How a Star’s Death Can Reveal a Black Hole

Studying invisible objects in space that are hundreds of millions of light years away may sound impossible. But, in recent years, astronomers have developed a new way to investigate a type of invisible and distant objects—super-massive black holes. Black holes are the most densely packed objects in the Universe. When stars get close to super-massive black holes they can be torn apart, which produces a relatively brief but informative flash of light. These star-destroying events can help us to discover the locations of the most massive black holes in the Universe, but only if we know how to find and interpret them. In this article, we will discuss different ways we can “see” black holes, and particularly what we do and do not yet understand about stars getting “tidally disrupted” by them. Light YearThe distance light travels in a year, which is 5,878,625,370,000 miles.

Spin of primordial black holes in the model with collapsing domain walls

The angular momentum (spin) acquisition by a collapsing domain wall at the cosmological radiation-dominated stage is investigated. During the collapses, primordial black holes and their clusters can be born in various mass ranges. Spin accumulation occurs under the influence of tidal gravitational perturbations from the surrounding density inhomogeneities at the epoch when the domain wall crosses the cosmological horizon. It is shown that the dimensionless spin parameter can have the small values aS < 1 only for primordial black holes with masses M > 10-3M☉, whereas less massive black holes receive extreme spins aS ≃ 1. It is possible that primordial black holes obtain an additional spin due to the vector mode of perturbations.

The AGN Fraction in Dwarf Galaxies from eROSITA: First Results and Future Prospects

Determining the fraction of nearby dwarf galaxies hosting massive black holes (BHs) can inform our understanding of the origin of “seed” BHs at high redshift. Here we search for signatures of accreting massive BHs in a sample of dwarf galaxies (M ⋆ ≤ 3 × 109 M ⊙, z ≤ 0.15) selected from the NASA-Sloan Atlas (NSA) using X-ray observations from the eROSITA Final Equatorial Depth Survey (eFEDS). On average, our search is sensitive to active galactic nuclei (AGNs) in dwarf galaxies that are accreting at ≳1% of their Eddington luminosity. Of the ∼28,000 X-ray sources in eFEDS and the 495 dwarf galaxies in the NSA within the eFEDS footprint, we find six galaxies hosting possible active massive BHs. If the X-ray sources are indeed associated with the dwarf galaxies, the X-ray emission is above that expected from star formation, with X-ray source luminosities of L 0.5–8 keV ∼ 1039–40 erg s−1. Additionally, after accounting for chance alignments of background AGNs with dwarf galaxies, we estimate there are between zero and nine real associations between dwarf galaxies and X-ray sources in the eFEDS field at the 95% confidence level. From this we find an upper limit on the eFEDS-detected dwarf galaxy AGN fraction of ≤1.8%, which is broadly consistent with similar studies at other wavelengths. We extrapolate these findings from the eFEDS sky coverage to the planned eROSITA All-Sky Survey and estimate that upon completion, the all-sky survey could yield as many as ∼1350 AGN candidates in dwarf galaxies at low redshift.

A Study on the detection and formation mechanisms of ultra-massive black holes

With the discovery of Ultra-massive black holes and Super-massive black holes, humans have yet to find out the cause of their formation with modern technology. Based on the analysis, we will look at the detection methods and calculation methods for black holes and their mass. Besides, we will also dive deeper into the actual formation of these Ultra-massive black holes. Taking a closer look at black holes’ sizes, there are many black holes between 0.1Ms and up to its maximum 150Ms, but something interesting is that after 150 Ms, we can barely find any black holes bigger than that until we reach black holes with millions of times the mass of our sun. This is quite fascinating, as if the knowledge we have now suggests that bigger black holes are formed through devouring and merging of other black holes. It is simply impossible for some of these black holes to even exist, as looking at the amount of time the universe existed, that is impossible for black holes of this mass to even form. In this paper, the detection method for black holes and black holes’ mass and the formation model of ultra-massive black holes will be discussed, which involves concepts like Quasi Stars and Quasi Black holes. These results shed light for us to discover the formation of ultra-massive black holes.

Exploring New Redshift Indicators for Radio-Powerful AGN

Active Galactic Nuclei (AGN) are relevant sources of radiation that might have helped reionising the Universe during its early epochs. The super-massive black holes (SMBHs) they host helped accreting material and emitting large amounts of energy into the medium. Recent studies have shown that, for epochs earlier than z∼5, the number density of SMBHs is on the order of few hundreds per square degree. Latest observations place this value below 300 SMBHs at z≳6 for the full sky. To overcome this gap, it is necessary to detect large numbers of sources at the earliest epochs. Given the large areas needed to detect such quantities, using traditional redshift determination techniques—spectroscopic and photometric redshift—is no longer an efficient task. Machine Learning (ML) might help obtaining precise redshift for large samples in a fraction of the time used by other methods. We have developed and implemented an ML model which can predict redshift values for WISE-detected AGN in the HETDEX Spring Field. We obtained a median prediction error of σzN=1.48×(zPredicted−zTrue)/(1+zTrue)=0.1162 and an outlier fraction of η=11.58% at (zPredicted−zTrue)/(1+zTrue)>0.15, in line with previous applications of ML to AGN. We also applied the model to data from the Stripe 82 area obtaining a prediction error of σzN=0.2501.