From Webb: Three articles

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James Webb Space Telescope

1. How Do We Know There Are Black Holes?


Motion of “S2” and other stars around the central Black Hole
An international team of astronomers, lead by researchers at the Max-Planck Institute for Extraterrestrial Physics (MPE), has directly observed an otherwise normal star orbiting the supermassive black hole at the center of the Milky Way Galaxy.

S2 was followed closely over a period of years by Andrea Ghez, UCLA, on the UCO/Caltech Keck telescope.

Keck Observatory, Maunakea, Hawaii, USA.4,207 m (13,802 ft), above sea level, showing also NASA’s IRTF and NAOJ Subaru

Black holes are among the most mysterious and fascinating features of the universe, captivating scientists since the 18th century, including Albert Einstein and Stephen Hawking. They are often described as consuming their surrounding gas, the result of gravity so intense that nothing can escape its pull, not even the fastest known traveler in the universe: light itself. But if black holes don’t emit or reflect light, which means we can’t see them, how do astronomers know they are there?

The answer actually applies to many subjects studied in physics and deep-space astronomy—when you can’t observe something directly, or you can’t explain something you are seeing, you make educated guesses based on what you do see: the effect on other objects. On Earth, you can know it’s a windy day without stepping outside, because a flag is flapping. Astronomers know there is a black hole when the stars or gas around it are distorted or otherwise changed. These effects show up in a few ways.

Astronomers can observe a star accelerating in orbit around an unseen companion, rather than a detectable binary companion star (see video above). By measuring the orbiting star’s rate of acceleration, astronomers can calculate the mass of the object pulling on it; when this mass is so large that nothing else can explain it, astronomers conclude it is a black hole.

In other instances, X-ray telescopes can observe electromagnetic radiation from a star that comes close to a black hole and is pulled apart by its gravity.

NASA/Chandra Telescope

ESA/XMM Newton X-ray telescope

NASA NuSTAR X-ray telescope

These black holes accumulate cosmic matter around themselves in a swirling pattern called an accretion disk. Gas particles in the disc accelerate and collide, heating to millions of degrees and giving off the detectable X-rays.

Black holes causing these types of phenomena are at least three times the mass of the Sun and are classified as stellar black holes.

On a larger scale, supermassive black holes have a mass of more than one million Suns, and so must develop and grow very differently than stellar black holes. According to observations of intense gravitational attraction and energy in the center of galaxies made by the Hubble Space Telescope since the early 1990s, there is evidence for supermassive black holes at the heart of nearly all large galaxies, including our Milky Way.

NASA/ESA Hubble Telescope

With greater mass and thus greater gravity, supermassive black holes attract more matter that becomes hotter and more volatile. In some cases this super-heated matter shoots off into the universe as jets of gas that can be millions of light-years long. Astronomers have observed these gas ejections, known as outflow, and see it as a way of regulating galaxy expansion and the birth of new stars.

To see the dynamic dance of dust, stars, and gas clouds being shred apart and falling into a black hole, astronomers need powerful telescopes. Hubble made significant progress in confirming and studying galactic supermassive black holes.The James Webb Space Telescope’s powerful infrared instruments will see through the cosmic dust and analyze the details of outflow, providing new information about this process and its role in galaxy evolution.

NASA/ESA/CSA Webb Telescope annotated

Webb mirror compared to Hubble mirror

Webb will also be able to “see” deeper into space, and thus further back in time, to the formation of the first stars, galaxies, and perhaps black holes. Astronomers think early black holes developed at a much faster rate than black holes that are closer/more recent, which means observing these earlier cosmic citizens would shed light on the nature of their descendants, our neighbors we know well and have studied for decades.

2. Webb and the Infancy of the Universe


The Great Photon Escape
In a flash known as the Big Bang, our universe was born. Yet for hundreds of thousands of years, light from the Big Bang was scattered and trapped in a dense fog. Eventually, though, that light made its “great escape” and the universe was plunged into total darkness. These cosmic “Dark Ages” lasted for millions of years until the first stars and galaxies burst to life and began to illuminate the universe. However, no one knows just when this happened, or what the earliest stars and galaxies were really like, because we’ve never seen them. The Webb telescope will use its powerful infrared vision to spy the very first stars and galaxies forming out of the darkness of the early universe and help us understand how today’s universe came to be.

The era of the universe called the “Dark Ages” is as mysterious as its name implies.

