Young star’s disk confirms how giant planets form

Coalescing gas giants observed sucking in debris from dust ring


Astronomers using the most advanced land telescope in the world have unlocked knowledge about how formidable gas giant planets such as Jupiter and Saturn come into being.

These vast but uninhabitable worlds are created by gobbling up gas and dust that envelop young stars in a murky disk, they believe.

The evidence comes from observations of a youthful star called HD 142527, which is more than 450 light-years from Earth.

Stars are born from a cloud of cosmic gas and dust that continues to surround the star for millions of years after the star bursts into light.

Around HD 142527, the astronomers found an intriguing gap in the dusty disk, and they believe this was carved out by newly forming gas giants.

The planets absorb the debris into their expanding mass as they circle the star, according to the investigation, which appeared in the journal Nature.

The planets also feast on gas that streams across the gap from the outer zone of the disk to the inner zone, which helps to feed the infant star.

“Astronomers have been predicting that these streams must exist, but this is the first time we’ve been able to see them directly,” said University of Chile astronomer Simon Casassus.

Casassus’ team used the Atacama Large Millimeter/submillimeter Array (ALMA), a high-tech telescope still under construction at the European Southern Observatory’s site in Chile’s Atacama Desert.

By observing light at submillimeter wavelengths, ALMA’s images do not suffer from glare in the infrared and visible portions of the light spectrum.

Using it, the team spotted two dense streams of gas flowing across the gap, as well as residues of gas within the gap itself.

“We think that there is a giant planet hidden within (the gap) and causing each of these streams,” said Casassus’ colleague, Sebastian Perez.

“The planets grow by capturing some of the gas from the outer disk, but they are really messy eaters. The rest of it overshoots and feeds into the inner disk around the star.”

The gap itself is huge. It starts at about 10 astronomical units from the star — meaning 10 times as much as the distance of our Earth from the sun — and ends at more than 140 AUs. The putative planets probably lie at around 90 AUs from the star.

Imaging the planets was not crucial to the study’s findings, said a report by Sky & Telescope magazine. Just by observing the gas streams and the residual gas in the cavity, the astronomers were able to measure roughly how much gas was flowing from the outer disk into the inner one.

Since the star is accreting gas at a steady rate, the evidence is heavily in favor of planet-led gas streams. In future observations, the authors hope to measure just how much gas is streaming and get a better idea of the mass of the planets themselves.

In a separate paper, also published by Nature, astronomers using a radio telescope in Australia said an outpouring of gas and charged particles from the center of the Milky Way is a byproduct of the birth of new stars.

The mysterious energy was first detected in 2010, but only now has it been mapped.

The outflow contains about a million times the energy of an exploding star, and extends 50,000 light-years — about half the diameter of our galaxy — and may play a role in generating the Milky Way’s magnetic field.

The energy blast would be lethal for life on Earth if it were directed at us, but the jets are moving in a different direction.