43,000 Light Years Long Bridge Of Stars Connects Two Milky Way Satellite Galaxies

Posted: Feb 8 2017, 1:10am CST | by , Updated: Feb 8 2017, 1:50am CST, in News | Latest Science News

43,000 Light Years Long Bridge of Stars Connects two Milky Way Satellite Galaxies
Credit: V. Belokurov, D. Erkal and A. Mellinger / Phys.Org

Two largest satellite galaxies of the Milky Way -- the enigmatic Magellanic Clouds -- appear to be connected by a bridge stretching across 43,000 light years, a study says.

The discovery, reported in the journal Monthly Notices of the Royal Astronomical Society (MNRAS), is based on the Galactic stellar census being conducted by the European Space Observatory, Gaia.

"Stellar streams around the Clouds were predicted but never observed," said one of the researchers Vasily Belokurov from University of Cambridge.

The research team concentrated on the area around the Magellanic Clouds and used the Gaia data to pick out pulsating stars of a particular type -- the so-called RR Lyrae, very old and chemically un-evolved.

As these stars have been around since the earliest days of the Clouds' existence and they offer an insight into the pair's history.

The Large and Small Magellanic Clouds (LMC and SMC respectively) are the brightest, and largest, examples of dwarf satellite galaxies around the Milky Way.

Known to humanity since the dawn of history (and to Europeans since their first voyages to the Southern hemisphere) the Magellanic Clouds have remained an enigma to date.

Studying the Large and Small Magellanic Clouds (LMC and SMC respectively) has always been difficult as they sprawl out over a large area. But with Gaia's all-sky view, this has become a much easier task.

"Having marked the locations of the Gaia RR Lyrae on 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 from the Small Cloud by the Large. The rest may actually be the LMC stars pulled from it by the Milky Way," Belokurov noted.

The researchers believe the RR Lyrae bridge will help to clarify the history of the interaction between the clouds and our galaxy.


We present the discovery of stellar tidal tails around the Large and the Small Magellanic Clouds in the Gaia DR1 data. In between the Clouds, their tidal arms are stretched towards each other to form an almost continuous stellar bridge. Our analysis relies on the exquisite quality of the Gaia’s photometric catalogue to build detailed star-count maps of the Clouds. We demonstrate that the Gaia DR1 data can be used to detect variable stars across the whole sky, and in particular, RR Lyrae stars in and around the LMC and the SMC. Additionally, we use a combination of Gaia and Galex to follow the distribution of Young Main Sequence stars in the Magellanic System.

Viewed by Gaia, the Clouds show unmistakable signs of interaction. Around the LMC, clumps of RR Lyrae are observable as far as ∼20°, in agreement with the most recent map of Mira-like stars reported in Deason et al. (2016). The SMC's outer stellar density contours show a characteristic S-shape, symptomatic of the on-set of tidal stripping. Beyond several degrees from the center of the dwarf, the Gaia RR Lyrae stars trace the Cloud's trailing arm, extending towards the LMC.

This stellar tidal tail mapped with RR Lyrae is not aligned with the gaseous Magellanic Bridge, and is shifted by some ∼5° from the Young Main Sequence bridge. We use the offset between the bridges to put constraints on the density of the hot gaseous corona of the Milky Way.

Vasily Belokurov et al, Clouds, Streams and Bridges. Redrawing the blueprint of the Magellanic System withDR1, Monthly Notices of the Royal Astronomical Society (2016). DOI: 10.1093/mnras/stw3357

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