The Largest Things in the Universe: From Primordial Black Holes to Ton 618

Overview

The video traces the hierarchy of black holes, from hypothetical primordial seeds to the ultramassive giants at galactic centers, and identifies the current observational anchors such as Ton 618 and Sagittarius A*. It also touches on the challenges of ranking black holes due to limited data and measurement uncertainties.

Key insights

• Black holes span a vast range in mass, from potentially tiny primordial remnants to tens of billions of solar masses in ultramassive objects.
• Stellar black holes grow by accreting matter and by merging with other black holes, with gravitational waves now opening a window into these mergers.
• Quasi stars and alternative seed formation scenarios are proposed explanations for how the most massive black holes could grow in the early universe.
• Ton 618 is the largest observed single black hole, while imaging of M87 and jets in Cygnus A illustrate the extreme scales involved in ultramassive systems.

Introduction and scope

This article summarizes a video that surveys the scale of black holes in the universe, from the smallest conceivable primordial black holes to the largest single bodies known today. It emphasizes that while many black hole formation pathways exist, the focus here is on the size spectrum and observational anchors rather than detailed formation physics.

Primordial black holes and stellar remnants

The video starts with the smallest possible black holes, primordial in origin, which could have formed in the intensely dense early universe just after the Big Bang. If they exist, these black holes could range from mass scales comparable to a mountain (around 10^12 kilograms) up to Earth mass or more, yet their physical size would be extremely tiny, making them very difficult to detect. The discussion notes that such objects, if they exist, could even be candidates for dark matter. Moving to black holes that we can observationally infer today, the video describes stellar black holes formed from stellar collapse or violent mergers. Using a sun-like unit for scale, it highlights the range of masses, from a few solar masses up to tens of solar masses, with specific examples such as a black hole orbiting a red giant and a well-studied X7 system. Through these examples the video illustrates how accretion disks glow intensely and how the shadow of a stellar black hole can be observed indirectly.

Growth and the mass gap

The narrative then explains the growth of black holes via two main pathways: accretion of matter and mergers with other black holes. It points out a notable observational gap: black holes are commonly seen up to about 150 solar masses, but there is a dearth of objects in the intermediate mass range, raising questions about how the most massive black holes formed within the age of the universe. The video suggests that faster growth mechanisms beyond simple eating stars are needed in the early cosmos, such as the presence of very massive seed stars or quasi stars that could feed a developing black hole for extended periods.

Quasi stars and seeds for supermassive holes

The concept of quasi stars is discussed as a potential driver of rapid early growth. In quasi stars, dense accreting matter may feed a central black hole while radiation pressure stabilizes the surrounding star, enabling a rapid increase in mass over millions of years and potentially laying the groundwork for the most massive black holes we observe in the present universe.

Largest black holes: supermassive, ultramassive, and Ton 618

The core of the video then climbs the scale into the realm of supermassive black holes that reside in galactic centers. It cites the Milky Way’s Sagittarius A* with about 4 million solar masses and a radius of about 17 solar radii as a calm anchor. It adds that many galaxies host such monsters, often accompanied by relativistic jets in some cases. Examples include the giant Cygnus A with a 2.5 billion solar mass black hole and a 14.7 billion kilometer diameter, producing enormous radio lobes. The video also references the M87 black hole, famous for the first direct image of a black hole shadow. Beyond these, ultramassive black holes—tens of billions of solar masses—are described as the extreme end of single-body growth, powering quasars and extraordinary accretion disks.

Ton 618: the king of single bodies

The crown of the ranking goes to Ton 618, a black hole with approximately 66 billion solar masses. It shines with the luminosity of 100 trillion stars and is visible from 18 billion light-years away. Its event horizon would accommodate several solar systems side by side, and because of its distance we see it as it was about 10 billion years ago. The video notes that Ton 618 represents the upper extreme of the observable universe and hints that the true size of such objects could be even larger than observed due to observational limits and evolution over cosmic time.

Behind the scenes and uncertainties

The video closes with a candid behind the scenes discussion about the challenges of ranking black holes. It emphasizes that we do not directly observe black holes; instead we infer properties from gravitational effects on nearby matter and from relativistic modeling. The Schwarzschild radius and the assumption of spherical, non-spinning black holes are simplifications that carry uncertainties. The creators acknowledge that many black holes remain poorly constrained and that the field continues to evolve as data improves, including new detections of mergers via gravitational waves and high-resolution imaging of accretion phenomena.