Shortly after the Big Bang, the universe was filled with a glowing plasma, or ionized gas. As the universe cooled and expanded, electrons and protons began to bind together to form neutral hydrogen atoms. As the last of the light from the Big Bang escaped, the universe — now about 378,000 years old — would have been a dark place, with no sources of light to illuminate its fog of cooling, neutral hydrogen gas.

Some of that gas would have begun coalescing into dense clumps, pulled together by gravity. As these clumps grew larger and denser, they would become stars, and eventually, galaxies. Slowly, light would begin to shine again in the universe. Eventually, as the early stars grew in numbers and brightness, they would have emitted enough ultraviolet radiation to “reionize” the hydrogen, removing the electrons from their bonded protons and neutrons.

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Matter in the early universe slowly accumulated into larger structures, from molecules and clouds of molecular gas to stars and eventually galaxies. Radiation from these early cosmic objects would eventually begin the time of the universe known as “reionization.” Credit: NASA/Goddard Space Flight Center and the Advanced Visualization Laboratory at the National Center for Supercomputing Applications.

Reionization era and first stars, Caltech

Webb, with its ability to see light from extremely distant objects that has had to travel for billions of years to reach us, will see some of the universe’s first objects. As Webb observes light that’s traveled from the far reaches of the cosmos, it captures images of distant stars and forming galaxies as they were in the earliest stages of the universe.

Astronomers know the universe became reionized because when they look out in space and back in time at the light of very distant quasars — incredibly bright objects thought to be powered by supermassive black holes at the centers of galaxies — they don’t see the dimming of their light that would occur through a fog of neutral hydrogen gas. They find clouds of hydrogen, but almost no detectable clouds of neutral hydrogen drifting between galaxies, meaning the gas was at some point reionized. Exactly when this occurred is one of the questions Webb will help answer, by looking for glimpses of very distant objects, like quasars, still dimmed by neutral hydrogen gas.

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The Hubble Ultra Deep Field is a look back in space and time that captures an estimated 10,000 galaxies in various stages of evolution, back to within 500 million years of the Big Bang. Webb’s infrared vision will allow it to reach back even farther, to see the very first stars and galaxies.

Cosmic Conundrums

Much remains to be uncovered about the time of reionization. The universe right after the Big Bang would have consisted of hydrogen, helium, and a small amount of lithium. But the stars we see today also contain heavier elements — elements that are created inside stars. So how did those first stars form from such limited ingredients? Webb will not be able to see the very first stars of the Dark Ages, but it’ll witness the generation immediately following, and analyze the kinds of materials they contain.

Webb will also show us how early galaxies formed from those first clumps of stars. The universe’s first stars, believed to be 30 to 300 times as massive as our Sun and millions of times as bright, would have burned for only a few million years before dying in tremendous explosions, or “supernovae.” These explosions spewed the recently manufactured chemical elements of stars outward into the universe before the expiring stars collapsed into black holes or dim, cinder-like cores.

Scientists suspect the black holes born from the explosion of the earliest stars devoured gas and stars around them, becoming the extremely bright objects called “mini-quasars.” The mini-quasars, in turn, may have grown and merged to become the huge black holes found in the centers of present-day galaxies. Webb will try to find and understand these supernovae and mini-quasars to put theories of early universe formation to the test.

Webb will show us whether the first galaxies formed along filaments and webs of dark matter, as expected, and when. Right now we know the first galaxies formed anywhere from 378,000 years to 400 million years after the Big Bang. Many models have been created to explain which era gave rise to galaxies, but Webb will pinpoint the precise time period.

3.Webb and the Universe

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The collision of the Antennae galaxies triggered the formation of millions of stars in clouds of gas and dust within the galaxies. Infrared observations in this image show warm dust clouds heated by newborn stars, with the brightest clouds lying in the overlapping region between the galaxies.

When we look out into the universe, we see galaxies with magnificent spiraling arms and galaxies that glow like giant lightbulbs. But these spiral and elliptical galaxies weren’t born in these familiar shapes. Galaxies in the early universe were probably small and clumpy. So how did these modest groups of stars evolve into the grand structures we see today?

When telescopes peer into the universe, they look back in time. The reason is simple — light needs time to travel through space. Even the light from the Moon is 1.3 seconds old when it arrives on Earth. The most distant galaxies Hubble has spied are more than 13 billion light-years away. That means the light Hubble captures left those galaxies over 13 billion years ago.

But there’s another complication. As the universe expands, light gets stretched into longer and longer wavelengths, turning visible light into infrared light. By the time visible light from extremely distant galaxies reaches us, it appears as infrared light. Hubble can detect some infrared light — the wavelengths closest to the red end of the visible spectrum. But infrared light will be the Webb telescope’s specialty.

