Molecular oxygen is what we breathe to live. But while it is abundant on Earth, it has been difficult to find in space. Astronomers have now discovered the molecule’s signature emission from another galaxy in the quasar known as Markarian 231.
The researchers of the discovery, published in The Astrophysical Journal, believe the presence of oxygen around the active core of this galaxy is important for two reasons. First, they can use detections such as this to better understand the motion of gas around bright and active galaxies. Elements and molecules shine at particular wavelengths of light, which allow researchers to track their motion in space. Second, the molecular oxygen could be acting as a coolant for the galaxy, although more detailed models are necessary to explain how it came to be there.
The detection is around 32,000 light-years from the center of the galaxy, likely a result between the outflow of material created by the supermassive black hole at the core and the molecule-rich nebulae in the outer disk of Markarian 231.
Oxygen is a very reactive and common element. Beyond Earth, it is found by itself as well as in many molecules. But its molecular form, where two oxygen atoms are joined, is rarely seen beyond our Solar System. Space observations have seen it in two nebulae, Rho Ophiuchi and the Orion Nebula, but never so far away as Markarian 231 at 581 million light-years from us. In fact, when the light from these oxygen molecules left the galaxy, simple animals were just about born on Earth.
The distance of Markarian 231 was key to its detection. When using a ground-based telescope, looking for oxygen is difficult because its line of sight is literally covered in signs of oxygen for the first 100 kilometers (62 miles). But Markarian 231 is far enough away that its light is redshifted. Every electromagnetic radiation emitted from Markarian 231 has a slightly longer wavelength than if it was very close. This quirk of physics allowed the clear detection of the molecular oxygen using two ground-based IRAM facilities, the 30-meter (98-foot) telescope in Spain and the Northern Extended Millimeter Array Interferometer in France. Both instruments look at the universe's emission in millimeter light.
Markarian 231 is the closest quasar to Earth and one of the most luminous galaxies in infrared light. It is forming stars at a rate of over 100 Suns per year.