TON 618 is a contender for largest black hole discovered, being 40 billion times the mass of the Sun and 30-40 as wide as our Solar System.

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Published: Tuesday, 16 July 2024 at 09:01 AM


TON 618 is, strictly speaking, a quasar, but the name also refers to the supermassive black hole (more properly TON 618*) that powers it, which is one of the largest ever discovered. 

Taking its name from the Tonantzintla Observatory in Mexico, it was first observed and catalogued by astronomers Braulio Iriarte and Enrique Chavira in 1957.

TON 618 lies some 18.2 billion lightyears from Earth, in the constellation Canes Venatici.

Artist’s impression of a quasar, a distant bright object generated by a supermassive black hole at the centre of a galaxy. Credit: NASA/JPL-Caltech

AGNs and quasars

When first observed, TON 618 was thought to be a blue star. Then in 1970 a radio survey conducted in Italy detected radio emissions coming from the object, identifying it as a quasar.

A quasar is type of active galactic nucleus (AGN).

An AGN is a region in the centre of a galaxy that emits significant amounts of electromagnetic radiation, which comes from the material falling into the supermassive black hole that lies at the galaxy’s very heart.

Image of TON 618 by Sloan Digital Sky Survey, Apache Point Observatory, Astrophysical Research Consortium - Aladin Lite, CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=97489739
Image of TON 618 by Sloan Digital Sky Survey, Apache Point Observatory, Astrophysical Research Consortium – Aladin Lite, CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=97489739

Not all galaxies have AGNs – our own Milky Way doesn’t, for starters.

It’s thought that, as supermassive black holes steadily ‘eat’ their way through all of the available gas and dust in the region, the material falling into them emits less and less radiation, so that eventually the galactic centre is no longer active.

AGNs can be broken down into numerous sub-classes based on the strength of the radio waves they emit, the relative proportions of visible, IR and UV light, whether or not they emit X-ray radiation and other spectral characteristics.

Two galaxies and an active galactic nucleus in Hercules Hubble Space Telescope, July 2022 Credit: ESA/Hubble & NASA, W. Keel
Two galaxies and an active galactic nucleus in Hercules, as seen by the Hubble Space Telescope. Credit: ESA/Hubble & NASA, W. Keel

These sub-classes include Seyfert galaxies, radio galaxies, LINERs (low-ionization nuclear emission regions) and, the most powerful of them all, quasars.

So, to recap: stuff falls into a black hole, stuff emits electromagnetic radiation, and that radiation shines out so brightly that we often can’t actually SEE the galaxy that the supermassive black hole (and hence the surrounding AGN) are at the heart of, because its stars’ light is simply outshone by that coming from the AGN.

Then that light reaches Earth X milllion or billion years later and we call it a quasar. TON 618 is one of those.

Got it?

Seyfert galaxy NGC 3718 Peter Hannah, capture remotely via IC Astronomy, Oria, Spain, March-May 2024 Equipment: FLI ProLine P9000 camera, PlaneWave CDK14 astrograph, 10Micron GM2000 HPS II mount
Seyfert galaxy NGC 3718, captured remotely by Peter Hannah via IC Astronomy, Oria, Spain.

Now, here’s the kicker: the supermassive black hole that powers TON 618 is absolutely enormous.

It’s so big, in fact, that words alone can’t really do it justice.

So over to NASA, who’ve put together this video that really brings the sheer size of these objects to life.