Weird Science

Whale Galaxy

Polish ver­sion is here

NGC 4631, known as the Whale Galaxy, is an impres­sive bar­red spi­ral galaxy loca­ted in the con­stel­la­tion Canes Vena­tici. Its shape, remi­ni­scent of a whale swim­ming thro­ugh the cosmic ocean, ear­ned it its name. Disco­ve­red on March 20, 1787, by Wil­liam Her­schel, it lies appro­xi­ma­tely 25 to 30 mil­lion light years from Earth and spans about 140,000 light years, making it sli­gh­tly lar­ger than the Milky Way. The galaxy is vie­wed almost exac­tly edge-on from Earth, which allows for deta­i­led stu­dies of its struc­ture and phy­si­cal pro­per­ties.

At the core of NGC 4631 lies a pro­mi­nent star­burst region, an area of intense star for­ma­tion. This vigo­rous stel­lar acti­vity is evi­dent in the emis­sion of ioni­zed hydro­gen and inter­stel­lar dust hea­ted by newly for­med stars. The most mas­sive of these stars undergo rapid hydro­gen fusion, quic­kly exhau­sting their fuel before ulti­ma­tely ending their lives as super­no­vae.

Altho­ugh no super­no­vae have been direc­tly obse­rved in NGC 4631, a lumi­nous red nova (LRN) desi­gna­ted AT 2021biy was disco­ve­red on Janu­ary 29, 2021, with an appa­rent magni­tude of 18.1m. LRNe are rare astro­no­mi­cal events belie­ved to result from the mer­ger of two stars in a binary sys­tem. AT 2021biy was moni­to­red both pho­to­me­tri­cally and spec­tro­sco­pi­cally, reve­a­ling spec­tral evo­lu­tion cha­rac­te­ri­stic of this class of objects.

Obse­rva­tions

March 6, 2025, aro­und 9:00 PM - Kato­wice (Poland)
urban envi­ron­ment, extre­mely high level of light pol­lu­tion

That night, the sky was excep­tio­nally clear, offe­ring excel­lent con­di­tions for astro­no­mi­cal obse­rva­tion. Despite the high level of light pol­lu­tion, good atmo­sphe­ric tran­s­pa­rency made deep-sky obse­rva­tions pos­si­ble, and pro­per ima­ging tech­ni­ques ena­bled suc­cess­ful astro­pho­to­gra­phy.

During the ses­sion, the elon­ga­ted form of the Whale Galaxy was cle­arly visi­ble. Its struc­ture, inc­lu­ding dark dust lanes and active star-for­ming regions, could be distin­gu­i­shed as sub­tle varia­tions in bri­ght­ness along the edge of the disk. Nearby, the satel­lite galaxy NGC 4627 was also detec­ted, altho­ugh its smal­ler size and lower lumi­no­sity deman­ded more care­ful obse­rva­tion.

Ilustracja: Fig. 1 - without labels

Fig. 1 - without labels

Ilustracja: Fig. 1 - with labels

Fig. 1 - with labels

NGC 4627 is a small ellip­ti­cal galaxy that is gra­vi­ta­tio­nally bound to its lar­ger com­pa­nion. Toge­ther, the Whale Galaxy and its satel­lite are cata­lo­ged as Arp 281 in Hal­ton Arp’s *Atlas of Pecu­liar Gala­xies*. Nearby, the distor­ted galaxy NGC 4656 points to past gra­vi­ta­tio­nal inte­rac­tions among all three, which likely led to struc­tu­ral defor­ma­tions, the for­ma­tion of tidal brid­ges, and incre­a­sed star for­ma­tion acti­vity.

2MASX J12420645+3245390 is a small galaxy that has not yet been inc­lu­ded in any of the widely reco­gni­zed cata­logs.

Photo 1 Para­me­ters:

  • Total expo­sure time: 25 minu­tes (stack of 50 RAW fra­mes at 30s each, using an appro­priate num­ber of dark, bias, and flat fra­mes)
  • Canon EOS 60D
  • ISO: 1500
  • Mak­su­tov-Cas­se­grain tele­scope (100/1400), 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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