However, he said now that astronomers knew when and where the supernova appeared in the sky, they can collaborate with Indigenous elders to match their traditions to the cosmic event.

The Murchison Widefield Array telescope captured a spectacular new view of the centre of the galaxy in which we live, the Milky Way (shown here). The image shows what our galaxy would look like if human eyes could see radio waves.

Curtin University astrophysicist Natasha Hurley-Walker, who is a member of the International Centre for Radio Astronomy Research, created the images using the Pawsey Supercomputing Centre in Perth as part of the GaLactic and Extragalactic All-sky MWA survey, or ‘GLEAM’.

The survey has a resolution of two arc-minutes (about the same as the human eye) and maps the sky using radio waves at frequencies between 72 and 231MHz (FM radio is near 100 MHz).

“Essentially, different objects have different ‘radio colours’, so we can use them to work out what kind of physics is at play,” Dr Hurley-Walker explained, with her colleagues having discovered the remnants of 27 massive stars that exploded into supernovae or stars at the end of their life. These stars would have been eight or more times more massive than our Sun before they self-destruct.

Younger and closer supernova remnants, or those in very dense environments, are easy to spot, and 295 are already known. Unlike other instruments, the WA telescope can find those which are older, further away, or in very empty environments.

Dr Hurley-Walker said one of the newly-discovered supernova remnants lies in an empty region of space, far out of the plane of our galaxy, so despite being quite young, it is also very faint.

“It’s the remains of a star that died less than 9,000 years ago, meaning the explosion could have been visible to Indigenous people across Australia at that time,” she said.

Dr Hurley-Walker said two of the supernova remnants discovered here are unusual “orphans”.

“This is really exciting for us, because it’s hard to find supernova remnants in this phase of life—they allow us to look further back in time in the Milky Way,” she said.

The WA telescope is a precursor to the world’s largest radio telescope, the Square Kilometre Array, which is due to be built in Australia and South Africa from 2021.