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The oldest of these stars is 1.5 billion years old and the youngest is only 100 million years old, according to a paper published in Astrophysical Journal Letters.
This infrared image from Hubble shows the Milky Way’s nuclear star cluster, the densest and most massive star cluster in our Galaxy. Photo credit: NASA / ESA / Hubble Heritage Team / STScI / AURA / T. Do & A. Ghez, UCLA / V. Bajaj, STScI.
The center of our Milky Way galaxy, about 27,000 light-years away in the constellation Sagittarius, is a crowded place.
This region is very dense and equal to one million stars are packed between the Sun and Alpha Centauri, which is 4.3 light years away.
This nuclear star cluster surrounds Sagittarius A*, the 4.3 million-solar-mass black hole at the center of the Galaxy.
In general, most nuclear star clusters coexist with supermassive black holes, and they can be found in more than 70% of galaxies that are more than 100 million – 10 billion times the size of the so.
“In a previous study, we put forward a hypothesis that these particular stars in the center of the Milky Way could be very different,” said Lund University astronomer Rebecca Forsberg.
“We can now confirm this. In our research we have been able to date three of these stars that are very young, at least according to astronomers, with an age of 100 million to about 1 billion years.
“This can be compared to the Sun, which is 4.6 billion years old.”
This image shows the center of the Milky Way Galaxy. It builds on previous observations from NASA’s Chandra X-ray Observatory and other telescopes, and extends Chandra’s high-resolution view above and below the plane of the Galaxy beyond previous imaging models. X-rays from Chandra are orange, green, and purple, indicating different X-ray energies, and radio data from MeerKAT are gray. Image credit: NASA / CXC / UMass / QD Wang / NRF / SARAO / MeerKAT.
In the study, Dr. Forsberg and his colleagues high data from the Keck II telescope in Hawaii, one of the largest telescopes in the world with a mirror ten meters in diameter.
For further evidence, they then measured how much of the heavy element, iron, the stars contained.
The element is very important for studying the development of the galaxy, because the astronomers’ ideas about the formation of stars and the development of galaxies show that young stars have more heavy elements, because Heavy elements are created at an increasing rate over time in the universe.
To determine the level of iron, the astronomers observed the stars in infrared light, compared to optical light, which are the parts of the light spectrum that are more easily reflected in the particles thickness of the Milky Way.
According to the researchers, the level of iron is very different.
“The wide range of high iron content can indicate that the inner parts of the Galaxy are very heterogeneous, that is, they are not mixed,” said Dr. Brian Thorsbro, an astronomer at Lund University.
“This is something we didn’t expect and it not only says something about the appearance of the center of the Galaxy, but also what the early universe looked like.”
“Personally, I think it is very interesting that we can now study the center of our Galaxy with a high level of detail,” said Dr. Forsberg.
“These types of measurements were common for observing the galactic disk where we are, but it is an unattainable goal for many distant and outer parts of the Galaxy.”
“We can learn a lot about how our galaxy was formed and developed from such studies.”
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B. Thorsbro etc. 2023. A Common Metallicity for Old-Old Stars in the Nuclear Cluster. ApJL 958, L18; doi: 10.3847/2041-8213/ad08b1