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For The First Time Cosmologists Have Observed A Massive ‘Cosmic Bridge’ Connecting Two Galaxies Next To The Milky Way

An international team of astronomers has found that two of the largest dwarf galaxies next to the milky Way—the Magellanic clouds—seem to be connected by a ‘supermassive bridge’—one that is composed of Stars—stretching across a staggering 43,000 light years.

“Stellar streams around the Clouds were predicted but never observe[d],” paper co-author Vasily Belokurov said in a statement. “We were surprised to see a narrow bridge-like structure connecting the two clouds.”
Image credit: V. Belokurov, D. Erkal and A. Mellinger

The discovery is reported in the journal Monthly Notices ofthe Royal Astronomical Society(MNRAS).

To make the discovery, experts used data gathered from the galactic stellar census made by the European Space Observatory, Gaia.

The Gaia all-sky-view has allowed scientists to study the Large and Small Magellanic Clouds—which spread across a very freakishly large area—with unprecedented detail.

What makes the Gaia observatory so unique is the fact that it uses two telescopes which share a one-meter-wide focal place. This means it can study the entire sky rather than just one small part of it, like traditional telescopes.

According to, What Gaia has sent to Earth is unique. The satellite’s angular resolution is similar to that of the Hubble Space Telescope, but given its greater field of view, it can cover the entire sky rather than a small portion of it.

Furthermore, the Gaia all-sky-view is exceptional because it does not just point and observe one part of the sky; it constantly rotates, exploring the entire sky in less than a MONTH.

These exceptional features have allowed scientists to measure the properties of the stars and tracks potential changes over time. This has lead to the discovery of various cosmic objects like pulsating stars.

Researchers from the University of Cambridge looked at the area surrounding the Magellanic clouds in search of a very old ‘pulsating star’ known as RR Lyrae.

These types of stars are believed to have existed since the earliest days of the cloud’s existence. By studying them, experts hope to find answers to questions about the history of the two dwarf galaxies and how they came into existence.

Researchers specifically wanted to know when both clouds came to our galaxies neighborhood, however, this is extremely difficult without knowing their particular orbits which is something very hard to come by.

Therefore, scientists studied the stellar stream. These cosmic stream form when a satellite, such as a dwarf galaxy or even a star cluster, starts feeling the tidal force of the body around which it orbits. Think of them as the Earth and the moon, only at a supermassive scale.

These tidal forces are able to stretch the satellite in two directions: one towards the host and one away from it.

“Stellar streams around the Clouds were predicted but never observe,” explains Dr. Belokurov. “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.”

The newly found ‘cosmic bridge’ will help astronomers find out more about them and clarify the complicated history of interaction between the Magellanic clouds and our galaxy the milky way.

Note: The very first recorded mention of the Large Magellanic Cloud was by Persian astronomer Shirazi, in his Book of Fixed Stars around 964 AD.

Furthermore, the new study has led experts to discover that the Large Magellanic cloud is much larger than previously thought.

“We have compared the shape and the exact position of the Gaia stellar bridge to the computer simulations of the Magellanic Clouds as they approach the Milky Way”, explains Dr. Denis Erkal, a co-author of the study. “Many of the stars in the bridge appear to have been removed from the SMC in the most recent interaction, some 200 million years ago when the dwarf galaxies passed relatively close by each other. “We believe that as a result of that fly-by, not only the stars but also hydrogen gas was removed from the SMC. By measuring the offset between the RR Lyrae and hydrogen bridges, we can put constraints on the density of the gaseous Galactic corona.”

Monthly Notices of the Royal Astronomical Society. DOI:10.1093/mnras/stw3357

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