Hunting exoplanets… in other galaxies?!

As we briefly mentioned the other day, the Astro2020 decadal survey recommended investment in three major areas of Astronomy. One of them can be summarized briefly as “exoplanets”.

Exoplanets by definition are planets orbiting stars other than our own Sun. Astronomers have been studying them intensely of late. Aside from the obvious novelty to science and the chance to look for life beyond Earth, studying exoplanets also gives us context for how normal - or abnormal - our own solar system is.

Of course, other stars are quite far away and hard enough to detect on their own, so finding new planets is not as simple as “zooming in” with a telescope. Typically, we cannot directly image them. Other techniques are required.

NASA has a great roundup of exoplanet detection techniques and how many have been discovered via each method.

The basic technique is to look for planets transiting in front of the stars they orbit. As the planets cut in front of their host star, the star’s brightness dims. That dimming can be quantified, especially if it drops periodically. This strategy was the entire mission of the Kepler Space Telescope.

Potentially, this technique may also help us identify exoplanets in a different galaxy! Rosanne Di Stefano and Nia Imara at the Harvard–Smithsonian Center for Astrophysics have recently proposed evidence for an exoplanet orbiting a bright X-ray binary star in the Whirlpool Galaxy, M51. The evidence in question? A potential transit observation in the X-ray spectra as measured by the Chandra X-ray telescope!Check out the details in Physics Today.