Finally, In a Galaxy Far, Far Away

Astronomers finally found molecular oxygen in a galaxy outside the Milky Way, for the first time.

Oxygen is the third most common element in the universe, right after hydrogen and helium. This is why the astronomers once thought that molecular oxygen (O2) would be common in the interstellar space.

Astronomers repeatedly searched for oxygen using different techniques. Despite these long-term efforts, however, no one had been able to find molecular oxygen beyond our galaxy. They only encountered it within the Milky Way, inside the Orion Nebula and the Rho Ophiuchi Cloud.

Astronomers think that the lack of interstellar molecular oxygen may be the result of oxygen’s habit of binding with hydrogen atoms and becoming water ice that cling on to dust particles. Since Orion and Rho Ophiuchi are star-producing environments, intense radiation from the newborn stars can sublimate this ice and detach oxygen atoms from hydrogen, releasing them to find each other and form molecular oxygen.

Junzhi Wang and his colleagues from the Shanghai Astronomical Observatory in China found the characteristic trace of molecular oxygen in a galaxy called Markarian 231. Located in the constellation of Ursa Major, 560 million light years away, Markarian 231 is the closest galaxy to us containing a quasar, where gas heats around a supermassive black hole and therefore shines excessively. In fact, astronomers consider that there might be two active supermassive black holes at the centre of Markarian 231, spinning around each other at an incredible speed.

The team’s measurements showed that the oxygen abundance (compared to hydrogen) in Markarian 231 was about 100 times higher than that found in the Orion Nebula, so the galaxy might be going through a more intense version of the same molecule-splitting period.

On the other hand, these findings may also mean that astronomers need to make more observations to confirm they are correct in interpreting the results as oxygen. If the results are confirmed, the findings can be used to learn more about the molecular oxygen in galaxies and the molecular flow out of an active galactic nucleus.