Quasars Explained

Quasars represent some of the most luminous entities in the cosmos, believed to be energized by supermassive black holes situated at the centers of galaxies. Typically, these quasars shine about one hundred times brighter than the galaxies they inhabit. Occasionally, the jets emitted from their centers can exceed the size of the host galaxy. Discovered around six decades ago, quasars are thought to arise when light escapes the edge of a supermassive black hole, just before crossing the event horizon. While certain particles are drawn into the black hole, others are propelled away at speeds nearing that of light, forming brilliant jets known as quasars (source: space.com).

Although still largely mysterious to astronomers, quasars are believed to form in areas of space with significantly higher-than-average matter density (source: space.com). Over the past fifty years, nearly 2,000 quasars have been identified, most located billions of light-years from Earth. More than one hundred thousand potential quasar candidates are currently under scrutiny by NASA and the scientific community. Their vast distances afford scientists a unique glimpse into the past, observing these phenomena as they were billions of years ago (source: space.com).

Early Investigations into Quasars

Prior to the launch of the Hubble Space Telescope, understanding of quasars was limited. Many scientists speculated that these objects were isolated stars nestled deep in space. However, the reason behind their intense radiation emissions across various frequencies remained unclear. Moreover, the rapid fluctuations in their luminosity perplexed scientists, as their observed characteristics appeared to contradict established principles.

The Hubble Space Telescope revolutionized the study of these celestial bodies by providing a fresh perspective. It revealed that quasars are not solitary stars but rather central components of distant galaxies.

Scientific Attributes of Quasars

Currently, scientists believe that quasars can emit energy levels hundreds or even thousands of times greater than that of our galaxy, making them among the most energetic objects in the universe. Some of the largest known quasars are estimated to produce energy equivalent to trillions of volts of electricity—surpassing the total energy output of all stars in the Milky Way combined.

Quasars are classified under a category known as "active galactic nuclei" or "AGNs," which encompasses quasars, blazars, and Seyfert galaxies. The unifying factor among these objects is their reliance on supermassive black holes for energy. While some researchers propose that these three types are variations of the same phenomenon, further observation is required to validate this hypothesis.

Quasars also emit strong, non-stellar radio waves and can experience variations in brightness over short timeframes, ranging from days to hours. Their jets, primarily composed of electrons and protons, are expelled into space. The formation of these jets is still under investigation, with some theorists suggesting that strong magnetic fields in the black hole's accretion disk could play a role in their alignment.

The first video titled "What Is A Quasar?" provides an introduction to these fascinating celestial objects, exploring their characteristics and significance in the universe.

Observation of Quasars

Despite being the brightest known entities in the universe, quasars cannot be observed from Earth without telescopes due to their immense distances, which often reach billions of parsecs. However, their brightness allows scientists to use quasars as "background light sources" for studying intervening galaxies and diffuse gas through a technique known as absorption spectroscopy.

Quasars also serve as excellent reference points for measuring cosmic distances. The "International Celestial Reference System" is primarily based on quasars because their great distances make them appear nearly stationary from Earth, enabling accurate position measurements for nearby galaxies and stars.

Currently, the brightest identified quasar from Earth's perspective is 3C 273, located in the Virgo constellation. With an apparent magnitude of 12.8, it can be seen with a medium-sized telescope and possesses an absolute magnitude of -26.7. If placed 33 light-years from Earth, it would shine as brightly as our Sun. Scientists estimate that 3C 273 has a luminosity approximately four trillion times that of the Sun, or nearly one hundred times that of the total light emitted by the Milky Way. Even brighter quasars, such as APM 08279+5255, have been identified, although their brightness varies depending on the angle of their jets as viewed from Earth.

The second video titled "Infinity & Beyond - Episode 20: What are quasars?" delves deeper into the nature of quasars and their role in the cosmos.

The Life Cycle of Quasars

Recent research has focused on the life cycle of quasars to understand their physical properties better. It is theorized that quasars will continue to emit light as long as there is a consistent supply of fuel for their accretion disks. Estimates suggest that quasars consume approximately one thousand to two thousand solar masses annually (source: astronomy.swin.edu.au). Some of the largest quasars are believed to consume enough material to equal 600 Earths every minute. Consequently, quasars are thought to have lifespans ranging from one hundred million to several billion years. Once they deplete their fuel reserves, they essentially "turn off," leaving only the light from their host galaxies visible in the universe.

It is believed that quasars were more abundant during the early universe, although more evidence is needed to confirm this theory as research into their fundamental properties continues.

Types of Quasars

Like black holes, quasars exhibit diversity and can be categorized into various subtypes, including:

• Radio-Loud Quasars: These quasars possess powerful jets that emit high-frequency radio waves, comprising about ten percent of the quasar population.
• Radio-Quiet Quasars: In contrast, these quasars emit weaker radio waves and account for nearly ninety percent of known quasars.
• Broad Absorption-Line (BAL) Quasars: Typically radio-quiet, these quasars exhibit broad absorption lines blueshifted relative to their rest frame, indicating gas flowing outward.
• Type II Quasars: These quasars have obscured accretion disks and emission lines due to dust and gas.
• Red Quasars: Characterized by their reddish color, these quasars are believed to have formed from dust extinction in their host galaxies.
• Optically Violent Variable (OVV) Quasars: Radio-loud quasars with jets directed towards Earth, displaying rapid fluctuations in luminosity.
• Weak Emission-Line Quasars: These exhibit faint emission lines in the ultraviolet spectrum.

Quasars and Stellar Formation

Recent findings have suggested that quasars might also influence star formation, a property previously overlooked. Some researchers, such as David Elbaz from CEA in France, propose that quasars could facilitate the formation of entire galaxies during their lifetimes. Observations of the quasar HE0450–2958 revealed the absence of an accompanying galaxy, while a nearby galaxy produced approximately 350 stars annually, significantly faster than typical galaxies. Scientists hypothesize that the quasar's jets and emissions of gas and dust contribute to this rapid star formation, although further research is necessary to substantiate this theory. The possibility of quasars playing a role in star formation is exciting for the scientific community, as it may reshape our understanding of early cosmic development.

Concluding Remarks

In conclusion, quasars remain a source of intrigue for both amateur and professional astronomers. Their mysterious origins and immense energy levels contribute to their complexity and the scientific community's ongoing research. As technology advances and investigations into the universe's depths continue, new insights about quasars may emerge, potentially illuminating the universe's origins and the formation of neighboring galaxies and stars. Only time will reveal the secrets held by these celestial beacons.