The Pinwheel Galaxy (also known as Messier 101, M101 or NGC 5457) is a face-on, counterclockwise intermediate spiral galaxy located from Earth in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

Ursa Major Ursa Major, also known as the Great Bear, is a constellation in the Northern Sky, whose associated mythology likely dates back into prehistory. Its Latin name means "greater (or larger) bear", referring to and contrasting it with nearby Ursa M ...

. It was discovered by

Pierre Méchain Pierre François André Méchain (; 16 August 1744 – 20 September 1804) was a French astronomer and surveyor who, with Charles Messier, was a major contributor to the early study of deep-sky objects and comets. Life Pierre Méchain was bo ...

in 1781 and was communicated that year to

Charles Messier Charles Messier (; 26 June 1730 – 12 April 1817) was a French astronomer. He published an astronomical catalogue consisting of 110 nebulae and star clusters, which came to be known as the ''Messier objects'', referred to with th ...

, who verified its position for inclusion in the '' Messier Catalogue'' as one of its final entries. On February 28, 2006,

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...

and the

European Space Agency The European Space Agency (ESA) is a 23-member International organization, international organization devoted to space exploration. With its headquarters in Paris and a staff of around 2,547 people globally as of 2023, ESA was founded in 1975 ...

released a very detailed image of the Pinwheel Galaxy, which was the largest and most detailed image of a galaxy by

Hubble Space Telescope The Hubble Space Telescope (HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the Orbiting Solar Observatory, first space telescope, but it is one of the largest and most ...

at the time. The image was composed of 51 individual exposures, plus some extra ground-based photos.

Discovery

Pierre Méchain, the discoverer of the galaxy, described it as a "nebula without star, very obscure and pretty large, 6' to 7' in diameter, between the left hand of Bootes and the tail of the great Bear. It is difficult to distinguish when one illuminates the

rating A rating is an evaluation or assessment of something, in terms of a metric (e.g. quality, quantity, a combination of both,...). Rating or rating system may also refer to: Business and economics * Credit rating, estimating the credit worthiness ...

wires."

William Herschel Frederick William Herschel ( ; ; 15 November 1738 – 25 August 1822) was a German-British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline Herschel. Born in the Electorate of Hanover ...

wrote in 1784 that the galaxy was one of several which "...in my 7-, 10-, and 20-feet ocal lengthreflectors shewed a mottled kind of nebulosity, which I shall call resolvable; so that I expect my present telescope will, perhaps, render the stars visible of which I suppose them to be composed." Lord Rosse observed the galaxy in his 72-inch-diameter Newtonian reflector during the second half of the 19th century. He was the first to make extensive note of the spiral structure and made several sketches. Though the galaxy can be detected with

binoculars Binoculars or field glasses are two refracting telescopes mounted side-by-side and aligned to point in the same direction, allowing the viewer to use both eyes (binocular vision) when viewing distant objects. Most binoculars are sized to be held ...

or a small telescope, to observe the spiral structure in a telescope without a camera requires a fairly large instrument, very dark skies, and a low-power eyepiece.

Structure and composition

M101 is a large galaxy, with a diameter of 252,000 light-years. By comparison, the

Milky Way The Milky Way or Milky Way Galaxy is the galaxy that includes the Solar System, with the name describing the #Appearance, galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galax ...

has a diameter of 87,400 light-years. It has around a trillion stars. It has a disk mass on the order of 100 billion solar masses, along with a small central bulge of about 3 billion solar masses. Its characteristics can be compared to those of

Andromeda Galaxy The Andromeda Galaxy is a barred spiral galaxy and is the nearest major galaxy to the Milky Way. It was originally named the Andromeda Nebula and is cataloged as Messier 31, M31, and NGC 224. Andromeda has a Galaxy#Isophotal diameter, D25 isop ...

. M101 has a high population of

H II region An H II region is a region of interstellar atomic hydrogen that is ionized. It is typically in a molecular cloud of partially ionized gas in which star formation has recently taken place, with a size ranging from one to hundreds of light year ...

s, many of which are very large and bright. H II regions usually accompany the enormous clouds of high density molecular hydrogen gas contracting under their own gravitational force where stars form. H II regions are ionized by large numbers of extremely bright and hot young stars; those in M101 are capable of creating hot superbubbles. In a 1990 study, 1,264 H II regions were cataloged in the galaxy. Three are prominent enough to receive

New General Catalogue The ''New General Catalogue of Nebulae and Clusters of Stars'' (abbreviated NGC) is an astronomical catalogue of deep-sky objects compiled by John Louis Emil Dreyer in 1888. The NGC contains 7,840 objects, including galaxy, galaxies, star cluste ...

