“The Last of Its Kind” – Gravity of the Ancient Globular Cluster Cluster Milky Way 2 Billion Years Ago

An artist representation of the Phoenix Steller Stream. Originally a ball of stars, known as a spherical cluster, the Phoenix is ​​spread across a stream of stars by the Milky Way’s gravity bridge. In a few billion years, the Phoenix will be completely destroyed and absorbed into our galaxy. Credit: Illustration is courtesy of the collaboration of Geraint F. Lewis and S5.

“Stellar Archeology” suggests that a stellar stream was formed from the remains of an ancient spherical cluster that was further apart. GalaxyGravity 2 billion years ago.

A team of astronomers, including Ting Li and Alexander G. of Carnegie, discovered a stellar stream made up of the remains of an ancient spherical cluster that broke apart from the Milky Way’s gravity 2 billion years ago, when Earth’s most complex lifeforms were single – Cells were organisms. This amazing discovery was published in Nature, Enhances traditional knowledge about how these celestial bodies are formed.

Imagine a sphere made up of one million stars bound by gravity and orbiting a galactic core. It is a circular cluster. The Milky Way is home to about 150 of them, forming a rigid halo that encircles our galaxy.

But the spherical cluster that aroused this newly discovered stellar current had a lifecycle that was very different from the spherical clusters seen today.

“This is stellar archeology, exposing the remains of something ancient, swept away in a more recent event,” Ji explained.

The stream was revealed by S5, the Southern Stellar Stream Spectroscopic Survey Collaboration, using the Anglo-Australian Telescope. Under Lee’s leadership, the initiative aims to map the motion and chemistry of stellar currents in the Southern Hemisphere.

Phoenix Stream and Red Giant Stars

An artist’s impression of a thin stream of strands torn from Phoenix circular clusters, wrapping around our Milky Way (left). For the study, astronomers targeted bright red giant stars, to measure the chemical composition of the fragmented phoenix globular cluster (right). Credit: Illustration is courtesy of James Josephides (Swinburne Astronomy Productions) and S5 Collaboration.

In this study, the collaborator focused on a stream of stars in the Phoenix constellation.

“The spherical cluster remnants that make up the Phoenix Stream were disrupted several billion years ago, but fortunately the very early universe retains the memory of its formation, which we can read from the chemical composition of its stars,” Lee said

The team measured the abundance of heavy elements – what astronomers call the metallicity of a star.

A star is made up of a cloud of galactic gas from which it originates. More earlier generations of stars have seeded this material with heavier elements that they produced during their lifetime, more rich, or metallic, stars are called. Therefore, a very ancient, primitive star would have almost no heavy elements.

“We were really surprised to find that Phoenix Stream is different from the other spherical bunches of the Milky Way.” University of Sydney lead author Jane Vann explained. “Even though the cluster was destroyed billions of years ago, we can tell it formed in the early universe.”

Since other known spherical flakes are enriched by the presence of heavy elements formed by earlier generations, it was proven that there was minimal abundance of heavy elements required for spherical clusters.

But Phoenix stream ancestors are well below this minimal metallurgy prediction, an important problem for previous ideas about how spherical clusters are produced. “One possible explanation is that the Phoenix Stream represents the last of its kind, a remnant of a population of spherical clusters that originated in radically different environments for those we see today.”

The researchers proposed that these no-now-with-us-globular clusters were continuously reduced by the gravitational forces of the Milky Way, tearing them to pieces. The remnants of other ancient spherical clusters may also remain in the form of misty currents which may be destroyed before time.

“We have a lot of theoretical work left to do and now we have many new questions about how galaxies and spherical clusters are formed,” said co-author Geraint Lewis of the University of Sydney.


Reference: 29 July 2020, Nature.
DOI: 10.1038 / s41586-020-2483-6

The study was part of the Southern Stellar Stream Spectroscopic Survey, or just S5 for short, using an international collaboration 2dF / AAOmega Instrument at the Anglo-Australian Telescope in Coonabarabran, NSW, for survey streams of stars opened during the Dark Energy Survey Des).

The Carnegie Institution for Science (carnegiescience.edu) is a private, non-profit organization headquartered in Washington, DC, with six research departments across the US, since its founding in 1902, Carnegie Pollution Basic Scientific Research Has been a leading force in Carnegie scientists are pioneers in plant biology, developmental biology, astronomy, materials science, global ecology and earth and planetary science.

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