Energy emitted from newly born stars, such as the large O type stars seen in this open cluster, Melotte 15, often erode and carve surrounding molecular gas clouds. However, depending on conditions, this energy can also help initiate compression of surrounding clouds, prompting a surge in new star formation. Several of the O stars in this cluster have a mass more than 50 times that of our sun. These large, luminous behemoths are rare in the Milky Way. It is estimated that there are only 20,000 type O stars in our galaxy. (About 1 in every 10,000,000 stars) I was wondering what impact these large stars might have on their surroundings and did a quick search. I imagine it is similar for you, but much of the enjoyment I find in exploring the cosmos with our telescopes, is trying to understand just a little bit more about the image that emerges after processing!

Melotte 15 is part of a larger ionization bubble, commonly known as the Heart Nebula, IC 1805. IC 1805 is part of the W3/4/5 complex, it being W4 and sandwiched between 3 and 5 inside of the Perseus Arm of our Milky Way. (W3/4/5 owe their name to astronomer Gart Westerhout, who first identified them in the 1950’s, as the 3rd, 4th and 5th sources of his radio survey of the galaxy.)

Last year a paper was published in the Astrophysical Journal Letters, (Zuniga, et al., 2019) entitled “Evidence of Hubble Flow-like Motion of Young Stellar Populations away from the Perseus Arm”. Zuniga’s team mapped the motion of a group of stars surrounding the W3/4/5 complex. What they discovered as they reviewed the vectors of the selected stars was a common origin. They all appeared to be moving away from the W4 region (IC 1805) with an averaged velocity of 15/km/kpc. Zuniga points out a supernova remnant that was found in the area. A neighborhood of O type stars, such as the ones in W3,4,5, would see frequent supernovae due to their short life span of close to 10 million years. He suggests that this supernova, other supernovae originating from deceased O type stars in the past, as well as the massive stars themselves, may be the source of energy driving the nearby stars out of the region. (I have included a screen shot of the velocity map. Note IC 1805 at the center)

While this study is not conclusive, and there are other possible explanations, I found it interesting that the energy from stars and supernovae near Melotte 15 may be helping to carve surrounding molecular clouds; initiate significant new star formation in the adjacent eastern wall of W3 (IC 1848, Soul Nebula); and last but not least, be responsible for pushing a large number of nearby stars of the Perseus arm out into the surrounding galactic neighborhood.

This is an Ha,OIII, RGB blend.

Happy New Year!

Image acquisition info:

Date: November 2020

Location: Starlodge Observatory, Fairview, UT

Telescope: AT 16 Ritchey-Chretien

Camera: Atik 16200

HaOIIIRGB: 320:380:50:180:100 (17.2 hrs)