M51, the Whirlpool Galaxy!

Updated: Aug 1, 2022

Image Credit: NASA/ESA Hubble Space Telescope/ Alexandra Nachman. Image processed using FITS Liberator and Photoshop CC.

Quick Stats

Name: Messier 51 (M51)
Nickname: Whirlpool Galaxy
Distance: 28-31 million light-years
Constellation: Canes Venatici (Northern Celestial Hemisphere)

Messier 51 encompasses two galaxies— Messier 51a (M51a)— the large spiral galaxy front and center, and Messier 51b (M51b)— the smaller galaxy that M51a appears to be touching. Messier 51a is famously known as the Whirlpool Galaxy due to its well-defined spiral structure. This beautiful, grand-design spiral galaxy also goes by NGC 5194 while its smaller companion, a dwarf galaxy, also goes by NGC 5195. This galaxy pair is located about 28-31 million light-years away in the constellation Canes Venatici in the Celestial Northern Hemisphere. It is a part of the M52 group; a group of six galaxies total that also include M63, NGC 5023, NGC 5229, UGC 8313, and UGC 8331.

The Whirlpool Galaxy is about 76,000 light-years across and is about 43% the size of our Own Milky Way Galaxy. While it is on the smaller side as compared to our galaxy, it is a very active galaxy with many supernovae and an active supermassive black hole! There have been three observed supernovae in M51a. The first was in 1994 and was given the name, SN 1994I. SN 1994I was discovered on April 2, 1994 by amateur astronomers and is a type IC supernova. Supernova are quite explosive events- they occur when a star at the end of its evolution sequence burns the rest of the fuel in its core and contracts before exploding outward. The core of the star then becomes a neutron star or a black hole, depending on its original mass. Supernovae are characterized by either type I or type II and then further subdivided into A, B, or C. A type I explosion is characterized by the absence of hydrogen seen in a spectrum, whereas type II have hydrogen. Type IC, like SN 1994I, do not have the characteristic singly ionized silicon line at 635.5 nm and also do not have a helium line at 587.6 nm. So, they lack hydrogen, silicon, and helium spectral lines.

Another supernova was observed in 2005 and was given the name, SN 2005cs. It was discovered on June 28, 2005 by an amateur astronomer. This was a type II-P supernova. A type II supernova has that hydrogen in its spectra and the -P means that its luminosity (how bright the star is) decays more slowly than a normal type II supernova. The progenitor star may have been a red supergiant star. The last supernova observed was found in 2011 and was given the name, SN 2011dh. It was discovered on May 31, 2011 and was a type II supernova. Its progenitor star may have been a yellow supergiant star.

There are also imposter supernovae! These are events that look like supernova explosions, but are not actually one. One such one was found in M51a in 2019 from images taken by the Spitzer Space Telescope. While the Hubble Space Telescope images in visible light wavelengths of light, the Spitzer Space Telescope took images in infrared wavelengths of light. Because of this, it was able to see a star that Hubble could not. This star was called AT2019abn and looked a lot like a supernova. But it turned out to actually be a luminous red nova! A luminous red nova is a type of stellar explosion; however, it doesn’t come about at the end of a star’s life like a supernova. It is thought to be caused when two stars merge together. They are often red in color and shine brightly in infrared wavelengths of light. They are often brighter than a standard nova, but dimmer than a supernova.

While the Whirlpool Galaxy has exciting supernovae events, it also harbors something else that is very energetic as well- a supermassive black hole at its center that is actively gobbling up the matter around it. Because the black hole is active, M51 is classified as a Seyfert Galaxy with an active galactic nucleus. While most of the light from a galaxy comes from stars, galaxies with active nuclei emit light from non-stellar sources, which are usually black holes. Because the black hole in the center of M51 is active, it is emitting a lot of light and thus is classified as a Seyfert galaxy. These are galaxies where the core of the galaxy shines very brightly in ultraviolet or other wavelengths of light that are not coming from stars. Although these galaxies look normal under visible light conditions, when imaged with ultraviolet light or other wavelengths of light, they look very luminous and bright! M51 is a Type II Seyfert, which means it also shines brightly at infrared wavelengths of light.

In addition to its supernovae and black holes, an extragalactic planet has been detected! This planet, designated M51-ULS-1b, would be the first time we have detected something so small outside of our own galaxy. Planets are incredibly tiny, and one has been thought to be found around a binary pair of stars known as M51-ULS-1. It is thought that this binary pair consists of a massive star and a stellar remnant. The planet detected would be about the size of Saturn and orbit the pair at about 10 Astronomical Units from the binary pair of stars. One Astronomical Unit is the distance from the center of the Earth to the center of the Sun. So 10 AU is ten times the distance from the center of the Earth to the center of the Sun!

M51a and M51b have an interesting relationship. M51a is a grand-design spiral galaxy is a galaxy where the spiral arms are very prominent and organized- which is definitely true for M51a! The well-defined arms of M51a are thought to have been influenced by its companion galaxy. The gravitational interactions between the two galaxies have allowed M51a to get a very nice spiral structure. Most of the arms in other spiral galaxies are not so well-defined and easy to distinguish. The extra energy from the interaction between these two galaxies has allowed for massive star formation to occur in the arms of M51a. All the red areas in the image below are nebulous areas where new stars are being created!

The red areas in this image are nebulous areas where stars are being created.

Image Credit: NASA/ESA Hubble Space Telescope/ Alexandra Nachman. Image processed using FITS Liberator and Photoshop CC.

NGC 5195 (or M51b), is a small dwarf galaxy that is interacting with the large spiral, M51a. An image of this small galaxy is shown below. It is tugging at one of the spiral arms of M51a and thus there is a tidal tail that connects the two. Because they are viewed face-on, the tail is not visible. The dust that is in front of NGC 5195 is evidence of the tidal tail and is shown in the image above by the brownish-red colors. The shape of NGC 5185 is highly irregular and is due to distortion from its interactions with M51a.

A close up of NGC 5195.

Image Credit: NASA/ESA Hubble Space Telescope/ Alexandra Nachman. Image processed using FITS Liberator and Photoshop CC.

This image of M51 is a fun one to work with. It was among one of the first images that I processed when I was learning how to process data from the Hubble Space Telescope. It is also a massive file that can be hard to work with. Because it is so large, it takes a bit longer to process in Photoshop than other images from Hubble. I had a lot of fun creating these images! Because Hubble is funded by the US government, the data is free to the public, since we pay for it! This image is such a stunning image and I want everyone to be able to download and use this data! Below are links to resources so you can process your own image! Questions? Email me at peculiargalexyastro@gmail.com or reach out to me here!

RESOURCES

This image was taken over multiple days by the Hubble Space Telescope. Those days were January 12-22 of 2005. It was an image created using three greyscale images assigned to the RGB channels in Photoshop CC. A luminosity layer was also used. The images used were:

RED: hlsp_heritage_hst_acs-wfc_m51_f814w
GREEN: hlsp_heritage_hst_acs-wfc_m51_f555w
BLUE: hlsp_heritage_hst_acs-wfc_m51_f435w
HALPHA LUM: hlsp_heritage_hst_acs-wfc_m51_f658n

Interested in learning how to process your own image? Check out the tutorial here!

The files for this image can be downloaded from NASA here!

To watch the work that goes into creating an image like this, check out this video here.

These images are associated with HST proposal 10452.

REFERENCES- ALL INFORMATION IN THIS ARTICLE WAS TAKEN FROM THE SITES BELOW

M51, the Whirlpool Galaxy!

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