We’ve never seen anything quite like this.
For the first time, astronomers have actually found a baby planet responsible for carving out gaps in the dusty disk surrounding a newborn star.
Previous observations of such disks showed gaps, but the objects sculpting them remained elusive to our telescopes.
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The discovery of WISPIT-2b, as the exoplanet has been named, finally confirms long-held theories about how baby planets form and grow. It represents something of a game changer for planetary astronomy, actually: now scientists can flesh out their theories, confident that they are, indeed, correct.
“Dozens of theory papers have been written about these observed disk gaps being caused by protoplanets, but no one’s ever found a definitive one until today,” says astronomer Laird Close of the University of Arizona.
“It’s been a point of tension, actually, in the literature and in astronomy in general, that we have these really dark gaps, but we cannot detect the faint exoplanets in them. Many have doubted that protoplanets can make these gaps, but now we know that in fact, they can.”
The process whereby stars and their planets are born is a complex one. First, a region in a cold molecular cloud needs to become compressed enough that a large, dense knot collapses under gravity. That’s the seed of the star, or protostar. As it spins, material from the cloud around it is forced by angular momentum into a disk that feeds the growing protostar.
Eventually, the protostar becomes so massive that the pressure and temperature in the core are high enough to ignite nuclear fusion. At the same time, stellar wind pushes the inner disk away, out of reach of the star’s gravitational pull. What’s left of that disk continues to orbit the star, clumping together to form the star’s planets, asteroids, and comets.
During this clumping together, gaps open up in the protoplanetary disk, which we see as rings around the star. The Atacama Large Millimeter/submillimeter Array, for example, has imaged many of these disks and the gaps therein. But the actual planets carving them are a lot harder to see.
Planets in the throes of formation are particularly rich in hot hydrogen gas that emits a great deal of light called H-alpha. To detect this signature in the gaps in protoplanetary disks, an international team of scientists designed MagAO-X, an adaptive optics regime for the Magellan Telescope.
“As planets form and grow, they suck in hydrogen gas from their surroundings, and as that gas crashes down on them like a giant waterfall coming from outer space and hits the surface, it creates extremely hot plasma, which in turn, emits this particular H-alpha light signature,” Close says.
“MagAO-X is specially designed to look for hydrogen gas falling onto young protoplanets, and that’s how we can detect them.”
The star TYC-5709-354-1 – now also known as WISPIT-2 – is a baby Sun-like star about 434 light-years away. Previous observations revealed a large disk around it with what the researchers called a “spectacularly large” gap. They used MagAO-X to study a selection of stars, but it wasn’t until WISPIT-2 that they got a hit.
And what a hit. Combined with observations in near-infrared taken using the ESO’s Very Large Telescope, the researchers were able to determine some key properties of the still-forming system.
The protoplanet WISPIT-2b, a gas giant about five times the mass of Jupiter, sits in that spectacularly large gap, about 54 astronomical units from its star. That’s 54 times the distance between Earth and the Sun; for context, Pluto orbits at 40 astronomical units.
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It’s an incredible discovery, one that reveals what our own Solar System may have looked like as it was forming around a baby Sun, the researchers say. As such, it can give us insight into not just system formation in general, but how our own little corner of the galaxy came into being.
“This is the first ring-forming embedded planet ever observed, giving the planet-formation community a unique chance to learn more about the physics of planet-forming discs – especially how viscous they are, a key factor in how they spread over time and transport material and angular momentum,” says astronomer Richelle van Capelleveen of Leiden University in the Netherlands.
“This system will likely remain a benchmark for many years.”
The discovery has been published in two papers in The Astrophysical Journal Letters. They can be found here and here.