An international research team led by scientists from Vilnius University (VU) has announced the “exceptional” discovery of a rare gas giant exoplanet far from the Galactic bulge using microlensing.
Dr Marius Maskoliūnas, the head of the VU team, said discovering distant planets with microlensing, where the gravity of a massive, closer object magnifies the light from a more distant object, requires “a lot of expertise, patience, and, quite frankly, a bit of luck.”
“This is only the third such discovery in the entire history of observations,” an email to The Debrief explained. “The discovery is even more exceptional due to the method used – the phenomenon known as microlensing.”
The theoretical phenomenon of microlensing was first proposed by the famed scientist Albert Einstein. Since then, the method has proven particularly useful, especially when hunting the cosmos for phenomena too far away to see with conventional observatories.
Most of the 5,000-plus confirmed exoplanets were discovered using a different approach called the transit method that measures the dimming of a star’s light as a planet passes between it and Earth. Although some exoplanets have been discovered using microlensing, the researchers behind the latest discovery note that the majority of those occurred in parts of the cosmos where the odds of discovery were much higher.
“Observations of gravitational microlensing events have the potential to find exoplanets, and the event rate is by far the highest in the direction of the Galactic bulge,” the researchers write in Astronomy & Astrophysics. “Hence, microlensing surveys focused their observing efforts on the Galactic bulge (because of the highest event rate) and the Magellanic Clouds (in order to verify if low-mass black holes can be a main component of dark matter).”
Curious if they could find exoplanets farther away from the Galactic bulge, the VU team joined forces with Professor Lukasz Wyrzykowski from the University of Warsaw, who suggested they comb through observation data from the European Space Agency’s “Gaia” telescope. If they witness an observed object suddenly pulsing with light, there is a chance that the team is seeing a microlensing event in real time. Still, according to Maskoliūnas, even those odds aren’t favorable.
“You have to wait for a long time for the source star and the lensing object to align and then check an enormous amount of data,” the researchers explained. “Ninety per cent of observed stars pulsate for various other reasons, and only a minority of cases show the microlensing effect.”
After comparing several pulses found in Haia with observations from ground-based observatories, the team found an ideal candidate. Further analysis of the pulses confirmed that the team had discovered an exoplanet orbiting an M-dwarf star.
Dubbed AT2021uey b, the gas giant is estimated to have an overall mass around 1.3 times greater than Jupiter and orbits its host star every 4,170 days, roughly one kiloparsec, or 3,200 light years, from Earth. The team said the planet’s size helped make the discovery possible, as detecting an Earth-like planet “would have been much more difficult.”
Notably, the initial phenomenon hinting at AT2021uey b’s existence was first spotted in 2021. However, the new observations were the first to confirm it. Dr. Maskoliūnas said the rarity and quality of this discovery show the benefit of using microlensing to reveal the secrets of the cosmos.
“What fascinates me about this method is that it can detect those invisible bodies. Other methods work like selective receivers, which, as if with a magnifying glass, focus on a specific cosmic zone that interests you.”
Assoc. Prof. Edita Stonkutė, the leader of the joint project in Lithuania, said that while discovering an exoplanet via microlensing is an uncommon event, finding one this way in this part of the cosmos is exceptionally rare.
“Most microlensing effects are recorded at the densest part of the galaxy – in its centre and disk. However, we managed to find this microlensing phenomenon quite far from the centre, in the so-called galactic halo.”
“This is only the third planet in observational history to be discovered so far from the Galactic bulge,” the researcher added.
Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.