M 101

## Pinwheel Galaxy

Pinwheel galaxy is known for its famous, clearly defined grand design spiral structure.

## Galactic properties

### Is undergoing through

Strong star formation due to interactions with its galaxies

## Overview

The Pinwheel Galaxy is a face-on, grand design spiral galaxy in the Ursa Major constellation, sometimes referred to as Messier 101 or M101. It is among the spiral galaxies in the night sky with the most recognition. The galaxy's pronounced pinwheel-like shape, which features large spiral arms spreading from a bright central core, is where it derives its name. There are several areas of star-forming nebulas scattered across the spiral arms of the galaxy, these nebulas are regions of massive molecular hydrogen clouds where intensive star creation is occurring. The spiral arms are formed by hot, blue, newborn stars grouped together in bright groups.

## Observational history

The French astronomer Pierre Méchain made the discovery of Messier 101 on March 27, 1781. Méchain worked with Charles Messier, who created a list of celestial objects that helped comet hunters distinguish them from actual comets. Messier was informed of Méchain's discovery and included it in his catalogue.

The discoverer Pierre Méchain described the object as it follows ***“N*ebula 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 lits the [grating] wires.*”***

Because of its relative size and brightness, the Pinwheel Galaxy is a favourite target for both amateur and professional astronomers. Under dark skies, it may be possible to observe with binoculars or a small telescope; bigger telescopes can bring out more details of its spiral structure. April is the ideal month for observing the Pinwheel Galaxy, and a small telescope is usually recommended to see the galaxy.

## Structure

M 101 is a face-on spiral galaxy, featuring a pronounced and distinct spiral arms and a bright central nucleus. The Pinwheel galaxy possess a diameter of about 24.58 Mly. It features a modest centre bulge of roughly 3 billion solar masses, and a disc mass of about 100 billion solar masses. H II regions are abundant in M101, with many of them being quite massive and luminous. Where stars develop, H II regions usually accompany massive clouds of high-density molecular hydrogen gas that are collapsing due to their own gravitational pull. Numerous young, bright, hot stars ionise H II regions; those in M101 have the ability to form hot superbubbles.

The tidal effects from interactions with its neighbouring galaxies cause M101 to be asymmetrical. Ultraviolet observations of M101 show intense star formation activity in the spiral arms due to the compression of interstellar hydrogen gas by these gravitational interactions.

## M 101 Group

The Pinwheel galaxy owns a group of galaxies dubbed the M 101 Group, named after the brightest galaxy in the group, the Pinwheel galaxy. The six galaxies of the M 101 Group are NGC 5204, UGC 8837, NGC 9405, NGC 5477, NGC 5474, and NGC 5585. Additional potential member galaxies of the M 101 Group may include NGC 5238 and UGC 8508. These dwarf galaxies may possibly have produced the well-defined spiral arms the Pinwheel galaxy possesses.

## Gallery

1. ↑ 1.0 1.1 https://science.nasa.gov/mission/hubble/science/explore-the-night-sky/hubble-messier-catalog/messier-101/
2. ↑ http://www.messier.seds.org/Mdes/dm101.html
3. ↑ https://ui.adsabs.harvard.edu/abs/1979A&A....72...73C
4. ↑ https://ui.adsabs.harvard.edu/abs/2001ApJ...554..202I
5. ↑ https://ui.adsabs.harvard.edu/abs/1997ApJ...481..169W