numbers—NGC 5461, NGC 5462, and NGC 5471. M101 is asymmetrical due to the tidal forces from interactions with its companion galaxies. These gravitational interactions compress interstellar hydrogen gas, which then triggers strong

star formation Star formation is the process by which dense regions within molecular clouds in interstellar space—sometimes referred to as "stellar nurseries" or "star-forming regions"—Jeans instability, collapse and form stars. As a branch of astronomy, sta ...

activity in M101's spiral arms that can be detected in ultraviolet images. In 2001, the X-ray source P98, located in M101, was identified as an ultra-luminous X-ray source—a source more powerful than any single star but less powerful than a whole galaxy—using the

Chandra X-ray Observatory The Chandra X-ray Observatory (CXO), previously known as the Advanced X-ray Astrophysics Facility (AXAF), is a Flagship-class space telescope launched aboard the during STS-93 by NASA on July 23, 1999. Chandra is sensitive to X-ray sources ...

. It received the designation M101 ULX-1. In 2005, Hubble and

XMM-Newton ''XMM-Newton'', also known as the High Throughput X-ray Spectroscopy Mission and the X-ray Multi-Mirror Mission, is an X-ray space observatory launched by the European Space Agency in December 1999 on an Ariane 5 rocket. It is the second corners ...

observations showed the presence of an optical counterpart, strongly indicating that M101 ULX-1 is an X-ray binary. Further observations showed that the system deviated from expected models—the black hole is just 20 to 30

solar mass The solar mass () is a frequently used unit of mass in astronomy, equal to approximately . It is approximately equal to the mass of the Sun. It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxie ...

es, and consumes material (including captured stellar wind) at a higher rate than theory suggests. It is estimated that M101 has about 150

globular clusters A globular cluster is a spheroidal conglomeration of stars that is bound together by gravity, with a higher concentration of stars towards its center. It can contain anywhere from tens of thousands to many millions of member stars, all orbiting ...

, the same as the number of the

's globular clusters.

Companion galaxies

M101 has six prominent companion galaxies: NGC 5204, NGC 5474, NGC 5477, NGC 5585, UGC 8837 and UGC 9405. As stated above, the gravitational interaction between it and its satellites may have spawned its grand design pattern. The galaxy has probably distorted the second-listed companion. The list comprises most or all of the M101 Group.

Supernovae and luminous red nova

Six

supernovae A supernova (: supernovae or supernovas) is a powerful and luminous explosion of a star. A supernova occurs during the last evolutionary stages of a massive star, or when a white dwarf is triggered into runaway nuclear fusion. The original ob ...

have been recorded in M101: * SN 1909A (type unknown, mag. 10) was discovered by

Max Wolf Maximilian Franz Joseph Cornelius Wolf (21 June 1863 – 3 October 1932) was a German astronomer and a pioneer in the field of astrophotography. He was the chairman of astronomy at the University of Heidelberg and director of the Heidelberg-K� ...

on 21 February 1909. * SN 1951H (type unknown, mag. 17.5) was discovered by

Milton Humason Milton La Salle Humason (August 19, 1891 – June 18, 1972) was an American astronomer. He worked with Edwin Hubble to measure the redshift of nebulas in the early 20th century, providing evidence of the expansion of the universe. Biography ...

on a photographic plate taken on 3 February 1951. Analysis of the light curve suggested that the supernova was probably of type II, with maximum magnitude of 11 to 12 occurring around October 1950. * SN 1970G ( typeII, mag. 11.5) was discovered by Miklós Lovas on 30 July 1970. * SN 2011fe ( type Ia, mag. 17.2) was discovered by the

Palomar Transient Factory The Palomar Transient Factory (PTF, obs. code: I41), was an astronomical survey using a wide-field survey camera designed to search for optical transient and variable sources such as variable stars, supernovae, asteroids and comets. The projec ...

on 24 August 2011. Initially designated PTF 11kly, it reached

visual magnitude Apparent magnitude () is a measure of the brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction of the object's light ca ...

9.9 at its peak, making it the brightest supernova of 2011. * M101 OT2015-1, a luminous red nova, was discovered by Dumitru Ciprian Vîntdevară on 10 February 2015. * SN 2023ixf (type II, mag. 14.9) was discovered by

Kōichi Itagaki is an amateur astronomer based in Yamagata, the capital city of Yamagata Prefecture in the Tōhoku region of northern Honshu island, Japan. He is responsible for discovering many comets, and over 170 supernovae.Type II supernova A Type II supernova or SNII (plural: ''supernovae'') results from the rapid collapse and violent explosion of a massive star. A star must have at least eight times, but no more than 40 to 50 times, the mass of the Sun () to undergo this type ...

. File:Supernova in M101 2011-08-25.jpg, Type Ia supernova SN 2011fe from August 2011 File:SN2023ixf_in_Messier_101.png, Type II supernova SN 2023ixf from May 2023

References

External links