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The European Space Agency (ESA) released the largest and most detailed visible light image ever taken of the core of the Milky Way.
In simple terms, a microlensing event occurs when one star passes almost directly in front of another.
When that happens, the star closest to us acts like a magnifying glass: its gravity bends and amplifies the light from the star behind it.
If a planet orbits the nearest star, its gravity also alters that light. That little extra change in brightness tells astronomers that an exoplanet is there.
“What you can do, if you’re lucky, is identify a planet or even more than one,” Dupac explains.
Jean-Philippe Beaulieu, from the Institute of Astrophysics of Paris, in France, and the University of Tasmania, in Australia, who promoted this study of the galactic bulge, points out that “during the last twenty years, almost 300 exoplanets have been discovered using this technique.”
But it will not be possible to discover new exoplanets with this Euclid image alone. To detect a microlensing event, a telescope needs to observe a star for more than 20 days, something Euclid’s exceptional single-day mission was unable to do.
But if a future telescope detects two overlapping stars in the area that Euclid photographed, that image could help confirm the presence of new planets.
Valeria Pettorino told the BBC that she believes this image could lead to the discovery of “more than a thousand planets”, mainly cold planets orbiting stars, using the microlensing technique, as well as wandering planets that have drifted away from their stars.
For example, NASA’s Nancy Grace Roman space telescope is scheduled to take off at the end of August. Euclid has already captured the entire region of the sky that he will monitor in his search for planets.
“Anyone who detects a microlensing event in that same region, for example with Roman, will now be able to use the Euclid data as a reference to the past and see what the stars were like before they overlapped,” explains Natalia Rektsini, from the Institute of Astrophysics in Paris, who led the publication of these Euclid data.
The data also opens the door for scientists to calculate the mass of these planets.
Pettorino explains that, with the passage of time, the separation between the two stars increases. If the nearest star hosts an exoplanet, measuring its motion relative to the background star whose light has been amplified allows astronomers to calculate the mass of the planet with a precision that improves with greater time.
This technique could even provide new information about planets discovered in the past.
Twenty years ago, Beaulieu led the team that discovered a new exoplanet.
“It’s an icy planet, a bit like Hoth, Star Wars“he describes. “After all this time, I’m excited that Euclid can finally allow us to measure its mass accurately.”
Knowing the mass of a planet can reveal very important information, such as its potential to host life, explains Dupac.
“In general, as in our Solar System, very massive planets tend to be gas giants or icy planets… while smaller and less massive ones, located close to their star, tend to be rocky planets,” he points out. “If you want conditions favorable for the development of life, you probably want a rocky planet.”
If a good candidate is found, Dupac adds, “it is possible to make follow-up observations with other telescopes designed to study the atmosphere of planets” and find out if it could also support life.
And the Euclid image will not only be useful for studying exoplanets.
This data can also be used in other scientific research, from the study of brown dwarfs and binary star systems to the movement of stars and the distribution of dust in our galaxy.