• Chris Baker

JULY OBJECT OF THE MONTH: HEART OF THE HEART


The ‘Heart of the Heart’ is catalogued as Melotte 15 and is a small cluster of stars at the centre of the Heart Nebula, located in the constellation Cassiopeia, on the Perseus Arm (one of the two main spiral arms of our galaxy). It is roughly 7,500 lightyears away from Earth.


The Heart Nebula, discovered by William Herschel in 1787, is aptly named because of its heart-like shape and red hue. It has a diameter of about 330 lightyears (which is about 165 times bigger than our Solar system) and glows bright red because of the excited hydrogen gas emitting that colour. This glow comes from the radiation emitted from Melotte 15 which, shown in this picture, spans about 15 lightyears. (The entire Heart Nebula is very difficult to photograph due to its size.)


This cluster is made up of very young, hot super-giants which are only 1.5 million years old- for perspective, the Sun is over 4.5 billion years old which makes these stars babies in comparison. Some of these stars are incredibly bright (luminosities up to 1 million times that of the Sun) and have masses nearly 50 times the mass of the Sun, with surface temperatures up to 50,000 Kelvin, while others are very faint with masses just a fraction of the Sun’s.


The clouds that can be seen in the picture are shaped by stellar winds and radiation from the massive stars within Melotte 15. These are made up of dust and are the birthplace of the young stars. The reason some are so dark is because they are so dense that they block out the light and radiation from behind them. The shape of these clouds give rise to this cluster’s nickname: the Pegasus Cluster.


Imaging the Heart of the Heart


This object is extremely faint from Earth and not much light is reaching the telescope and camera. It emits light at specific wavelengths associated with certain ionized states of gases.

I use specialist filters which capture certain emissions from these gases, in this case Hydrogen Alpha (Ha), Oxygen III (OIII) and Sulphur II (SII). Using my telescope and cameras I captured 10’s of hours of data through these three filters over many nights. Each exposure was 20 minutes and at the end of each night I discard the sub optimal images, such as when the seeing conditions were not perfect or a satellite crossed the field of view. Over time I build up the data for each filter and eventually have enough to start the long process of calibration and processing.


During this process I want to extract the beautiful detail that exists buried within the raw data and at the same time make it look stunning for the Galaxy on Glass range. I use a convention to assign the colours developed for the Hubble Space telescope. This means that I assign the SII to the red channel, Ha to the green and OIII to the blue channel. Using this convention shows rich blues and golds and the wispy details of the nebulosity.


I hope you enjoy viewing this beautiful object and you can see the details of how to purchase it here


Written by Katy Hollands, University of York student and summer intern for Galaxy on Glass.

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