Confirmation of New Study: The Milky Way Galaxy Exhibits Unusual Characteristics

Our Milky Way Galaxy, often portrayed as an ordinary massive spiral, is believed to have formed earlier than expected, according to a new study submitted to The Astrophysical Journal.

It is clear that the Milky Way, along with other similar galaxies, was sufficiently massive to begin forming its disk within a few billion years after the big bang. This conclusion is supported by recent observations conducted by NASA’s Webb Space Telescope.

The findings suggest that the Milky Way accumulated most of its mass in the early stages and did not experience significant mergers with other galaxies that could disrupt its disk formation. Vadim Semenov, a NASA Hubble and ITC postdoctoral fellow at Harvard University, explained that computer simulations of Milky Way-like galaxies indicate that most of them formed their disks later than our own galaxy. However, around ten percent of galaxies with a similar mass to the Milky Way formed their disks early, like ours.

Semenov clarified by stating, “We examined a large sample of 61 Milky Way analogs from simulations of a representative cosmological volume. We found that galaxies tend to form disks when they reach a certain mass. Once the disk is formed, the galaxy’s evolution needs to remain relatively calm without major mergers that could disrupt the disk formation process.”

So, why is this discovery important?

Semenov explains, “Understanding the formation of disk galaxies is a fundamental question in astrophysics. It also has implications across various fields, from cosmology to planet formation. Most of the stars in the universe are formed in disk galaxies, and these stars synthesize chemical elements, shaping the chemical evolution of the universe.”

The early universe was a turbulent place.

Semenov describes how the rate of star formation was higher back then, resulting in more frequent supernovae explosions. This turbulence disturbed the gas in the early disks, making them thicker. Additionally, there was active gas accretion from the intergalactic medium and a higher frequency of galaxy mergers.

Now, let’s focus on our own Milky Way.

Semenov explains, “Galactic archeology data indicates that our Galaxy went through several stages of evolution. Initially, there was a chaotic state without a clear disk, known as a ‘proto-galaxy.’ The progenitor of our galaxy experienced vigorous accumulation of gas from the intergalactic medium and frequent mergers with other galaxies. Over time, the evolution settled down, and a galactic disk emerged. This early disk was different from the one we observe today; it was thicker and more turbulent. Eventually, it transformed into the thin disk we see now.”

One surprising aspect of the study’s findings:

Semenov says, “We were surprised to find that Milky Way analogs are not as rare as expected. Based on these results, one might have anticipated only a small fraction, if any, of Milky Way-mass disks to have formed early. However, the fact that around 10% of these galaxies formed their disks early is quite significant.”

Nevertheless, the authors acknowledge that there is still no consensus on the exact mechanism of galactic disk formation.

Semenov concludes, “This remains an open question in astrophysics.”

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