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Scientists discover a Fossil Relic of early Milky Way harboring stars of hugely different ages

These similarities could make Terzan 5 a fossilised relic of galaxy formation, representing one of the earliest building blocks of the Milky Way

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Milky Way Galaxy. Image Source: Wikimedia Commons.
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LONDON, Sept 08, 2016: An international team of researchers has found that a stellar system classified as a globular cluster for the 40-odd years since its detection actually has properties uncommon for a globular cluster that make it the ideal candidate for a living fossil from the early days of the Milky Way.

The cluster, known as Terzan 5 — 19,000 light-years from Earth- harbours stars of hugely different ages — an age-gap of roughly seven billion years and bridges the gap in understanding between our galaxy’s past and its present, the study said.

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“Such galactic fossils allow astronomers to reconstruct an important piece of the history of our Milky Way,” explained lead author of the study Francesco Ferraro from University of Bologna in Italy.

While the properties of Terzan 5 are uncommon for a globular cluster, they are very similar to the stellar population which can be found in the galactic bulge, the tightly packed central region of the Milky Way.

These similarities could make Terzan 5 a fossilised relic of galaxy formation, representing one of the earliest building blocks of the Milky Way.

“Terzan 5 could represent an intriguing link between the local and the distant Universe, a surviving witness of the Galactic bulge assembly process,” Ferraro said.

The team scoured data from the Advanced Camera for Surveys and the Wide Field Camera 3 on board Hubble, as well as from a suite of other ground-based telescopes.

They found compelling evidence that there are two distinct kinds of stars in Terzan 5 which not only differ in the elements they contain, but have an age-gap of roughly seven billion years.

The ages of the two populations indicate that the star formation process in Terzan 5 was not continuous, but was dominated by two distinct bursts of star formation.

“This requires the Terzan 5 ancestor to have large amounts of gas for a second generation of stars and to be quite massive. At least 100 million times the mass of the Sun,” co-author of the study Davide Massari from National Institute for Astrophysics (INAF) , Italy.

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Its unusual properties make Terzan 5 the ideal candidate for a living fossil from the early days of the Milky Way, said the study published in the Astrophysical Journal.

Somehow Terzan 5 has managed to survive being disrupted for billions of years, and has been preserved as a remnant of the distant past of the Milky Way.

The researchers believe that this discovery paves the way for a better and more complete understanding of galaxy assembly. (IANS)

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Cosmic Crash with Dwarf Galaxy Reshaped Milky Way: Study

This spacecraft has been mapping the stellar content of our galaxy, recording the journeys of stars as they travel through the Milky Way

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Cosmic Crash with Dwarf Galaxy Reshaped Milky Way: Study
Cosmic Crash with Dwarf Galaxy Reshaped Milky Way: Study. (IANS)

A dramatic head-on collision with a dwarf galaxy, dubbed the “Gaia Sausage” galaxy, about 10 billion years ago reshaped the structure of our galaxy, the Milky Way, fashioning both its inner bulge and its outer halo, new research suggests.

The dwarf did not survive the impact. It quickly fell apart, and the wreckage is now all around us, according to the findings.

“The collision ripped the dwarf to shreds, leaving its stars moving in very radial orbits” that are long and narrow like needles, said Vasily Belokurov of the University of Cambridge and the Center for Computational Astrophysics at the Flatiron Institute in New York City.

The stars’ paths take them “very close to the centre of our galaxy. This is a telltale sign that the dwarf galaxy came in on a really eccentric orbit and its fate was sealed.”

The results detailed in a series of new papers in the journals the Monthly Notices of the Royal Astronomical Society, The Astrophysical Journal Letters and arXiv.org outline the salient features of this extraordinary event.

Several of the papers were led by Cambridge graduate student GyuChul Myeong. He and colleagues used data from the European Space Agency’s Gaia satellite.

Cosmic rays
Representational image. Pixabay

This spacecraft has been mapping the stellar content of our galaxy, recording the journeys of stars as they travel through the Milky Way.

Thanks to Gaia, astronomers now know the positions and trajectories of our celestial neighbours with unprecedented accuracy.

The paths of the stars from the galactic merger earned them the moniker the “Gaia Sausage,” explained Wyn Evans of Cambridge.

“We plotted the velocities of the stars, and the sausage shape just jumped out at us. As the smaller galaxy broke up, its stars were thrown onto very radial orbits. These Sausage stars are what’s left of the last major merger of the Milky Way,” Evans said.

Also Read: NASA’s Hubble finds ‘relic galaxy’ near Milky Way

The new research also identified at least eight large, spherical clumps of stars called globular clusters that were brought into the Milky Way by the Sausage galaxy.

Small galaxies generally do not have globular clusters of their own, so the Sausage galaxy must have been big enough to host a collection of clusters.

“While there have been many dwarf satellites falling onto the Milky Way over its life, this was the largest of them all,” said Sergey Koposov of Carnegie Mellon University in Pittsburgh, Pennsylvania, US. (IANS)