The violent events that led to the death of a star would likely displace all planets. The newly discovered Jupiter– large object may have arrived long after the star died.
An international team of astronomers with NASATransiting Exoplanet Survey Satellite (Tess) and the retired Spitzer Space Telescope have reported what is possibly the first intact planet found in close orbit a white dwarf, the dense remnant of a sun-like star, only 40% larger than Earth.
The Jupiter-sized object with the designation WD 1856 b is about seven times larger than the white dwarf with the designation WD 1856 + 534. It orbits this star slag every 34 hours, more than 60 times faster than Mercury orbits our sun.
How could a giant planet have survived the violent process that turned its parent star into a white dwarf? Astronomers got some ideas after discovering the Jupiter-sized object WD 1856b. Photo credit: NASA /JPL-Caltech / NASA Goddard Space Flight Center
“WD 1856b somehow got very close to its white dwarf and managed to stay in one piece,” said Andrew Vanderburg, assistant professor of astronomy at the University of Wisconsin-Madison. “The process of forming the white dwarf destroys nearby planets, and anything that comes too close later is usually torn apart by the star’s immense gravity. We still have many questions about how WD 1856b got to its current location without meeting either of those fates. “
An article about the system, led by Vanderburg and involving several NASA co-authors, appears in the September 16, 2020 issue of nature.
TESS monitors large parts of the sky, so-called sectors, for almost a month. This long gaze enables the satellite to find exoplanets or worlds beyond our solar system by capturing changes in star brightness that occur when a planet crosses or crosses its star.
The satellite discovered WD 1856b about 80 light years away in the northern constellation Draco. It orbits a cool, calm white dwarf approximately 18,000 kilometers in diameter, can be up to 10 billion years old, and is a distant member of a triple star system.
When a sun-like star runs out of fuel, it swells up to hundreds to a thousand times its original size, forming a cooler red giant star. Eventually it expels its outer layers of gas and loses up to 80% of its mass. The remaining hot core becomes a white dwarf. Any nearby objects are usually engulfed and burned during this process, which in this system would have included WD 1856b in its current orbit. Vanderburg and his colleagues estimate that the possible planet must have formed at least 50 times further away from its current location.
“We have known for a long time that distant small objects like asteroids and comets can scatter inward to these stars after the birth of white dwarfs. They’re usually pulled apart by the strong gravity of a white dwarf, turning into a disk of debris, ”said co-author Siyi Xu, an assistant astronomer at the Gemini International Observatory in Hilo, Hawaii, a program of the National Science Foundation’s NOIRLab. “That’s why I was so excited when Andrew told me about this system. We saw evidence that planets could also scatter inward, but this appears to be the first time we’ve seen a planet that made the entire journey intact. “
The team suggests several scenarios that WD 1856b could encounter on an elliptical path around the white dwarf. That trajectory would have become more circular over time as the star’s gravity stretched the object, creating enormous tides that dissipated its orbital energy.
“The most likely case involves several other Jupiter-sized bodies near the original orbit of WD 1856 b,” said co-author Juliette Becker, 51 Pegasi b Fellow in Planetary Science at Caltech in Pasadena. “The gravitational impact of objects this big could easily allow the instability you need to push a planet inward. However, at this point we have more theories than data points. “
Other possible scenarios are the gradual pulling of gravity of the other two stars in the system, the red dwarfs G229-20 A and B, over billions of years, and a rogue star fly by to disrupt the system. The Vanderburg team believes these and other explanations are less likely, as they require finely tuned conditions in order to achieve the same effects as the potential giant companion planets.
However, Jupiter-sized objects can occupy a wide variety of masses, from planets only a few times more massive than Earth to low-mass stars that are a thousand times the mass of Earth. Others are brown dwarfs that span the planet-star boundary. Typically, scientists turn to radial velocity observations to measure the mass of an object, which can be indicative of its composition and nature. This method studies how an orbiting object pulls on its star and changes the color of its light. In this case, however, the white dwarf is so old that its light has become too weak and too strange for scientists to see any discernible change.
