A groundbreaking discovery in the realm of astronomy has confirmed the existence of the earliest and most distant black hole known to date. This astonishing black hole, located in a galaxy identified as CAPERS-LRD-z9, boasts a staggering mass of approximately 300 million times the mass of the Sun. Remarkably, this black hole existed a mere 500 million years after the Big Bang, when the Universe was only about 3 percent of its current age.
This discovery also shines a light on a previously enigmatic category of celestial objects known as Little Red Dots (LRDs). These intriguing, small, and bright red objects emerged around 600 million years following the Big Bang. However, they began to vanish less than a billion years later. Recent advancements in technology, particularly the James Webb Space Telescope (JWST), have enabled astronomers to examine these ancient objects from the Cosmic Dawn, the Universe's earliest epochs. During this period, the light reaching JWST has been stretched to longer, redder wavelengths due to its extensive journey through the expanding fabric of spacetime.
The newly identified supermassive black hole at the center of CAPERS-LRD-z9 is classified as an active galactic nucleus (AGN). This designation refers to a bright, rapidly feeding black hole that resides at a galaxy's core. The black hole appears red because it is surrounded by a glowing cocoon of gas and dust, which may give it a striking appearance reminiscent of science fiction. The immense gravity of this supermassive black hole causes the surrounding gas to whirl around at astonishing speeds of approximately 3,000 kilometers (1,864 miles) per second, or about 1 percent of the speed of light.
Astronomers utilize a technique known as spectroscopy to identify the presence of black holes by analyzing the light emitted from the gas surrounding them. This method involves splitting incoming light into its various wavelengths, yielding a spectrum that provides valuable information about the object in question. When gas moves away from an observer, the light waves become stretched and appear redder. Conversely, light waves compress and shift to the blue spectrum when moving toward an observer. These shifts in light reveal crucial details about the object's velocity.
The spectroscopic confirmation of CAPERS-LRD-z9 supports the hypothesis that LRDs may house supermassive black holes. In fact, some black holes can reach up to 10 million solar masses within their first billion years. For context, the supermassive black hole at the center of our own Milky Way galaxy has a mass of about 4 million solar masses. The black holes found in LRDs may not just be supermassive but could also be classified as "overmassive," with mass ratios approaching 10 to 100 percent of the stellar mass of their host galaxies. Specifically, the supermassive black hole in CAPERS-LRD-z9 comprises about half the mass of all the stars within its galaxy, whereas central black holes in more local galaxies typically represent only about 0.1 percent of their stellar mass.
For a size perspective, CAPERS-LRD-z9 is remarkably compact, measuring at most 1,140 light-years wide, comparable to the dimensions of dwarf galaxies that orbit the Milky Way. Researchers propose that there are two primary pathways for a black hole to attain such a massive size within a mere 500 million years of cosmic time. Both scenarios begin with a substantial seed black hole that could either grow at the theoretical upper limit, known as the Eddington rate, starting with around 10,000 solar masses, or begin with a smaller seed of just 100 solar masses that must grow even more rapidly at the super-Eddington rate, fueled by dense gas surrounding it.
These seed black holes might have originated as primordial black holes formed during the Big Bang or from the collapse of Population III stars, the first stars to light up the cosmos. They could also emerge from runaway collisions in dense star clusters or the direct collapse of massive primordial gas clouds. Understanding this growth and formation of black holes is crucial, as it provides insight into the evolution of galaxies.
As researchers delve deeper into the cosmos, they acknowledge the challenges in observing these distant black holes. "We're really pushing the boundaries of what current technology can detect," explains lead author Anthony Taylor, an astrophysicist at the University of Texas at Austin. This research not only enhances our understanding of black holes but also provides evidence that LRDs represent a fleeting phenomenon in the early Universe—potentially a pivotal step in the galactic evolution that may have contributed to the formation of the Milky Way itself.
