Weird Science

M51 - Whirlpool Galaxy

Polish ver­sion is here

The Whirl­pool Galaxy, occu­py­ing posi­tion 51 in the Mes­sier cata­log (M51, disco­ve­red by the cata­log’s cre­a­tor on Octo­ber 13, 1773), is a spi­ral galaxy with an unu­su­ally small core. Its distance from Earth is appro­xi­ma­tely 23 mil­lion light-years. In the cele­stial sphere, it can be obse­rved within the boun­da­ries of the con­stel­la­tion Canes Vena­tici, near the Big Dip­per aste­rism, which is part of Ursa Major.

Altho­ugh the Whirl­pool Galaxy is for­mally loca­ted in Canes Vena­tici, it is much easier to locate by fin­ding the region of the Big Dip­per. In the pho­to­graph below, I have circ­led the area where the galaxy can be found.

Ilustracja
Loca­tion of the M51 Galaxy

Dubhe (Alpha, α UMa) is an orange giant star obse­rved from a distance of over 120 light-years. Sli­gh­tly clo­se­r—at a distance of about 100 light-year­s—is Merak (Beta, β UMa), which, along with Dubhe, helps locate Pola­ris, the alpha star of Ursa Minor (α UMi). Merak is sur­ro­un­ded by a gase­ous disk that may give rise to pla­nets. The next two stars, Phecda (Gamma, γ UMa) and Megrez (Delta, δ UMa), are loca­ted at a simi­lar distance from Ear­th—just over 80 light-year­s—and have distinc­tly blue-white hues. Alioth (Epsi­lon, ε UMa) is the bri­gh­test star in the entire con­stel­la­tion of Ursa Major. It is a varia­ble star of the Alpha2 Canum Vena­ti­co­rum type, with a varia­bi­lity period of about five days and an appa­rent magni­tude that ran­ges from 1.76m to 1.79m. Alioth is about three times more mas­sive than the Sun and has a radius four times gre­a­ter than that of our star. Its hydro­gen rese­rves are likely nea­ring deple­tion. An inte­re­sting case is Mizar (Zeta, ζ UMa), which is actu­ally a qua­dru­ple star sys­tem. Nearby is the dou­ble star Alcor (80 UMa), which can be dif­fi­cult to spot with the naked eye due to the bri­ght­ness of Miza­r—tho­ugh a per­son with good vision can see it under sui­ta­ble con­di­tions. Accor­ding to the latest mea­su­re­ments, Mizar and Alcor are also likely gra­vi­ta­tio­nally bound, which would make this a sextu­ple sys­tem. At the end of the Big Dip­per’s han­dle lies Alkaid (Eta, η UMa), a young blue star appro­xi­ma­tely 15 mil­lion years old, belon­ging to spec­tral type B3. Its mea­su­red sur­face tem­pe­ra­ture ran­ges from 15,700 to 17,900 K, likely due to its rapid rota­tion, which cau­ses hot­ter polar regions where the stel­lar enve­lope is thin­ner. The Whirl­pool Galaxy can be found appro­xi­ma­tely 3.5° below Alkaid.

In my expe­rience, this beau­ti­ful galaxy can be obse­rved using rea­dily ava­i­la­ble pho­to­gra­phic equ­ip­ment (Photo 1, using a tele­photo lens instead of a tele­scope), which is highly satis­fy­ing. Howe­ver, using equ­ip­ment with a lar­ger aper­ture (Photo 2, a 152/760 refrac­tor) allows for much more deta­i­led obse­rva­tions.

Obse­rva­tions

July 11, 2021, aro­und 11:00 PM – Jaworzno (Poland), gar­den
urban con­di­tions, high level of light pol­lu­tion

Une­xpec­te­dly, the sky was clear that night, allo­wing me to enjoy obse­rving the sky. This was despite the fact that I was obse­rving from a gar­den loca­ted in the city, where con­di­tions for such acti­vi­ties are far from ideal. Using bino­cu­lars, I could see an almost uni­form glow thro­u­ghout the nor­thern region of the sky, cau­sed by street ligh­ting. Without high expec­ta­tions, I set up a camera equ­ip­ped with a zoom tele­photo lens (maxi­mum focal length = 250mm) on a mount whose axes had been pre­vio­u­sly ali­gned with the cele­stial pole using a  home­made con­trol­ler that also served as an inte­rva­lo­me­ter with dithe­ring func­tio­na­lity. To my sur­prise, the cha­rac­te­ri­stic shape of the Whirl­pool Galaxy was visi­ble even in the first one-minute expo­sure. The result of a cumu­la­tive 20-minute expo­sure is shown in the crop­ped pho­to­graph below, pre­sen­ted in both raw form and with labels.

