By deploying NASA's Hubble Space Telescope and Europe's Herschel Space Observatory, astronomers have solved the mystery surrounding the evolution of compact elliptical galaxies, which have perplexed them for a while now.

These galaxies apparently erupted and burned out when the universe was just 3 billion years old. The research was supported by NASA's Spitzer Space Telescope and several ground-based telescopes. The infrared imaging capabilities of the Hubble Space Telescope aided the astronomers in getting insights and assembling "a representative spectroscopic sampling of ultra-compact, burned-out elliptical galaxies."

The 10-year old mystery regarding the growth of the massive elliptical galaxies as we know them today is finally solved. Astronomers now have a clearer picture regarding the formation of the massive galaxies, right from their burst of star formation to their evolution with dense stellar cores to the "ultimate reality as giant ellipticals."

Sune Toft of the Dark Cosmology Center at the Niels Bohr Institute in Copenhagen is the leader of the study and revealed that they can finally show how these compact galaxies former, as well as the manner and time of the process. Per them, this is the missing link in understanding how massive galaxies formed and eventually evolved into giant ellipticals of present day.

"We at last show how these compact galaxies can form, how it happened, and when it happened. This basically is the missing piece in the understanding of how the most massive galaxies formed, and how they evolved into the giant ellipticals of today," said Toft. "This had been a great mystery for many years because just 3 billion years after the big bang we see that half of the most massive galaxies have already completed their star formation."

So how did Toft find out what had happened? Apparently, he had to research further back in time. Tift had the theory that massive galaxies formed as a result of collision or fusion of smaller galaxies, but that in itself was not sufficient to explain why they became huge so quickly and were now dead.

"We studied the galaxies that existed when the universe was between 1 and 2 billion years old. My theory that it must have been some galaxies with very specific properties that were part of the formation process made me focus on the special SMG galaxies, which are dominated by intense stare formation hidden under a thick blanket of dust," notes Toft.

Via the research, astronomers have established that the compact ellipticals avidly consumed the gas available for star formation. The consumption was so high that they were unable to create new stars as a consequence and eventually merged with smaller galaxies to form giant ellipticals.

The results of the research are published online in The Astrophysical Journal.