Chandra Spies Exoplanet Candidate M51-ULS-1


Let us not launch the boat ...
Valued Senior Member

It's okay to swoon; it is Chandra, after all:

Signs of a planet transiting a star outside of the Milky Way galaxy may have been detected for the first time. This intriguing result, using NASA’s Chandra X-ray Observatory, opens up a new window to search for exoplanets at greater distances than ever before.


It isn't just the pretty pictures; Chandra is a perpetually jawdropping mission. Rosanne Di Stefano and her team took a different approach when looking at M51.

Astronomers using both ground-based and space-based telescopes – like those on NASA's Kepler and TESS missions – have searched for dips in optical light, electromagnetic radiation humans can see, enabling the discovery of thousands of planets.

Di Stefano and colleagues have instead searched for dips in the brightness of X-rays received from X-ray bright binaries. These luminous systems typically contain a neutron star or black hole pulling in gas from a closely orbiting companion star. The material near the neutron star or black hole becomes superheated and glows in X-rays.

Because the region producing bright X-rays is small, a planet passing in front of it could block most or all of the X-rays, making the transit easier to spot because the X-rays can completely disappear. This could allow exoplanets to be detected at much greater distances than current optical light transit studies, which must be able to detect tiny decreases in light because the planet only blocks a tiny fraction of the star.

The team used this method to detect the exoplanet candidate in a binary system called M51-ULS-1, located in M51. This binary system contains a black hole or neutron star orbiting a companion star with a mass about 20 times that of the Sun. The X-ray transit they found using Chandra data lasted about three hours, during which the X-ray emission decreased to zero. Based on this and other information, the researchers estimate the exoplanet candidate in M51-ULS-1 would be roughly the size of Saturn, and orbit the neutron star or black hole at about twice the distance of Saturn from the Sun.

The problem with this one is confirmation. The math by which it all works out says it will take seventy years or so to confirm. "And because of the uncertainties about how long it takes to orbit," says co-author Nia Imara, "we wouldn't know exactly when to look." Still, if Di Stefano and her colleagues sought "to open up a whole new arena for finding other worlds", this result should be sufficient to move some scientists to accept the challenge. The Chandra result surveyed 238 systems in three galaxies (M51, M101, M104); the authors are preparing to dive into Chandra and XMM-Newton data for more than twenty galaxies, including M31 and M33, where shorter transits should be visible.

Maybe there should be an anime version, with elite schools under competing megalomaniacal scientists trying to find, confirm, and describe the most distant or exotic exoplanets. We'll need to invoke fantasy Buddhism, or something, to justify the timescales of confirmation, but how many sly pushing-glasses moments can we justify, and we can probably settle the long question of whether there is actually any sexy way to properly depict a true male nerd pushing up his glasses, or if it always looks creepy and dangerous. Oh, right, never mind. We don't need mystical eyes, just pretend there are lots and lots of satellites and then just make stuff up about dodecangulating the data.

Oh, right. Never mind.

Anyway, yeah, Chandra found an exoplanet candidate ... in M51.


NASA. "Chandra Sees Evidence for Possible Planet in Another Galaxy". 25 October 2021. 25 October 2021.

See Also:

Di Stefano, Rosanne, Julia Berndtsson, Ryan Urquhart, Roberto Soria, Vinay L. Kashyap, Theron W. Carmichael, and Nia Imara. "A possible planet candidate in an external galaxy detected through X-ray transit". Preprint. 2021. 25 October 2021.