TON 618

A black hole is a region in space where an enormous amount of mass is packed into an extremely small volume, creating a gravitational pull so powerful that nothing, not even light, can escape from it. This makes black holes invisible to direct observation, as they emit no light or radiation that telescopes can detect. Most black holes are formed when massive stars reach the end of their life cycle and collapse under their own gravity. This collapse produces a superdense point called a singularity, surrounded by a boundary known as the event horizon. The event horizon acts as a one-way door: once matter or light crosses it, escape is impossible. The largest known black hole in the universe is TON 618, classified as an ultra-massive black hole. Its estimated mass is about 66 billion times that of the Sun, making it the most massive black hole ever observed. TON 618 (i.e., Tonantzintla 618) is a hyper-luminous, broad-absorption-line, radio-loud quasar, and Lyman-alpha blob located near the border of the constellations Canes Venatici and Coma Berenices, with the projected co-moving distance of approximately 18.2 billion light-years from Earth. It is so enormous that if it were placed at the centre of our solar system, its event horizon would extend far beyond the orbit of Pluto. 
 
Another candidate, the black hole at the centre of the galaxy Holm 15A, has an estimated mass of around 40–44 billion solar masses. Some sources mention the black hole in the Phoenix A galaxy as potentially reaching up to 100 billion solar masses, but this figure is less widely confirmed in the scientific literature.
 
Astronomers measure black hole masses using several techniques, depending on the black hole’s type and environment. Here are the primary methods:
1. Orbital Dynamics (Keplerian Motion)
For stellar-mass black holes in binary systems, astronomers track the orbital motion of the companion star. Using Kepler’s laws, they calculate the black hole’s mass from the star’s velocity and orbital radius.
SMBHs at galaxy centers, astronomers observe the motion of stars or gas clouds orbiting the black hole. For example, the Milky Way’s SMBH (4.3 million solar masses) was measured by tracking stars over decades.

2. Reverberation Mapping
This method measures the time delay between light fluctuations in the bright accretion disk (near the black hole) and the response of gas in the surrounding broad-line region. The delay reveals the gas’s distance from the black hole, which, combined with its velocity (from Doppler shifts), gives the mass. Used for distant quasars and active galactic nuclei, though it requires months to years of observations.

3. Spectro-astrometry
A newer technique analyzing spectral shifts in light from gas swirling around SMBHs. Even unresolved regions can provide velocity data through blue/redshifted emissions, enabling mass estimates via modeling. This was successfully applied to quasar J2123-0050 (1.8 billion solar masses).

4. Gravitational Wave Analysis
For merging black holes (e.g., neutron star or black hole binaries), the gravitational waves emitted during collisions encode the masses of the original objects.

5. Galaxy Scaling Relationships
For SMBHs, astronomers use empirical correlations between black hole mass and properties of the host galaxy’s bulge (e.g., stellar velocity dispersion).
 
Future Advances
The James Webb Space Telescope and upcoming Extremely Large Telescope will enhance spectro-astrometry and reverberation mapping for high-redshift quasars.
 
Supermassive black holes (SMBHs) play a crucial role in regulating the growth and evolution of their host galaxies. When active, SMBHs consume surrounding gas and dust, releasing vast amounts of energy and radiation. This activity, often seen in active galactic nuclei (AGN), can heat or expel gas from the galaxy, making it more difficult for new stars to form. In some cases, powerful winds and jets from the SMBH can disperse star-forming material, directly influencing the rate and location of star formation within the galaxy. This process, known as “feedback,” can both suppress and trigger star formation. While energy outflows often inhibit star formation by heating or blowing away gas, there are cases where jets from black holes compress gas clouds, aiding in the birth of new stars. The balance between these effects shapes the structure and future evolution of galaxies.
 
Studies show a tight relationship between the mass of a galaxy’s central black hole and the galaxy’s stellar mass, suggesting that galaxies and their SMBHs grow together. If a black hole becomes too large relative to its galaxy, reduced gas availability slows its growth; if it is too small, abundant gas allows it to catch up, creating a self-regulating system. The activity level of an SMBH can also influence the broader galactic environment. Excessive black hole activity can halt star and planet formation, while too little activity may leave the galaxy unstable or overly dense with young, explosive stars. The presence of a moderately active SMBH, like in the Milky Way, may help maintain a stable, life-friendly galactic zone.
 
References:
(2018, January 11). How massive is supermassive? Astronomers measure more black holes, farther away.
The Pennsylvania State University. https://www.psu.edu/news/research/story/how-massive-supermassive-astronomers-measure-more-black-holes-farther-away
 
(2023, May 18). How do astronomers calculate the mass of a black hole? Astronomy. https://www.astronomy.com/science/how-do-astronomers-calculate-the-mass-of-a-black-hole/
 
(2025, April 30). Black Hole Basics. NASA. https://science.nasa.gov/universe/black-holes/

Smethurst, B. (2024, August 4). The new mystery hidden inside the Universe's biggest ever black hole. BBC Science Focus. https://www.sciencefocus.com/space/black-hole-mystery
 
​Sutter, P. (2023, March 24). What's the biggest black hole in the universe? LiveScience. https://www.livescience.com/whats-the-biggest-black-hole-in-the-universe