The NGC 281 is also known as pacman nebula, because roughly resembles the character of the famous video game. The NGC 281 is hydrogen region (HII) in the Perseus spiral arm. He was discovered in 1883 by E. E. Barnard, who described it as "great faint nebula, very diffuse." It Contains the open stellar cluster IC 1590 with the multiple star HD 5005, which is the main source of ionizing radiation (the primary star has magnitude +8 with four attendants in apparent distances from 1.4 to 15.7 seconds of arc) and several Bok beads (see. Following reference). Generally high-mass stars are essential for pumping energy in the universe. It is difficult to observe them, because usually they are very far from us and covered by clouds of gas and thus the understanding of star formation mechanisms are difficult to study. But the nebula NGC 281 and the stellar cluster IC 1590 are located just 9,200 light years from us and 1,000 light-years above the galactic plane, events that enable the observation and study of the phenomena occurring in it.

 

     The massive multiple-star system HD 5005 at the center of the star cluster IC 1590, is by far the brightest source of ionizing radiation within the cluster. You can see how remnants of the original molecular cloud point like accusing fingers at the source of their natal cloud's demise. Due to the higher density of material at their tips these "fingers" or "pillars" of material manage to cling on while the surrounding dark nebula is stripped away. This higher density material is gravitationally collapsing and forming yet more stars.

Backlit by the glow of ionized gas within the nebula, several small isolated black patches of material are evident. These are known as "Bok globules" after Bart Bok, a dutch astronomer who first observed and studied them. Most Bok globules contain one or more protostars that will eventually become visible once the globule dissipates.

   

     Originally NGC 281, must have been a huge dark molecular cloud. The massive stars that originally formed at its center, gave start to many events in the galactic environment through the very strong winds that start from theirs surface and the intense radiation heating up around existing gas, displacing to them to the interstellar space. So with these mechanisms, the stars formed in the center of NGC 281 gradually began to form cavities. The gases in and around these regions were ionized by abundant ultraviolet radiation formed by the winds from the stellar cluster IC 1590. So existing ionized hydrogen clouds forms as they began to emit radiation in the visible spectrum, creating this nebula appearence.

 

Bok globules : They observed in the 1940s by Bart J. Bok. The initial assumption was that this is a dark cloud in which stars are formed due to gravitational collapse of these existing material. They form dark molecular clouds, extremely cold (3 K), relatively small and of high density. Their dimensions are just of one light year. Their study is difficult because they absorb the entire visible spectrum radiation events that occur within. Today it is considered that this star formation mechanism, gives multiple star systems. These beads are located within regions of mainly molecular hydrogen with masses on the order of 2 to 50 solar masses. Further observations have revealed that some Bok globules contain embedded warm sources, some contain Herbig–Haro objects, and some show outflows of molecular gas. Millimeter-waveemission line studies have provided evidence for the infall of material onto an accreting protostar.

 

Telescope  :  Takahashi FSQ 106 ED

Mount       :    AP Mach1 GTΟ

Camera     :    QSI 683
Guiding    :    Off axis, Zwo 120 mm, PHD

Ha-OIII-SII RGB
Ha 18x600s, OIII 18x600s, SII 8x600s
R 10x600s, G 9x600s, B 8x600s

Processed in PixinSight and Photoshop
Skyros Island, August 2015