What is it about galaxies and dark matter? Most, if not all galaxies are surrounded by halos of this mysterious, unknown, but ubiquitous material. And, it also played a role in galaxy formation. The nature of that role is something astronomers are still figuring out. Today, they\u2019re searching the infant Universe, looking for the tiniest, brightest galaxies. That\u2019s because they could help tell the tale of dark matter\u2019s role in galactic creation.<\/p>\n
<\/p>\n An international team of astronomers led by UCLA\u2019s Smadar Naoz is doing simulations of early galaxy formation. Their computer programs track the circumstances of galactic births not long after the Big Bang. These \u201chot off the press\u201d computer models include some new wrinkles. They take into account previously neglected interactions between dark matter and the primordial \u201cstuff\u201d of the Universe. That would be hydrogen and helium gas. The result of the simulations: tiny, bright galaxies that formed more quickly than in computer models that didn\u2019t include those motions. Now astronomers just need to find them, using JWST, in an effort to see if their theories of dark matter hold up.<\/p>\n How would interactions between baryonic matter and dark matter make a difference? Here\u2019s one likely story: in the early Universe, clouds of gas moved at supersonic speeds past clumps of dark matter. It bounced off the dark matter. Eventually, after millions of years, the gaseous material fell back together to form stars in a blast of star birth. The team\u2019s simulations track the formation of those galaxies right after the Big Bang. <\/p>\n Naoz\u2019s team thinks that the existence of those smaller, brighter, more distant galaxies could confirm the so-called \u201ccold dark matter\u201d model. It suggests that the Universe was in a hot dense state containing only gases after the Big Bang. Over time, it evolved to a lumpy distribution of galaxies (and eventually galaxy clusters). Along the way, stars and galaxies formed, but the earliest steps likely depend on gravitational interaction with dark matter. If the supersonic interactions that Naoz\u2019s team modeled actually happened, then those little galaxies would be the result.<\/p>\n JWST has seen some pretty early galaxies during its time in operation. It hasn\u2019t detected the very earliest ones\u2014yet. However, the images it HAS provided are tantalizing hints at what might exist in earlier epochs and could provide insight into the role of dark matter. So, it makes sense that astronomers want to push its view back in time as far as they can. And, that means looking for bright patches of light that existed a few hundred million years after the Big Bang. <\/p>\n \u201cThe discovery of patches of small, bright galaxies in the early universe would confirm that we are on the right track with the cold dark matter model because only the velocity between two kinds of matter can produce the type of galaxy we\u2019re looking for,\u201d said Naoz. \u201cIf dark matter does not behave like standard cold dark matter and the streaming effect isn\u2019t present, then these bright dwarf galaxies won\u2019t be found and we need to go back to the drawing board.\u201d<\/p>\n In a paper by the team member and first author Claire Williams (published in Astrophysical Journal Letters<\/em>) the team suggests that scientists using JWST begin to look for galaxies that are much brighter than expected. If they exist, that will likely prove the interactions occurred early in cosmic time. If none can be found, then maybe scientists still might not understand dark matter interactions. The big question to answer is, if they exist, then how did they form so quickly and why are they so bright?<\/p>\n Let\u2019s examine that by looking at the role of dark matter. The standard cosmological model says that the gravitational pull of clumps of dark matter in the early Universe attracted ordinary matter. Eventually, that caused stars to form, followed by galaxies. Dark matter is thought to move more slowly than light. So, astronomers predicted that the star- and galaxy-formation processes happened very gradually. At least, that\u2019s what earlier simulations suggest.<\/p>\n But, what if something else was going on more than 13 billion years ago? How would that change things? It was a time before the first galaxies formed. But, it was a time when ordinary matter in the form of large overdensities of hydrogen and helium gas streamed through the expanding Universe. It bounced off slower-moving clumps of dark matter and outran its gravitational pull, at least for a time. Then, the baryonic matter massed together again, under the influence of dark matter. That\u2019s when the star birth fireworks began.<\/p>\n \u201cWhile the streaming suppressed star formation in the smallest galaxies, it also boosted star formation in dwarf galaxies, causing them to outshine the non-streaming patches of the universe,\u201d Williams said. Essentially, the accumulated gas began to fall together after millions of years. That led to a huge burst of star formation. Lots of massive hot, young stars began to shine, out-brilliancing the stars in other small galaxies. Ultimately what this means is that since dark matter is impossible to \u201csee\u201d, those brightly shining patches of galaxies could be indirect evidence of its existence. And, they\u2019d prove the role dark matter played in the creation of galaxies.<\/p>\n Nobody\u2019s seen exactly what Naoz and the team are looking for\u2014yet. Once they do, it will go a long way toward providing insight into the role of cold dark matter. \u201cThe discovery of patches of small, bright galaxies in the early universe would confirm that we are on the right track with the cold dark matter model because only the velocity between two kinds of matter can produce the type of galaxy we\u2019re looking for,\u201d said Naoz.<\/p>\n Of course, JWST is a perfect telescope to help see these galaxies. It should be able to peer into regions of the Universe where tiny infant galaxies are brighter than astronomers expect them to be. That extreme luminosity will help JWST spot them, showing them as they looked at a time when the Universe was only a few hundred million years old. Because dark matter is impossible to study directly, searching for those bright patches of baby galaxies in the early Universe could offer an effective test for theories about dark matter and its role in shaping the first galaxies.<\/p>\n Bright Galaxies Put Dark Matter to the TestDark Matter Interactions with Supersonic Baryonic Matter<\/h3>\n
Simulating Galaxy Formation and Dark Matter Influence<\/h3>\n
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Streaming Through Dark Matter Corridors<\/h3>\n
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Finding Those Bright Patches<\/h3>\n
For More Information<\/h4>\n
The Supersonic Project: Lighting Up the Faint End of the JWST UV Luminosity Function<\/p>\nLike this:<\/h3>\n