We don’t fully understand what the first stars in the universe looked like. We know it must have formed from hydrogen and helium because most of the heavier elements were only produced after stars formed. We know that the lack of these heavier elements altered the dynamics of star formation in a way that meant that the first stars were very large. But how big it is remains an unanswered question.
Now, researchers announce that they may be a step closer to directly observing one of those stars. Thanks to the transverse alignment between a distant star and an intervening galaxy cluster, the gravitational reversal inflated an object that existed less than a billion years after the Big Bang. The object is likely either a single star or a compact system of two or three stars. Its discoverers say they have already booked time to follow up on observations with NASA’s latest space telescope.
Lenses work by arranging materials so that light travels in a curved path through them. Gravity, which distorts space-time itself, can perform a similar function, that is, change space so that light travels in a curved path. There have been plenty of examples of gravitational effects of objects in the foreground creating a lens-like effect, magnifying and/or distorting light from an object very far behind.
This success prompted the formation of a team called Reionization Lensing, or RELICS. The group pointed space telescopes at large groups of galaxies in the expectation that strong gravitational fields there would likely create lensing effects. The team is looking for objects dating back to the reionization period, when light from the first stars began stripping electrons from hydrogen in interstellar matter.
Due to the uneven distribution of matter in the natural world, gravitational lenses are uneven and often create entertaining effects and refined images. Using these effects, along with information about the distribution of the material in the foreground, it is possible to make an approximate map of where the lens effects are strongest.
This map can include a “critical lens curve”, which can be specified because most background objects appear as two images, one on either side of the curve. But a handful of things will end up on the same curve and you’ll experience the strongest magnification.
As you can see in the image at the top of this article, most objects on the critical curve of the lens appear to extend along its length, indicating that they are likely to be larger structures, such as galaxies or star clusters. The exception, indicated by the arrow, is WHL0137-LS. Researchers named it Earendel, the Old English term for morning star, because it appears to date back to the morning of the universe, about 900 million years after the Big Bang.
Various models of lens effects indicate that the Earendel is magnified by a factor of at least 1,000 – and possibly as high as 40,000. Based on this, it is possible to put limits on the size of the object being lensed. These limits show that its maximum possible size is smaller than the star clusters we identified earlier, meaning that Earendel is likely to be a small star system with three or fewer stars. It could also be 1 star.
Even if Earendel is a multi-star system, most of the mass of these systems tends to end up in one of the stars. Working on the assumption that most of what they were looking at was a single star, the researchers infer its properties based on the light that was originally emitted in the ultraviolet range. They found that Earndel’s mass may be anywhere from 40 to 500 times the mass of the Sun. It also contains only about 10 percent of the heavier elements found in the sun.
More precise details are not possible at the moment. But the researchers indicated that they will use the Webb telescope to determine the exact type of star.
Based on the estimated time that Earndel has been around and the presence of at least some of the heavier elements, we can say that it is not one of the first stars in the universe. But during Webb’s launch, scientists noted that the telescope would be able to image early star clusters if it was also imaged sufficiently.
We’ll hear more about this imaging technology in the near future.
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