Far out cosmology: colliding galaxies (Introduction)

by David Turell , Saturday, January 23, 2021, 22:40 (1398 days ago) @ David Turell

Very common:

https://www.universetoday.com/149689/the-universe-in-formation-hubble-sees-6-examples-o...

"10 billion years ago, galaxies of the Universe were ablaze with the light of newly forming stars. This epic phase of history is known as “Cosmic Noon” – the height of all star creation. Galaxies like our Milky Way aren’t creating stars at nearly the rates they were in the ancient past. However, there is a time when galaxies in the present can explode with star formation – when they collide with each other. This recently published collage of merging galaxies by the Hubble HiPEEC survey (Hubble imaging Probe of Extreme Environments and Clusters) highlights six of these collisions which help us understand star formation in the early Universe.

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"The Milky Way creates between 1.5 to 3 solar masses (mass of our own Sun) worth of stars each year. Colliding galaxies can create upwards of 100 solar masses per year. These six mergers are all in various stages of collision. Galaxies, for all their hundreds of billions of stars, are mainly empty space. It’s actually possible for two galaxies to merge and yet no two individual stars collide with each other. Rather galaxies pass through one another several times until they finally coalesce. Eventually the nuclei of both galaxies merge to become one larger galaxy – an epic cosmic dance routine over billions of years.

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"The targets were selected because they are oriented face-on meaning Hubble can scan the entire surface of the galaxy for star forming clusters. The clusters themselves are enshrouded by massive clouds of dust and gas, the raw material for star formation.

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"Interstellar dust causes “extinction” a process where light is literally extinguished as it’s absorbed. However, star forming clusters are powerful sources of infrared light and a particular red light known as Hydrogen-Alpha created by young massive stars blasting hydrogen gas with their intense radiation. Both infrared and H-Alpha can cut through the shroud to be observed by Hubble. Merging galaxies are ablaze with infrared light. Classified as “Luminous Infrared Galaxies” (LIRG) they are brighter in infrared than the entire light spectrum of other galaxies.

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"Researchers discovered enormous star forming clusters within the merging systems – far larger than found in our own galaxy. The largest young star clusters in the Milky Way can reach tens of thousands of solar masses. As galaxies merge, more and more massive clusters form – the largest created in the later stages of coalescence. NGC 34 features a cluster upwards of 20 million solar masses that is 100 million years old. The younger mergers have a greater percentage of clusters less than 10 million years old indicating the rate of star formation has been steadily increasing.

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"The raw material to form stars is interstellar hydrogen gas. Galaxies contained a greater abundance and density of this gas in the past which was consumed during Cosmic Noon. Hydrogen remains in galaxies like the Milky Way but the gas isn’t nearly as concentrated resulting in lower rates of star formation and smaller star clusters. The merging of galaxies create tidal forces through gravity that funnel this remaining gas into high density, concentrated regions resulting in massive star forming clusters and a cascade of star formation – a “starburst.”

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"While the Milky Way doesn’t feature massive young clusters of stars, our galaxy does have very large old clusters of stars known as Globular Clusters. The largest we’ve observed in the Milky Way is called Omega Centauri which contains about 10 million stars weighing in at 4 million solar masses that are billions of years old. The origin of globular clusters is not entirely known but they are thought to originate from the Milky Way’s own collision with other galaxies in the past or formed during Cosmic Noon."

Comment: the text I presented is informative, but the images are breathtaking. As an aside dhw worries that the universe is too large and complicated and wonders why God did it that over-sized way. Not to worry, NASA says the number of galaxies in the hundreds of billions not trillions:

https://justthenews.com/nation/science/experts-say-number-galaxies-universe-may-be-sign...