A giant elliptical galaxy called NGC 3640 has engulfed several smaller galaxies in the past, according to an analysis of data from ESO’s VLT Survey Telescope (VST) at Paranal Observatory in Chile.
This VST image shows two elliptical galaxies: NGC 3640 and NGC 3641. Image credit: ESO / INAF / Mirabile et al. / Ragusa et al.
NGC 3640 resides some 88 million light-years away from Earth in the constellation of Leo.
Also known as LEDA 34778 and UGC 6368, the galaxy has a diameter of 90,000 light-years.
It was discovered on February 23, 1784 by the German-British astronomer William Herschel.
NGC 3640 is part of a dynamically young group composed of at least eight galaxies.
It also forms an interacting pair with a fainter elliptical galaxy called NGC 3641.
“Throughout their extremely long lifetime, galaxies change,” Dr. Marco Mirabile from the Italian National Institute for Astrophysics and colleagues said in a statement.
“As they soar through space, they may steal gas and stars from other galaxies, or even engulf and merge with them.”
“After these events, galaxies can become distorted, as exemplified by the misshaped NGC 3640 and the diffuse light around it.”
“The galaxy is then left with ‘scars’ that hint at a violent past, which astronomers can use to know its past and present history.”
To trace the history behind the NGC 3640-NGC 3641 pair, Dr. Mirabile and co-authors used the VST to analyze their globular clusters, spherical and compact aggregations of stars bound by gravity.
These usually contain some of the first stars created within a galaxy and can therefore act as fossil markers, revealing the galaxy’s history, even after merging events.
“The results confirm that NGC 3640 has engulfed other galaxies before, an ominous sign for the smaller NGC 3641,” the astronomer said.
“Yet, this small galactic underdog shows a distinct lack of distortions in its shape or the globular clusters within.”
“This suggests that their interaction, while fast, is not happening close enough for NGC 3640 to pose a threat. NGC 3641 might be safe — for now.”
The findings appear in the journal Astronomy & Astrophysics.
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Marco Mirabile et al. 2024. VEGAS-SSS: Tracing globular cluster populations in the interacting NGC 3640 galaxy group. A&A 691, A104; doi: 10.1051/0004-6361/202451273
