Astronomers have discovered a massive extrasolar planet, or “exoplanet,” orbiting an ultra-cool dwarf star that is too small to host such a world, challenging scientists’ models of how planets and planetary systems are born.
The planet in question, called LHS 3154 b, is 13 times larger than itself. SoilIn other words, it has a mass similar to the ice giant in the solar system. Neptuneyet it orbits a small dwarf star whose mass is nine times smaller. Sun.
This means the ratio between the Neptune-like world and its parent star, LHS 3154, located around 51. light years far away – 100 times greater than the mass ratio between Earth and the sun, something researchers did not think was possible. This is the first time a planet with such a large mass has been found around one of the universe’s smaller stars.
“This discovery really shows how little we know about it. Universe,” study co-author and Verne M. Willaman Professor of Astronomy at Penn State University and AstrophysicsSuvrath Mahadevan, he said in a statement. “We did not expect such a heavy planet to exist around such a low-mass star.”
Relating to: This rare exoplanet system has 6 ‘sub-Neptunes’ with mathematically perfect orbits.
Challenging how stars and planets are born
Stars form when vast clouds of gas and dust accumulate extremely dense patches that grow until they collapse under their own gravity. This causes a newborn star to be surrounded by a disk of residual material called a “protoplanetary disk.”
As the name suggests, scientists believe planets eventually emerged from this disk of material. The amount of material left over from the formation of the star sets a limit on how large these potential planets can be.
The team determined that LHS 3154 b has a planetary core so heavy that the disk forming the planet from which it came must hold large amounts of solid material. In short, it must have more material than existing models can predict, study co-author and astronomy Megan Delamer, a graduate student at Penn State, explained.
Thus, the discovery of this special outer planet It also raises questions regarding its formation. stars. This is because the dust/mass and dust/gas content ratios of the original protoplanetary disk of LHS 3154 would have to be ten times higher than predicted for a Neptune-like world as large as LHS 3154 b to arise. .
“The planet-forming disk around the low-mass star LHS 3154 is not expected to have enough solid mass to form this planet,” Mahadevan explained. “But it’s out there, so now we need to re-examine our understanding of how planets and stars form.”
Habitable Zone Planet Finder exceeds expectations
Mahadevan and colleagues detected the exoplanet LHS 3154 b using the Habitable Zone Planet Finder (HPF), an astronomical spectrograph on the Hobby-Eberly Telescope. McDonald Observatory In Texas. HPF is designed to detect exoplanets orbiting some of the coldest stars on the planet. Milky Way.
The particular focus of the device, which Mahadevan helped build with a team, is on planets that are neither too close nor too far from their stars to host liquid water, a basic requirement for life. These would be the planets located in the so-called region. habitable zone around their stars.
Detecting such planets is not easy, in part because the habitable zone of cool stars is much closer to these stars than the zone in our field. solar system, for example. This means that these worlds are often obscured by the light from their relatively small parent stars.
Additionally, these planets themselves are expected to be small, making them difficult to detect.
“Think of the star as a campfire. The colder it gets, the closer you’ll have to get to the fire to stay warm,” Mahadevan said. “The same goes for planets. If the star is cooler, the planet will need to be closer to that star if it is to be hot enough to contain liquid water.
“If a planet orbits close enough to its ultra-cool star, we can detect it by seeing a very slight change in color in the star’s spectrum, or light, as it is pulled by an orbiting planet.”
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The detection of LHS 3154 b is important to HPF because it demonstrates the potential of the instrument and its crew to deliver significant exoplanet results. NASA This result exceeded all expectations for the device, says the Sagan Fellow in the Department of Astrophysics at Princeton University.
“What we discovered provides an extraordinary test case for all current theories of planet formation,” Mahadevan concluded. “We built HPF to do just that—explore how the most common stars in our galaxy form planets and find those planets.”
The team’s research was published Nov. 30 in the journal. Science.