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EI2GYB > ASTRO 28.09.23 00:04l 149 Lines 7534 Bytes #999 (0) @ WW
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Subj: Astronomers discover newborn galaxies with the James Webb S
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Astronomers discover newborn galaxies with the James Webb Space Telescope
Date:
September 22, 2023
Source:
University of Copenhagen - Faculty of Science
Summary:
With the launch of the James Webb Space Telescope, astronomers are now able
to peer so far back in time that we are approaching the epoch where we think
that the first galaxies were created. Throughout most of the history of the
Universe, galaxies seemingly tend to follow a tight relation between how many
stars they have formed, and how many heavy elements they have formed. But for
the first time we now see signs that this relation between the amount of stars
and elements does not hold for the earliest galaxies. The reason is likely that
these galaxies simply are in the process of being created, and have not yet had
the time to create the heavy elements.
With the launch of the James Webb Space Telescope, astronomers are now able to
peer so far back in time that we are approaching the epoch where we think that
the first galaxies were created. Throughout most of the history of the
Universe, galaxies seemingly tend to follow a tight relation between how many
stars they have formed, and how many heavy elements they have formed. But for
the first time we now see signs that this relation between the amount of stars
and elements does not hold for the earliest galaxies. The reason is likely that
these galaxies simply are in the process of being created, and have not yet had
the time to create the heavy elements.
The Universe is teeming with galaxies -- immense collections of stars and gas
-- and as we peer deep into the cosmos, we see them near and far. Because the
light has spent more time reaching us, the farther away a galaxy is, we are
essentially looking back through time, allowing us to construct a visual
narrative of their evolution throughout the history of the Universe.
Observations have shown us that galaxies through the last 12 billion years --
that is, 5/6 of the age of the Universe -- have been living their life in a
form of equilibrium: There appears to be a fundamental, tight relation between
on one hand how many stars they have formed, and on the other hand how many
heavy elements they have formed. In this context, "heavy elements," means
everything heavier than hydrogen and helium.
This relation makes sense, because the Universe consisted originally only of
these two lightest elements. All heavier elements, such as carbon, oxygen, and
iron, was created later by the stars.
James Webb peers deeper
The very first galaxies should therefore be "unpolluted" by heavy elements. But
until recently we haven't been able to look so far back in time. In addition to
being far away, the reason is that the longer light travels through space, the
redder it becomes. For the most distant galaxies you have to look all the way
into the infrared part of the spectrum, and only with the launch of James Webb
did we have a telescope big and sensitive enough to see so far.
And the space telescope did not disappoint: Several has James Webb broken its
own record for the most distant galaxy, and now it finally seems that we are
reaching the epoch where some of the very first galaxies were created.
In a new study, published today in the scientific journal Nature Astronomy, af
team of astronomers from the Danish research center Cosmic Dawn Center at the
Niels Bohr Institute and DTU Space in Copenhagen, has discovered what seems
indeed to be some of the very first galaxies which are still in the process of
being formed.
"Until recently it has been near-impossible to study how the first galaxies are
formed in the early Universe, since we simply haven't had the adequate
instrumentation. This has now changed completely with the launch of James
Webb," says Kasper Elm Heintz, leader of the study and assistant professor at
the Cosmic Dawn Center.
Fundamental relation breaks down
The relationship between the total stellar mass of the galaxy and the amount of
heavy elements is a bit more complex than that. How fast the galaxy produces
new stars also has something to say. But if you correct for that, you get a
beautiful, linear relationship: The more massive the galaxy, the more heavy
elements.
But this relation is now being challenged by the latest observations.
"When we analyzed the light from 16 of these first galaxies, we saw that they
had significantly less heavy elements, compared to what you'd expect from their
stellar masses and the amount of new stars they produced," says Kasper Elm
Heintz.
In fact the galaxies turned out to have, on average, four times less amounts of
heavy elements that in the later Universe. These results are in stark contrast
to the current model where galaxies evolve in a form of equilibrium throughout
most of the history of the Universe.
Predicted by theories
The result is not entirely surprising though. Theoretical models of galaxy
formation, based on detailed computer programs, do predict something similar.
But now we've seen it!
The explanation, as proposed by the autors in the article, is simply that we
are witnessing galaxies in the process of being created. Gravity has gathered
the first clumps of gas, which have begun to form stars.
If the galaxies then lived their lives undisturbed, the stars would quickly
enrich them with heavy elements. But in between the galaxies at that time were
large amounts of fresh, unpolluted gas, streaming down to the galaxies faster
than the stars can keep up.
"The result gives us the first insight into the earliest stages of galaxy
formation which appear to be more intimately connected with the gas in between
the galaxies than we thought.
This is one of the first James Webb observations on this topic, so we're still
waiting to see what the larger, more comprehensive observations that are
currently being carried out can tell us.
There is no doubt that we will shortly have a much clearer understanding of how
galaxies and the first structures began their formation during the first
billion years after the Big Bang," Kasper Elm Heintz concludes.
The study is published in Nature Astronomy.
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