“Star Archeology”; reveals a stream of stars consisting of an ancient globular cluster torn down Milky Waygravity 2 billion years ago.
A team of astronomers, including Carnegie’s Ting Li and Alexander Ji, discovered a stellar stream of remnants of an ancient globular cluster torn apart 2 billion years ago by the gravity of the Milky Way, when the most complex life forms on Earth were unicellular organisms. This surprising finding, published in 2006 nature, uses the usual wisdom of how these celestial objects are formed.
Imagine a sphere made up of a million stars bounded by gravitational forces and orbiting the galactic nucleus. It is a ball cluster. About 150 of them live in the Milky Way, forming a tense halo surrounding our galaxy.
However, the spherical cluster that caused this newly discovered stream of stars was very different in its life cycle from the spherical clusters seen today.
“It’s a stellar archeology that reveals remnants of something ancient, encompassing a more recent phenomenon,” she explained.
Using an Anglo-Australian telescope, the flux was revealed by S5, a collaborative spectroscopic study of the flow of southern stars. The Li-led initiative aims to link stellar motion and chemistry in the southern hemisphere.
This study collaborates with stellar flow in the Phoenix constellation.
“The remnants of the global clusters that make up the Phoenix stream were destroyed billions of years ago, but fortunately there will be a memory of its formation in a very early universe that we can read from the chemical composition of its stars,” Li said.
The team measured the abundance of heavier elements – what astronomers call stellar metallicity.
The makeup of the star reflects the cloud of gas in the galaxy from which it is born. The more previous generations of stars sow this material with the heavy elements they produced during their lifetimes, the richer or more metallic the stars are. Therefore, a very ancient primitive star will have almost no heavy elements.
“We were surprised to see that Phoenix Creek is markedly different from all other Milky Way ball clusters,” explained lead author Zhen Wan of the University of Sydney. “Although the cluster was destroyed billions of years ago, we can still say that it formed in the early universe.”
Since other known spherical clusters are enriched by the presence of forged heavy elements from previous generations of stars, it has been theorized that a minimal amount of heavier elements is required to form a spherical cluster.
However, the ancestor of the Phoenix Stream is well below this predicted minimum metallicity, which poses a significant problem to previous ideas about how ball clusters are born. “One possible explanation is that the Phoenix stream is the last form of its kind – a remnant of groups of globular groups born in a radically different environment than the one we see today,” Li said.
The researchers suggested that these no longer communicating ball swarms were stably depleted by the gravitational forces of the Milky Way, which tore them to pieces. Remnants of other ancient globular clusters may also live as weak streams that can still be detected before they dissipate over time.
“There’s a lot of theoretical work left, so we now have a lot of new questions on how to figure out how galaxies and globular clusters form,” said co-author Geraint Lewis, also from the University of Sydney.
Reference: 2020 July 29 nature.
DOI: 10.1038 / s41586-020-2483-6
This study was part of the “Southern Stellar Flow” spectroscopic study or, in short, only S5, an international collaboration using a 2dF / AAOmega instrument with an Anglo-Australian telescope in Koonabarabran, NSW, to examine stellar fluxes detected during a dark energy study (DES).
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