Astronomers have discovered a super-Earth exoplanet orbiting a dwarf star or a brown dwarf around 7,580 parsecs (24,723 light-years) from Earth.
An artist’s impression of a super-Earth exoplanet. Image credit: NASA.
Gravitational microlensing is a technique that facilitates the discovery of distant objects by using background stars as flashlights.
When a star crosses precisely in front of a bright star in the background, the gravity of the foreground star focuses the light of the background star, making it appear brighter. A planet orbiting the foreground object may cause an additional blip in the star’s brightness.
This technique has found the most distant known exoplanets from Earth, and can detect low-mass planets that are substantially farther from their stars than Earth is from our Sun.
The newfound world is one of the lightest planets yet detected by gravitational microlensing.
Designated OGLE-2018-BLG-0677Lb, it has a mass of 3.96 times the mass of the Earth.
The host star is a dwarf star or a brown dwarf with mass of just 0.12 solar masses.
The projected separation between the star and the planet is between 0.6 and 0.7 AU.
“OGLE-2018-BLG-0677Lb was discovered using a technique called gravitational microlensing,” said Dr. Antonio Herrera Martin, an astronomer in the School of Physical and Chemical Sciences at University of Canterbury.
“The combined gravity of the planet and its host star caused the light from a more distant background star to be magnified in a particular way. We used telescopes distributed around the world to measure the light-bending effect.”
“The microlensing effect is rare, with only about one in a million stars in the galaxy being affected at any given time.”
“Furthermore, this type of observation does not repeat, and the probabilities of catching a planet at the same time are extremely low.”
The OGLE-2018-BLG-0677 microlensing event was independently detected in 2018 by the Optical Gravitational Lensing Experiment (OGLE) using a telescope in Chile, and the Korea Microlensing Telescope Network (KMTNet) using three identical telescopes in Chile, Australia, and South Africa.
“These experiments detect around 3,000 microlensing events each year, the majority of which are due to lensing by single stars,” said co-author Dr. Michael Albrow, also from the School of Physical and Chemical Sciences at University of Canterbury.
The discovery is reported in a paper in the Astronomical Journal.
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Antonio Herrera-Martín et al. 2020. OGLE-2018-BLG-0677Lb: A Super-Earth Near the Galactic Bulge. AJ 159, 256; doi: 10.3847/1538-3881/ab893e
