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| Closeup of the region on the sky, 1/250 of a degree across, where the gravity of a foreground cluster of galaxies magnifies the distant background star—nicknamed Earendil—thousands of times. Credit: NASA/ESA/Brian Welch (JHU)/Dan Coe (STScI)/Alyssa Pagan (STScI). |
With a fortuitous lineup of a massive cluster of galaxies, astronomers
discovered a single star across most of the entire observable Universe. This
is the farthest detection of a single star ever. The star may be up to 500
times more massive than the Sun. The discovery has been published today in
the journal Nature.
Gazing at the night sky, all the stars that you see lie within our own
galaxy, the Milky Way. Even with the most powerful telescopes, under normal
circumstances individual stars can only be resolved in our most nearby
galactic neighbors. In general, distant galaxies are seen as the blended
light from billions of stars.
But with the marvelous natural phenomenon known as "gravitational lensing,"
astronomers from the Cosmic Dawn Center at the Niels Bohr Institute and DTU
Space were nevertheless able to detect a distance where even detecting
entire galaxies is challenging.
A cosmic telescope predicted by Einstein
Among the wonders predicted by Einstein's theory of relativity is the
ability of mass to "curve" space itself. As light passes close to massive
objects, its path follows the curved space and changes direction. If a
massive object happens to lie between us and a distant background source of
light, the object may deflect and focus the light toward us as a lens,
magnifying the intensity.
Galaxies magnified several times are routinely discovered by way of this
method. But 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 toward us, magnifying its light thousands of times.
A combination of this gravitational lens and nine hours of exposure time
with the Hubble Space Telescope enabled an international team of astronomers
to detect the star.
Earendel—the morning star
The astronomers nicknamed the star Earendel, from the Old English word
meaning "morning star," or "rising light." They calculate that the star it
at least 50 times as massive as our Sun, possibly up to 500, and millions of
times as bright.
Besides being an astonishing achievement in itself, the observation of
Earendel offers a unique possibility of investigating the early Universe:
"As we peer into the cosmos, we also look back in time, so these extreme
high-resolution observations allow us to understand the building blocks of
some of the very first galaxies," explains Victoria Strait, postdoc at the
Cosmic Dawn Center, Copenhagen, and a collaborator and co-author of the
study. She elaborates:
"When the light that we see from Earendel was emitted, the Universe was less
than a billion years old; only 6% of its current age. At that time it was 4
billion lightyears away from the proto-Milky Way, but during the almost 13
billion years it took the light to reach us, the Universe has expanded so
that it is now a staggering 28 billion lightyears away."
The previous record is a star seen when the Universe was around a third of
its current age, at which time most of its structure had already formed and
evolved. So Earendel is indeed a ground-breaking record.
A target for the James Webb Space Telescope
To measure the brightness of Earendel, the astronomers constructed a
physical model of the gravitational lens. The exact nature of the light
source depends on their model, but when the astronomers are so certain that
the little dot is in fact a single star, it is in part because many
different models all give roughly the same answer.
Nevertheless, Earendel could in principle be more than one star, located
very close to each other. To test whether this is the case, the team applied
for—and were awarded—observing time with the recently launched James Webb
Space Telescope.
"With James Webb, we will be able to confirm that Earendel is indeed just
one star, and at the same time quantify which type of star it is," says Sune
Toft, leader of the Cosmic Dawn Center and professor at the Niels Bohr
Institute, who also participated in the study. "Webb will even allow us to
measure its chemical composition. Potentially, Earendel could be the first
known example of the Universe's earliest generation of stars."
Reference:
Welch, B., Coe, D., Diego, J.M. et al. A highly magnified star at redshift
6.2. Nature 603, 815–818 (2022).
DOI: 10.1038/s41586-022-04449-y
Tags:
Space & Astrophysics