At simultaneous press conferences around the world on Thursday (12 May), including at the Wits Planetarium at the University of the Witwatersrand, Johannesburg, astronomers have unveiled the first image of the supermassive black hole at the centre of our own Milky Way galaxy.
This means we now have overwhelming evidence that the object is indeed a black hole, and it brings us a little closer to understanding. these giants which are thought to reside at the centre of most galaxies.
The image was produced by a global research team of 300 researchers – including two in South Africa – and is called the Event Horizon Telescope (EHT) Collaboration. They used observations from a worldwide network of radio telescopes from 80 international institutes.
The two researchers from South Africa – the only researchers on the team on African soil – are Wits postdoctoral fellow, Dr Iniyan Natarajan, and Prof Roger Deane, Director of the Wits Centre for Astrophysics and Extraordinary Professor at the University of Pretoria.
Watch the brilliant video below as Prof Deane recalls how he first fell in love with what was to become his career, lying on his back on a trampoline looking at the amazing Free State night sky; and how he’s laughed at the UK headlines about the image looking like Brexit from space – explaining that he lived in England for three years and would’ve been a Remainer if he were still there.
Dean’s and Natarajan’s contributions included precision measurements of the black hole ring size using a suite of algorithms, as well as developing the sophisticated software suite used to simulate realistic EHT datasets. These were critical to robustly compare the observations with predictions from Einstein’s General Theory of Relativity.
WATCH Professor Roger Deane on black holes, galaxies and lying on a trampoline in the Free State
The image is a long-anticipated look at the massive object that sits at the very centre of our galaxy. Scientists had previously seen stars orbiting around something invisible, compact, and very massive at the centre of the Milky Way. This strongly suggested that this object — known as Sagittarius A* (Sgr A*, pronounced “sadge-ay-star”) — is a black hole, and yesterday’s image provides the first direct visual evidence of it.
Although we cannot see the black hole itself, because it is completely dark, glowing gas around it reveals a tell-tale signature: a dark central region (called a “shadow”) surrounded by a bright ring-like structure. The new view captures light bent by the powerful gravity of the black hole, which is four million times more massive than our Sun.
“We were stunned by how well the size of the ring agreed with predictions from Einstein’s Theory of General Relativity,” says EHT Project Scientist Geoffrey Bower from the Institute of Astronomy and Astrophysics, Academia Sinica, Taipei.
Because the black hole is about 27,000 light-years away from Earth, it appears to us to have about the same size in the sky as a doughnut on the Moon. To image it, the team created the powerful EHT, which linked together eight existing radio observatories across the planet to form a single “Earth-sized” virtual telescope . The EHT observed Sgr A* on multiple nights, collecting data for many hours in a row, similar to using a long exposure time on a camera.
The breakthrough follows the EHT collaboration’s 2019 release of the first image of a black hole, called M87*, at the centre of the more distant Messier 87 galaxy.
The two black holes look remarkably similar, even though our galaxy’s black hole is more than a thousand times smaller and less massive than M87. “We have two completely different types of galaxies and two very different black hole masses, but close to the edge of these black holes they look amazingly similar,” says Sera Markoff, Co-Chair of the EHT Science Council and a professor of theoretical astrophysics at the University of Amsterdam, the Netherlands. “This tells us that General Relativity governs these objects up close, and any differences we see further away must be due to differences in the material that surrounds the black holes.”
Scientists are particularly excited to finally have images of two black holes of very different sizes, which offers the opportunity to understand how they compare and contrast.
Progress on the EHT continues with more telescopes being added.
Wits’ Professor Deane says: “Southern Africa holds a distinct geographic advantage to host new EHT telescopes, especially if we wish to make movies of the Milky Way’s supermassive black hole, which passes directly above us in the southern sky.”
Efforts to add these African nodes to the global network are underway with several national and international partners, including Wits and the University of Pretoria. In addition to enabling higher precision tests of General Relativity, the expansion of the EHT into Africa has a strong synergy with the future continental expansion of the Square Kilometre Array mid-frequency array centred in the Northern Cape, with the South African Radio Astronomy Observatory’s MeerKAT telescope serving as its precursor.
ALSO READ: Say hi to Sagittarius A* – Black Hole at the centre of our Milky Way Galaxy – which explains in plain language why this image is such a big deal!