Galactic conditions during the epoch known as "cosmic noon" may have significantly influenced the formation of planets in the Milky Way, according to recent astronomical studies. This period, characterized by intense star production and high levels of background radiation, has been linked to a reduced number of small planets around older stars in the galaxy's thick disk. The findings suggest that while super-Earths and sub-Neptunes are the predominant outcomes of planet formation, the environmental conditions during cosmic noon played a crucial role in shaping planetary development.
Astronomers have found that stars in the Milky Way predominantly reside in two main regions: the thin disk and the thick disk. The thick disk is home to older stars, approximately ten billion years old or more, whose orbits extend above and below the galaxy's main plane. While most thin disk stars are thought to host at least one planet, those in the thick disk appear to have about half as many small planets. The disparity is attributed to the cosmic tumult experienced by thick disk stars during their formation.
Stars born during cosmic noon, a period of furious star production, faced a challenging environment with background radiation levels between one million to ten million times higher than present-day star-forming regions. This intense radiation likely disrupted protoplanetary disks, curtailing their ability to form planets within just a few hundred thousand years.
“These stars, having been born at cosmic noon, had less opportunity to form planets because their disks were destroyed,” – Hallatt
The study reveals that the violent conditions of cosmic noon hindered thick disk stars from developing and retaining planets. Nearly half of the stars in the thin disk host planets ranging in size between Earth and Neptune, highlighting the stark contrast in planet formation outcomes between the two stellar populations.
“As far as we can tell, the dominant outcome of planet formation in the Milky Way is to produce these super-Earths and sub-Neptunes,” – Hallatt
The research also underscores how these conditions impact not only smaller planets but potentially larger ones as well. The insights gained extend beyond super-Earths and mini-Neptunes, suggesting that the broader planetary architecture of the Milky Way has been shaped by its tumultuous past.
“It’s fantastic to be able to make that link … to draw a conclusion that says, here’s a real discernable impact of the radiation environment on the planets.” – Thomas Haworth
During cosmic noon, the Milky Way experienced its most vigorous period of star formation ever recorded, which led to an environment hostile to planet formation. The intense radiation emitted during this time likely played a pivotal role in eroding planet-forming disks around emerging stars.
“It was the most intense period of star formation ever.” – Hallatt
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