From Keck Observatory: “Astronomers See ‘Cosmic Ring of Fire,’ 11 Billion Years Ago”

Keck Observatory, operated by Caltech and the University of California, Maunakea Hawaii USA, 4,207 m (13,802 ft)

From Keck Observatory

May 25, 2020
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An artist’s impression of the ring galaxy. Credit: James Josephides, Swinburne Astronomy Productions

A composite image of the ring galaxy R5519 compiled from single-color images taken by the Hubble Space Telescope. Credit: Tiantian Yuan/Hubble Space Telescope

NASA/ESA Hubble Telescope

Astronomers have captured an image of a super rare type of galaxy – described as a “cosmic ring of fire” – as it existed 11 billion years ago.

The galaxy, which has roughly the mass of the Milky Way, is circular with a hole in the middle, like a titanic doughnut; its discovery is set to shake up theories about the earliest formation of galactic structures and how they evolve.

The study, which includes data from W. M. Keck Observatory on Maunakea in Hawaii, is published in today’s issue of the journal Nature Astronomy.

“It is a very curious object that we’ve never seen before,” said lead researcher Tiantian Yuan, from Australia’s ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D). “It looks strange and familiar at the same time.”

The galaxy, named R5519, is 11 billion light-years from the Solar System. The hole at its center is truly massive, with a diameter two billion times longer than the distance between the Earth and the Sun. To put it another way, it is three million times bigger than the diameter of Pōwehi, the supermassive black hole in the galaxy Messier 87, which in 2019 became the first ever to be directly imaged.

“It is making stars at a rate 50 times greater than the Milky Way,” said Yuan, who is an ASTRO 3D Fellow based at the Centre for Astrophysics and Supercomputing at Swinburne University of Technology, in the state of Victoria. “Most of that activity is taking place on its ring – so it truly is a ring of fire.”

To identify the unusual structure, Yuan worked with colleagues from around the U.S., Australia, Canada, Belgium and Denmark, using Keck Observatory’s adaptive optics combined with its OH-Suppressing Infrared Imaging Spectrograph (OSIRIS), as well as the Observatory’s Multi-Object Spectrograph for Infrared Exploration (MOSFIRE) to gather spectroscopic data of the ring galaxy. The team also used images recorded by NASA’s Hubble Space Telescope.


Keck/MOSFIRE on Keck 1, Mauna Kea, Hawaii, USA

The evidence suggests R5519 is a type known as a “collisional ring galaxy,” making it the first one ever located in the early universe. There are two kinds of ring galaxies. The more common type forms because of internal processes. The other type forms from immense and violent collisions with other galaxies.

In the nearby “local” universe, collisional ring galaxies are 1000 times rarer than the internally created type. Images of the much more distant R5519 stem from about 10.8 billion years ago, just three billion years after the Big Bang. They indicate that collisional ring galaxies have always been extremely uncommon.

ASTRO 3D co-author Ahmed Elagali, who is based at the International Centre for Radio Astronomy Research in Western Australia, said studying R5519 would help determine when spiral galaxies began to develop.

“Further, constraining the number density of ring galaxies through cosmic time can also be used to put constraints on the assembly and evolution of local-like galaxy groups,” said Elagali.

Another co-author, Kenneth Freeman, Duffield Professor of Astronomy at the Australian National University, said the discovery has implications for understanding how galaxies like the Milky Way formed.

“The collisional formation of ring galaxies requires a thin disk to be present in the ‘victim’ galaxy before the collision occurs,” he explained. “The thin disk is the defining component of spiral galaxies: before it assembled, the galaxies were in a disorderly state, not yet recognizable as spiral galaxies.”

Freeman added, “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.”

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The W. M. Keck Observatory operates the largest, most scientifically productive telescopes on Earth. The two, 10-meter optical/infrared telescopes on the summit of Mauna Kea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometer and world-leading laser guide star adaptive optics systems. Keck Observatory is a private 501(c) 3 non-profit organization and a scientific partnership of the California Institute of Technology, the University of California and NASA.

Today Keck Observatory is supported by both public funding sources and private philanthropy. As a 501(c)3, the organization is managed by the California Association for Research in Astronomy (CARA), whose Board of Directors includes representatives from the California Institute of Technology and the University of California, with liaisons to the board from NASA and the Keck Foundation.

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