Galaxy Mergers

As we have learned in class, it is difficult to observe phenomena in space. However, through developments in scientific instruments, we can study objects in space with more precision. Despite these advancements, we are unable to clearly view and explain certain events, such as the merger of two galaxies.  In certain instances, like the merge of two galaxies, large amounts of gas and dust particles mask visible light, and thus, we are unable to view the phenomena using a typical telescope. Thankfully, a group of researchers recently published a study that provides new information about galaxies and their collisions.


In the article titled Growing supermassive black holes in the late stages of galaxy mergers are heavily obscured, researchers examine 52 supermassive black holes in nearby galaxies using NASA’s NuSTAR telescope. The telescope is essential to the study due to its sensitivity to high-energy X-rays. When galaxies merge, material orbiting the vicinity of the black hole in each respective galaxy fall within the black hole, causing the black hole to grow and become an active galactic nucleus. As this process occurs, a “cocoon” of gas and dust particles forms around the black hole, making it difficult to study. However, we can detect light at higher energies, such as high-energy X-rays, as they are able to escape the obscuration. According to the formula E=hc/ℷ, energy increases as the wavelength decreases. X-rays have relatively low wavelengths and therefore have higher energies. So, since the NuSTAR telescope can detect high-energy X-rays, the researchers compared the results to that using of a telescope that can detect low-energy X-rays. The researchers concluded that when high-energy X-rays are detected but low energy X-rays are not, the active galactic nucleus is covered by a “cocoon” of gas and dust particles.


The material within a galaxy is capable of orbiting the supermassive black hole that resides in its center. However, we know that as galaxies merge, the supermassive black holes become surrounded by shrouds of gas and dust since the black holes disrupt the material that surround them. Therefore, researchers who were a part of the study wanted to determine the distance between active galactic nuclei that creates the most obscuration. According to the study, obscuration reaches its maximum when the active galactic nuclei of merging galaxies are at a distance of 0.4-10.8 kPc. Since the obscuration typically reaches its maximum at relatively small distances, we can conclude that the obscuration occurs during the late stages of galaxy mergers. Of the 52 galaxies studied, the active galactic nuclei of those that were in its late stages of merging possessed obscuring material that covered 95% of the X-ray source.



Ricci, C., et al. “Growing supermassive black holes in the late stages of galaxy mergers are heavily obscured.” Monthly Notices of the Royal Astronomical Society (2017). Web.

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