NASA’s Hubble detects the most distant single star ever found

A team of astronomers using NASA’s venerable Hubble Space Telescope (HST) has observed light from the most distant single star ever detected – a massive star born within the first billion years of our universe’s existence . Estimated to be at least 50 times the mass of our own Sun and millions of times brighter, NASA reports that the newly detected star dubbed Earendel rivals the most massive stars known.

NASA says the discovery was made using data collected during the Hubble Reionization Lensing Cluster Survey (RELICS) program, led by Dan Coe at the Space Telescope Science Institute (STScI) in Baltimore. The observations are detailed in an article published in the journal Nature.

Located in the southern constellation of Cetus, in the same sky neighborhood as Mira, the newly detected star is so far away that its light took 12.9 billion years to reach Earth. So it appears to us as it was when the universe was only 7% of its current age, at a redshift of 6.2, according to NASA.

“We almost didn’t believe it at first, it was so much further away than the previous most distant and highest redshifted star,” said astronomer Brian Welch of Johns Hopkins University in Baltimore and lead author of the article, in a statement.

The team was able to make these observations via microlensing, in which light from a more distant background object is gravitationally amplified by light from a closer invisible foreground object. In this case, the star dubbed Earendel has been magnified by a factor of thousands of times by the huge galaxy cluster, WHL0137-08, which lies relatively close at a redshift of 0.566.

As NASA notes, the mass of the galaxy cluster distorts the fabric of space, creating a powerful natural magnifying glass.

“Normally, at these distances, entire galaxies look like small specks, the light from millions of stars blending together,” Welch said in a statement. “The galaxy hosting this star has been magnified and distorted by gravitational lensing into a long crescent that we have named the sunrise arc.”

But as Welch told me, without gravitational lensing, this star would be far too faint and far too small to be detected with Hubble or Webb.

Is Earendel part of a galaxy?

Welch told me that the host galaxy is cast in the long red arc that can be seen in Hubble images.

“The galaxy is small like galaxies, but it’s quite greatly magnified by the lens of the galaxy cluster in the foreground,” Welch told me.

As for how long will he be detectable via this rare lens alignment?

For many years to come; long enough to be studied at longer infrared wavelengths by NASA’s new James Webb Space Telescope.

At this point, astronomers are unable to determine if Earendel is a binary star, although most massive stars have at least one smaller companion star, according to NASA. Nor are they able to determine its spectral type, although it is sure to be on the massive, hotter end of the stellar spectrum as an o-, b-, or a-type star. If so, it’s probably long gone.

“Given its mass (estimated at more than 50 times the mass of the sun), the star won’t survive more than a few million years. So it’s almost certainly gone by now,” Welch told me.

The authors note that confirmation of the detection and exact spectral classification of the star will come from approved observations with the James Webb Space Telescope (JWST).

What will the Webb telescope tell us about this new find?

“In the first year of observations, JWST will give us a stronger constraint on mass, as well as a temperature measurement,” Welch told me. “That will tell us exactly what kind of star it is. Future observations could also reveal its chemical makeup, tell us more about how it formed.

If Earendel is composed of only primordial hydrogen and helium, NASA says it would be the first evidence of the category of Population III stars, believed to be the very first stars in the cosmos formed after the big bang. However, Welch thinks that’s not likely.

At 900 million years after the big bang, there was likely chemical enrichment of previous generations of stars, Welch told me. However, it’s unlikely to be Pop III, given that it’s near the outskirts of its host galaxy, he says.

“If Population III stars could still form at this time, they would likely be in that periphery where there are fewer other objects around to pollute the primordial hydrogen gas with heavier elements,” m Welch said.

As for how this discovery promotes astronomy and cosmology?

“It gives us a way to study a star in the first billion years of the universe, when the stars are probably very different,” Welch told me. “Studying this object in detail along with future observations will tell us a lot about how these distant stars form and evolve.”

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