Our Milky Way is a bit of an oddball galaxy, a new study confirms.

Our Milky Way Galaxy, often billed as an ordinary giant spiral galaxy, one of billions of disk galaxies filling the observable universe, had an unusually early start. or the new paper you just submitted Astrophysical Journal.

What is clear is that the Milky Way and many other galaxies like it were massive enough to begin forming disks within the first few billion years after the Big Bang. This is also confirmed by new observations from NASA’s Webb Space Telescope.

Our findings suggest that the Milky Way initially gathered most of its mass and then did not experience any significant mergers with other galaxies that could disrupt the disk, Vadim Semenov, an ITC postdoctoral fellow at NASA Hubble and Harvard University, told me. . cell phone.

Using computer simulations of a representative sample of galaxies like the Milky Way, the authors point out that most such galaxies formed galactic disks much later than our own. However, about 10% of the Milky Way’s mass galaxies formed disks very early, similar to our own, the authors write.

Semenov says he looked at 61 relatively large samples drawn from simulations of representative cosmic volumes (essentially cosmic chunks). “We’ve found that when galaxies get massive enough, they tend to form disks,” he says. After the disk forms, Semenov says, the rest of the galaxy’s evolution should be relatively quiet, with no significant mergers with other galaxies that could destroy the disk.

Why is this important?

Understanding disk galaxy formation is a fundamental question in astrophysics, but also has connections to many other fields, from cosmology to planetary formation, says Semenov. Most stars in the universe form in disk galaxies, he says. And stars, Semenov says, in turn synthesize chemical elements to define the chemical evolution of the universe.

The early universe appears to be rough and hairy.

The rate of star formation was higher. Newly formed massive stars exploded more frequently as supernovae, causing turbulence in the gas in the nascent disk and making it thicker, Semenov says. Gas accretion from the intergalactic medium was also more active, and galactic mergers were more frequent, he said.

What about our Milky Way?

Galactic archaeological data suggest that there were multiple stages in the evolution of our galaxy, Semenov says. First, he says, there was a chaotic state (“protogalaxy”) without a transparent disk.

The progenitors of our galaxy were highly irregular and experienced violent and chaotic accumulations of gas from the intergalactic medium and frequent mergers with other galaxies, Semenov says. Over time, he says, this active evolution settled and the galactic disk appeared. These early disks were likely very different from the disks we see today, he points out, and were much thicker and turbulent.

But it later settled on the thin discs we see today, Semenov says.

What surprised you most about your team’s results?

One surprise, says Semenov, is that Milky Way analogues are no more rare than we found. From these results, he says, only a small fraction (if any) of the Milky Way’s mass disk could be expected to form early. But 10 percent of those early-forming galaxies is a fairly significant fraction, says Semenov.

However, the authors point out that there is still no consensus on how galactic disks actually form.

That remains an open question, says Semenov.

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