Chapter 1: Understanding Cold Quasars

This artistic rendering illustrates a dynamic quasar that has cleared the center of its galaxy of gas and dust, with winds now sweeping toward the outer regions. Eventually, this galaxy will be devoid of gas and dust, leaving only a radiant blue quasar behind. (Michelle Vigeant)

Recent research into “cold quasars” indicates that our understanding of galaxy demise and the behavior of supermassive black holes may require significant revision.

Allison Kirkpatrick, an assistant professor of physics and astronomy at the University of Kansas, has identified “cold quasars” — galaxies that possess a significant amount of cold gas and are capable of forming new stars despite hosting a quasar at their core. This groundbreaking discovery challenges previously held beliefs about galaxy maturation and suggests a previously unrecognized stage in the lifecycle of galaxies.

A quasar, short for “quasi-stellar radio source,” is essentially a supermassive black hole actively consuming matter, resulting in the formation of an accretion disk as gas spirals inward. The extreme conditions within these disks generate vast quantities of electromagnetic energy, often outshining entire galaxies by hundreds of times.

Kirkpatrick elaborates: “The gas being pulled into the black hole heats up, emitting X-rays. The wavelength of emitted light directly correlates to temperature. For instance, humans emit infrared light, while X-ray emissions indicate some of the hottest phenomena in the universe.”

As gas accretes at relativistic speeds, it generates a magnetic field that can become twisted, leading to jets of material shooting away from the black hole, much like solar flares.

Kirkpatrick notes: “These jets effectively cut off the gas supply to the galaxy, halting new star formation. Once a galaxy ceases to create stars, we refer to it as a passive dead galaxy.”

However, in her observations, about 10% of galaxies with an active supermassive black hole still retain a supply of cold gas and continue to form new stars.

Kirkpatrick shared her findings, titled “A New Population of Cold Quasars,” at the annual meeting of the American Astronomical Society in St. Louis, Missouri, on June 12. She remarked, “This is intriguing in itself.

“This diverse group includes galaxies with clear signs of merging, some resembling the Milky Way with distinct spiral arms, while others are more compact. Among this varied group, we identified a unique subset — about 10% — that is exceptionally distinct.”

This latter category consists of compact, luminous blue sources, which should typically be devoid of star-forming material, suggesting a transition toward a passive elliptical galaxy. Despite this, Kirkpatrick's team found substantial amounts of cold gas in these galaxies, which she terms “cold quasars.”

She hypothesizes that these cold quasars represent a brief, yet to be recognized, phase in the final stages of a galaxy’s life cycle.

Kirkpatrick continues: “These galaxies are rare because they are in a transition phase — we’ve detected them just before star formation is completely quenched, making this transition period likely very brief.”

Kirkpatrick and her team first pinpointed these intriguing objects in a region of the Sloan Digital Sky Survey, the most comprehensive digital map of the universe available, known as Stripe 82. They then reanalyzed this region using the XMM Newton telescope, targeting the x-ray spectrum. “X-rays serve as key indicators of active black holes. Following this, we surveyed with the Herschel Space Telescope, which can identify dust and gas in the host galaxy. We chose galaxies that appeared in both x-ray and infrared observations.”

Her findings provide a new perspective on how star formation quenching occurs in galaxies, challenging long-held beliefs about quasars.

Kirkpatrick further explains: “We were already aware that quasars undergo a dust-obscured phase. We knew they experience a heavily concealed phase where dust envelops the supermassive black hole — referred to as the red quasar phase.

“However, we’ve now identified this unique transitional phase that was previously unknown. If you told someone you had discovered a luminous blue quasar with significant dust and gas, alongside active star formation, they might have dismissed it as impossible.”

Looking forward, Kirkpatrick aims to determine whether this cold quasar phase is characteristic of specific types of galaxies or applies universally.

She states: “We previously thought that the progression involved a growing black hole becoming enshrouded in dust and gas, eventually expelling that material and becoming a luminous blue object. We assumed that when it expelled its own gas, it would also eliminate the host gas. Yet, in these cases, they have expelled their own dust, appearing blue, but have not yet ejected the dust and gas from their host galaxies.”

This research implies the existence of a transition phase — Kirkpatrick suggests a duration of around 10 million years, which is exceptionally brief on cosmic timescales, making it challenging for astronomers to observe.

Kirkpatrick concludes: “We are conducting a blind survey to discover objects we weren’t actively searching for. Finding these objects could suggest this phenomenon occurs in every galaxy.”

Original research was funded by NASA and the National Science Foundation, and presented at the 234th meeting of the American Astronomical Society.

Chapter 2: The Impact of Quasars on Galaxy Formation

The first video, "Unbelievable Quasar Killed All Galaxies Within 16 Million Light Years," explores the dramatic effects quasars have on surrounding galaxies, revealing how they can influence star formation across vast distances.

The second video, "The Black Hole That Kills Galaxies - Quasars," delves into the mechanisms by which quasars can extinguish star formation in their host galaxies, providing insights into their power and reach.