The NASA/ESA Hubble Space Telescope has established an extraordinary new benchmark: detecting the light of a star that existed within the first billion years after the Universe’s birth in the Big Bang (at a redshift of 6.2) — the most distant individual star ever seen.
This sets up a major target for the NASA/ESA/CSA James Webb Space Telescope in its first year
This find is a huge leap back in time compared to the previous single-star record holder; detected by Hubble in 2018. That star existed when the universe was about 4 billion years old, or 30 percent of its current age, at a time that astronomers refer to as “redshift 1.5.”
Scientists use the word “redshift” because as the Universe expands, light from distant objects is stretched or “shifted” to longer, redder wavelengths as it travels toward us.
But the newly detected star is so far away that its light has taken 12.9 billion years to reach Earth, appearing to us as it did when the universe was only 7 percent of its current age, at redshift 6.2.
“We got lucky. This is really extreme; it’s really exciting to find something with such a high magnification,” said Brian Welch, a PhD student from Johns Hopkins University in Maryland, US told the BBC. “If you happen to hit that right sweetspot, like we have in this case, the magnification can grow up to factors of 1000s.” he said.
The smallest objects previously seen at such a great distance are clusters of stars, embedded inside early galaxies.
The previous record-setter was a star called Icarus.
Again, captured by Hubble, the light from this star took 9 billion years to reach us.
Thanks to the rare alignment with the magnifying galaxy cluster, the star Earendel appears directly on, or extremely close to, a ripple in the fabric of space.
This ripple, which is known in optics as a “caustic,” provides maximum magnification and brightening. The effect is analogous to the rippled surface of a swimming pool creating patterns of bright light on the bottom of the pool on a sunny day.
The ripples on the surface act as lenses and focus sunlight to maximum brightness on the pool floor.
This caustic causes the star Earendel to pop out from the general glow of its home galaxy.
Its brightness is magnified a thousandfold or more.
At this point, astronomers are not able to determine whether Earendel is a binary star, but most massive stars do have at least one smaller companion star.
Astronomers expect that Earendel will remain highly magnified for years to come.
The name Earendel comes from an Old English word meaning “morning star” or “rising light“.
It’s not much to look at in the Hubble photo – just a faint blob on a long crescent of light created by the lens that’s been dubbed the “Sunrise Arc”.
There’s uncertainty around Earendel’s size.
It’s at least 50 times the mass of our own Sun, but depending on the exact amount of magnification it could be a great deal larger still.
Even at 50 solar masses, though, it would be among the biggest stars ever observed.
Some astronomers will question whether Earendel isn’t just a tight cluster of many stars, but there are limits on how large the phenomenon could be before the lensing effect started to smear the light into a more elongated, cigar-like shape.
It’s more likely that Hubble has detected one, or at most, two stars (a binary).
Then there’s the question of what the star is made of.
It’s possible it is a Population III star – one that formed from the pristine hydrogen and helium gas that was around after the big bang.
If Earendel is as large as 50 solar masses, such stars tend to live short lives – on the order of 1,000,000 years.
Yet it’s there, 900 million years after the Big Bang.
If it is a Population III star, then it would have needed a lot of gas to keep fuelling it.
Not impossible but very unlikely.
“Yes, we expect that Earendel is more likely to be a star that has been a little bit enriched in heavier elements, but not so much as the local stars around us today,” Brian Welch said.
“There is a small chance that it’s a Population III star. A few other studies predict you could get them in the outskirts of some galaxies. But that’s something we’re going to need much more detailed follow-up from other telescopes such as James Webb.”
Earendel will be observed by the NASA/ESA/CSA James Webb Space Telescope later in 2022.
Webb’s high sensitivity to infrared light is needed to learn more about Earendel, because its light is stretched (redshifted) to longer infrared wavelengths by the expansion of the Universe.
Check the annotated version of the above image here.
Top image: Earendel (encircled) is positioned along a ripple in spacetime that gives it extreme magnification, allowing it to emerge into view from its host galaxy, which appears as a red smear across the sky.
The whole scene is viewed through the distorted lens created by a massive galaxy cluster in the intervening space, which allows the galaxy’s features to be seen, but also warps their appearance — an effect astronomers call gravitational lensing.
The red dots on either side of Earendel are one star cluster that is mirrored on either side of the ripple, a result of the gravitational lensing distortion.
The entire galaxy, called the Sunrise Arc, appears three times, and knots along its length are more mirrored star clusters.
Earendel’s unique position right along the line of most extreme magnification allows it to be detected, even though it is not a cluster.
With this observation, the NASA/ESA Hubble Space Telescope has established an extraordinary new benchmark: detecting the light of a star that existed within the first billion years after the Universe’s birth in the Big Bang (at a redshift of 6.2) — the most distant individual star ever seen. T
his sets up a major target for the NASA/ESA/CSA James Webb Space Telescope in its first year.
Filed under: Space Telescopes
