Using a technique called gravitational microlensing, which occurs when a star close to Earth momentarily aligns with a more distant star, astronomers have discovered a giant exoplanet in a Jupiter-like orbit around a white dwarf star. Located at approximately 2,000 parsecs (6,523 light-years) towards the center of our Milky Way Galaxy, this system is likely to represent an analogue to the end stages of the Sun and Jupiter in our own Solar System.
An artist’s rendition of the MOA-2010-BLG-477Lb exoplanet and its white-dwarf host. Image credit: W.M. Keck Observatory / Adam Makarenko.
“Microlensing is a technique that is sensitive to cold planets down to the mass of Earth and can probe objects around all kinds of stars, including white dwarfs,” said lead author Dr. Joshua Blackman from the University of Tasmania and colleagues.
“Unlike other detection methods, it does not rely on the light coming from the host.”
A microlensing event designated MOA-2010-BLG-477L was first detected by the Microlensing Observations in Astrophysics (MOA) Collaboration on August 2, 2010.
The target was subsequently observed with the near-infrared camera 2 (NIRC2) instrument on the Keck-II telescope at the W.M. Keck Observatory in 2015, 2016, and 2018.
Strangely, when Dr. Blackman and colleagues tried to look for the lensed star, they unexpectedly discovered the starlight wasn’t bright enough to be an ordinary, main sequence star.
The astronomers also ruled out the possibility of a brown dwarf star as the host.
“We have also been able to rule out the possibility of a neutron star or a black hole host,” said Professor Jean-Philippe Beaulieu, a researcher at the University of Tasmania, CNRS and the Institut d’Astrophysique de Paris.
“This means that the planet is orbiting a white dwarf.”
“It offers a glimpse into what our Solar System will look like after the disappearance of the Earth, whipped out in the cataclysmic demise of our Sun.”
Adaptive optics imaging of MOA-2010-BLG-477L from the Keck Observatory: (a) an image obtained with the narrow-camera on the NIRC2 imager in 2015 centered on MOA-2010-BLG-477; (b) a 0.36-arcsec zoomed-in view of the same image as in (a); the bright object in the center is the source; to the northeast (top left) is an unrelated star; (c) the field in 2018; the contours indicate the probable positions of a possible main-sequence host using constraints from microlensing parallax and lens-source relative proper motion; no such host is detected. Image credit: Blackman et al., doi: 10.1038/s41586-021-03869-6.
Using near-infrared Keck data, the researchers determined that the MOA-2010-BLG-477L system contains a white-dwarf host with a mass of 0.53 solar masses.
The star is orbited by a 1.4 Jupiter-mass planet — named MOA-2010-BLG-477Lb — with a separation on the plane of the sky of 2.8 AU (astronomical units).
The system is evidence that planets around white dwarfs can survive the giant and asymptotic giant phases of their host’s evolution, and supports the prediction that more than half of white dwarfs have Jupiter-like planetary companions.
“Given that this system is an analog to our own Solar System, it suggests that Jupiter and Saturn might survive the Sun’s red giant phase, when it runs out of nuclear fuel and self-destructs,” Dr. Blackman said.
“Earth’s future may not be so rosy because it is much closer to the Sun,” said Dr. David Bennett, a researcher at the University of Maryland and NASA’s Goddard Space Flight Center.
“If humankind wanted to move to a moon of Jupiter or Saturn before the Sun fried the Earth during its red supergiant phase, we’d still remain in orbit around the Sun, although we would not be able to rely on heat from the Sun as a white dwarf for very long.”
The discovery is reported in a paper published this week in the journal Nature.
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J.W. Blackman et al. 2021. A Jovian analogue orbiting a white dwarf star. Nature 598, 272-275; doi: 10.1038/s41586-021-03869-6
