Almost a decade ago, astronomers concluded that the expansion of the Universe was taking place at accelerating rates mainly due to a mysterious force that they called “dark energy.” However, the technology back then was unable to answer all the questions about dark energy and the rate to which the Universe was expanding.

But now, for the first time, ever, astronomers at NASA’s Chandra X-ray Observatory have managed to observe the effects of dark energy on the most massive collapsed objects in the Universe, and learn more about what the Universe could be like in the future.

Back in 1915, Albert Einstein’s General Theory of Relativity assumed the Universe was neither expanding, nor contracting. However, he did mention that even empty space contains energy, which countered gravity in order to maintain balance. Einstein called it a “cosmological constant.” But, 14 years later, Einstein backed down on his own theory when Edwin Hubble discovered the expansion of the Universe.

Today, cosmologists know more about the dark energy than ever, although they are still dealing with uncertainties about what this energy really is. Based on the most recent X-ray research, they concluded that dark energy is most probably the cosmological constant Einstein was talking about.

In order to establish which of the theories about dark energy is closest to reality, the astronomers observed how cosmic acceleration affects the growth of galaxy clusters over time. Up until recently, making these observations on a large scale was impossible, but luckily, the first test of general relativity has now proved successful.

Alexey Vikhlinin of the Smithsonian Astrophysical Observatory in Cambridge, Mass., who led the research, explained that whatever is forcing the Universe to expand is also forcing its development to slow down, in what he called “arrested development of the Universe.”

Scientists used Chandra to make observations on the hot gas in dozens of galaxy clusters, some of them relatively close, and some halfway across the Universe. They found that the increase in mass of the galaxy clusters over time aligns with a Universe dominated by dark energy. Furthermore, they say, the results confirmed that general relativity applies, as expected, on large scales.

“Putting all of this data together gives us the strongest evidence yet that dark energy is the cosmological constant, or in other words, that ‘nothing weighs something’,” said Vikhlinin. “A lot more testing is needed, but so far Einstein’s theory is looking as good as ever.”

But the quest for knowledge is far from being over. Even though the new data strengthens the idea that dark energy is the cosmological constant, theoretically, it should be 10 to the power of 120 times larger than observed, which implies there are also other possible theories out there, such as those referring to hidden dimensions, scientists explained.

Learning more about the dark energy and about how it really works will offer scientists an insight into the fate of the Universe. If Einstein’s cosmological constant is indeed the explanation they’ve been looking for, this means the Milky Way and Andromeda will never merge with the Virgo cluster, and that a hundred billion years from now, other galaxies will disappear from Milky Way’s view, causing local superclusters of galaxies to disintegrate.