The Hubble Space Telescope has taken a beautiful picture of the interacting galaxies NGC 5765A and B, which were first discovered in 1830. They are not just beautiful, but hidden inside NGC 5765B (the blue one) there’s a powerful astronomical feature. This galaxy is a megamaser.
A maser is the microwave equivalent of a laser – just like laser is an acronym for "light amplification by stimulated emission of radiation", maser is the acronym for "microwave amplification by stimulated emission of radiation". Lasers emit visible light in one specific wavelength and masers behave in the same way but using microwaves. Masers can be constructed in labs like lasers, but they also naturally occur in space. Masers can form around comets, planets, and stars. One just needs to have certain molecules (like water or formaldehyde) being excited in a coherent manner.
But NGC 5765B (also snappily known as MCG+01-38-005) is no regular maser. It’s 100 million times brighter than what we see in the Milky Way, and the maser light originates from water inside a gigantic gas cloud near the center of the galaxy. The cloud surrounds a supermassive black hole.
The supermassive black hole is sloshing material around and releasing a lot of energy into the gas cloud. Molecules of water are absorbing that energy and re-emitting it, producing the megamaser that researchers have detected. The megamaser is estimated to be 1,000 times more luminous in microwaves than the Sun is in all its wavelengths combined.
The properties of the megamaser were not the only facet the astronomers were interested in understanding. The most recent study on NGC 5765B, published in the Astrophysical Journal, was able to estimate that the supermassive black hole within the maser weighs about 45 million Suns.
The researchers were also capable of other observations that were even more cosmic in scope. One measurement that they were able to estimate with good precision is known as the Hubble constant, a quantity that tells us how fast the universe is expanding. This is not the most precise measurement we have but it has come at a crucial time. Two different methods of estimating the Hubble constant appear to disagree.
The estimate from the megamaser is not as precise as estimates from the other two methods, so both values are valid under its uncertainty. The researchers think that it’s possible to improve the measurement of the Hubble constant in the future by performing more observations of NGC 5765B. If measurements can be enhanced, megamasers might be useful in working out the correct value for the constant.
