The Magellanic clouds, the two largest satellite galaxies in the Milky Way, appear to be connected by a star bridge that spans 43,000 light-years , as reported by an international team of astronomers led by researchers from the University of Cambridge (USA). .) The incredible find has been published in the Monthly Notices of the Royal Astronomical Society magazine and is based on the galactic stellar census carried out by the European Space Observatory Gaia.
The Gaia mission has returned data of unprecedented quality: a catalog of the positions and brightness of a trillion stars in and around our Milky Way galaxy . What Gaia has sent to Earth is unique in that it has a greater field of view than the Hubble Space Telescope and can cover the entire sky instead of just a small portion.
Gaia sweeps across the sky in less than a month, so she is able to track her changes over time. Thus, the experts concentrated on the area around the Magellanic Clouds and used the Gaia data to select pulsating stars of a particular type: the so-called RR Lyrae , very old and chemically not evolved. As these stars have been around since the very first days of the existence of the Clouds, they offer a glimpse into the history of this curious cosmic couple.
What the Gaia mission has discovered
Around the Milky Way, clouds are the brightest and largest examples of dwarf satellite galaxies. Known to mankind since the dawn of history, the Magellanic Clouds have represented an enigma to date. Thanks to the RR Lyrae stars, they were able to trace the extent of the Large Magellanic Cloud, discovering that it had a diffuse low-luminosity “halo” that extended up to 20 degrees from its center. In the absence of an orbit, the researchers found something amazing: a stellar stream.
Star streams are formed when a satellite – a dwarf galaxy or star cluster – begins to feel the tidal force of the body around which it orbits. Gravitational tides cause small regions to be created where the gravitational pull of the satellite is balanced by the pull of the host, each star leaving a light trail that hints at the orbit.
“The stellar currents around the clouds were predicted but never observed. Having marked the positions of the RR Lyrae in the sky, we were surprised to see a narrow bridge-like structure connecting the two clouds . We believe that at least in part this bridge is composed of stars stripped of the small cloud by the big one “, explains Vasily Belokurov, leader of the study.
The researchers believe that this star bridge will help clarify the history of the interaction between the Magellanic clouds and our galaxy .
“Many of the stars on the bridge appear to have been extracted from the Small Magellanic Cloud in a recent interaction, about 200 million years ago, when the dwarf galaxies passed relatively close to each other, ” says Denis Erkal, co-author of the work.
