Earendel, a name from the world that J.R.R. Tolkien created in his novels such as The Lord of The Rings, means ‘morning star’ or ‘rising light’ in old English. In an engaging symbolism, astronomers have given this nickname to a newly spotted star that happens to be the most distant one to be seen until now. It is believed to be a whopping 12.9 billion light years away from us.
The finding, published in the journal Nature, was the result of careful observations over nearly four years, made possible by a phenomenon known as ‘gravitational lensing’.
Light from a star that is one light year away would take one year to reach us. Hence, the astronomers are seeing the star Earendel as it existed 12.9 billion years ago. If confirmed by further studies and by the James Webb Space Telescope, it would be the discovery of one of the earliest stars, formed less than a billion years after the Big Bang. It may be made up of raw materials quite unlike those making up the stars that formed much later — say, our Sun, which is only 4.5 billion years old.
Astronomer Brian Welch from Johns Hopkins University, Baltimore, the corresponding author of the Nature paper, said in a press release posted on NASA’s Hubble site that studying Earendel would be like opening a window into the era of the universe that we are unfamiliar with but which led to everything we know. “It’s like we have been reading a really interesting book, but we started with the second chapter, and now we will have a chance to see how it all got started,” Welch says.
Gravitational lensing
It was possible to see this particular star only because of a phenomenon called gravitational lensing. It is known that when light from a star or galaxy passes close to a massive object such as another galaxy, a black hole or any massive entity, it gets bent by gravity. Thus the image of the source of the light may appear distorted from the original. This phenomenon is called gravitational lensing. Just like the optical lens in a magnifying glass magnifies the letters on a page, the distortion due to a gravitational effect may magnify the object.
There are multiple effects of gravitational lensing: If the original object, say a huge star or galaxy, is directly behind a massive galaxy, there will be four images on four sides of the intervening galaxy. This produces four luminous spots in the image, which are collectively called Einstein’s cross.
If the original object is not exactly behind the intervening galaxy, but is slightly off-centre, the image produced will be like a curve or arc.
Sunrise Arc
This is what the researchers first saw. They saw an arc of light which they gauged was a lensed image of an old, old galaxy. Further analysis and study of this arc, which they nicknamed ‘The Sunrise Arc’, showed them the image of Earendel.
“Normally, at these distances, entire galaxies look like small smudges, with the light from millions of stars blending together. The galaxy hosting this star has been magnified and distorted by gravitational lensing into a long crescent that we have named ‘the Sunrise Arc’.”
How then did the astronomers manage to see this star?
Matter of chance
It was really quite by chance. There is a huge galaxy, WHL-0137-08, between us and Earendel creating a powerful gravitational lens that warps the space around it and distorting and magnifying the light from objects behind it. In this manner, while the galaxy to which Earendel belongs was generally amplified as an arc, the star alone was magnified to more than a thousand times its size. The scientists deduce that this is because the starlight happened to pass through a ripple in space-time caused by the distorting effect of the intervening galaxy. This kind of a ripple is known as a ‘caustic’. Lying on the caustic provides maximum magnification and brightening of Earendel’s image.
Scientists are always cautious about voicing the results of their observations, and in the sighting of Earendel, too, they put down the factors about which they are doubtful in the paper. For one, the object that they see and call Earendel could be not one star but a binary or a cluster. It could be much closer than they have calculated, if it is not part of the Sunrise Arc but only appears to be part of it. To verify all of this, more observations and independent observations are needed.
For this, they will need the James Webb Space Telescope.
