Study finds link between dust and radio emission in quasars

Astronomers have uncovered a remarkable connection between the quantity of dust enveloping supermassive black holes and the intensity of radio emissions in brilliantly luminous galaxies.

An international team of astronomers, spearheaded by Newcastle University and Durham University in the UK, harnessed fresh data from the Dark Energy Spectroscopic Instrument (DESI), currently undertaking a five-year survey of the universe’s vast structures. This endeavor involves capturing optical spectra for approximately 3 million quasars—exceptionally radiant galaxies fueled by supermassive black holes.

Their investigation disclosed a pattern: quasars enveloped in more dust, rendering them reddish in appearance, exhibited stronger radio emissions when contrasted with their counterparts lacking dust, appearing in a vivid blue hue. These findings are detailed in the Monthly Notices of the Royal Astronomical Society.

Nearly every known galaxy harbors a supermassive black hole at its core, with masses that can span millions to billions of times that of our sun. Some galaxies possess substantial matter at their cores, nourishing and augmenting these supermassive black holes, rendering them exceptionally energetic and “active.”

The most potent among these active galaxies are classified as “quasars,” standing as some of the most luminous entities in the cosmos. The majority of quasars radiate a vibrant blue light, attributable to the luminous disk of matter encircling and sustaining the central supermassive black hole, especially bright in optical and ultraviolet wavelengths.

Yet, astronomers have identified a significant segment of quasars that exhibit a deep red hue, although the true nature of these phenomena remains somewhat elusive.

To gain insights into the physics governing these crimson quasars, “spectroscopic” measurements are indispensable. These measurements analyze quasar light across a spectrum of wavelengths, shedding light on the quantity of dust enshrouding the central region. Concurrently, the observation of radio emissions from quasars offers a window into the energy dynamics of the central supermassive black hole—whether it is propelling formidable “winds” or “jets” that may influence the surrounding galaxy.

Understanding the mysteries of red quasars

In a groundbreaking study led by Dr. Victoria Fawcett, formerly of Durham University and now with Newcastle University, spectroscopic observations from the Dark Energy Spectroscopic Instrument (DESI) have been harnessed to assess the degree of dust (reddening) in approximately 35,000 quasars and connect it to their observed radio emissions. The research reveals that DESI is adept at detecting exceptionally red (dusty) quasars, a feat that surpasses similar previous spectroscopic surveys, such as the Sloan Digital Sky Survey (SDSS). Moreover, it unveils that quasars exhibiting a deeper red hue are significantly more likely to boast robust radio emissions compared to their conventionally blue counterparts.

Dr. Fawcett expressed her excitement, noting the remarkable quality of DESI data and the identification of thousands of these previously elusive red quasars. This study, she believes, consolidates various elements in our comprehension of red quasars, conclusively linking quasar dust to their radio emissions. It represents, in her view, the most compelling evidence to date that red quasars play a pivotal role in the evolutionary processes of galaxies.

The connection between reddening and radio emissions is likely attributed to potent gas outflows propelled from the supermassive black hole, which collide with the surrounding dust, instigating shocks and subsequent radio emissions. These outflows eventually disperse all the dust and gas within the galaxy’s central region, unveiling a blue quasar and diminishing radio emissions.

This narrative aligns with the emerging concept that red quasars represent a youthful, “blow-out” phase in the life cycle of galaxies. Consequently, red quasars might hold profound significance in unraveling the intricate tapestry of galaxy evolution.

Dr. Fawcett acknowledges that unanswered questions persist regarding red quasars, particularly in determining whether black hole winds or radio jets are the ultimate drivers of heightened radio emissions. Nonetheless, with the DESI red quasar dataset poised for expansion in the coming survey years, she expresses confidence in the imminent full comprehension of the nature of these enigmatic cosmic phenomena.

Source: Newcastle University

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