When the James Webb Space Telescope (JWST) began operations, one of its earliest surveys was of galaxies that existed during the very early universe.
In December 2022, these observations revealed multiple objects that appeared as “little red dots” (LRDs), fueling speculation as to what they might be.
Each model has significant implications for how these galaxies subsequently evolved to become the types of galaxies observed more recently.
Their theory would unify these two interpretations by suggesting that they represent different evolutionary stages of these early galaxies.
As Escala noted, their theory is supported by essentially the same evidence as the BH and galaxy interpretation.
The James Webb Space Telescope (JWST) conducted one of its first surveys of galaxies from the very early universe when it first started up. These observations in December 2022 showed several objects that looked like “little red .s” (LRDs), which stoked conjecture about what they might be. There is still disagreement regarding the composition of these objects and what causes their extreme redness, despite the general agreement that they are compact, early galaxies. The “stellar-only” theory, on the one hand, contends that the red color of LRDs is due to their dense star and dust populations.
This suggests that they might resemble the “dusty galaxies” that are currently being seen in the universe. Conversely, the “MBH and galaxy” theory suggests that LRDs are early instances of active galactic nuclei (AGNs), which are present in the modern universe. The way these galaxies later changed to become the kinds of galaxies seen more recently is significantly impacted by each model.
The various scenarios were examined by a global team of astronomers in a recent paper published on the arXiv preprint server. They came to the conclusion that LRDs started out as “stellar only” galaxies, which subsequently gave rise to the seeds of the modern supermassive black holes (SMBHs) at the center of galaxies.
Professor of astronomy Andres Escala of the Universidad de Chile led the study. Colleagues from Yale University, Sapienza University of Rome, and the University of Heidelberg’s Astronomical Computing Institute joined him. The Astrophysical Journal is presently reviewing the arXiv paper “On the Fate of Little Red Dots,” which describes their findings.
Because LRDs have some traits in common with contemporary astronomical objects, but with some significant differences, their discovery has baffled astronomers. For example, the “stellar only” interpretation suggests that LRDs are dusty, highly star-forming galaxies with extremely dense core regions. One of the most distinctive characteristics of LRDs is their red appearance, which is explained by this theory. They would cause long-term instability, though, because the widths of their hydrogen spectral line emissions (Balmer-series lines) imply velocity dispersions that are significantly higher than those seen in early galaxies.
Conversely, the existence of broad Balmer emission lines, which are indicative of massive black holes at their centers, supports the MBH interpretation. The black holes believed to be present are overmassive in relation to their host galaxies, and the majority of LRDs do not seem to emit a sizable amount of X-ray radiation, which is typical for quasars. But according to Professor Escala’s email to Universe Today, these two theories are thought to be the most plausible for two reasons.
Strong evidence supports these two popular interpretations, which are also regarded as ‘less exotic’ than the alternatives. However, at low redshift values (z), LRDs remain objects that have never been observed before. The BH and galaxy interpretation is advantageous since these objects have different “weights” but are “normal” in the local universe. “…
“For LRDs, the MBH mass would be 10 percent of the host galaxy (a factor of 100 larger) whereas in the local universe it is 0–1% of the galactic mass. According to the stellar-only interpretation, LRDs could be just another galaxy in the universe, but with one significant difference: they are at least ten times smaller than the smallest galaxies that have been observed so far (100pc vs. 1kpc) and with a significantly greater mass. “.
On the other hand, Escala and his associates looked at how LRDs might change to accommodate the BH and galaxy interpretation after starting with the stellar-only interpretation. By arguing that these two interpretations reflect distinct evolutionary stages of these early galaxies, their theory would reconcile them. Escala pointed out that the evidence for their theory is nearly identical to that of the BH and galaxy interpretation. This includes how, in the more recent universe, quasars are more detectable than LRDs in X-rays.
“The absence of X-rays essentially indicates that the majority of LRDs are still in the early phases of the evolutionary path that we suggest in our paper. It is possible that LRDs can only be seen in their early stages, evolving later to systems (or parts of them) more akin to those seen at lower redshifts. This is supported by the fact that they are transitory, only occurring in the universe between z=8 and 4, or 10% of the universe’s age. “.
Since the extreme densities of LRDs suggest that a significant portion of their inner regions will eventually form a massive black hole that will be over-massive with respect to the host, even under the stellar-only interpretation, their theory asserts that LRDs will eventually host an MBH. A more thorough explanation for Webb’s observations of the early universe is provided by this evolutionary approach to LRDs. The recent discovery of these extremely compact and deep red galaxies has put our current models of cosmology and galactic evolution to the test, and this could have a big impact. Escala said:.
Accordingly, LRDs are most likely the best locations for MBH formation. Even if these systems are made entirely of stars, our research suggests that they would unavoidably have a tendency to form MBHs and cannot be stable, at least not in their inner regions. Considering that the formation of MBHs is one of the most unsolved issues in structure formation and cosmology, LRDs will serve as locations for newly formed or ongoing MBHs in all of the scenarios that have been suggested. “..”.
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