3 December 2016 | Brief Encounter


Image credit: Thomas Henne & Frank Sackenheim | Click image to enlarge

Image Data

  • Camera: SBIG ST8300
  • Optics: TMB 80/600 (focal lenght 520mm)
  • Filters: LRGB, Hα
  • Mount: Losmandy G11
  • Exposure: 30 x 20min Lum, 19 x 20min R, 9 x 20min B, 9 x 20min G, 7 x 20min Hα. Total 14h 40min.

Through the power of serendipity, a chance encounter between the Bok globule B175 and a bright blue star is beautifully illustrated in this stunning snapshot of a part of the Cepheus Flare region. Despite their unchanging and static appearance in the sky in the context of human lifetimes, stars move through space and orbit the centre of the Milky Way.

Some stars produce a reflection nebula if they happen to encounter interstellar dust on their intergalactic sojourns. One famous example is the star cluster known as the Pleiades with its brightest member stars being surrounded by brilliant blue reflection nebulae as a result of it moving through a dusty region of space as opposed to being born in that particular dust cloud.

The elongated globule B175 is located roughly 1300 light years away and vdB152 (also catalogued as Ced 201) is the reflection nebula visible toward the ‘head’ of the globule with its ‘tail’ stretching upwards. Discovered in 1908 by the famous astrophotographer Max Wolf, he named it the “Cave Nebula” but this name is no longer used to refer to vdB152 and is attributed to the emission nebula Sh2-155.

Professional studies have concluded that the illuminating star of vdB152 entered into a chance encounter with the dusty globule approximately 30,000 years ago. Images taken with professional observatories have revealed the presence of the Herbig Haro object HH 450, a type of small ionized nebula produced by jets from young stars.

Appearing as a thin curved gossamer streak, the red filaments visible to the left of B175 represent the supernova remnant G110.3+11.3, which was discovered in 2001 and might be interacting with the globule. If both are located at the same distance, then this relatively peaceful snapshot is a prelude to a dramatic possible collision between the supernova remnant and the dusty globule! Countdown to a ‘shocking’ encounter between the two has been estimated to commence in 1000 years time! If such a collision does take place in the future, any invisible structures present in the area might become ionized by the energy generated by the collision and become optically visible.

Last but not least, the colourful pink and purple cloud to the north of G110.3+11.3 is catalogued as DeHt 5. Originally catalogued as a planetary nebula, recent studies have identified it as a ‘planetary nebula impostor’. This class of object represent emission nebulae that contain OIII emission and are ionized by a white dwarf, some of the main hallmarks of true planetary nebulae. However these nebulae are not the remains of a dying star but parts of the interstellar medium that have become ionized by the ultraviolet radiation of a white dwarf star. Measurements of the radial velocity of the gas in DeHt 5 and the ionizing star show a difference between the two components strengthening the ionized ISM interpretation. Other examples of ‘PN mimics‘ are PHL 932 and Abell 35.

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