Awesome beauty of Supermassive Black Holes are featured on Melbourne Mints latest silver coin

One of the most popular themes in modern numismatics, astronomy has given us some terrific coin designs over the last few years from such luminaries as the Mint of Poland, the Royal Canadian Mint and Coin Invest Trust. Joining this elite group is Melbourne Mint with its latest commemorative coin issue, following their excellent Tyrannosaurus Rex coin from back in April.

An ounce of fine silver in weight and antique finished, the coin reverse depicts an artistic view of the maelstrom that is believed to form around a supermassive black hole. The spiral disintegration of solar and planetary bodies as they become trapped in the gravitational pull of the black hole is well depicted. This is ably enhanced by a spiralling scattering of proof-finish ‘debris’ that falls into the hole in the centre. The whole impression is one of movement. A border contains inscriptions and they’ve been kept to a minimum – just the date (2017) and title (SUPERMASSIVE BLACK HOLE).

The obverse carries the Ian Rank Broadly effigy of Queen Elizabeth II in the centre, surrounded by inscriptions denoting the coin issue and composition. Surrounding that is a border filled with a geometric pattern. The coin will come boxed and with a certificate of authenticity. Just 999 of these will be made available and they should be shipping in a couple of weeks time for around $129.00 AUD. A fine addition to the astronomy coin selection.



A black hole is a region of spacetime exhibiting such strong gravitational effects that nothing—not even particles and electromagnetic radiation such as light—can escape from inside it. The theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole. The boundary of the region from which no escape is possible is called the event horizon. Although the event horizon has an enormous effect on the fate and circumstances of an object crossing it, no locally detectable features appear to be observed.

A supermassive black hole (SMBH) is the largest type of black hole, on the order of hundreds of thousands to billions of times the mass of our sun, and is found in the centre of almost all currently known massive galaxies. In the case of the Milky Way, the SMBH corresponds with the location of Sagittarius A*, a bright and very compact astronomical radio source at the center of the Milky Way, near the border of the constellations Sagittarius and Scorpius.

The origin of supermassive black holes remains an open field of research. Astrophysicists agree that once a black hole is in place in the center of a galaxy, it can grow by swallowing new matter and by merging with other black holes. There are several hypotheses for the formation mechanisms, the most obvious being that the seeds are black holes of tens or perhaps hundreds of solar masses that are left behind by the explosions of massive stars and grow by accretion of matter. They range from around 100,000 to over 30 million solar masses.

Amazingly, they are theorised as potentially being bigger. So-called ultramassive black holes (UMBHs), which are at least ten times the size of supermassive black holes, appear to have a theoretical upper limit of around 50 billion solar masses, as anything above this slows growth down to a crawl (the slowdown tends to start around 10 billion solar masses) and causes the unstable accretion disk surrounding the black hole to coalesce into stars that orbit it. (Source: Wikipedia)


COMPOSITION 0.999 silver
WEIGHT 31.1 grams
DIAMETER 38.60 mm
FINISH Antique
MODIFICATIONS Colour, selective proof
BOX / COA Yes / Yes