Unusual Galaxy Prompts Researchers to Rethink How Structures in the Universe Form
Maunakea, Hawaii – 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.”
An animation showing how the ring galaxy formed. Credit: James Josephides, Swinburne Astronomy Productions
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.
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.”
ABOUT ADAPTIVE OPTICS
W. M. Keck Observatory is a distinguished leader in the field of adaptive optics (AO), a breakthrough technology that removes the distortions caused by the turbulence in the Earth’s atmosphere. Keck Observatory pioneered the astronomical use of both natural guide star (NGS) and laser guide star adaptive optics (LGS AO) and current systems now deliver images three to four times sharper than the Hubble Space Telescope at near-infrared wavelengths. AO has imaged the four massive planets orbiting the star HR8799, measured the mass of the giant black hole at the center of our Milky Way Galaxy, discovered new supernovae in distant galaxies, and identified the specific stars that were their progenitors. Support for this technology was generously provided by the Bob and Renee Parsons Foundation, Change Happens Foundation, Gordon and Betty Moore Foundation, Mt. Cuba Astronomical Foundation, NASA, NSF, and W. M. Keck Foundation.
The OH-Suppressing Infrared Imaging Spectrograph (OSIRIS) is one of W. M. Keck Observatory’s “integral field spectrographs.” The instrument works behind the adaptive optics system, and uses an array of lenslets to sample a small rectangular patch of the sky at resolutions approaching the diffraction limit of the 10-meter Keck Telescope. OSIRIS records an infrared spectrum at each point within the patch in a single exposure, greatly enhancing its efficiency and precision when observing small objects such as distant galaxies. It is used to characterize the dynamics and composition of early stages of galaxy formation. Support for this technology was generously provided by the Heising-Simons Foundation and the National Science Foundation.
The Multi-Object Spectrograph for Infrared Exploration (MOSFIRE), gathers thousands of spectra from objects spanning a variety of distances, environments and physical conditions. What makes this large, vacuum-cryogenic instrument unique is its ability to select up to 46 individual objects in the field of view and then record the infrared spectrum of all 46 objects simultaneously. When a new field is selected, a robotic mechanism inside the vacuum chamber reconfigures the distribution of tiny slits in the focal plane in under six minutes. Eight years in the making with First Light in 2012, MOSFIRE’s early performance results range from the discovery of ultra-cool, nearby substellar mass objects, to the detection of oxygen in young galaxies only two billion years after the Big Bang. MOSFIRE was made possible by funding provided by the National Science Foundation. It is currently the most in-demand instrument at Keck Observatory.
ABOUT W. M. KECK OBSERVATORY
The W. M. Keck Observatory telescopes are among the most scientifically productive on Earth. The two, 10-meter optical/infrared telescopes on the summit of Maunakea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometers, and world-leading laser guide star adaptive optics systems.
Some of the data presented herein were obtained at Keck Observatory, which is a private 501(c) 3 non-profit organization operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.
The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the Native Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.