Just like it can be hard to fully understand a city’s skyline from the sidewalk view in the theatre district, it is hard to understand our galaxy’s structure from our perspective about halfway out from the galactic center.

We do the best we can, and we spend a lot of time looking at other galaxies and hoping that what we learn about them also applies to us. For many years, astronomers have been aware that distant young galaxies first form stars in their core, and that star formation moves outward.  Confirming if that happened in our Milky Way has been a challenge both because there is gas and dust blocking a lot of our view of the galactic core and because when we can peer in, the galaxies are so packed together that they are hard to study individually.

Now, using high-resolution infrared images taken with the Very Large Telescope (VLT) in Chile, researchers have been able to peer through the gas and dust and resolve individual stars. Infrared light isn’t scattered off dust and gas the same way the colors of light we see with our eyes are scattered. Just like a soldier can see people through plaster walls with infrared glasses, telescopes can see stars through walls of gas. And the VLT is not just any telescope; it is actually a suite of 4-8 meter telescopes with numerous one-meter helper scopes that can combine their light to obtain the highest currently possible resolution images. In this case, they were able to make out objects just two-tenths the width of a hair held at arm’s length.

In new research published in Nature Astronomy, researchers led by Francisco Nogueras-Lara use 150 VLT images to map out three million stars in the Milky Way’s central region. Previously, we’d only had data for a few stars in this region.

In going from data on a few stars to a few million stars, researchers were able to determine stellar ages as a function of distance from the galactic core in a statistically significant way. While there are young stars and old stars everywhere, the average age was found to change, with the innermost stars forming more than seven billion years ago. They also found that while modern stars away from the galactic center are often formed in massive clusters, the stars in the galactic center formed in small associations that quickly fell apart, leaving the core with a mess of elder stars with no clear groupings remaining.

According to Nogueras-Lara: Our study represents a big step forward in finding the young stars in the Galactic Center. The young stars we found have a total mass of more than 400,000 solar masses. That is nearly ten times higher than the combined mass of the two massive star clusters that were previously known in the central region.

Now that we’ve tested our theory that stars formed from the inside out, we may be ready to start asking just how did those stars end up forming the peanut-shaped distribution of stars that we see?

More Information

MPIA press release

“Detection of an excess of young stars in the Galactic Centre Sagittarius B1 region,” Francisco Nogueras-Lara, Rainer Schödel, and Nadine Neumayer, 2022 August 25, Nature Astronomy