New Delhi: Indian scientists have played a role in the discovery of a huge early-universe structure, known as the Loktak Protocluster, located around 12.6 billion light-years from Earth. The research was led by Manipuri astrophysicist Dr Ronaldo Laishram and using observations from NASA’s James Webb Space Telescope and Japan’s Subaru Telescope.
Some of the structure was seen as it existed just 1.2 billion years after the Universe’s formation and is one of only a handful of events that give astronomers insight into how early galaxies began to take shape in the heart of cosmic history.
Named after Loktak Lake
The protocluster is named after the popular fresh water lake of Manipur-Keibul Lamjao National Park in Loktak Lake, where floating islands known as phumdis are found. Though the researchers described the complex web of nearby galaxy concentrations as vaguely reminiscent in appearance to the characteristic features of the lake.
The title also acknowledges a scientist from Manipur who worked on an international project in astronomy studying the origin and development of giant structures in the cosmos.
Led by Manipuri astrophysicist
Dr Ronaldo Laishram, a Manipur-born astrophysicist and postdoctoral researcher at Japan’s National Astronomical Observatory, led the international research team. In a recent study, published in the journal The Astrophysical Journal Letters.
Astronomers involved in the research included researchers from India, Japan and elsewhere. The study combined wide-field observations from Subaru Telescope with high-resolution infrared capabilities of the James Webb Space Telescope.
A city of young galaxies
A protocluster is an archetypal but comparatively immature cluster of galaxies capable of subsequently undergoing gravitational collapse to become a massive galaxy cluster. Protoclusters are different than mature galaxy clusters in that unlike the relatively stationary and gravitationally bound objects of researchers, protoclusters are still actively assembling under the pull of gravity drawing galaxies and their surrounding matter together.
Scientists described the Loktak Protocluster as a happening young “city of galaxies.” It includes many dense knots of young galaxies stretching across one of the largest observable regions in space.
This finding demonstrates that significant structures in the universe were already forming when it was just a tenth of its current age.
Four concentrations identified
This is composed by four separate overdense regions of galaxies, the so-called Loktak Protocluster. They cover about 65 by 36 comoving megaparsecs, a scale that would be hundreds of millions of light-years in the much expanded universe we see today.
The central region consists of 18 Lyman-alpha-emitting galaxies in a radius of ∼1.5 physical megaparsecs. Almost four times denser than the surrounding field regions in galaxies.
That high density suggests that the region was an essential location for galaxy formation relatively early in the history of the universe.
How the discovery was made
The structure was originally detected through observations made by the Subaru Telescope located in Hawaii. With its wide-field imaging capability, the survey was able to explore a vast area of the far-away universe in search for where young galaxies might be clustered together.
They performed a more detailed analysis of the galaxies using data from the NIRCam instrument aboard the James Webb Space Telescope. The infrared sensitivity of JWST is also critically important for observing light that has been stretched to longer wavelengths during its passage through the continuing expansion of the universe.
From the two datasets combined, the team identified a large-scale protocluster and studied its galaxies population.
Redshift reveals its age
This supramassive black hole prototype is located at a redshift of z = 4.90 within the Loktak Protocluster Redshift is a way of measuring the extent to which, by means of the expension of the universe, light has been stretched out in astronomy.
Higher redshift means that the astronomers are looking at a farther away, and therefore further in time object. The Loktak Protocluster is found at z = 4.9; meaning that it was around when the universe was about ~1.2 Gyr old!
Scientists tend to refer to the distance as 12.6 billion light-years, which is a reasonable approximation of the length of time it took for the light from the structure to make its way — and therefore signify that distance — to us here on Earth. The universe is still expanding so the distance we see now from this part of space is far greater today.
Clues about early galaxy growth
They also dated this giant into the current epoch, calling into question a long-held assumption in astrophysics that the evolution of enormous cosmic structures did not take off until much later in the history of the universe. The early existence of such a large protocluster indicates that dense environments have played an important role in the evolution of galaxies earlier in cosmic time than we had previously recognized.
Galaxies in crowded regions are fed larger reservoirs of gas and dark matter, promoting swift star formation and growth. The galaxy–galaxy interactions and mergers can also play a role in determining their size, structure and star-formation history.
Astronomers have a natural laboratory to study these processes in the Loktak Protocluster.
Comparing dense and quiet environments
One important aspect of the research is the comparison between galaxies inside the protocluster and galaxies in less crowded field regions. This helps scientists determine whether the environment affects the way galaxies form and evolve.
Researchers can compare:
- Galaxy size.
- Shape and morphology.
- Star-formation activity.
- Distribution of young galaxies.
- Density of surrounding matter.
- Frequency of interactions and mergers.
Such comparisons may reveal whether galaxies in dense early environments grew faster or developed different structures from galaxies in more isolated locations.nedispatch
Future massive galaxy cluster
The localization of the protocluster indicates that the Loktak Protocluster will eventually evolve into one of the largest clusters in today’s universe. How it looks today is an early step in a lengthy process of gravitational assembly.
Over billions of years individual concentrations may become bound tighter, as gas and dark matter merge with a larger cluster already containing galaxies. Astronomers investigating the protocluster today can catch a glimpse of those early forming conditions, which will ultimately create the gigantic galaxy clusters we see in our own universe.
Importance of James Webb observations
The ability to observe faint, distant galaxies at nearby infrared wavelengths has revolutionised the understanding of the early universe by JWST. They give us insight into the first generations of galaxies, their star formation and surroundings.
The Loktak Protocluster was observed with a space-based telescope, providing deeper and more comprehensive imaging than is available from ground-based surveys. Subaru’s wide-field data was useful in mapping the large-scale structure while JWST aided in characterising its member galaxies.
India’s contribution to astronomy
This adds to the increasing significance of India in global astrophysics. It also shows how Indian researchers used some of the most advanced astronomical facilities in the world to probe fundamental questions about our universe.
The naming of the structure after Loktak Lake thus imbues the discovery with a regional and cultural sense of place for Manipur. The recognition of the state and a scientist from the Northeast brings international attention to both
A window into cosmic history
Astronomers see what Loktak Protocluster looked like about 7.5 billion years ago when the first massive structures within galaxies were just beginning to form. This first determined interconnected concentrations of up to four ways – which showed that complex cosmic environments were forming just 1.2 billion years after the Big Bang.
Analyzing the galaxies within these structures should reveal how dense environments speed up galaxy growth and how early protoclusters evolve into the behemoth galaxy clusters that we see today.
Thus the finding of the Loktak Protocluster is not only a scientific milestone for India, but also an important step in humankind’s quest to understand how our universe constructed its most massive structures.