DIY Supermassive Black Holes

DIY Supermassive Black Holes

Title: Massive star formation in dense regions of the early universe

author: John A. Reagan

First Author Foundation: CASM, University of Maynooth, Ireland

condition: Submitted to the Open Journal of Astrophysics [open access]available at arXiv

In most of the large galaxies we observe – such as the Milky Way – there appears to be a A supermassive black hole (SMBH) in the center. These black holes are staggeringly massive (Finally an unexplained name in astronomyover here Some examples of how not to do this), ranging from a million times the mass of the Sun to billions of solar masses. Here’s the problem: How supermassive black holes gained massive mass? A lot of things can happen once a lot of time has passed, and the universe existed for a long time. However, astronomers are still not sure how these black holes grow into such amazing masses. Moreover, in the early universe – even before its billionth birthday – there were SMBHs with over a billion solar masses around. Currently, the general idea is that They are the product of mergers; Small black holes melt together into larger ones until they reach masses of SMBH. The main problem is that it’s really hard to explain why these mergers are progressing so quickly, and then why we’re seeing them at all.

How did we get here?

One of the most annoying things about black holes is (and that’s not surprising). Now, the Black Hole Zoo is a diverse park. The ones we’ve actually observed are stellar-mass black holes – dying stars left (there are plenty of them) – and supermassive black holes, usually found in the centers of galaxies – they’re very bright, or at least their surroundings be. There is also a suspicion that the so-called Medium-mass black holes They exist, with masses between one thousand and one million solar masses. These massive black holes (MBH) are neither bright nor abundant: they have not been observed. While this is sometimes considered a red flag in astronomy, these objects are still believed to be the key to understanding the formation of SMBHs.
There is a wide range of explanations for how MBHs are formed, with two main categories (see also shape 1):

  • Light seed: MBH grows from many standards Population III stars or its remains, or it can simply grow into huge clumps by consuming a very dense local gas cloud.
  • Heavy Seeds: Much heavier structures (on the order of at least a thousand solar masses) are formed and fused into MBHs.
Figure 1: Overview of potential MBH seed formation scenarios, Figure 1.2 of Becerra (2018).

The main problem with the photosynthetic seed scenario is that there is a maximum rate at which black holes consume matter: when matter falls into the black hole, disc material (= Accumulation disk In scientific parlance) around it is heating up and emitting more and more light. At some point, the disk will become so bright that the massive amount of light is so powerful that it effectively prevents more material from falling through. When we reach the maximum amount of material falling into the black hole, everything else will be stopped by just radiation from the disk. This is called Eddington border. This is the limit (pun intended) to the rapid formation of MBHs in a light seed scenario: it simply cannot occur fast enough.

In terms of heavy seeds, it’s hard to explain how these massive bodies were formed in the first place. But it is not impossible!

stars

To get the heavy seeds MBHs need, today’s author of the paper is looking to supermassive stars (SMS). As a very special case of third population stars, it should consist of hundreds of thousands of solar masses, which is a bit astonishing considering that the stars we have today are only a few hundred solar masses in size. Now there are two problems with Population III stars: they only occurred a very long time ago (so we need to look at vast distances) and would have faded very quickly. So, unfortunately, we haven’t seen them yet.
However, these stars will theoretically form Dark matter halos in the beginnings of the universe. Fortunately, cosmic simulations are very good at that. For our SMS, we especially need dense dark matter halos to have any chance of them forming. Cosmic simulation is not easy, but a Zoom in stages on structures of interest It can reduce the effort. This is shown in Figure 2.

Figure 2: Simulation of dark matter clusters. The right side shows the low-resolution simulation where a high-density region is highlighted. On the left is a higher-resolution version of this region, where three promising high-density clusters are encircled. Figure 1 of the paper.

There, the author outlines an interesting dense area. In the hyperboloid region in picture 2, the author points out three groups (appropriately called C1, C2, and C3) which can contain dark matter halos where SMS can have a chance to form. This is still easier said than done, as there seem to be a set of conditions we need to form these crazy stars:

  • Basically we need almost zero “minerals” in our halos. This works best if no other stars form spewing harmful metals (in the astrological sense of the word) making it easier for low-mass stars to form and giving our SMS no chance.
  • We need a lot of physical movement in the aura; The more local the motion, the better it prevents clouds from collapsing early into smaller stars.
  • The aura should form quickly. The heat generated by the rapid formation of the corona as it shrinks should be higher than radiative cooling of the materials in the corona.

So, we basically want to prevent stars with less mass from forming in order to get the star monstrosity we need to get the MBH. Analysis of these three clusters shows that at least C2 and C3 contain dark matter halos that can form SMS messages. A rough estimate of star formation in these promising halos shows that some stars with a hundred thousand solar masses can form – in the mass range of what we need for MBHs. These giant stars would have been somewhat rare given their very satisfactory formation requirements, but they could have been there.

As these SMS live their lives (very short, a few million years), they will eventually collapse into fairly heavy black holes. Black holes are in the mass range we want for MBHs, so SMS works well like heavy seeds for MBH formation. In any case, the possibility of the existence of these supermassive stars brings us one step closer to the supermassive black hole and the eventual formation of the supermassive black hole.

Astrobite Edited by Katja Guzman

Featured Image Credit: Figure 15c) from James et al. 2015

About Roel Lefevre

Roel is a first-year doctoral student at the University of Heidelberg, studying astrophysics. It works on massive stars and simulates their atmosphere/outflows. In his spare time, he loves hiking/biking in nature, playing (lots of) video games, playing/listening to music (movie soundtracks!) and reading (currently the wheel of time, but any imagination really).

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