Dark matter has always been a mysterious phenomenon when it comes to its influence on gravity. Being entirely hypothetical, its theorized existence is solely to explain some of the anomalies in gravitational theories.
Dark matter itself comes with some issues of its own, however. Seeing as it’s entirely hypothetical, it’s never been observed and draws a lot of criticism and provokes alternative theories to explain gravity.
Instead, an extra force has been theorised that could explain this lack of understanding. A team of researchers from the University of California have been trying to gather enough evidence to prove the existence of this new force. The study was led by Andrea Ghez, who is the director of the UCLA Galactic Centre Group.
“This is really exciting. It’s taken us 20 years to get here, but now our work on studying stars at the centre of our galaxy is opening up a new method of looking at how gravity works,” explained Ghez.
WHAT DO WE KNOW SO FAR?
There are currently 4 known types of forces:
The weak force, typically between half-integer spin fermions, which is also the cause for radioactive decay in elements.
The electromagnetic force, which is a physical interaction between electrically charged particles.
Finally, the gravitational force, which is experienced by all particles. It is by far the weakest of the 4 forces, which means it only shows a noticeable effect when the bodies are a substantially large size.
It’s this gravitational force that shows some discrepancies when it comes to the maths that’s used to explain it. Despite the scepticism around dark matter, it’s generally accepted by astronomers to exist.
This hypothetical fifth force, however, could potentially be used to generate entirely different gravitational models.
WHAT DID THE CALIFORNIAN RESEARCHERS DO?
The two stars, S0-2 and SO-38, are located near the Milky Way’s supermassive black hole and will be used to test Einstein’s Theory of General Relativity.
By closely monitoring the orbital path of the stars over a 20 year period and measuring how much of an effect gravity has on their orbit, they were able to examine whether there were any deviations which would insinuate another force was acting upon the stars.
These deviations in the calculated gravitational force could potentially be due to this theorized fifth force changing the stars orbital path.
The images were taken at the W.M. Keck Observatory using adaptive optics (AO). Designers from the University of California started working on the Keck Observatory’s telescope in 1977.
“By watching the stars move over 20 years using very precise measurements taken from Keck Observatory data, you can see and put constraints on how gravity works. If gravitation is driven by something other than Einstein’s theory of General Relativity, you’ll see small variations in the orbital paths of the stars,” said Ghez.
Previously, this fifth force has been attempted to be observed using our own sun’s gravitational field. This is the first time a supermassive black hole with a sufficiently strong gravitational force has been examined.
“It’s exciting that we can do this because we can ask a very fundamental question – how does gravity work?” said Ghez. “Einstein’s theory describes it beautifully well, but there’s lots of evidence showing the theory has holes. The mere existence of supermassive black holes tells us that our current theories of how the universe works are inadequate to explain what a black hole is.”
In 2018, S0-2 will be at its closest distance to our galaxy’s supermassive black hole. This will mean that the gravitational force acting upon it will be at its strongest and any discrepancy to Einstein’s Theory of Relativity will be at its maximum.