The stars at the center of our galaxy did not form in tightly knit, massive clusters but rather in isolated stellar associations.
The Milky Way’s dense central regions provide a natural laboratory for studying rapid star formation, a common phenomenon in galaxies during the universe’s first billion years.
Its dense star population, however, prevents it from being studied in detail. The Galactic Center’s star formation history has been reconstructed for the first time by a paper published in Nature Astronomy.
In light of data provided by the Galacticnucleus project, led by the Institute of Astrophysics of Andalusia (IAA-CSIC), scientists are now able to see that stars didn’t form in massive clusters but rather in isolated stellar associations that have dispersed over time.
“The Milky Way galaxy isn’t very productive.” Francisco Nogueras-Lara, the leader of the research at the Max Planck Institute for Astronomy (MPIA), says the stars that form in a year are not much more than a few solar masses.
“In contrast, the much more productive so-called starburst galaxies give rise to tens or even hundreds of solar masses of stars per year over episodes lasting a few million years. More generally, about ten billion years ago, that kind of high productivity seems to have been the norm among galaxies,” he adds.
In spite of the fact that our galaxy may seem unproductive for studying starbursts, star formation rates have been ten times higher in the 1300 light-year region around the central black hole in the last hundred million years.
In other words, the core of our galaxy has as much productivity as ten billion years ago’s hyperproductive galaxies.
As the center of our galaxy lies behind copious amounts of dust, it poses a double observational challenge: it obstructed the observation of radio waves and infrared waves, which was eventually resolved with the use of radio, infrared, and millimeter wave telescopes.
On the other hand, the crowding of the stars interferes with the ability to distinguish them, so only very massive and bright individual stars can be detected.
It was unknown until recently what the stars at the center of the Milky Way look like because only 10% of their mass had been detected.
Researchers at the Institute of Astrophysics of Andalusia (IAA-CSIC) developed the Galacticnucleus project to resolve this issue. A survey was conducted by the Very Large Telescope (VLT) of the European Southern Observatory using the HAWK-I infrared camera and covering an area of 64,000 square light-years around the galactic center. Through the project, we have been able to map three million stars where only a few had previously been mapped.
With these new data, it was possible to confirm that Sagittarius B1’s region was different and study its stars more closely.
Even though their high-resolution study could only distinguish giant stars, Nogueras-Lara says they were able to determine the brightness and luminosity of each star.
It was particularly interesting to see how the luminosity of these stars was distributed statistically. The luminosity distribution of stars that form at the same time changes over time in a predictable and regular manner. It is then possible to determine the approximate history of star formation.
According to the research team, there are several phases of star formation in Sagittarius B1. The older stars formed between two and seven billion years ago, as well as a younger population formed within the last ten million years.
In spite of the fact that these newly discovered young stars are found in a particular region, their examples suggest a more general mode of galaxy center star formation. As stars orbit the galactic center over a time scale of several million years, they dissolve as they do not form massive clusters but rather in dispersed stellar associations.
Hence, high-resolution surveys such as the present one are necessary to detect young stars in the galactic center.
The oldest population of stars is also found in Sagittarius B1. Stars with an age exceeding seven billion years can be found in the galactic center, but stars with an age between two and seven billion years are almost nonexistent.
The Milky Way’s innermost region may have begun the star formation process before spreading to the galaxy’s outer regions. There are other galaxies in the universe that demonstrate this inside-out mechanism for creating the nuclear disks surrounding the galactic center.
According to the new findings, our galaxy’s central region may be experiencing the same phenomenon.
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