NASA’S Hubble Detects Farthest Single Star Yet Found

A team of astronomers using NASA’s venerable Hubble Space Telescope (HST) has taken observations of light from the farthest 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 that the discovery was made from data collected during the Hubble RELICS (Reionization Lensing Cluster Survey) program, led by Dan Coe at the Space Telescope Science Institute (STScI) in Baltimore. The observations are detailed in a paper appearing in the journal Nature.

Located in the southern constellation of Cetus, in the same vicinity of the sky as Mira, The newly detected star is so far away that its light has taken 12.9 billion years to reach Earth. Thus, it appears to us as it did when the universe was only 7 percent of its current age, at redshift 6.2, says NASA.

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

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

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

“Normally at these distances, entire galaxies look like small smudges, with 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 named the Sunrise Arc.”

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

Is Earendel part of a galaxy?

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

“The galaxy is small as galaxies go, but it is quite highly magnified by the foreground galaxy cluster lens,” Welch told me.

As for how long it will be detectable via this rare lensing alignment?

For several 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 neither able to determine if Earendel is a binary star, though most massive stars have at least one smaller companion star, says NASA. Nor are they able to determine its spectral type, though it’s sure to be lie on the massive, hotter end of the stellar spectrum as either an o, b, or a-type star. If so, it’s likely long gone by now.

“Given its mass (estimated to be greater than 50 times the mass of the sun) the star will not survive for more than a few million years. So it is almost certainly gone by now,” Welch told me.

The authors note that confirmation of the detection and the star’s exact spectral classification will be forthcoming 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 the mass, as well as a measurement of the temperature,” Welch told me. “This will tell us exactly what kind of star this is. Future observations could also reveal its chemical composition, telling us more about how it formed.”

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

At 900 million years after the big bang, there has likely been some chemical enrichment from previous generations of stars, Welch told me. However, there is a slim chance that it could be Pop III, given that it is near the outskirts of its host galaxy, he says.

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

As for how this find furthers astronomy and cosmology?

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

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