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.
Galaxies from the very early universe were one of the first surveys conducted by the James Webb Space Telescope (JWST) when it first started up. These observations in December 2022 uncovered several objects that looked like “little red .s” (LRDs), which fueled conjecture about their possible nature. 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. On the one hand, the “stellar-only” theory contends that the red color of LRDs is due to their dense star and dust populations.
This implies that they might resemble the “dusty galaxies” that are currently being seen in the universe. On the other hand, 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.
An international group of astronomers examined the various possibilities in a recent paper that was uploaded to the arXiv preprint server. They came to the conclusion that LRDs were originally “stellar only” galaxies, which later gave rise to the seeds of the modern supermassive black holes (SMBHs) at the core of galaxies.
Andres Escala, a professor of astronomy at the Universidad de Chile, led the investigation. Colleagues from the University of Heidelberg’s Astronomical Computing Institute, Yale University, and Sapienza University of Rome joined him. Their findings are described in the arXiv paper “On the Fate of Little Red Dots,” which is presently being reviewed for the Astrophysical Journal.
Since LRDs have some traits in common with contemporary astronomical objects, but also some significant differences, their discovery has baffled astronomers. For example, according to the “stellar only” interpretation, LRDs are dusty galaxies with incredibly dense core regions that are actively star-forming. The appearance of these galaxies, which are two of the most distinctive characteristics of LRDs, is explained by this theory. Long-term instability would result, though, from the widths of their hydrogen spectral line emissions (Balmer-series lines), which indicate velocity dispersions significantly greater 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. But unlike quasars, the majority of LRDs don’t seem to emit a lot of X-ray radiation, and the black holes that are believed to be present are too massive in relation to their host galaxies. However, Professor Escala emailed Universe Today to say that 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. At low redshift values (z), however, LRDs remain objects that have never been observed beforehand. Since these objects have different “weights” but are “normal” in the local universe, the BH and galaxy interpretation is advantageous. “…
“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. LRDs could be just another galaxy in the universe, according to the stellar-only interpretation, 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. “.”.
Escala and his associates, on the other hand, contemplated how LRDs might change to accommodate the BH and galaxy interpretation after starting with the stellar-only interpretation. By implying that these two interpretations reflect distinct evolutionary stages of these early galaxies, their theory would reconcile them. As Escala pointed out, the evidence for their theory is nearly identical to that of the BH and galaxy interpretation. This includes the fact that quasars in the more recent universe have more detectable LRDs than X-rays.
“The majority of LRDs are essentially in the early stages of the evolutionary path that our paper proposes, as indicated by the absence of X-rays. LRDs are transitory; they only appear in the universe between z=8 and 4, which is equivalent to 10% of the universe’s age. This suggests that these objects can only be seen in their early stages before changing into systems (or parts of them) that resemble those seen at lower redshifts. “,”.
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, in short, suggests that LRDs will eventually host an MBH. Webb’s observations of the early universe can be explained more thoroughly by this evolutionary approach to LRDs. This could have a big impact on our current cosmological and galactic evolution models, which have been put to the test by the discovery of these deep red, extremely compact galaxies. Escala said.
This indicates that 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 brought forth. “..”.
