3792 -
JAMES WEBB TELESCOPE
- 2022 accomplishments. It's been a year since the James Webb space
telescope was launched toward the L2 Lagrange point on the far side of the
Earth from the sun.
--------- 3792
- JAMES WEBB TELESCOPE - 2022
accomplishments
- SEEING FARTHER INTO THE PAST THAN EVER
BEFORE. To see the precious rare photons
from the most distant galaxies in the universe, the bigger the telescope, the
better. Space telescopes don't come
bigger than JWST, with its 21-foot (6.5 meters) primary mirror.
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- The farther a galaxy is from us, the faster
it is receding from us because of the expansion of the universe, so the more
its light becomes stretched, shifting the light toward redder wavelengths.
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- The most distant galaxies, which are also the
earliest galaxies we can see, emit light that is shifted all the way into
near-infrared wavelengths by the time it reaches Earth. It's this redshift that
prompted scientists to design JWST to specialize in near- and mid-infrared
light.
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- Prior to JWST's launch, the most distant
known galaxy was one called GN-z11. It has a redshift of 11.1, which
corresponds to seeing the galaxy as it was 13.4 billion years ago, just 400
million years after the Big Bang. That was the absolute limit of what
telescopes before JWST could detect.
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- Objects of great mass, such as galaxy
clusters, warp space with their gravity, creating a magnifying lens-like effect
that amplifies light from more distant objects. Astronomers began finding
faint, red smudges in the background of these lenses. These smudges have turned out to be the most
distant galaxies ever seen.
-
First was a
galaxy at a redshift of 12.5, called GLASS-z12 (GLASS is the name of a specific
survey program, the "Grism Lens-Amplified Survey from Space"). We see
this galaxy as it existed 13.45 billion years ago, or 350 million years after
the Big Bang.
-
- Galaxies with even greater redshifts soon
followed. One, nicknamed Maisie's Galaxy, is seen as it existed just 280
million years after the Big Bang, at a redshift of 14.3, while another, at
redshift 16.7, is seen just 250 million years after the Big Bang. There have
even been claims for a galaxy at an astounding redshift of 20, which if
confirmed would have existed just 200 million years after the Big Bang.
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- DISCOVERING WHAT LIT UP THE UNIVERSE. Following the Big Bang, but before stars and
galaxies had formed, the universe was dark and shrouded in a fog of neutral
hydrogen gas. Ultimately light, particularly ultraviolet radiation, ionized
that fog. But where did that light initially come from to end the cosmic dark
ages?
-
- Astronomers believe that light came either
from young galaxies filled with stars, or from active supermassive black holes,
which are surrounded by accretion disks of brilliantly hot gas and shoot
powerful jets into space
-
- This characteristic suggests that
fully-formed galaxies were on the scene quickly, but whether they already
contained supermassive black holes remains to be seen.
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- JWST MEASURES EXOPLANET ATMOSPHERE. Astronomers have now found more than 5,000
exoplanets and counting, but despite this remarkable haul, we still know next
to nothing about many of them.
-
- When a planet passes in front of its star,
some of the star's light filters through the planet's atmosphere, and molecules
in the atmosphere can absorb some of that starlight, creating dark lines in the
star's spectrum, a barcode-like breakdown of light by wavelength. Knowing
what's in a planet's atmosphere, or even whether it has an atmosphere at all,
can teach astronomers about how a planet might have formed and evolved, what
its conditions are like and what chemical processes are taking place in that
atmosphere.
-
- In August, 2022, astronomers announced
that JWST had made the first confirmed detection of carbon dioxide gas in the
atmosphere of an exoplanet, in this case WASP-39b, which is 700 light
years-away.
-
- Later, in November, astronomers released a
more complete spectrum showing the absorption lines of elements and molecules
in WASP-39b's atmosphere, including not only carbon dioxide but also carbon
monoxide, potassium, sodium, sulfur dioxide and water vapor.
