Weird Science

M101 - Pinwheel Galaxy

Polish ver­sion is here

Among the most fasci­na­ting astro­no­mi­cal objects obse­rva­ble with ama­teur tele­sco­pes, spi­ral gala­xies hold a spe­cial place. Their cha­rac­te­ri­stic struc­ture, fea­tu­ring arms that gra­ce­fully curve aro­und a cen­tral core, cap­ti­va­tes the ima­gi­na­tion of both pro­fes­sio­nal astro­no­mers and ama­teur star­ga­zers. One of the most visu­ally stri­king exam­ples of such a galaxy is Mes­sier 101, also known as the Pin­wheel Galaxy.

Spi­ral gala­xies are among the most beau­ti­ful and fre­qu­en­tly stu­died struc­tu­res in the Uni­verse. They are cha­rac­te­ri­zed by a flat disk con­ta­i­ning more or less distinct spi­ral arms and a cen­tral bulge known as the galac­tic nuc­leus. These arms are regions of intense star for­ma­tion, popu­la­ted with young, bri­ght stars and nebu­lae. Spi­ral gala­xies clas­si­fied within Hub­ble’s sys­tem exhi­bit various arm struc­tu­res. Sa and SBa gala­xies have tigh­tly wound arms, while Sc and SBc gala­xies fea­ture loo­sely wound arms. The most famous spi­ral galaxy is our own Milky Way, home to the Solar Sys­tem.

One of the most visu­ally stri­king spi­ral gala­xies is the Pin­wheel Galaxy (M101), disco­ve­red in 1781 by Pierre Méchain and later cata­lo­ged by Char­les Mes­sier as num­ber 101 in his cata­log.

Obse­rva­tions

June 26, 2024, aro­und 11:00 PM – Kato­wice (Poland), city cen­ter
Urban con­di­tions with a very high level of light pol­lu­tion

The Pin­wheel Galaxy is a spi­ral galaxy with a rela­ti­vely faint core and well-deve­lo­ped arms. In the cele­stial sphere, it can be found within the boun­da­ries of the con­stel­la­tion Ursa Major, near the last star of the Big Dip­per’s han­dle (Alkaid, η UMa), making it visi­ble year-round. The galaxy has an ave­rage appa­rent magni­tude of 7.9m and an appa­rent size of appro­xi­ma­tely 24.5′ by 23.4′. Its actual dia­me­ter is 170,000 light-years, and its mass is appro­xi­ma­tely 180 bil­lion solar mas­ses. The Pin­wheel Galaxy is obse­rved from a distance of 21 mil­lion light-years.

This galaxy, toge­ther with other smal­ler or less visi­ble objects, forms what is known as the M101 Group of gala­xies. It is likely that gra­vi­ta­tio­nal inte­rac­tions within this group have cau­sed the Pin­wheel Galaxy’s spi­ral arm pat­tern to become visi­bly distor­ted (Photo 1). Addi­tio­nally, it is belie­ved that a close pas­sage by ano­ther gala­xy­—pos­si­bly NGC 5474—a­bout 250 mil­lion years ago trig­ge­red incre­a­sed star-for­ming acti­vity in cer­tain regions of the galaxy, resul­ting in a higher con­cen­tra­tion of young, blue stars in its nor­the­a­stern arm.

Ilustracja: Photo 1 – without labels

Photo 1 – without labels

Ilustracja: Photo 1 – with labels

Photo 1 – with labels

As shown, the area of the Pin­wheel Galaxy is rich in inte­re­sting objects. Most of these (NGC 5447, NGC 5449, NGC 5450, NGC 5451, NGC 5453, NGC 5455, NGC 5458, NGC 5461, NGC 5462, and NGC 5471) are star clo­uds and H II region­s—c­lo­uds of ioni­zed gas, pri­ma­rily hydro­gen and pla­sma, exten­ding up to seve­ral hun­dred light-years across, where new stars are born. Nota­bly, the image also inc­lu­des the Magel­la­nic-type galaxy NGC 5477.

To date, five super­no­vae have been obse­rved in this galaxy, in chro­no­lo­gi­cal order: SN 1909A, SN 1951H, SN 1970G, SN 2011fe, and SN 2023ixf.

The Pin­wheel Galaxy and its sur­ro­un­dings are such stun­ning regions of the night sky that they are well worth dedi­ca­ting time to obse­rve.

Photo 1 Para­me­ters:

  • Total expo­sure time: 30 minu­tes (stack of 30 RAW fra­mes at 60s each, using an appro­priate num­ber of dark, bias, and flat fra­mes)
  • Canon EOS 60D
  • ISO: 2000
  • New­ton tele­scope (150/750), prime focus expo­sure
  • A fil­ter was used to reduce the effects of arti­fi­cial light pol­lu­tion and atmo­sphe­ric glow
  • Mount: equ­a­to­rial mount with trac­king, ali­gned using the drift method and con­trol­led by a custom-built sys­tem

Fur­ther rea­dings:

Marek Ples

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