New Discoveries on Galactic Mergers and Their Impact on Stars
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Chapter 1: The Nature of Galactic Mergers
Recent observations have unveiled the phenomenon of galactic mergers, raising the question: why do these cosmic unions often spell disaster for certain galaxies? Historically, such mergers were a frequent occurrence billions of years ago and have significantly influenced the Universe's structure. However, not every merger leads to a thriving new galaxy; for some, it results in a premature decline.
As a result of ongoing research, it is evident that while only a handful of galaxies are merging today, this process was much more prevalent approximately 6 to 10 billion years ago, fundamentally shaping the cosmos we observe today.
Section 1.1: Insights from NASA's Spitzer Space Telescope
NASA's Spitzer Space Telescope has provided three new images showcasing pairs of galaxies on the verge of merging. While these galaxies appear distinct at present, gravitational forces are steadily drawing them together, leading to their eventual combination into new galactic entities.
The primary image features the merging galaxies NGC 7752 (the larger) and NGC 7753 (the smaller), also referred to collectively as Arp86. The various colors depicted represent different wavelengths of infrared light, with blue and green primarily emitted by stars and red indicating wavelengths predominantly produced by dust. Credit: NASA/JPL-Caltech
Section 1.2: The Life Cycle of Merged Galaxies
Some galaxies will thrive for billions of years following a merger, while others may trigger processes that halt star formation altogether, leading to their gradual decline. For over a decade, scientists involved in the Great Observatories All-sky LIRG Survey (GOALS) have been investigating nearby galaxies to understand the intricacies of these mergers and their implications for the history of the universe.
The survey concentrated on 200 nearby galaxies, many of which are in various stages of merging. The images captured by Spitzer reveal three of these targets.
Chapter 2: The Role of Supermassive Black Holes
The first video, Galaxy Mergers: Past and Present, discusses the historical prevalence of galactic mergers and their long-term effects on star formation and galaxy evolution.
During these galactic mergers, a critical factor is the central supermassive black hole, which can be millions to billions of times heavier than our Sun. The merger process drives gas and dust toward the galaxy's core, where it can foster the creation of new stars while also feeding the black hole.
This image illustrates the merger of NGC 6786 (right) and UGC 11415 (left), known collectively as VII Zw 96. It comprises images from three Spitzer Infrared Array Camera (IRAC) channels: channel 1 in blue, channel 2 in green, and channel 3 in red. Credit: NASA/JPL-Caltech
Section 2.1: The Impact of Black Hole Activity
This intense activity can create a volatile environment. The shockwaves or powerful winds generated by the active black hole can sweep through the galaxy, expelling significant amounts of gas and effectively stalling star formation. If these outflows are sufficiently powerful or occur frequently, they can impede the galaxy's ability to produce new stars.
The relationship between mergers, star formation surges, and black hole dynamics is intricate, and researchers continue to explore its complexities. A specific newly merged galaxy is currently under detailed investigation at the W.M. Keck Observatory in Hawaii, where scientists are searching for signs of galactic shockwaves driven by the active galactic nucleus—an incredibly bright entity powered by a supermassive black hole that is consuming surrounding material.
This image captures the two galaxies in a merger known as Arp 302, also called VV 340. The various colors represent different wavelengths of infrared light, with blue and green indicating star emissions and red primarily signaling dust emissions. Credit: NASA/JPL-Caltech
Chapter 3: Observations and Future Studies
The second video, New Image of Merging Galaxies Marks Two Years of NASA Space Telescope Mission, highlights the significant findings from recent observations of merging galaxies, showcasing their vibrant nature and the ongoing research into their effects.
Galactic mergers in the nearby universe emit particularly bright signals detectable by infrared observatories like Spitzer. The GOALS studies have also utilized data from other space-based telescopes, including NASA’s Hubble and Chandra, as well as ground-based facilities like the Keck Observatory and the National Science Foundation’s Very Large Array.
Originally published at sciscomedia.co.uk on February 27, 2019.