A star is reborn: how Hubble astronomers saw the first light | Space
Earendel – “morning star” in Old English – is among the first stars to exist in our universe, born less than a billion years after the Big Bang. And the Hubble Space Telescope has just achieved the remarkable feat of detecting the light.
Most of the time, the telescope gives us images of nearby galaxies with intricate detail, but those of distant galaxies are very blurry indeed. Astronomer Brian Welch and his team at Johns Hopkins University in Baltimore discovered the star while searching for clues to early galaxies. These galaxies are very difficult to see, and the team chose to examine a selection of Hubble images for clues.
Astronomers are not new to observing ancient light. This very week it revealed incredible images of a galaxy as it was, half a billion years before Earendel. While it’s beyond what we’d hoped Hubble could do, it’s not quite as remarkable a feat as resolving a single star, and when you see the shapeless blob of this primeval galaxy, it shows just how special Earendel is.
In crime fiction, the detective uses a magnifying glass to study the evidence left at the crime scene, shifting the lens to magnify the clue. We can’t launch ever larger glass lenses into space, but fortunately nature offers us an alternative, much more powerful method.
Massive clusters of galaxies provide such gravitational pull that light from background stars bends around the cluster, much like light bends in a magnifying glass. This effect – “gravitational lensing” – is used in astronomy to see objects that are too faint or too far away to be seen otherwise. However, we can’t just move galaxies around to grow where we want; we must follow where the universe leads us.
In a snapshot, Welch and his team saw a distant galaxy that had been enlarged and distorted. Nothing new there. But in this distorted galaxy, there was an unexpected bright spot. A star in the galaxy aligned with the lens so precisely that its image was enhanced a thousand times, making it appear large and bright. And the color of Earendel’s light indicates that we are seeing an ancient light.
Light has different properties depending on its energy: the electromagnetic spectrum extends from low-energy, long-wavelength radio waves, through infrared, a rainbow of optical light, and up to high-energy, short-wavelength X-rays. Starlight loses energy on its journey to us, sliding along the spectrum, becoming redder as it goes. Eearendel’s light is indeed very red, suggesting that the light has traveled enormous distances over the better part of 13 billion years, placing it in the era of the first stars. Observations of early galaxies are rare, and images of individual stars from this era have been nonexistent until now.
Earendel isn’t one of the oldest generation of stars, but she’s incredibly close. Studying this era is like discovering the early evolution of humanity, but on a galactic scale. Our ancestors are like us, but there are important differences to explore. So it is with the universe now, compared to the universe then. We need to go as far back as possible to the Big Bang to fill in the gaps.
Earendel sighting breaks records. He didn’t just improve on the previous record, he shattered it, and it could be a record that’s here to stay. Earendel’s light is so faint that if it hadn’t been perfectly aligned with the cosmic lens, we wouldn’t have seen it at all. There’s no guarantee we’ll stumble upon another cluster with an equally fortuitous alignment, and more distant stars may be too faint to see. In common with other major scientific advances, years of hard work, expertise and speculation have been helped to the finish line by a generous helping of luck.
As with all evidence testing our powers of observation, there is the possibility of mistaken identity. While light from a distant blue star will have lost energy and appear more red, we might just be looking at something much closer that is red to begin with. The odds of a random reddish star aligning with this old warped galaxy are low, but not impossible, so the team will use infrared data from the brand new James Webb Space Telescope to rule out the suspect.
Next in line is a black hole, which can look like a star if the surrounding inward spiraling matter is magnified in some way. This time it is the X-ray observations that will help us decide for sure. The combination of different wavelengths of light is not new in astronomy; nor is it new in everyday life. Imagine a doctor diagnosing a broken arm in person. They’ll examine your arm in a well-lit room, but how do they know for sure it’s broken? How serious is the break? Will you ever play tennis again? You hope they would at least send you for an x-ray. To distinguish what we see in space, we must use different wavelengths of light just as comprehensively and interpret our observations with as much expertise as a doctor.
Earendel appears to be the most distant star we have ever detected and may never detect. A fortuitous alignment of celestial objects, seen from an incomprehensibly vast distance, provided exciting evidence of the early universe. We may be firmly on the trail of the faintest stars in the universe, but we’ll need more than a magnifying glass to be sure. We’re going to have to think on a whole different wavelength.