An Australian-led international team of astronomers has reported the discovery of an extremely rare type of galaxy, early in the history of the universe. The galaxy, designated R5519, was discovered using spectroscopic data collected by the WM Keck Observatory in Hawaii and images taken by the Hubble Space Telescope.
R5519 lies nearly 11-billion light years from Earth, meaning that we are now seeing what it looked like almost 11-billion years ago. This is just three-billion years after the start of the universe with the Big Bang.
The galaxy takes the form of an absolutely gigantic ring, with a hole in the middle, like a cosmic doughnut. It has a mass similar to that of our galaxy, the Milky Way. R5519’s central void has a diameter that is two-billion times greater than the distance between the Earth and the Sun.
“It is a very curious object that we’ve never seen before,” states Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions researcher and study lead author Dr Tiantian Yuan. “It looks strange and familiar at the same time.”
“It is making stars at a rate 50 times greater than the Milky Way,” he highlights. “Most of that activity is taking place on its ring – so it truly is a ring of fire.”
The current evidence is that R5519 was formed by an immense collision with another galaxy. Such collisional ring galaxies are very rare, throughout galactic history. R5519 is the only collisional ring galaxy ever found in the early galaxy. As a result, it is set to upset current theories on the earliest formation of galactic structures and on their evolution.
“The collisional formation of ring galaxies requires a thin disk to be present in the ‘victim’ galaxy before a collision occurs,” explains study co-author and Australian National University professor Kenneth Freeman. “The thin disk is the defining component of spiral galaxies: before it assembled, the galaxies were in a disorderly state, not yet recognisable as spiral galaxies. In the case of this ring galaxy, we are looking back into the early universe by 11-billion years, into a time when thin disks were only just assembling. For comparison, the thin disk of our Milky Way began to come together only about nine-billion years ago. This discovery is an indication that disk assembly in spiral galaxies occurred over a more extended period than previously thought.”
The team that discovered R5519 is composed of astronomers from Australia, Belgium, Canada and Denmark. Their discovery was announced in the journal Nature Astronomy.