The core of our Milky Way is buzzing with stars. Recently astronomers reported that it contains at least one ancient star that formed outside our galaxy. Now, an international research team reports finding a grouping of very young ones there, as well. Their presence upends ideas about star birth in that densely packed region of space.<\/p>\n
<\/p>\n These stellar youngsters live in a dense collection called the \u201cnuclear star cluster\u201d (NSC). It lies about 27,000 light-years away from us and surrounds the area holding the supermassive black hole Sagittarius A*. Observers have long considered the NSC to be one of the more ancient parts of the Galaxy. Proving that requires detailed observations of the stellar populations in the core. But, studying this region is somewhat difficult, at least visually. That\u2019s because of dense clouds of gas and dust that block the view. In addition, the thick population of stars makes it difficult to distinguish their characteristics.<\/p>\n One of those characteristics is age, which is not always easy to determine. Since astronomers want to know more about the lifetimes of stars in the galaxy\u2019s core, the best way to find out how old they are is to look at something called their \u201cmetallicity\u201d. As a general rule, old ones tend to be more metal-poor, while younger ones are more metal-rich. Recent observations found several very young stars there with very high metallicities. That\u2019s an indication that things in the core aren\u2019t always what they seem.<\/p>\n A team of astronomers at Lund University in Sweden used the Keck II telescope in Hawaii to take infrared spectra of stars comprising the NSC to determine their ages and metallicities. Previous observations hinted that at least three members of the cluster could be unusually young in a region where older ones normally predominate. \u201cWe can now confirm this,\u201d said Rebecca Forsberg, a Lund graduate student and member of the research team. \u201cIn our study, we have been able to date three of these stars as relatively young, at least as far as astronomers are concerned, with ages of 100 million to about 1 billion years. This can be compared with the Sun, which is 4.6 billion years old.\u201d<\/p>\n The three stars they studied in-depth have interestingly high amounts of heavy elements, including iron. Their metallicity is a measure of how many elements heavier than hydrogen and helium they contain. Metal-poor stars are usually born early in a galaxy\u2019s history (or in the early Universe). Metal-rich ones contain materials shed from older ones when they die\u2014including such heavy elements as calcium and iron. The cluster itself shows a range of metallicities, and the youngest ones have the most abundance of iron.<\/p>\n Astronomers began studying star formation in the NSC back in the mid-1990s. Most of its stars are likely at least five billion years old, or older. Normally, you\u2019d expect that star birth stopped there a long time ago because of the influence of the nearby black hole, and other factors. But, those young ones confuse the picture. They came from recent episodes of star birth. Understanding how those happened gives important clues to the mix of star-forming materials at the Galaxy\u2019s core, and may even tell how the Milky Way itself formed. And, because these types of clusters exist in other galaxies, understanding how ours formed would explain what happened in other places.<\/p>\n There are a couple of theories about the creation of nuclear star clusters. One is that early in a galaxy\u2019s history, globular clusters formed and spiraled into the galactic core. There they became nuclear star clusters. The other idea is that their stellar populations formed \u201cin place\u201d as a galaxy evolved. Either idea could explain our Galaxy\u2019s central cluster. The way to figure it out is to look at the chemical makeup (i.e., the metallicity) of the cluster\u2019s stars since it correlates with when and where they formed.<\/p>\n The Lund team took infrared spectra of the cluster members, which revealed the large variation in metallicity between the older and younger members. The three youngest ones with high metallicity indicate that they likely formed in place inside the Milky Way within the last few hundred million years. Interestingly, even these three vary in their metal content from each other. That means they formed in clouds that themselves had different abundances of heavier elements. <\/p>\n Interestingly, the one with the lowest metallicity of the three may be what\u2019s called a \u201cblue straggler\u201d. That\u2019s a star that could be much older but stole mass from a nearby companion. That additional material could make it look younger than it is. Further observations could confirm if this is a new star or an imposter.<\/p>\n The heavy element iron was of particular interest to the team. This element is an important clue to a galaxy\u2019s continuing evolution. Iron is the heaviest element a massive star can \u201ccook up\u201d inside its nuclear furnace. When it explodes as a supernova, the iron and other heavy elements (such as calcium, carbon, nickel, and others) get scattered into space. In time, that material gets mixed into clouds of gas and dust where star birth can take place. So, the oldest, metal-poor stars in any galaxy (and indeed, in the Universe) are ones that formed early on. But, the younger ones that come along later are more abundant in heavy elements because they form in metal-enriched clouds of gas and dust.<\/p>\n That process of stellar birth and death played out in the nuclear star cluster at our Galaxy\u2019s heart. And, it spread heavier elements across the region. \u201cThe very wide spread of iron levels [in the cluster] could indicate that the innermost parts of the galaxy are incredibly inhomogeneous, i.e. unmixed,\u201d said Brian Thorsbro, lead researcher and Lund astronomer. \u201cThis is something we had not expected and not only says something about how the center of the galaxy appears but also how the early Universe may have looked.\u201d<\/p>\n The Lund University infrared spectral studies of the stars at the heart of the Milky Way will certainly be extended to other stellar populations. Those future observations should provide answers to why astronomers found a wide range of metal abundances in stars in that tightly packed region of the Galaxy.<\/p>\n Astronomers Determine the Age of Three Mysterious Baby Stars at the Heart of the Milky Way![\"This](\"https:\/\/www.universetoday.com\/wp-content\/uploads\/2015\/04\/spitzer_milkyway-e1436391756885.jpg\")
Studying the Nuclear Star Cluster<\/h3>\n
Metallicity and Stars<\/h3>\n
![\"Omega](\"https:\/\/www.universetoday.com\/wp-content\/uploads\/2023\/02\/1149px-Omega_Centauri_by_ESO-580x545.jpg\")
Determining Metallicity in the Galaxy Core<\/h3>\n
Iron as a Tracer of Galaxy Evolution<\/h3>\n
For More Information<\/h4>\n
A Wide Metallicity Range for Gyr-old Stars in the Nuclear Star Cluster<\/p>\nLike this:<\/h3>\n