Galactic imbalance: Ancient radiation “killed” planets in embryo

The planets in the Milky Way are not evenly distributed. Stars in the thin, flat disk of the Galaxy are much richer in planets than their neighbors in the thicker layer of the disk. Scientists believe this is due to the conditions under which these stars formed.

Exoplanets in the galactic disk. Illustration generated by artificial intelligence Dall-E

Influence of “cosmic noon”

Tim Hallatt, an astrophysicist at the Massachusetts Institute of Technology, along with Eve Lee of the University of California, San Diego, investigated why stars in a thick disk had fewer planets. They concluded that it depended on the time of their formation. The results were published in The Astrophysical Journal.

10 billion years ago, during the so-called “cosmic noon,” the Milky Way was actively forming new stars. This period was extremely chaotic, with young stars emitting huge amounts of radiation that destroyed the disks of gas and dust around other stars, preventing the formation of planets.

The researchers calculated that the background radiation at that time was 1 to 10 million times greater than today’s radiation. This led to the rapid destruction of planet-forming disks — in a few hundred thousand years. By comparison, such disks in the modern Milky Way have existed for millions of years, giving time for planets to form.

The Age of Planetary Formation

Modern stars that form in the thin disk have better conditions for planet formation. Astronomers have found that about half of these luminaries have planets between the size of Earth and Neptune. These super-Earths and mini-Neptunes are the dominant types of planets in the Milky Way. 

The Milky Way Galaxy in an artist’s impression

In the thick disk, however, such planets are twice as rare. This supports the idea that stars that formed under extreme conditions in the galactic past had much fewer chances to form planets due to the destruction of their protoplanetary disks.

Hallatt notes that the findings apply not only to super-Earths, but also to larger planets. If planet-forming disks collapse in such a short time, the formation of giant planets such as Jupiter or Saturn becomes even more difficult.

Importance of discovery 

This research helps us understand how the conditions of star formation affect their planetary systems. Thomas Haworth, an astrophysicist at Queen Mary University of London, calls the idea reasonable and logical. Typically, studies have focused on isolated protoplanetary disks or young stars, whereas this analysis links these environments to galaxy-scale planet formation.

“This allows us to see the real impact of the galactic environment on planet formation,” Haworth concludes.

We previously reported on how ALMA discovered a protoplanetary disk outside the Milky Way for the first time.

According to sciencenews.org

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