The James Webb telescope has arrived

The Hubble Space Telescope's worthy successor - the James Webb Space Telescope - has arrived.

The James Webb telescope has arrived

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• The story: The James Webb Space Telescope (JWST), named after NASA's boss in the 1960s, is a true beast. Its technology is exquisite. The mirrors’ surfaces, made from gold-plated beryllium, are so smooth that, scaled up to the size of America, their irregularities would be mere centimetres high. An instrument behind the primary is so complicated that it has 2,50,000 individually controlled shutters, to ensure its illumination by the correct narrow slice of the sky. No uncrewed science mission so sophisticated has previously been sent into orbit.
• Delayed launch: All the earlier launch dates have been breached. Those delays continue till date! The most recent scheduled launch date is December 22nd.

1. The Hubble Space Telescope (HST), the JWST's most famous predecessor, scans the universe mainly in the part of the spectrum visible to human eyes, and in the ultraviolet. It makes only a small foray into the infrared.
2. But besides having a primary more than seven times as big as the Hubble’s, the JWST also has sensors optimised specifically for these longer wavelengths.
3. The fact that the project was not simply cancelled at some point in its chequered career is testament in part to the potential this infrared capability grants—for much infrared is absorbed by Earth’s atmosphere, so ground-based telescopes do not work well in this part of the spectrum. It will enable the device to scry three crucial types of objects more effectively than the Hubble can: the old, the cold and the dusty.
4. The old objects are those from so long ago that their ultraviolet and optical-frequency emissions have been stretched by the expansion of the universe into the infrared’s longer wavelengths.

• Doppler effect: A regular version of this phenomenon is the Doppler effect, noticeable when the pitch of a siren drops as the vehicle blaring it goes by. The cosmic equivalent is “redshift”, and becomes more pronounced the farther back you go. The jwst will be sensitive to redshifted photons dating from 13.5bn years ago, a mere 300m years after the universe’s birth, and thus old enough to have come from the first generation of stars and galaxies.

1. The cold objects are those with temperatures as low as 100° above absolute zero (100k). All bodies in the universe radiate electromagnetic waves in a spectrum related to their temperature. For hot objects like stars this peaks in the wavelengths of visible light. For cooler bodies, like newly forming planets, it peaks in the infrared.
2. The dusty objects are those hidden in so-called “dark” nebulae. These nebulae are composed of grains of matter that scatter visible light. But the effect of their dust on the infrared is less pronounced, meaning that the jwst will be able to scan their interiors in unprecedented detail, witnessing the nurseries of young stars which some of them contain, and the clouds of matter falling into the black holes found at the centres of others.

• Precision equipments: Accomplishing all this requires precision instruments. The many-shuttered device, called the Near-Infrared Spectrograph, is one. It will split incoming light into its constituent wavelengths to reveal information about its source. There is also the Near-Infrared Camera, which will generate most of the images that will, no doubt, adorn coffee cups and screensavers in years to come. The Fine Guidance Sensor/Near Infrared Imager and Slitless Spectrograph will provide reference points used to stabilise the telescope, and will study its brightest targets, including stars orbited by exoplanets. And the Mid-Infrared Instrument will look at wavelengths from five to 28 microns instead of the 0.6 to five microns to which the Near-Infrared devices are sensitive. This will let it see the oldest, coldest and dustiest objects of all.
• Once it begins working: When the JWST does start sending back images, among the most eagerly awaited will be those of the first few hundred million years after the universe was born. These may reveal how galaxies emerged from a flat and shapeless cosmos, as places with slightly higher densities of matter attracted other matter towards them, to form ever larger agglomerations. These galaxies hosted the first generation of stars, formed from hydrogen and helium created in the Big Bang. Those would then have become factories for heavier elements, formed by fusion in their cores and distributed by supernova explosions that ended the lives of many of them—though a few may survive, hiding in plain sight among their younger brethren in the galaxies of nowadays. Indeed, the jwst might find some. A second stellar generation would have repeated this, producing yet-heavier elements as it did so and paving the way for a third generation, of which the sun (at 4.55bn years, almost exactly a third of the age of the universe) is part.

1. Stars of the first generation are thought likely to have had a huge impact on the rest of the cosmos by emitting radiation that blasted apart its primordial hydrogen atoms to create a plasma of electrons and protons. Unblasted, those atoms would have interfered with the passage of light.
2. So the advent of stars made the universe transparent. This is the epoch of “reionisation”, sometimes called the cosmic dawn. The jwst should not only make this dawn visible, but also help understanding of the details of how it happened.
3. The new telescope will also peer into planetary origins. When stars form, they are surrounded by discs of leftover material that condense into planets and smaller bodies, such as asteroids and comets. The farther this material is from the star, the cooler it will be. And the frequencies the jwst will best detect tally nicely with those emitted by dust grains in the bits of the disc that are optimal for planet-forming.

• Hunt for exoplanets: Observations of these regions will put the Solar System in context. One problem faced by planetary scientists is information imbalance. Despite the discovery in recent decades of thousands of exoplanetary systems, these are known about in nothing like as much detail as the Solar System is. Yet generalising from this single, well-studied example is hazardous. For example, based on pre-existing assumptions about the Solar System no one expected to find gas giants akin to Jupiter and Saturn orbiting close to their parent stars. But that is actually quite common. The JWST will look for exoplanets in two ways. It will take pictures of some of them directly—blocking out the parent star’s light with a special mask in order to do so. Others it will watch as they pass in transit in front of their parent stars, thus diminishing those stars’ apparent brightness.
• Dark side: One of the biggest questions in modern cosmology is the nature of dark energy. This is the name given to an unknown 68% of the universe’s content, which is somehow responsible for its accelerating expansion. A big problem with understanding dark energy is that the expansion rate can be measured in two ways.

1. One approach, used since the 1920s and gradually refined since then, measures the distances to far-off stars and stellar explosions of known absolute brightness (so-called “standard candles”) by comparing that brightness with their perceived brightness from Earth. It then calculates the expansion rate from the redshift of this light.
2. The other method looks at the cosmic microwave background, a sky-filling signal from the early universe discovered in the 1960s. Measuring irregularities in this allows the expansion rate at the time it formed (380,000 years after the Big Bang) to be determined. The current rate can then be calculated by feeding that number into an equation based on cosmologists’ understanding of fundamental physics.
3. The JWST should help with the first method by measuring the distances of stars up to five times farther away than is now possible. That may resolve the puzzle, by bringing the first method into line with the second, or—if the discrepancy persists—force a rethink of the basic science.

• Dark matter: Another mysterious entity that the JWST may help explain is dark matter. This substance is reckoned by most researchers to make up a further 27% of the cosmos (the familiar matter of atoms and so on constitutes less than 5% of the total). It, too, is elusive, for it interacts with familiar matter only via the force of gravity. Dark matter is believed crucial to galaxy formation. Dark matter was first hypothesised in the 1930s, to explain odd behaviour by stars in the Milky Way and by galaxies in clusters. A more recent conundrum concerns Fast Radio Bursts (frbs). These are unexplained flashes of radiation, first spotted in 2006, that last for milliseconds and are detectable from billions of light-years away.
• EXAM QUESTIONS: (1) Explain the concepts of Dark Matter and Dark Energy. (2) What is the structural difference between JSWT (James Webb Space Telescope) and the HST (Hubble Space Telescope)? Explain.

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