The nucleus of an enormous spiral galaxy 160 million light years away –at a point where the universe is vastly expanded, and the atmosphere is at its most transparent (red-shifted at 676 μm)–contains an equivalent amount of water 30 trillion times that of Earth’s oceans combined, and has a diameter 15 million times the distance from Earth to the Sun, according to a study led by physicist Miguel Pereira Santaella, at Oxford University that detected the water transition in space, for the first time.
Most of the water in space takes either the form of vapor or forms ice mantles stuck to interstellar dust grains because the extremely low density of interstellar space – which is trillions of times lower than Earth’s air, prevents the formation of liquid water. The only way to study the water molecule in such dust obscured environments is through the infrared light; detecting water transitions capable of detecting this light, is of vital importance.
The term refers to the best point for scientific observation, which is the exact wavelength at which water molecules go from one quantum state to another, emitting light and increasing their visibility as they do so.
Water molecules experience fluctuating quantum energy levels, which allows us to observe them and is known as a water transition. The best point for scientific observation is the exact wavelength at which water molecules go from one quantum state to another, emitting light increasing their visibility, says Santella.
The majority of these transitions are not very energetic so they appear in the far-infrared and sub-millimeter ranges of the electromagnetic spectrum, with tiny wavelengths Observing these water transitions from the ground is very difficult because the thick vapor in Earth’s atmosphere almost completely blocks the emission from view.
Water transitions –that appear in the far-infrared and sub-millimeter ranges of the electromagnetic spectrum, with tiny wavelengths–are best seen from telescopic observatories situated at high-altitude, in extremely dry sites such as, the Atacama Large Millimeter Array (ALMA), which is located in Chile’s Atacama desert 5000 meters above sea level.
The Oxford teams analysis revealed that these water molecules intensify their rate of emission when they come into contact with infrared light photons, which makes them easier to observe. Water molecules are most attracted to photons with specific wavelengths of 79 and 132 μm, which, when absorbed, strengthen the transition’s outline, therefore increasing its visibility. For this reason, this specific water transition has the ability to show the intensity of the infrared light in the nucleus of galaxies, at spatial scales much smaller than those allowed by direct infrared observations.
Infrared light is produced during events like the growth of supermassive black holes or extreme bursts of star-formation. These events usually occur in extremely dust obscured environments where the optical light is almost completely absorbed by dust grains. The energy absorbed by the grains increases their temperature and they begin to emit thermal radiation in the infrared. Since the only way to study them in such dust obscured environments is through the infrared light, detecting water transitions that capture this infrared light, is vital.
Tthe Oxford team plans to observe this water transition in more galaxies where dust blocks all the optical light. This will reveal what hides behind these dust screens and help us to understand how galaxies evolve from star-forming spirals, like the Milky Way, to dead elliptical galaxies where no new stars are formed.
Image credit: NASA spiral galaxy NGC 4151 has a bright, active core powered by a supermassive black hole