Gaia Discovers the Milky Way’s Protogalaxy Heart, Even excluding Andromeda, the Milky Way is much larger than any of the other galaxies in the nearby group by several orders of magnitude. The process of consuming smaller galaxies to get larger is known as cannibalism.
The GAIA space telescope has made it possible to trace the origins of groups of stars by comparing their velocities and ages.
It seems likely that the Milky Way has a core population of stars that have been there since the galaxy’s infancy, but pinpointing them has proven difficult. However, in a recent study that is currently being peer-reviewed, Professor Hans-Walter Rix of the Max Planck Institute for Astronomy and co-authors claim to have done just that.
Finding the Milky Way’s first stars is difficult since they must be as old as the galaxy itself, which is roughly 12.5 billion years. Because stars with a mass greater than the Sun don’t live for very long, astronomers must focus their efforts on finding low-mass stars.
Some of these stars, however, are already in their giant phase, the point at which they expand to vast sizes and become luminous enough to be seen from great distances
Another issue is that, from our vantage point, the core of the galaxy (Sagittarius) is already quite busy, and these stars should be there
“People have long believed that such a massive population [of old stars] should exist in the heart of our Milky Way,” Rix said in an interview with ScienceNews. These stars would be made almost entirely of hydrogen and helium, making them very metal-poor.
The first stars to explode as supernovae produced a lot of metals, which were then dispersed across the surrounding areas to be used in the construction of subsequent generations of stars. Littler stars that formed before the blasts didn’t get any of the metals
Using GAIA data for 2 million stars within 30 degrees of the galactic center, Rix and co-authors discovered a cluster of 18,000 stars with metal abundances less than 3 percent of those of the Sun.
Because stars taken from smaller merged galaxies can also be relatively metal-poor, the report explains, it can be difficult to tell which stars are original to the Milky Way and which were sucked in during the merger.
However, the authors maintain that the stars’ motions relative to the galactic center can be utilized to pinpoint their birthplaces. The authors estimate that 0.2% of the mass of the Milky Way comes from this original population of stars that are obscured by dust and other debris.
Rix contends that the mass-boosting mergers actually nourished more distant regions of the galaxy. Since the core hasn’t been expanded through subsequent mergers, Rix claims, “we didn’t have any later mergers that significantly entered into the core and shook it up.”
One Twitter user said it was “Easily the most poetic title of a scientific study in a long time” because the paper was titled “The Poor Old Heart of the Milky Way.”