A team of astronomers identified a new way to detect how large galaxies such as Messier 87 grow by absorbing smaller ones, a process typically difficult to observe.

Their study published in the journal the Astrophysical Research Letters, the researchers examined the dust clouds surrounding stars near the M87 galaxy. When looking directly at the galaxy, which is extremely luminous and packed with stars, it can be hard to notice it eating a smaller galaxy.

Led by Alessia Longobardi, a PhD student at the Max Planck Institute, the researchers found the surrounding stars' nebulae shone in a different light that made observations easier.

"This result shows directly that large, luminous structures in the Universe are still growing in a substantial way - galaxies are not finished yet!" Longobardi said in a press release. "A large sector of Messier 87's outer halo now appears twice as bright as it would if the collision had not taken place."

M87 is the centerpiece of the Virgo Cluster, a gargantuan collection of stars 50 million light years from Earth that is millions upon millions of times more massive than the sun.

"We are witnessing a single recent accretion event where a medium-sized galaxy fell through the center of Messier 87, and as a consequence of the enormous gravitational tidal forces, its stars are now scattered over a region that is 100 times larger than the original galaxy," study co-author Ortwin Gerhard, head of the Max Planck team's dynamics group, said in the release.

For their observations, the researchers used the European Southern Observatory's (ESO) Very Large Telescope and its FLAMES spectrograph.

"It is very exciting to be able to identify stars that have been scattered around hundreds of thousands of light-years in the halo of this galaxy - but still to be able to see from their velocities that they belong to a common structure," study co-author Magda Arnaboldi, an ESO researcher, said in the release. "The green planetary nebulae are the needles in a haystack of golden stars. But these rare needles hold the clues to what happened to the stars."

(Source: European Southern Observatory)