Thanks to Hubble Space Telescope, old and dim white dwarf stars offer early Milky Way formation blueprint. A new analysis published in the Astrophysical Journal reveals how the ancient stars found in the myriad of stars in the bulge of the Milky Way shed light on the early phases of formation of our galaxy.
Forming almost two billion years back, the foundation of the Milky Way is a bulge of stars, once populated by intensely bright stars. Now, some of the stars found here are white dwarfs, difficult to detect and analyze. Thanks to detailed Hubble Space Telescope images, a team of astronomers was able to pinpoint the white dwarf stars, selecting 70 of the hottest ones for a deeper analysis.
White dwarf stars are only remnants of the early formation phases of a galaxy. Located in the crowded center bulge of the Milky Way, they are still comparable in size to Earth, only 200,000 times denser.
The bulge, believed to be the building stone of the Milky Way is home to approximately 70,000 stars. The images used by the research team portray this region at the heart of the galaxy and were taken over a period of ten years. Due to the timespan, the team was able to analyze the movement of the stars over time, as well as any other changes. Stars found right in the bulge move slower than the rest. Clearly visible, the bulge resides approximately 26,000 light years away from Earth.
Of the 70,000 stars, the team picked out the hottest 70 white dwarf stars, using theoretical models that would help them identify the stars and detect them in the Hubble Space Telescope images.
Looking at the color of the stars in the region, the astronomers were also able to detect the white dwarf stars thanks to their blue hue. While different when they would have formed, the white dwarfs tend to lose luminosity and become cooler as they age. Due to this process, it becomes increasingly difficult even for Hubble’s instruments to detect them accurately.
Nonetheless, old and dim white dwarf stars offer early Milky Way formation blueprint. The analysis reinforced the hypothesis according to which the first formation phase of our home galaxy started within the bulge. The disk and arms of the galaxy followed in time.
While this analysis offers a fresh perspective, the team suggested that the bulge image captured by Hubble Space Telescope may be in fact home to 100,000 such stars. However, until new, more performant tools are deployed for in-depth observations, they will remain hidden.
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