A cosmic cradle in sight: Astronomers have gained insights into the formation process of a distant giant planet. Images from the Hubble space telescope show how the planet’s offspring absorbs hot gas from its environment, which glows in the UV range. It was also possible to estimate the rate of growth of the already huge planet, which is probably at the end of its formation process.
Distant worlds have gone online en masse in recent years – that’s why the focus is now on the special specimens and astronomers are trying to coax more and more secrets from them. The baby planets are of particular interest. Because insights into the planetary nurseries can also shed light on the history of our solar system, in which the earth and its siblings once also formed from a protoplanetary disk.
In the field of research into young planetary systems, images from the Very Large Telescope caused a sensation in 2018: They showed a planet that is growing in the dust disk around a young star and has already reached five times the mass of Jupiter. The exoplanet with the designation PDS 70b was estimated to be five million years old on an astronomical scale. It orbits a dwarf star 370 light years from Earth in the constellation Centaurus.
An astro celebrity in the UV perspective
This giant planetary baby was once again the target of an international team of astronomers. “So far, we know little about how giant planets are formed. This system provided opportunities to watch material fall on a planet, ”says co-author Brendan Bowler of the University of Texas at Austin. NASA’s Hubble Space Telescope was used in their investigations. As the astronomers explain, its special sensitivity to ultraviolet radiation (UV) enabled insights into the planetary growth process. Because in this wavelength range the hot gas glows when the planet absorbs it from its environment.
In order to be able to “see” this with Hubble, however, there was a daunting challenge to master: the astronomers had to hide the parent star. Because it shines more than 3000 times brighter in the UV wavelength range than the Planet PDS 70b. The researchers finally succeeded in developing an image processing method that removes the star’s glare so that only the light emitted by the planet can be seen. This is an important aspect of the study, the scientists emphasize. Because the process expands the possibilities of planetary investigation using Hubble.
With their UV observations, the astronomers have now been able to illustrate how the material of the star’s gas and dust disk becomes the food of the young planet. The PDS 70b is surrounded by its own gas and dust disk, which in turn sucks material out of the much larger circumstellar disk. The researchers suspect that magnetic field lines extend from the circumstellar disk into the exoplanet’s atmosphere and conduct material onto the planet’s surface.
The growth rate is emerging
Through their observations over five months, the astronomers were also able to estimate the extent of the material influx: “With the observations from Hubble we were able to calculate how quickly the planet was gaining mass,” says co-author Yifan Zhou of the University of Texas. “Our measurements suggest that PDS 70b is at the end of its formation process.” Because with the currently measured accretion rate, it will only increase by about a hundredth of a Jupiter’s mass in another million years. In the estimated five million years of its existence, however, it has already accumulated five times the mass of the largest planet in our solar system.
In order to be able to assess more precisely how PDS 70b will develop further, however, further data are necessary, say the scientists. They could show how the rate of mass gain changes over time. “We can now examine this system repeatedly, and in addition, our observation strategy and post-processing technology now open new windows to examine similar systems with Hubble,” says Bowler. With future observations, we could possibly gain clues as to when the majority of the gas and dust fall on planets as they are formed and whether this happens at a constant rate, ”says the astronomer.
Source: NASA, technical article: The Astronomical Journal, doi: 10.3847 / 1538-3881 / abeb7a