**Unique Ultra-Luminous Infrared Galaxy Discovered Behind Cloverleaf Quasar**

*By Dwaipayan Roy | Oct 11, 2025, 05:28 PM*

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**Astronomers Uncover a Rare ULIRG**

An international team of astronomers has made a groundbreaking discovery of an ultra-luminous infrared galaxy (ULIRG) located behind the well-known quasar H1413+117, famously known as the Cloverleaf. This discovery was achieved using the Atacama Large Millimeter/submillimeter Array (ALMA) and has been detailed in the *Monthly Notices of the Royal Astronomical Society*.

ULIRGs are some of the most intense star-forming galaxies in the universe, making this find particularly significant in studying early cosmic star formation.

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**About the Cloverleaf Quasar**

The Cloverleaf quasar is a unique astronomical object characterized by its quadruply-lensed structure and a redshift of approximately 2.56. The recent study, led by Natsuki H. Hayatsu, detected the ULIRG while observing this quasar with ALMA.

According to the researchers, “Dusty, submillimeter-selected galaxies without optical counterparts contribute a non-negligible fraction of the star formation in the early universe.” The discovery of this ULIRG adds valuable insight into these optically dark galaxies.

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**Features of the Newly Discovered ULIRG**

The newly found ULIRG is situated about six arcseconds away from the Cloverleaf quasar and has a higher redshift of around 3.39, indicating it lies even farther away.

Key properties include:
– Molecular mass ranging between 40 to 230 billion solar masses
– Estimated black hole mass of approximately 0.1 billion solar masses
– Extremely high total X-ray luminosity of around 4 × 10^44 erg/s (400 tredecillion erg/s)
– Infrared luminosity estimated at 2.8 trillion times that of our Sun

These massive values underline the galaxy’s extraordinary energetic activity.

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**Gas Dynamics and Evolutionary State**

The molecular gas within this ULIRG appears to be dynamically unsettled. This instability is likely due to a major gas-rich galaxy merger in its early stages. Astronomers believe this galaxy is undergoing a starburst phase fueled by its abundant molecular gas and triggered by the ongoing merger.

The team also suggests that this ULIRG might represent a progenitor phase of hot dust-obscured galaxies (DOGs) or could be evolving toward a phase characterized by naked active galactic nuclei (AGN).

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**The Road Ahead: Future Research**

While this discovery is promising, researchers emphasize the need for further observations focused on the molecular gas within this galaxy to better understand its physical state and confirm its evolutionary stage.

As stated by the team, “To infer the evolutionary stage of such an optically dark galaxy, be it a massive starburst, QSO [quasi-stellar object], or hot DOG, it is essential to clarify the physical state of the gas.”

Future follow-up studies will aim to shed light on these questions, deepening our understanding of galaxy formation and evolution in the early universe.

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*Stay tuned for more updates on this exciting discovery as astronomers continue to explore the mysteries of the cosmos.*
https://www.newsbytesapp.com/news/science/astronomers-discover-rare-galaxy-behind-famous-quasar-using-alma/story