Scientists have always suspected, but have never been sure, whether or not galaxies grow by merging with other galaxies, but new research could provide definitive proof.
A team of researchers used an observational "proof" that a giant elliptical galaxy Messier 87 merged with a smaller spiral galaxy in only the past billion or so year, the European Space Agency reported.
"This result shows directly that large, luminous structures in the Universe are still growing in a substantial way -- galaxies are not finished yet!" said Alessia Longobardi, of the Max-Planck-Institut für extraterrestrische Physik , in Garching, Germany . "A large sector of Messier 87's outer halo now appears twice as bright as it would if the collision had not taken place."
To make their findings, the researchers looked at planetary nebula (the "shells of dying stars) in the nearby galaxy, and observed their motion with the the FLAMES spectrograph on the Very Large Telescope.
"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!" adds Ortwin Gerhard, head of the dynamics group at the Max-Planck-Institut für extraterrestrische Physik, Garching, Germany, and a co-author of the new study.
The stunning observations revealed light that had come from stars in the galaxy and was pulled apart, most likely when the younger galaxy was gobbled up and younger blue stars were added.
"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. 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," concluded co-author Magda Arnaboldi, of ESO.
The findings were published in a recent edition of the journal Astronomy & Astrophysics Letters.
