What's really at the heart of our GALAXY?

Colin Stuart investigates the radical claim that our Milky Way's central supermassive black hole may not exist after all

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Stare to the south in the summer months and the constellation Sagittarius sits resplendent. Its meandering stars take on various shapes, including a teapot and spoon. Just next to the teapot, close to where steam would rise from its spout, is the Galactic centre - the heart of the Milky Way.

The Sun and every star you can see in the night sky belongs to this sprawling stellar metropolis. A population of hundreds of billions of stars swirl around this central mass, like planets circle the Sun. For decades, astronomers felt confident they knew what it was that all these bodies were orbiting. A Nobel Prize has even been awarded for the discovery. But now, new research is calling the idea into question - and with it could come a deeper understanding of the Galaxy we call home.

The Milky Way stretches out like a dusty river either side of Sagittarius. This dust is so plentiful that it blocks our view of the Galactic core in visible light. If astronomers want to see what's going on there, they need to use longer wavelengths of light that can penetrate the dust. As far back as the 1950s, radio astronomers were picking up signals that suggested something interesting was happening in the heart of our Galaxy, but it took until the 1990s for them to begin peering through the dust with infrared telescopes built atop Hawaii's towering volcanoes.

"There are observations of stars orbiting around the centre of our Galaxy - the so-called S-stars - and from their motion we can infer there is a very massive and compact object there," says Valentina Crespi from the Institute of Astrophysics La Plata in Argentina.