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New clues in the search for the oldest galaxies in the universe by Jon Willis | University of Victoria Victoria, Canada (The Conversation) Feb 26, 2020
A galaxy cluster can be likened to a great city of galaxies, a galactic conurbation where each galaxy represents an individual, twinkling structure. Just as an archaeologist might seek evidence of the oldest cities on Earth, astronomers have long sought to discover the oldest galaxy clusters in the universe - each the cosmic equivalent of an ancient civilization like Jericho or Ur. I have been fortunate to lead a team of astronomers in discovering just such an example of an old galaxy cluster. How old? The light from the galaxy cluster, named XLSSC 122 has taken 10.4 billion years to travel across the universe to us.
A youthful universe XLSSC 122 is a remarkably precocious presence in a youthful universe, a clue perhaps that the universe - at least the densest parts of it - can form stars, accumulate into galaxies and eventually be drawn into galaxy clusters with surprising rapidity. Given that computer simulations of the assembly of galaxy clusters indicate more gradual growth, the discovery of XLSSC 122 suggests that our current ideas of how structure forms in the universe may be incomplete.
Discovering galaxy clusters However, visible light images taken with the Canada-France-Hawaii Telescope revealed no galaxies associated with the X-ray source. This was an interesting clue that we may have discovered a distant galaxy cluster where the expansion of the universe had shifted the visible light emitted by the cluster galaxies into the infrared. From this realization, we proceeded to obtain an image of our candidate cluster using the European Southern Observatory's Very Large Telescope. This image, taken with an infrared camera, revealed the telltale presence of faint red objects - distant galaxies; but exactly how distant remained a mystery.
Hubble Space Telescope brings ultimate clarity Although the Hubble telescope is nearly 30 years old, it remains a pre-eminent astronomical facility. Our images of XLSSC 122 appeared sharp and clear compared to the fuzzy images obtained from ground-based observatories. Although I have been a professional astronomer for 20 years, seeing the Hubble images of our cluster represented a near-unique discovery moment. It was immediately clear from the galaxy colours and spectra that XLSSC 122 was supremely distant: it lay at a redshift of two, meaning that the light from XLSSC 122 had taken 10.4 billion years to reach Earth.
Simulating galaxies One can identify clusters in these simulations that have the same properties as XLSSC 122. As a simulation is similar to a movie of the universe, we can fast forward to the present. When we did this for XLSSC 122 we realized that it would become one of the most massive clusters in the universe - comparable to the great cluster in Coma, our closest collection of galaxies. The same simulations indicate that XLSSC 122 might only have existed as a cluster of galaxies for perhaps a billion years before the moment we observed it. Herein lies the mystery. Our study of the starlight from the galaxies that make up XLSSC 122 tells us they are more than one billion years old, perhaps as much as three billion years old. Moreover, they all appeared to start forming stars at almost the same time. But as all of this happened long before these galaxies ever clumped together to form XLSSC 122, we are left with the question as to what caused them to start forming stars in such a synchronized manner in the early universe? Fortunately, we have a pretty good idea of where to look next. NASA plans to launch the James Webb Space Telescope in March 2021, and we are already planning ahead to target XLSSC 122. The Webb telescope will collect approximately six times more light than Hubble and will analyze that light with a number of sensitive instruments. Our aim is to use high-resolution infrared spectroscopy to greatly improve our knowledge of the stellar ages of the galaxies that make up XLSSC 122 and pin down the early life story of this remarkable cluster of galaxies.
A Cosmic Jekyll and Hyde Boston MA (SPX) Feb 21, 2020 A double star system has been flipping between two alter egos, according to observations with NASA's Chandra X-ray Observatory and the National Science Foundation's Karl F. Jansky Very Large Array (VLA). Using nearly a decade and a half worth of Chandra data, researchers noticed that a stellar duo behaved like one type of object before switching its identity, and then returning to its original state after a few years. This is a rare example of a star system changing its behavior in this way. Astro ... read more
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