Instead, the team observed the system in infrared with a sharpener just a few months before the telescope was taken out of service. If WD 1856b were a brown dwarf or a low-mass star, it would give off its own infrared light. This means that Spitzer would record a brighter transit than if the object were a planet blocking rather than emitting light. When the researchers compared the Spitzer data with visible-light transit observations taken with the Gran Telescopio Canarias in the Spanish Canary Islands, they found no discernible difference. Along with the star’s age and other information about the system, they concluded that WD 1856 b is most likely a planet no more than 14 times the size of Jupiter. Future research and observation may confirm this conclusion.
The search for a possible world that closely orbits a white dwarf prompted co-author Lisa Kaltenegger, Vanderburg and others to examine the effects on the study of the atmosphere of small rocky worlds in similar situations. Suppose an Earth-sized planet was in orbit around WD 1856 where water could exist on its surface. Using simulated observations, the researchers show that NASA is imminent James Webb Space Telescope was able to detect water and carbon dioxide in the hypothetical world by observing only five transits.
The results of these calculations, led by Kaltenegger and Ryan MacDonald, both at Cornell University in Ithaca, New York, were published in The astrophysical diary letters and are available online.
“What’s even more impressive is that Webb can detect combinations of gases in just 25 transits that may indicate biological activity in such a world,” said Kaltenegger, director of the Carl Sagan Institute in Cornell. “WD 1856 b suggests that planets could survive the chaotic history of the white dwarfs. Under the right conditions, these worlds could maintain conditions favorable to life longer than the timescale predicted for the earth. Now we can explore many new fascinating possibilities for worlds orbiting these dead star cores. “
There is currently no evidence that there are other worlds in the system, but it is possible that additional planets exist and have not yet been discovered. They can have orbits that exceed the time TESS is observing a sector, or they can be tilted so that no transits occur. The white dwarf is also so small that the possibility of catching transits from planets further away in the system is very slim.
Reference: “A Candidate for a Giant Planet Crossing a White Dwarf” by Andrew Vanderburg, Saul A. Rappaport, Siyi Xu, Ian JM Crossfield, Juliette C. Becker, Bruce Gary, Felipe Murgas, Simon Blouin, Thomas G. Kaye , Enric Palle, Carl Melis, Brett M. Morris, Laura Kreidberg, Varoujan Gorjian, Caroline V. Morley, Andrew W. Mann, Hannu Parviainen, Logan A. Pearce, Elisabeth R. Newton, Andreia Carrillo, Ben Zuckerman, Lorne Nelson, Greg Zeimann, Warren R. Brown, René Tronsgaard, Beth Klein, George R. Ricker, Roland K. Vanderspek, David W. Latham, Sara Seager, Joshua N. Winn, Jon M. Jenkins, Fred C. Adams, Björn Benneke, David Berardo, Lars A. Buchhave, Douglas A. Caldwell, Jessie L. Christiansen, Karen A. Collins, Knicole D. Colón, Tansu Daylan, John Doty, Alexandra E. Doyle, Diana Dragomir, Courtney Dressing, Patrick Dufour, Akihiko Fukui , Ana Glidden, Natalia M. Guerrero, Xueying Guo, Kevin Heng, Andreea I. Henriksen, Chelsea X. Huang, Lisa Kaltenegger, Stephen R. Kane , John A. Lewis, Jack JL Issauer, Farisa Morales, Norio Narita, Joshua Pepper, Mark E. Rose, Jeffrey C. Smith, Keivan G. Stassun and Liang Yu, September 16, 2020, nature.
DOI: 10.1038 / s41586-020-2713-y
TESS is a NASA Astrophysics Explorer mission directed and operated by WITH in Cambridge, Massachusetts and is administered by NASA’s Goddard Space Flight Center in Greenbelt, Maryland. Other partners include Northrop Grumman, based in Falls Church, Virginia, NASA’s Ames Research Center in Silicon Valley, California, the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, MIT’s Lincoln Laboratory, and the Space Telescope Science Institute in Baltimore. More than a dozen universities, research institutes and observatories around the world are participating in the mission.
NASA’s Jet Propulsion Laboratory in Southern California directed the Spitzer mission for the agency’s Science Mission Directorate in Washington. Spitzer’s scientific data will continue to be analyzed by the scientific community through the Spitzer Data Archive, which is located in the Infrared Science Archive, which is located in Caltech’s Infrared Processing and Analysis Center (IPAC). Scientific operations were performed at the Spitzer Science Center in Caltech. The spacecraft was operated at Lockheed Martin Space in Littleton, Colorado. Caltech manages JPL for NASA.