One of the most extraordinary objects in the Milky Way galaxy is Sagittarius A* (pronounced Sagittarius A star). This small object is a bright source of radio waves in the constellation of Sagittarius that was discovered in 1974.

Since then, astronomers have made numerous observations of Sagittarius A* and the stars nearby, some of which orbit it at very high velocity. That implies that Sagittarius A* is extremely massive and since it is so small it must also be hugely dense.

That’s why many astronomers believe this object is a supermassive black hole lying at the centre of the galaxy. In fact, Sagittarius A* is about 4 million times more massive than the Sun packed into a volume not much bigger than the orbit of Mercury.

But there is another explanation—that this massive dense object is a wormhole that connects our region of space to another point in the universe or even to another part of the multiverse. (Astrophysicists have long known that wormholes are allowed by the laws of general relativity and may well have formed soon after the Big Bang.)

And that raises an interesting question. If Sagittarius A* is a wormhole, how can astronomers distinguish it from a black hole? Today, we get an answer thanks to the work of Zilong Li and Cosimo Bambi at Fudan University in Shanghai.

These guys have calculated that plasma orbiting a black hole would look different to the same plasma orbiting a wormhole. They have calculated the difference and even simulated the resulting images that should be possible to collect using the next generation of interferometric telescopes. In other words, if there is a wormhole at the centre of our galaxy, we should be able to see it within the next few years.

The idea that a wormhole might exist at the centre of the galaxy is not as far-fetched as it sounds. In the early universe, quantum fluctuations may well have a connected different regions of the cosmos, creating wormholes that were preserved during inflation when universe increased in size by many orders of magnitude.

The presence of a wormhole would actually solve a major problem of galaxy formation. In recent years, astronomers have observed what appear to be supermassive black holes at the centre of many galaxies. Indeed, many believe that supermassive black holes are necessary for galaxies to form in the first place— they provide the gravitational pull to hold galaxies together in their early stages.

But if that’s true, how do supermassive black holes become so massive so quickly? After all, the one at the centre of our galaxy must have been in place about 100 million years after the Big Bang. That doesn’t leave much time to grow.

A wormhole, on the other hand, is a primordial object formed in the blink of an eye after creation. So if wormholes did form in this way, they would be present in the early universe to trigger the formation of the first galaxies.

That’s why telling one from the other is so significant— the difference provides important clues about the nature of the early universe.

On the face of it, it’s easy to imagine that telling them apart ought to be impossible. After all, both black holes and wormholes sit behind an event horizon from which light cannot escape. There is no way of seeing what’s going on inside an event horizon.

However, there is an important difference between black holes and wormholes— the latter is much smaller than the former and this is the basis on which Zilong and Bambi say they can be told apart.

They consider a cloud of hot plasma orbiting each body and emitting infrared light. They then calculate the trajectory the light must take to escape towards Earth where it can be imaged.

Because this light has difficulty escaping from the extreme gravitational fields of these objects, the image of the cloud of plasma becomes smeared out. But the difference in size between a black hole and a wormhole causes a crucial difference in this smearing. This distinctive pattern of smearing is the signature that astronomers can use to tell them apart.

Nobody has succeeded in viewing Sagittarius A* in the optical or near infrared part of the spectrum. But that is going to change in the next few years.

In particular, astronomers are building an infrared interferometer called GRAVITY at the Very Large Telescope Interferometer in the Atacama desert of northern Chile. This device will be capable of resolving clouds of plasma around Sagittarius A*and spotting the unique signature of a wormhole, if one is there.

These images will provide a fascinating insight into the nature of the massive dense object at the centre of our galaxy. The confirmation that it is a supermassive black hole will be important but the discovery that it is a wormhole will be mind-blowing.

GRAVITY is being shipped to Chile next year and will hopefully be in operation soon after that. If there is a wormhole at the heart of the Milky Way, the likelihood is that we’ll find out in the not too distant future.

Ref: arxiv.org/abs/1405.1883 : Distinguishing Black Holes And Wormholes With Orbiting Hot Spots