Shocking new discoveries from the James Webb Space Telescope (JWST) confirm evidence from the early Hubble Space Telescope that gas-rich giant planets may have formed more easily in the early universe than they do today.
2003, Harper Found a huge exoplanet. There’s nothing too unusual about this, but closer inspection reveals that the planet, named PSR B1620-26b, is rather strange. It orbits not one but two objects, one pulsar and a white dwarf. These are the ashes of two dead stars – one a supernova and the other a supernova. sunrespectively – quasi-star, and was the first discovered binary orbiting exoplanet (orbiting a binary means orbiting two stars, e.g. Tatooine exist”Star Wars“).
This planet is located in a globular cluster, Messier 4More than 6,000 light years From the earth. Globular clusters are ancient, tightly packed spheres of hundreds of thousands of stars. PSR B1620-26b remains the only planet discovered in a globular cluster.
All this evidence points to the most unusual thing about PSR B1620-26b, which is that it is very old. It is estimated to have formed 12.7 billion years ago, making it the oldest exoplanet known to date.
Yet Haber’s discovery was controversial. It is generally believed that planets could not have formed so early in their 13.7 billion year history. universe Because there is not enough time for generations of stars to produce many element Heavier than primordial hydrogen or helium, planets typically require these heavier elements. This is especially true for the dust, gas, planet-forming or “protoplanetary” disks surrounding young stars.
“Current theoretical models predict that because there are so few heavier elements, the disk around the star is short-lived, in fact too short for the planet to grow in size,” said co-investigator Elena Sabbi, principal scientist at the NOIRLab Gemini Observatory in Arizona. . statement. “But Hubble did see one of the planets, so what if the model is incorrect and the disk could have lived longer?”
Now John WestThe Near Infrared Spectrometer (NIRSpec) instrument has found solid evidence that planet-forming disks survive even when they contain relatively few heavy elements, strongly suggesting that planet formation was possible early in the universe’s history, even if we don’t fully understand it Understand what’s going on.
The James Webb Space Telescope specializes in observing galaxies from the first billion years of cosmic time, but in this mission it’s pointed closer to home: young star clusters NGC 346 exist Small Magellanic Cloud (SMC), which is a satellite galaxy Milky Way It’s about 200,000 light-years away.
Dwarf galaxies like the SMC are generally not chemically evolved because their star formation histories are not very long, so they have not had the opportunity to accumulate many heavy elements such as carbon, nitrogen, oxygen, silicon, or iron. For example, NGC 346 contains heavy element abundances in about 10% of the Milky Way’s star-forming regions. This makes star clusters such as NGC 346 excellent representatives for studying similar conditions in the early universe.
NGC 346 is still forming a large number of stars, and JWST found that many young stars, between 20 and 30 million years old, still have planet-forming disks around them. Their existence is confusing.
Guido de Marchi of the European Center for Space Research and Technology said: “With the Webb telescope, we have strong confirmation of the results seen by Hubble. We must rethink how to predict planets in the young universe. Create computer models of formation and early evolution.
20 to 30 million years is a very long time for a disk to survive. our protoplanetary disk solar system Not thought to survive that long. The discovery shows that protoplanetary disks can not only form and survive in environments lacking heavy elements, but can also last longer, giving planets more time to assemble. While there may not be enough heavy elements to create massive rocky worlds, gas giant planet For example Jupiter and saturn Mainly hydrogen and helium, which are everywhere.
Related: Have astronomers found the “secret recipe” for rapid planet growth?
So why do planet-forming disks around stars in NGC 346 (and possibly stars in the early universe) persist for so long? DeMarchi’s team has two possible explanations.
One is that a disk made almost entirely of hydrogen and helium is harder to blow away by starlight. Radiation pressure from emerging stars at the center of the disk usually determines the disk’s lifetime, but the process is more efficient when there are heavy, dust-forming elements in the disk for the star’s photons to push. Therefore, disks lacking heavy elements can last longer.
The second possibility goes back to the formation of the stars themselves. In nebulae lacking heavy elements, it is more difficult for the gas clouds to collapse into stars. The cloud would need to become more massive than is typical in today’s Milky Way to become cold enough for gravity to cause it to collapse. Larger clouds would result in a larger disk carrying more mass, and the mass would take longer to transfer the star’s radiation.
“The more material there is around the star, the longer accretion lasts,” Sabi said. “These disks can take 10 times longer to disappear. This has important implications for how planets form and what can be had in these different environments.” Planetary system types have an impact. ”
New findings published in The Astrophysical Journal December 16th.