 The lambda-cold-dark matter, Big Bang Theory, predicts that the early universe contained mostly hydrogen and some helium and only traces of other elements. All the first-generation stars, called Population III stars, had to be made from just these elements. But up to the summer of 2022, no telescope has ever seen a Population III star to determine if this theory is correct. Here we have a massive galaxy cluster. It has been studied for over five years since Hubble first captured the image in 2016. The galaxy was 4.5 billion light-years away from us when the light we see started its journey. The light traveled 5.6 billion light-years to get here, and it's currently 7 billion light-years away. In this cluster, Hubble discovered a gravitationally-lensed galaxy, nicknamed the Sunrise Arc. Its redshift is 6.2, with an angular size on the sky exceeding 15 arc seconds. At that distance, this makes it 410,000 light-years long. The galaxy was only 3.9 billion light-years away from the Milky Way when the light we see started its journey. The light traveled 12.9 billion light-years to get here, and it is currently 28 billion light-years away, receding faster than the speed of light and beyond the visible horizon. No light leaving that galaxy now will ever reach the Milky Way. In this galaxy, Hubble discovered a single star. The star, LSZ-6, is nicknamed Arundel. The light we see from this star began its journey 900 million years into the universe's expansion. This makes it the oldest most distant individual star ever seen. In addition, it is at least 50 times the mass of our sun, and hundreds of thousands of times brighter. This makes it one of the most massive stars known. Stars that massive only last for a few million years, so Arundel is long gone, having spewed the heavier elements it created into ZD-1 to become part of the next generation stars. This find represents a significant jump back in time compared to the previous single star record holder, Icarus, covered in our 2018 review. Its redshift is 1.5. Arundel is almost twice as far away from us now as Icarus. It's interesting to note that these views can be transient. Icarus is no longer visible. But Arundel has been stable and studied for over three and a half years. On July 30, 2022, a few months after Hubble's discovery, a team of astronomers called Cosmic Spring worked with Webb to train its near-infrared imaging camera on the sunrise arc for over four hours as part of a survey of the galaxy cluster. It also managed to capture the red dot corresponding to Arundel. Their analysis of the image has already confirmed that this is indeed a single star system and not a group of several stars. The red dots on either side of Arundel are a single mirrored star cluster. Just how this object in the distorted image of the sunrise arc galaxy was determined to be an individual star instead of a star cluster represents a major achievement in astronomy. But how do we know on this one will be repeated over and over again as the James Webb Space Telescope examines the first billion years of the universe. Strong gravitational lensing and a natural optical physical process called caustics are used extensively. Without them we would never see let alone analyze objects like the sunrise arc and Arundel. So we'll take a few minutes to cover how it's done. From general relativity we know that matter curves space and light travels the shortest distance through this curved space called geodesics. Large masses such as a galaxy cluster bend light passing through it just like a lens. Here's the basic geometry of gravitational lensing. This is the sunrise arc light on a direct path to us as if the galaxy cluster was not there. We could not detect this light. It is too dim for even our most powerful space telescopes. Here's its light heading in another direction. As it encounters the cluster it is bent towards us by the cluster's mass. We can estimate the deflection angle once we know the mass and center of mass of the cluster. Analyzing clusters like this one in order to discover these quantities is a major astronomical project that can take years. On Earth we observe the image to be on a straight line at an angle from its actual direction. The lens equation gives us these angles. This geometry enables us to map points seen on the lens plane back to its position on the source plane. The typical magnification created by this lensing is around 30 times the source area. This is great for finding galaxies, 12 billion light years away, but it is not nearly enough to find a single star or star cluster inside a galaxy that far away. The key to finding Erendale is the increased magnification created by a process called caustics. It can magnify objects up to thousands of times their source sizes. Here's how it works. Picture a set of uniformly distributed particles on a line. Each with slightly different velocities. They start out with a uniform particle density. But because of the small velocity differences, the particle density will vary as time goes by. Areas of high and low density will develop. The density at a later time, T, is described by an equation. The equation has hotspots when the denominator approaches zero. Expanding this to two dimensions, we get density peaks along curved lines that themselves intersect at points with maximum intensity. I see this phenomena in my own backyard swimming pool. Sunlight is evenly distributed as it reaches the water's surface. Small waves on the surface are creating small changes in the sunlight's direction. It's the caustic process that generates the lines at the bottom of the pool. These lines are not ripples in spacetime. They are simply lines of intense light magnification. Light passing through a galaxy cluster is impacted in exactly the same way. Lines of extreme magnification, referred to as lensing critical curves, are created by the caustic process. An image on or near a critical curve will be both magnified and distorted with the distortions providing a way to calculate the size of the magnification. Astrophysicists and astronomers model these lines and use the lens equations to map them back to their source. They can then reconstruct the shape and dimensions of an object, determine its deformation, calculate its observed magnification, and deduce its intrinsic luminosity. Here's a higher resolution image of the area around Arendelle, produced by the James Webb team. Objects close to a critical curve get mirrored into multiple images, like these two images of a star cluster inside the sunrise-art galaxy. The critical curve responsible for this will pass through the midpoint of the two images. An object found at this midpoint, like Arendelle, would be so close to the critical curve that its multiple images cannot be resolved. It will appear as a single object. Four different models were used to locate the lensing critical curves. Here's one of them. The others are quite different, but they all pass through Arendelle. It is important to note again that this is not a ripple in space-time. It is simply a line of maximum light magnification. The magnification drops off rapidly as the distance from the line increases. Arendelle's distance from the line is within 0.1 arc seconds. That's a very small angle, but at these distances, it represents 2,730 light years. This distance, along with its shape, puts its magnification between 1 and 40,000, with 9,000 being the most likely. With this, and the size of the image, we get a source object that has a radius less than 617 billion kilometers. That's 383 billion miles. This is a hundred times smaller than known small star clusters, leading to the conclusion that it is a single gigantic star or binary star system. As outlined in the How Far Away Is It chapter on distant stars, the black body radiation formula gives us the relationship between a star's color and its temperature. In addition, the mass versus luminosity relationship provides a way to relate a star's temperature to its mass. Hubble's visible and ultraviolet light measurements indicate that Arendelle is a hot blue star with a temperature between 13,000 and 16,000 degrees Kelvin. In addition, its delensed luminosity is around 630,000 times the luminosity of our sun. Its mass is then 50 times the mass of our sun. This fits the profile for a luminous blue variable star. Webb's analysis added the possibility that Arendelle is a binary star system with one star at 20,000 degrees and the other around 13,000 degrees. A spectrographic study by the James Webb Space Telescope is scheduled for November 2022. It will provide detailed data on its mass, radius, and the elements it's made of. This will be enough to place Arendelle on the Hertz-Bruggen-Russell diagram and we'll know if it is our first population three star. Here are the links to the sources for the material in this video.