Amateur and professional astronomers team up to reveal a spiral galaxy with a secret

Besides microwave emission from M106’s galactic center, the galaxy has another startling feature — instead of two spiral arms, it appears to have four.
By | Published: February 7, 2013 | Last updated on May 18, 2023
This image combines Hubble observations of M106 with additional information captured by amateur astronomers Robert Gendler and Jay GaBany. Gendler combined Hubble data with his own observations to produce this stunning color image. // NASA, ESA, the Hubble Heritage Team (STScI/AURA), and R. Gendler (for the Hubble Heritage Team). Acknowledgment: J. GaBany
The NASA/ESA Hubble Space Telescope, with help from an amateur astronomer, has produced one of the best views yet of nearby spiral galaxy M106. Located a little more than 20 million light-years away, practically a neighbor by cosmic standards, M106 is one of the brightest and nearest spiral galaxies to our own.

Despite its appearance, which looks much like countless other galaxies, M106 hides a number of secrets. Thanks to this image, which combines data from Hubble with observations by amateur astronomers Robert Gendler and Jay GaBany, they are revealed as never before.

At its heart, as in most spiral galaxies, is a supermassive black hole, but this one is particularly active. Unlike the black hole at the center of the Milky Way, which pulls in wisps of gas only occasionally, M106’s black hole is actively gobbling up material. As the gas spirals toward the black hole, it heats up and emits powerful radiation. Part of the emission from the center of M106 is produced by a process that is somewhat similar to that in a laser, although here the process produces bright microwave radiation.

As well as this microwave emission from M106’s heart, the galaxy has another startling feature — instead of two spiral arms, it appears to have four. Although the second pair of arms can be seen in visible light images as ghostly wisps of gas, they are even more prominent in observations made outside the visible spectrum, such as those using X-ray or radio waves.

Unlike the normal arms, these two extra arms are made up of hot gas rather than stars, and their origin remained unexplained until recently. Astronomers think that these arms, like the microwave emission from the galactic center, are caused by the black hole at M106’s heart, and so are a totally different phenomenon from the galaxy’s normal, star-filled arms.

The extra arms appear to be an indirect result of jets of material produced by the violent churning of matter around the black hole. As these jets travel through the galactic matter, they disrupt and heat up the surrounding gas, which in turn excites the denser gas in the galactic plane and causes it to glow brightly. This denser gas closer to the center of the galaxy is tightly bound, so the arms appear to be straight. However, the looser disk gas farther out is blown above or below the disk in the opposite direction from the jet so that the gas curves out of the disk, producing the arching red arms seen here.

Despite carrying his name, M106 was neither discovered nor cataloged by the renowned 18th-century astronomer Charles Messier. Discovered by his assistant, Pierre Méchain, the galaxy was never added to the catalog in his lifetime. Along with six other objects discovered but not logged by the pair, M106 was posthumously added to the Messier catalog in the 20th century.

Amateur astronomer Robert Gendler retrieved archival Hubble images of M106 to assemble a mosaic of the center of the galaxy. He then used his own and fellow astrophotographer Jay GaBany’s observations of M106 to combine with the Hubble data in areas where there was less coverage, and finally, to fill in the holes and gaps where no Hubble data existed.

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Credit: Hubble/ESA; Images: NASA/ESA/R. Gendler/J. GaBany/Digitized Sky Survey 2