Astronomers have taken unprecedented images of baby planets in a distant star system. The planets are still surrounded by rings of gas and dust from which moons appear to be taking shape.
The two imaged infant planets, or “protoplanets,” orbit the star PDS 70, located 370 light-years away in the constellation of Centaurus. PDS 70 is little more than a toddler in stellar terms, at just around 5 million years old. If this seems ancient, consider that our “middle-aged” solar system is around 4.6 billion years old.
The scientists behind this research believe that, billions of years ago, the solar system would have resembled a mini-version of the PDS 70 system.
Astronomers at the University of Arizona imaged the extrasolar planets, or “exoplanets,” using the sophisticated Magellan Adaptive Optics Xtreme (MagAO-X) instrument paired with the 6.5-meter Magellan Telescope at Las Campanas Observatory in Chile.
The team also observed, for the first time, changes in the brightness of the protoplanets, which indicates they are experiencing a turbulent growth process.
“We can see, for the first time, rings of dust surrounding protoplanets made visible by the bright starlight reflecting off of them,” team member Jialin Li, a doctoral student in astronomy at the University of Arizona, said in a statement.
Protoplanets are extremely rare, with these two, designated PDS 70 b and PDS 70 c, being the only ones confirmed in an exoplanet catalog containing over 5,000 worlds beyond the solar system.
Sharper images of rare protoplanets such as these and the dust around them could be vital to understanding how planets grow and how they go on to develop moons, or “exomoons,” when located beyond the solar system.
Examining feeding habits of baby planets
PDS 70 b and PDS 70 c are both already several times as massive as Jupiter, but their young age of 5 million years indicates they are still growing by gathering matter from the cloud of gas and dust, or “protoplanetary disk,” that surrounds their parent star.
“Multiple massive planets act kind of like brooms or vacuum cleaners,” team leader Laird Close, a professor of astronomy at Steward Observatory, said in a statement. “They basically scatter the dust away and clear the large gap that we observe in this great big disk of gas and dust that surrounds the star.”
An artist’s impression of the PDS 70 system with protoplanets, each surrounded by dust rings illuminated by starlight. The planets themselves (not to scale) have thin rings of plasma heated to around 14,000 degrees Fahrenheit, which glow at the red emission line of H-alpha light. (Image credit: Emmeline Close and Laird Close)
As matter composed predominantly of hydrogen gas “waterfalls” onto protoplanets, these infant worlds glow in the so-called H-alpha wavelength of light. This light comes from the gas being “shock heated” as it hits the protoplanet’s surface.
“Targeting that special wavelength of light allows MagAO-X to effectively limit noise and distinguish between protoplanets and their surrounding features or imaging artifacts,” Close said.
Over the course of three years, the team saw PDS 70 b fade to one-fifth of its original brightness while its sibling protoplanet, PDS 70 c, doubled its brightness. This indicated to the researchers a change in the amount of matter falling to these protoplanets.
“Essentially, one of the planets abruptly went on a diet while the other was feasting on hydrogen,” Close said.
As of now, the team isn’t sure what changed the dietary habits of these infant exoplanets.
The protoplanetary disk around the infant star PDS 70 as seen by ALMA. (Image credit: ALMA (ESO/NAOJ/NRAO)/Benisty et al.)
The observation of these protoplanets is a remarkable achievement for MagAO-X, which is an adaptive optics system. That means it corrects for turbulence in the atmosphere and eliminates the “twinkling” of stars. This allows MagAO-X to make images that rival those produced by an optical space telescope.
“The mirror shape-shifts at a rate comparable to adjusting an eyeglasses prescription 2,000 times per second. Because our technology removes disturbances from the atmosphere, it’s a bit like taking a 6-1/2-meter telescope mirror and putting it in outer space by clicking a computer mouse button,” Close explained. “This level of resolution revealed features around these planets in incredible detail.
“To give you an idea of the resolution, picture me standing in Phoenix and you standing in Tucson. With MagAO-X, you’d be able to see whether I’m holding up one quarter-dollar coin or two from 125 miles away.”
Close and colleagues will now use MagAO-X to search for more protoplanets around other young stars.
“While discovering these protoplanets is right at the edge of what is technically possible today, as technology improves we should discover more such systems in the near future,” he concluded.
The team’s research was published in The Astronomical Journal.
