What Was It Like When Starlight First Broke Through The Universe’s Neutral Atoms?
“The light created in the earliest era of stars and galaxies all plays a role. The ultraviolet light works to ionize the matter around it, enabling visible light to progressively farther and farther as the ionization fraction increases. The visible light gets scattered in all directions until reionization has gotten far enough to enable our best telescopes today to see it. But the infrared light, also created by the stars, passes through even the neutral matter, giving our 2020s-era telescopes a chance to find them.
When starlight breaks through the sea of neutral atoms, even before reionization completes, it gives us a chance to detect the earliest objects we’ll ever have seen. When the James Webb Space Telescope launches, that will be the first thing we look for. The most distant reaches of the Universe are within our view. We just have to look and find out what’s truly out there.”
Something existing in our Universe is not quite the same as something being detectable in our Universe. We know that, at some point in our past, we created the first generation of stars, the second generation of stars, and the very first galaxies to exist in our Universe. But in order to detect them, there has to be some way for that light to travel through the Universe to our observatories and telescopes monitoring the skies today. There’s an obstacle standing in the way of that, though: the neutral atoms formed just hundreds of thousands of years after the Big Bang. When the first hints of starlight begin permeating through space, they encounter these neutral atoms, which largely thwarts them. It takes hundreds of millions of years for starlight to win.
The world lost an amazing thinker today. Celebrated world-renowned physicist Stephen Hawking passed away in Cambridge on March 14th, 2018 (Pi Day), at age 76. Somehow, I think he would have found this to be very poetic.
Stephen William Hawking CH CBE FRS FRSA was an English theoretical physicist, cosmologist, author and Director of Research at the Centre for Theoretical Cosmology within the University of Cambridge.
Interacting galaxies (colliding galaxies) are galaxies whose gravitational fields result in a disturbance of one another. An example of a minor interaction is a satellite galaxy’s disturbing the primary galaxy’s spiral arms. An example of a major interaction is a galactic collision, which may lead to a galaxy merger.
A giant galaxy interacting with its satellites is common. A satellite’s gravity could attract one of the primary’s spiral arms, or the secondary satellite’s path could coincide with the position of the primary satellite’s and so would dive into the primary galaxy (the Sagittarius Dwarf Elliptical Galaxy into the Milky Way being an example of the latter). That can possibly trigger a small amount of star formation. Such orphaned clusters of stars were sometimes referred to as “blue blobs” before they were recognized as stars.
Colliding galaxies are common during galaxy evolution. The extremely tenuous distribution of matter in galaxies means these are not collisions in the traditional sense of the word, but rather gravitational interactions.
Colliding may lead to merging if two galaxies collide and do not have enough momentum to continue traveling after the collision. In that case, they fall back into each other and eventually merge into one galaxy after many passes through each other. If one of the colliding galaxies is much larger than the other, it will remain largely intact after the merger. The larger galaxy will look much the same, while the smaller galaxy will be stripped apart and become part of the larger galaxy. When galaxies pass through each other, unlike during mergers, they largely retain their material and shape after the pass.
Galactic collisions are now frequently simulated on computers, which use realistic physics principles, including the simulation of gravitational forces, gas dissipation phenomena, star formation, and feedback. Dynamical friction slows the relative motion galaxy pairs, which may possibly merge at some point, according to the initial relative energy of the orbits.
Astronomers have estimated the Milky Way galaxy, will collide with the Andromeda galaxy in about 4.5 billion years. It is thought that the two spiral galaxies will eventually merge to become an elliptical galaxy or perhaps a large disk galaxy.
This view of Saturn’s A ring features a lone “propeller” – one of many such features created by small moonlets embedded in the rings as they attempt, unsuccessfully, to open gaps in the ring material.
Daphnis’ Final Appearance
This image of Saturn’s outer A ring features the small moon Daphnis and the waves it raises in the edges of the Keeler Gap. The image was taken by NASA’s Cassini spacecraft on Sept. 13, 2017. It is among the last images Cassini sent back to Earth.
Saturn: Before the Plunge
This image of Saturn’s northern hemisphere was taken by NASA’s Cassini spacecraft on Sept. 13, 2017.
This image of Saturn’s rings was taken by NASA’s Cassini spacecraft on Sept. 13, 2017.
A galaxy cluster, or cluster of galaxies, is a structure that consists of anywhere from hundreds to thousands of galaxies that are bound together by gravity. They are the largest known gravitationally bound structures in the universe and were believed to be the largest known structures in the universe until the 1980s, when superclusters were discovered. One of the key features of clusters is the intracluster medium (ICM). The ICM consists of heated gas between the galaxies and has a peak temperature between 2–15 keV that is dependent on the total mass of the cluster. Galaxy clusters should not be confused with star clusters, such as open clusters, which are structures of stars within galaxies, or with globular clusters, which typically orbit galaxies. Small aggregates of galaxies are referred to as galaxy group rather than clusters of galaxies. The galaxy groups and clusters can themselves cluster together to form superclusters. source