Galactic chaos at cosmic noon may have stunned the formation of the planet of the Milky Way

The Milky Way keeps its planets near its chest. The stars on a thin, flat disk that bite the galaxy have more planets on average than stars on a thicker, wrapping disc – and astronomers now think they know why.

Stars currently living on the Galaxy thick disk have been born during a time of galaxy chaos, says astrophysicist my Hallatt. Violent stars exercise prevented their ability to grow and maintain planets, he and astrophysicist of Lee, formerly McGill University in Montreal, report January 22 in Astrophysics.

Milky Way stars live mainly in two neighborhoods. The new stars, hip climbing together on a thin disc, rotating as if they are all sitting in the same flat rotating record. Older stars, about 10 billion years and up, appear to have been moved to the suburbs, dwelling on a thick disk of stars whose orbits take them up and down this main plane.

Most stars in the hospitality of the thin disk at least one planet, astronomers think. Observations show that nearly half has a planet whose size is between Earth and Neptune. “As we can say, the predominant result of planet formation in the Milky Way is the production of these super-lands and sub-septunes,” Hallatt says.

But as a population, stars on the thick disk seem to have about half of these relatively small planets as the stellar population does thin.

“The mystery is, these planets are very common,” Hallatt says. “And yet when we look at this other prevailing population of the stars on the Milky Way, they are less common. So what’s going on?”

Hallalati thinks it’s a question of when these stars were born, not where they live now. Thick disk stars were born in an era when the Milky Way produced stars with anger, a time of astronomers call it cosmic noon. “It was the strongest period of star formation ever.”

All those newborn stars sent powerful radiation winds to their cosmic neighborhoods. This radiation could have wreaked havoc on any protoplanet trying to form around the stars, says Hallatt.

He and Lee, who is now at the University of California, San Diego, calculated how much radiation an average star at noon Cosmic would have experienced from his neighbors. They found that this background radiation was 1 million to 10 million times what stars experience in a modern region of star formation.

It too much radiation could erode a disk for the formation of the planet within a few hundred thousand years, the double calculation.

“These stars, after being born at noon Cosmic, had less opportunity to form planets because their discs were destroyed,” Hallatt says. Astronomers think that such disks around modern stars last for millions of years before they complete the formation of planets.

The Hallarat focused this study on the super-land and mini-neptunes, but he thinks the conclusion has even the biggest planets. “If our theory is correct, and these discs really wouldn’t live long at cosmic noon, we will expect it to be even harder to form the giant planets.”

The idea is smart and makes sense, says astrophysicist Thomas Haworth of Queen Mary University of London, who studies the planet’s formative discs in the local universe. Most of the early life studies of planetary systems are concentrated on the newborn star or the disk of planet formation in isolation. Linking those environments with eventual planets is difficult.

“It has been this question all over, do they care about the planets?” Says Haworth. “Fantastic is able to be able to make that connection … to draw a conclusion that says, here is a real noticeable impact of the planet radiation environment.”