Where Hubble sees young galaxies, Webb will show us newborns. Webb will capture the earliest stages of galaxy formation, and perhaps even reveal when galaxies first started forming in the universe. Webb could show how small galaxies in the early universe merged to form larger galaxies. Finally, Webb will see more of the ordinary early galaxies, where Hubble only sees the brightest outliers. This expanded sample of early galaxies will give astronomers a better idea of how galaxies really looked as they first came into being, and help to map the universe’s overall structure.

The Hidden Universe

Webb’s infrared prowess will also allow it to see inside dust-cloaked regions of galaxies that visible light cannot escape from, and find out what’s happening within them. For many different types and ages of galaxies, Webb will expose how stars are forming, how many stars are forming, and how star formation is affected by the surrounding environment. Webb will study star-birth regions in merging galaxies, revealing how these galactic encounters trigger and alter the course of star formation as their gaseous components collide and mix. Webb will analyze how elements are produced and distributed in galaxies, and also examine the exchange of material between galaxies and the space between them.

Webb will also explore an era known as the Dark Ages and the time immediately following it, the period of reionization. About 378,000 years after the Big Bang, as the universe cooled and expanded, electrons and protons began to bind together to form hydrogen atoms. As the last of the light from the Big Bang faded, the universe would have been a dark place, with no sources of light within the cooling hydrogen gas.

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Light must travel through space over time. As telescopes capture light emanating from objects in the distant universe, they observe different stages of development. Webb’s infrared vision will allow it to see the first stars and galaxies to develop after the Big Bang.

Eventually the gas would have coalesced to form stars and eventually galaxies. Over time, most of the hydrogen was “reionized,” turning it back into protons and electrons and allowing light to travel across space once again. Astronomers are currently unsure whether the energy responsible for reionization came from stars in the early forming galaxies, hot gas surrounding massive black holes, or some even more exotic source such as decaying dark matter. Webb’s infrared capabilities will allow it to identify the sources that gave rise to reionization. And perhaps Webb will see the stars and bright galaxies called “quasars” that unleashed enough energy to re-illuminate the universe.

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Hubble’s eXtreme Deep Field image combines a decade of Hubble observations, including some taken in infrared light, to create one of the deepest pictures of the universe ever taken, spanning 13.2 billion years of galaxy formation. About 5,000 galaxies appear in this image.

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The James Webb Space Telescope will be a large infrared telescope with a 6.5-meter primary mirror. Launch is planned for later in the decade.

Webb telescope will be the premier observatory of the next decade, serving thousands of astronomers worldwide. It will study every phase in the history of our Universe, ranging from the first luminous glows after the Big Bang, to the formation of solar systems capable of supporting life on planets like Earth, to the evolution of our own Solar System.

Webb telescope was formerly known as the “Next Generation Space Telescope” (NGST); it was renamed in Sept. 2002 after a former NASA administrator, James Webb.

Webb is an international collaboration between NASA, the European Space Agency (ESA), and the Canadian Space Agency (CSA). The NASA Goddard Space Flight Center is managing the development effort. The main industrial partner is Northrop Grumman; the Space Telescope Science Institute will operate Webb after launch.

Several innovative technologies have been developed for Webb. These include a folding, segmented primary mirror, adjusted to shape after launch; ultra-lightweight beryllium optics; detectors able to record extremely weak signals, microshutters that enable programmable object selection for the spectrograph; and a cryocooler for cooling the mid-IR detectors to 7K.

There will be four science instruments on Webb: the Near InfraRed Camera (NIRCam), the Near InfraRed Spectrograph (NIRspec), the Mid-InfraRed Instrument (MIRI), and the Fine Guidance Sensor/ Near InfraRed Imager and Slitless Spectrograph (FGS-NIRISS). Webb’s instruments will be designed to work primarily in the infrared range of the electromagnetic spectrum, with some capability in the visible range. It will be sensitive to light from 0.6 to 28 micrometers in wavelength.
Webb has four main science themes: The End of the Dark Ages: First Light and Reionization, The Assembly of Galaxies, The Birth of Stars and Protoplanetary Systems, and Planetary Systems and the Origins of Life.

Launch is scheduled for later in the decade on an Ariane 5 rocket. The launch will be from Arianespace’s ELA-3 launch complex at European Spaceport located near Kourou, French Guiana. Webb will be located at the second Lagrange point, about a million miles from the Earth.

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Canadian Space Agency