How big can black holes get?
According to a group of scientists, black holes could grow to “stupendously large
sizes”, each containing the mass of 100 billion suns or more.
They believe that discovering such massive black holes will shed light on the nature
of a major fraction of the mysterious dark matter that makes up four-fifths of the matter
in the Universe.
Supermassive black holes with masses millions to billions of times that of the sun can be
found at the centers of most, if not all, galaxies.
For example, Sagittarius A*, which is around 4.5 million solar masses in size, is located
at the center of our Milky Way galaxy.
So, what’s the largest black ever found to date?
That goes to TON 618, a quasar that shines brighter than the galaxy in which it resides.
A quasar is an active black hole consuming matter and surrounded by streams of particles.
TON 618 has a mass of around 66 billion suns and is as luminous as 140 trillion suns.
Being this massive makes it an ultramassive blackhole.
For comparison, the total mass of all the stars in our galaxy is merely 64 billion solar
masses.
TON 618 is 15,000 times more massive than Sagittarius A*, which is four million solar
masses.
That is an incredible figure.
Because our brains were not designed to comprehend such enormous figures, it’s unlikely that
any of us could ever completely grasp objects of this magnitude.
Yet for everything TON 618 may be, it isn’t even close to the black hole size limit.
Because quasars were not recognized until 1963, the nature of this object was unknown
when it was discovered in a 1957 study of faint blue stars that lie far from the plane
of the Milky Way.
It appeared “decidedly violet” on photographic plates taken with the 0.7 meter Schmidt telescope
at the Tonantzintla Observatory in Mexico.
Mexican astronomers Braulio Iriarte and Enrique Chavira catalogued it as entry number 618
in the Tonantzintla Catalogue.
In 1970, a radio survey in Bologna, Italy, detected radio emission from Ton 618, suggesting
that it was a quasar.
Marie-Helene Ulrich collected optical spectra of Ton 618 at the McDonald Observatory, which
revealed emission lines typical of a quasar.
Ulrich reasoned that Ton 618 was quite far based on the high redshift of the lines, and
thus was one of the most luminous quasars known.
As a quasar, TON 618 is thought to represent the active galactic nucleus at the heart of
a galaxy, the engine of which a supermassive black hole is feeding on intensely hot gas
and matter in an accretion disc.
It is estimated that the light from the quasar is 10.8 billion years old.
The brilliance of the central quasar outshines the host galaxy and hence is not observable
from Earth.
TON 618 is consuming extremely hot gas and matter in an accretion disk.
Friction causes the particles in the disk to heat up, causing it to shine with a luminosity
of 4 by 10 to the power of 40 watts, which is 140 trillion times brighter than the sun.
This makes it one of the brightest objects in the known Universe.
Even if we sat 30 light-years away from it, it would still be brighter than the sun is
from Earth.
In addition, the emission lines in the light spectrum of TON 618 are unusual, implying
that the gases in the accretion disk are moving very fast, probably at 7,000 km/s.
This also means that the black hole’s gravitational force is quite strong.
Being an ultra massive black hole, TON 618 has a Schwarzschild radius of 1,300 astronomical
units, which is around 195 billion kilometers.
This is more than 40 times the distance from Neptune to the sun.
Its event horizon can accommodate 11 Solar Systems side by side, so large that it would
take light a week to reach the singularity after crossing the event horizon.
But in reality, it is likely to be even larger.
We can only see what TON 618 looked like 10 billion years ago since it is so far away.
Currently, that is the only information available about TON 618, but scientists are working
around the clock to discover more of its properties and features.