-
- The spectrum showed that there was a lot
more oxygen in the planet's atmosphere than carbon, as well as an abundance of
sulfur. Scientists think that sulfur must have come from numerous collisions
that WASP-39b experienced with smaller planetesimals when it was forming,
giving us clues to the planet's evolution that could also hint at how the gas
giants in our own solar system, Jupiter and Saturn, formed.
-
- In addition, the existence of sulfur dioxide
is the first example of a product of photochemistry on a planet beyond the
solar system, since the compound forms when a star's ultraviolet light reacts
with molecules in a planetary atmosphere.
-
- WEBB SEARCHES FOR HINTS OF LIFE AND
HABITABILITY. The planets of the
TRAPPIST-1 system of seven rocky planets orbiting a red dwarf star located 40.7
light-years away from Earth. Four of these worlds lie in the star's putative
habitable zone, where temperatures would permit liquid water to persist on the
surface; given the right conditions they could potentially be habitable to
varying degrees.
-
- Models predict that TRAPPIST-1c will have
an atmosphere similar to Venus, with lots of carbon dioxide. While TRAPPIST-1c
is likely too hot to be habitable, determining whether it has an atmosphere
and, if so, whether that atmosphere possesses carbon dioxide will be a big step
toward characterizing Earth-size worlds.
-
- It will also be a big task, requiring 100
hours of observing time with JWST, which is tackling about 10,000 hours of
observations during its first year of science.
-
- JWST is targeting the other worlds in the
TRAPPIST-1 system that are more likely to be habitable, as well as similar
worlds around other nearby stars. Astronomers will be on the lookout for
biosignatures, such as the presence of both methane and oxygen in an
atmosphere.
-
- The discovery of photochemical reactions in
WASP-39b's atmosphere is also an important step, since photochemical reactions
drive the formation of the carbon-based molecular building blocks of life.
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- JWST STUDIES COSMIC CHEMISTRY & GALAXY
EVOLUTION. Some stars live for billions
upon billions of years, but others exist for just a short time before either
exploding in a supernova or expanding to become a red giant that then puffs off
its outer layers into deep space. In both situations, the stars disperse large
amounts of cosmic dust formed from elements heavier than hydrogen and helium
across space.
-
- It turns out that there is a relationship
between a galaxy's mass, its star-formation rate and its chemical abundances.
Deviations from this relationship at high redshift might indicate that galaxies
evolved differently in the early universe.
-
- Prior to JWST, astronomers could only
reliably measure the abundances of various elements in galaxies up to a
redshift of 3.3; in other words, galaxies that existed about 11.5 billion years
ago. But how abundant these heavy elements were in galaxies earlier than this
is a bit of a mystery.
-
- Early results from JWST have shown that the
relationship between star formation and mass does hold for galaxies at redshifts
as high as 8, but that their abundance of heavier elements is three times lower
than expected. This discrepancy suggests that stars and galaxies formed more
quickly than we realized, before enough generations of stars had the chance to
die out and disperse their elements into the cosmos.
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- JWST SETS ITS SIGHTS ON THE SOLAR
SYSTEM. Brilliant Jupiter, its faint
rings and several of its small moons imaged by JWST.
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- JWST's images showed Jupiter's faint rings
and some of its small moons, as well as the planet's atmospheric bands and
auroras. By observing in near- and mid-infrared light, with the high resolution
that JWST's giant mirror provides, astronomers are able to peer deeper into
Jupiter's atmosphere to see what's going on beneath the cloud tops and learn
how deeply the clouds extend.
-
- JWST has also imaged faraway Neptune,
Saturn's moon Titan and Mars. While JWST's portrait of the Red Planet shows
temperature variations on Mars' surface and absorption by carbon dioxide in its
atmosphere. In the future, JWST will observe Mars to track more tenuous gases,
such as mysterious seasonal plumes of methane that could originate in either
geological or biological activity.
