Hubble Detects Earendel, The Farthest Star Ever Seen. It’s 28 Billion Light Years Away

Earendel is at a distance of 28 billion light years from Earth. It appeared to astronomers as it did when the universe was only seven per cent of its current age. 

Earendel is the farthest individual star ever seen to date | Credit: NASA

New Delhi: NASA's Hubble Space Telescope has detected the farthest individual star ever seen to date. The star, called Earendel, existed within the first billion years after the universe's birth in the big bang. 

The star is at a distance of 28 billion light years from Earth. The light from Earendel has taken 12.9 billion years to reach Earth, and appeared to astronomers as it did when the universe was only seven per cent of its current age. 

The study, describing the discovery, was published in the journal Nature, on March 30. 

Detecting Earendel With ‘Gravitational Lensing’

With a natural phenomenon known as ‘gravitational lensing’, astronomers from the Cosmic Dawn Center at the Niels Bohr Institute, University of Copenhagen, Denmark, and the National Space Institute at the Technical University of Denmark were able to detect Earendel at a distance where even detecting entire galaxies is challenging. 

A gravitational lens can occur when a huge amount of matter, like a cluster of galaxies, creates a gravitational field that distorts and magnifies the light from distant galaxies which are behind it but in the same line of sight. The gravitational lensing effect is like looking through a giant magnifying glass, according to NASA. 

Farthest Detection Of A Single Star Ever

The discovery is the farthest detection of a single star ever, which may be up to 500 times more massive than the Sun.

The previous single-star record holder's light took nine billion years to reach Earth. It is an enormous blue star nicknamed "Icarus", which Hubble detected in 2018. Icarus existed when the universe was about four billion years old, or 30 per cent of its current age.

Quoting astronomer Brian Welch of Johns Hopkins University in Baltimore, the lead author of the study, a NASA statement said that the team of researchers almost did not believe the detection of Earendel at first, as it was so much farther than the previous most-distant, highest redshift star. The word "redshift" is used because as the universe expands, light from distant objects is stretched or "shifted" to longer, redder wavelengths, as it travels to the observer. In the visible light spectrum, the colour red has the longest wavelength. 

The researchers made the discovery using Hubble's RELICS (Reionization Lensing Cluster Survey) program. 

Earendel’s Host Galaxy Magnified By Gravitational Lensing

Welch said that normally at these distances, entire galaxies look like small smudges, with the light from millions of stars bending together. He explained that the galaxy hosting Earendel has been magnified and distorted by gravitational lensing into a long crescent which the researchers named the Sunrise Arc. 

Welch and his colleagues studied the galaxy in detail, and determined that one feature is an extremely magnified star that he called Earendel, which means "morning star", or "rising light" in old English.

Welch explained that Earendel existed so long ago that it may not have had all the same raw materials as the stars we see today. He said that studying Earendel will be a window into an era of the universe that we are unfamiliar with.

Cluster Of Galaxies Acted As A Cosmic Telescope

Einstein's theory of relativity predicted the ability of mass to "curve" space itself. The path of light follows the curved space and changes direction, as it passes close to massive objects. 

If a massive object happens to lie between an observer and a distant background source of light, the object may deflect and focus the light towards the observer as a lens, magnifying the intensity.

In an astounding cosmic coincidence, the galaxies in a cluster named WHL0137-08 happened to line up in such a way as to focus the light of a single star towards Earth, magnifying its light thousands of times. 

The international team of astronomers was able to detect Earendel with a combination of gravitational lens and nine hours of exposure time with the Hubble Space Telescope.

Earendel — The Morning Star

Astronomers calculated that Earendel is millions of times brighter than the Sun. However, even such a brilliant, very high-mass star would be impossible to see at such a great distance without the help of natural magnification by WHL0137-08, between Earth and Earendel. According to NASA, the mass of the galaxy cluster warps the fabric of space, creating a powerful magnifying glass that distorts and greatly amplifies the light from distant objects behind it. 

Due to the rare alignment with the magnifying galaxy cluster, Earendel appears extremely close to a ripple in the fabric of space. This ripple is described in optics as a "caustic", and provides maximum magnification and brightening. 

The ripple causes Earendel to pop out from the general glow of its home galaxy. Earendel's brightness is magnified a thousandfold or more. 

The observation of Earendel offers a unique possibility of investigating the early universe. 

Quoting Victoria Strait, who co-authored the study, a statement issued by University of Copenhagen said that as researchers peer into the cosmos, they also look back in time, so these extreme high-resolution observations allow them to understand the building blocks of some of the very first galaxies.

She explained that when the light the researchers saw from Earendel was emitted, the Universe was less than a billion years old. She said at that time, the star was four billion light years away from the proto-Milky Way, but during the almost 13 billion years it took to reach Earth, the Universe has expanded, so that it is now a staggering 28 billion light years away.

James Webb Space Telescope To Confirm If Earendel Is More Than One Star

The astronomers constructed a physical model of the gravitational lens to measure the brightness of Earendel. 

According to the study, Earendel could in principle be more than one star, located very close to each other. In order to know if this is true, the researchers applied for observing time with the James Webb Space Telescope.

Sune Toft, one of the authors of the study, said that with James Webb, the researchers will be able to confirm that Earendel is indeed just one star, and at the same time quantify which type of star it is. He further said that Webb will allow researchers to measure the chemical composition of Earendel.

Toft said that Earendel could be the "first known example of the Universe's earliest generation of stars."

Webb's high sensitivity to infrared light is needed to learn more about Earendel, because its light is stretched to longer infrared wavelengths due to the universe's expansion, according to NASA. 

Dan Coe, who co-authored the study, said that with Webb, the researchers expect to confirm Earendel is indeed a star, as well as measure its brightness and temperature, according to the NASA statement. Coe added that the researchers expect to find the Sunrise Arc galaxy is lacking in heavy elements that form in subsequent generations of stars, which would suggest that Earendel is a rare, massive metal-poor star. 

Since Earendel formed before the universe was filled with the heavy elements produced by successive generations of massive stars, its composition will be of great interest for astronomers. 

Welch said that with Webb, astronomers may see stars even farther than Earendel, which would be "incredibly exciting.”