(ORDO NEWS) — At a distance of billions of light years across the vast gap of space-time, at the dawn of the universe, astronomers discovered the light of a single star.
The discoverers named it Earendel, from the Anglo-Saxon word meaning “morning star”. It is by far the most distant object of its kind ever discovered, dating back only 900 million years after the Big Bang.
Because Earendel’s light has traveled so long to reach us, its properties are difficult to determine, but follow-up observations with the James Webb Space Telescope have already been approved.
The first billion years of the history of the universe after the Big Bang 13.8 billion years ago, also known as the “cosmic dawn”, is very difficult to see.
Not only is it dark and cloudy at the very beginning, when the first stars and galaxies form, but they are also very far away. Even the search for quasars, the brightest objects in the universe, limits the possibilities of our technologies and methods of analysis.
But there is one quirk of gravity that can show us small and distant objects that might otherwise be out of our reach. It is called gravitational lensing and is associated with the gravitational curvature of space-time around massive objects such as galaxies and clusters of galaxies.
If a massive object is exactly in the right place between us and a more distant object, the light from that distant object will travel along the gravitational curvature of spacetime. This has the effect of an absolutely huge magnifying glass: The light from a distant object may be smeared and distorted, but it is also magnified and often duplicated.
Astronomers can then reverse process the light to figure out what the magnified object was. At the distance of the cosmic dawn, these smears usually turn out to be galaxies.
Earendel’s home galaxy, whose real name is WHL0137-LS, was first discovered by the Hubble Space Telescope as such a spot, magnified by a massive cluster of galaxies. There, inside the galaxy, a team led by astrophysicist Brian Welch of Johns Hopkins University found a single bright object located right at the top of the critical lensing curve.
When we see bright single objects in other galaxies, they tend to be something much brighter than a normal star; but anything much brighter than an ordinary star also tends to be fleeting, like a new star or a tidal disruption event around a black hole.
Over 3.5 years of observations, the brightness of Earendel has not changed. This, combined with its location, suggests that it is not a transitional star, but a bright star that happened to be in the right place at the right time.
We know how far it is from the way the light is stretched. The expansion of the universe causes light waves to decay, a property known as redshift. Astronomers estimate the distance to objects in the early universe based on the redshift of light.
An analysis of ultraviolet light from Earendel showed that the object was about 50 times the mass of the Sun. But more detailed information is too difficult to obtain from the available data. For example, we do not know the spectral classification of a star, which would be useful.
We have seen some very ancient stars that have survived billions of years, but more massive stars tend to die earlier, so knowing the type of star would provide some insight into the early evolution of the universe.
We don’t even know if it’s a lone star or a binary with a total mass of about 50 solar masses. However, in the latter case, known massive binaries usually consist of a single, much more massive star that emits most of the system’s light, and the team expects Earendel to be the same.
The earliest star ever discovered could tell us some interesting things about the early universe. For example, we have not yet been able to observe the processes that allowed light to travel freely throughout the universe, known as reionization. Astronomers believe that stars and galaxies were behind this process, but they have no direct observations of how it unfolded.
We have seen galaxies in the Cosmic Dawn. Narrowing down our understanding to the types of individual stars that were around at the time would be very interesting.
Webb has been given time for Eärendel’s spectroscopic observations, which Welch and his colleagues hope will provide more information about the star, including its age, classification, more detailed mass, and whether it is a binary system or not.
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