-
- One of the Hubble Space Telescope's most
iconic images was that of the Pillars of Creation, columns of molecular gas
many light-years long found in the Eagle Nebula. Those columns are cosmic
nurseries where stars are born. JWST has revisited the Pillars of Creation, and
the resulting images in near- and mid-infrared light are just as special as the
original.
-
- JWST's infrared vision is able to penetrate
through the dust in the Pillars to gain a better view of the star formation
going on inside, showing knots of molecular gas on the verge of collapsing into
nascent stars. When those stars are just a few hundred thousand years old, they
begin to shoot out jets that erode the edges of the Pillars.
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- JWST CHANGED HOW SPACE TELESCOPES ARE
BUILT. JWST's massive, golden primary
mirror, formed by unfolding 18 hexagonal segment, was brand-new engineering to
permit a telescope of such great size to be launched into space.
-
- JWST was launched on December 25, 2021, the
$10 billion infrared observatory was
designed to learn how galaxies form and grow, to peer far back into the
universe to the era of the first galaxies, to watch stars be born inside their
nebulous embryos in unprecedented detail, and to probe the atmospheres of
exoplanets and characterize some of the closest rocky worlds.
-
- The complexity of the James Webb Space
Telescope, includes its fold-out, segmented 21-foot mirror and its delicate
sun-shield the size of a tennis cour
-
- The main reason that JWST is performing so
well is because of its superlative optics, which are able to achieve their maximum
potential resolution for the majority of infrared wavelengths that the
telescope observes in. This success means that JWST's images have a clarity to
them that were unobtainable by the likes of the Hubble Space Telescope and
NASA's retired Spitzer Space Telescope, or larger telescopes on the ground such
as those at the Keck Observatory in Hawaii, whose vision is blurred by Earth's
atmosphere.
-
- But with JWST, individual stars so close
together they were once indistinguishable can now be resolved; the structures
of very distant galaxies are now discernible; and even something close by such
as the rings of Neptune pop with the most detail seen in decades.
-
- Normally, faint details or features around a
bright object, such as the dark and tenuous rings around blue Neptune, are
difficult to see against the glare of the bright object. To counteract this, an
instrument is required to have the characteristic of "high dynamic
range" to take in both the faint and the bright at the same time.
-
- It's not only the planets of our solar system
that JWST is scrutinizing. A key aim of the telescope is to detect the
composition of exoplanets' atmospheres using a technique called transmission
spectroscopy. As a planet transits its star, the star's light shines through
the planet's atmosphere, but atoms and molecules within that atmosphere can
block some of the light at characteristic wavelengths, which gives away the
composition of the atmosphere.
-
- The first exoplanet result released from JWST
was the transmission spectrum of WASP-39b, which is a "hot Jupiter"
exoplanet orbiting a sun-like star located 700 light-years away. JWST detected
carbon dioxide in WASP-39b's atmosphere, the first time the gas has ever been
detected on an exoplanet.
-
- Other gases present included carbon
monoxide, potassium, sodium, water vapor and sulfur dioxide, the last of which
can only be created through photochemistry when atmospheric gases react with
the ultraviolet light from the planet's star.
-
- In particular, the TRAPPIST-1 planetary
system of seven worlds orbiting an M-dwarf 40 light-years away is a key target
of the JWST. Preliminary results, which failed to detect thick blankets of
hydrogen surrounding some of the TRAPPIST-1 worlds, were released during a conference
held at STScI in December, but we'll have to be patient for more comprehensive
results from these planets, of which up to four could reside in their star's
habitable zone.
-
- Currently, astronomers do not understand
what determines why stars form with the masses that they have, only that
low-mass stars are much more common than luminous high-mass stars, at least in
the local universe. Was this still the case over 13 billion years ago in the
first galaxies? Answering that question could help explain both how galaxies
formed and what ended the universe's dark ages.
-
- The JWST has impressed scientists in the six
months that it has been gathering data since becoming fully operational in
June, but the real fireworks are still to come with major discoveries awaiting
us.
-
December 24,
2022 3797
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--- Friday, December 30,
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