August Guest Post: Messier 51 — A Grand Design Spiral with a Dance Partner
Author: Jimmie Krager (Central Washington University Physics major/Astronomy minor alum)
The M51 Whirlpool galaxy imaged with H-alpha, R, G, B filters. Image Credit: Jimmie Krager/CWU
Messier 51, also known as the Whirlpool Galaxy, is an iconic Grand Design spiral galaxy found in the constellation Canes Venatici. Located around 31 million light years away, was the first galaxy to be classified as a spiral by William Parsons in 1845. It was discovered in 1773 by Charles Messier while cataloging objects that were not comets and has since been a popular target for researchers and amateur astronomers due to its stunning spiral arm structures and interaction with a companion galaxy known as NGC 5195. M51 has been an invaluable tool in the study of star formation, the motion of galaxies, and the evolution of our Cosmos as a whole.
During the summer months, amateur telescopes all over the northern hemisphere can be found pointed at the Whirlpool Galaxy. Its proximity to Earth, face-on perspective and brightness make it a convenient target. M51 is so bright because it is undergoing an incredible amount of star formation when compared to galaxies like our own. Its glittery blue spiral arms are packed full of blue, hot stars. Dotted all along its structures, bright pink regions of hydrogen-abundant stellar nurseries are further evidence of a heightened rate of star formation. Astronomers measure the rate of star formation in solar masses per year. For comparison, the Milky Way produces around one solar mass per year, while M51 produces around 7. The most likely cause for this behavior is twofold. First, when galaxies begin interacting gravitationally, it kicks off star formation due to compression of dust and gas. Second, there is strong evidence that Messier 51 has been stripping its companion of its own star-forming fuel via observations of gas bridges and tidal tails between both galaxies. At any rate, the gravitational waltz our partners are in provides viewers with an unforgettable view while also teaching astronomers how galaxies move and interact with each other.
The Whirlpool Galaxy is a natural laboratory for understanding gravitation and tidal forces on galactic scales. On Earth, gravity seems like a very weak force. Humans can hopscotch and send rockets into space. However, with enough mass present, gravity can forge stars and shape entire galaxies over hundreds of millions of years – as we see here. Interacting galaxies like M51/NGC 5195 help astronomers understand how interstellar dust distributes itself along spiral arms. Observations across the electromagnetic spectrum lets astronomers trace how gas motion, magnetic fields and supernovae affect the evolution of galaxies. For example, earlier this year the Hubble Space Telescope observed a dark “X” stretched across M51’s nucleus due to absorption of light by a thick ring of infalling gas surrounding the supermassive black hole at its center. It is clear that this interaction between both galaxies has had a massive effect on their past, present, and future.
The gravitational waltz M51 and NGC 5195 started around 500 million years ago and shows no signs of stopping any time soon. Over the next several hundred million years, they will continue to twirl about each other, getting ever closer, until they finally merge into a single, larger elliptical galaxy. This fate matches that of many larger clusters of galaxies and also serves as a harbinger of the Milky Way’s future. In around four billion years, the Milky Way and Andromeda galaxies will also merge. This is one of the few times in astronomy where looking back in time provides a brief glimpse of the future.
Messier 51 is both a pretty face and important tool in understanding galaxy evolution, gravitation, and star formation. Over human lifespans, these sentinels appear to be frozen in time, but to study them reveals the opposite is true. The Whirlpool Galaxy stands as a reminder that the universe is dynamic, interconnected, and constantly evolving.