Ilustracja: Photo 1 – without labels

Photo 1 – without labels

Ilustracja: Photo 1 – with labels

Photo 1 – with labels

The Whirl­pool Galaxy was the first galaxy in which a spi­ral struc­ture was obse­rved, as its orien­ta­tion allows for a clear view of its spi­ral arms from Earth. With an appa­rent magni­tude of 8.96m and angu­lar dimen­sions of 11.2′ by 6.9′ (toge­ther with its com­pa­nion galaxy, NGC 5195), it has a mass of about 160 bil­lion solar mas­ses and a dia­me­ter of 60,000 light-years. It is clas­si­fied as a type 2 Sey­fert galaxy.

In addi­tion to the afo­re­men­tio­ned gala­xies, the pho­to­graph also shows other objects:

Object HD 117815 is a varia­ble star within the con­stel­la­tion Canes Vena­tici.

Three super­no­vae have been recor­ded in the Whirl­pool Galaxy:



June 29, 2024, aro­und 11:30 PM – Jaworzno (Poland), gar­den
urban con­di­tions, high level of light pol­lu­tion

The first half of the night was quite cle­a­r—c­lo­uds began to appear aro­und mid­ni­ght, accom­pa­nied by the rising Moon. It was sur­pri­sin­gly warm, and the gen­tle wind pre­ven­ted moi­sture from con­den­sing on the optics. All of these fac­tors allo­wed me to cap­ture a much more deta­i­led and refi­ned image of the Whirl­pool Galaxy (Photo 2) com­pa­red to the pre­vious ses­sion.

Ilustracja: Photo 2 – without labels

Photo 2 – without labels

Ilustracja: Photo 2 – with labels

Photo 2 – with labels

The dwarf galaxy NGC 5195, which accom­pa­nies the Whirl­pool Galaxy, is loca­ted at the end of one of its spi­ral arms and belongs to the cate­gory of len­ti­cu­lar gala­xies. Both gala­xies gra­vi­ta­tio­nally inte­ract with each othe­r—the gra­vi­ta­tio­nal pull of NGC 5195 has stret­ched one of M51’s spi­ral arms, cre­a­ting a distinct stel­lar bridge between the two objects.

It is belie­ved that the pro­no­un­ced spi­ral struc­ture of the Whirl­pool Galaxy is the result of NGC 5195 pas­sing thro­ugh its disk, an event esti­ma­ted to have occur­red between 500 and 600 mil­lion years ago. Astro­no­mers believe that this event com­pres­sed hydro­gen in those regions, lea­ding to incre­a­sed star for­ma­tion acti­vity. Cur­rent evi­dence sug­ge­sts that, in the future, NGC 5195 will be com­ple­tely absor­bed by its lar­ger com­pa­nion.

Com­pa­red to Photo 1, Photo 2 reve­als two addi­tio­nal gala­xies: IC 4282 and IC 4278.



Photo 1 Para­me­ters:

  • Total expo­sure time: 20 minu­tes (stack of 20 B/W RAW fra­mes at 60s each, using an appro­priate num­ber of dark, bias, and flat fra­mes)
  • Canon EOS 600D
  • ISO: 1600
  • Lens: zoom type (used at fmax = 250mm)
  • 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

Photo 2 Para­me­ters:

  • Total expo­sure time: 80 minu­tes (stack of 40 RAW fra­mes at 120s each, using an appro­priate num­ber of dark, bias, and flat fra­mes)
  • Canon EOS 600D
  • ISO: 1600
  • Ach­ro­ma­tic refrac­tor Mes­sier AR-152S (152/760), 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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