How did Webb's NIRSpec gadget open 200 doors to our past?

Webb’s Near-Infrared Spectrograph (NIRSpec) reveals what is really going on in an intriguing region of the Tarantula Nebula. Astronomers focused the powerful instrument on what looked like a small bubble feature in the image from Webb’s Near-Infrared Camera (NIRCam). However, the spectra reveal a very different picture from a young star blowing a bubble in its surrounding gas. The signature of atomic hydrogen, shown in blue, shows up in the star itself but not immediately surrounding it. Instead, it appears outside the “bubble,” which spectra show is actually “filled” with molecular hydrogen (green) and complex hydrocarbons (red). This indicates that the bubble is actually the top of a dense pillar of dust and gas that is being blasted by radiation from the cluster of massive young stars to its lower right (see the full NIRCam image). It does not appear as pillar-like as some other structures in the nebula because there is not much colour contrast with the area surrounding it. The harsh stellar wind from the massive young stars in the nebula is breaking apart molecules outside the pillar, but inside they are preserved, forming a cushy cocoon for the star. This star is still too young to be clearing out its surroundings by blowing bubbles – NIRSpec has captured it just beginning to emerge from the protective cloud from which it was formed. Without Webb’s resolution at infrared wavelengths, the discovery of this star birth in action would not have been possible. NIRSpec was built for the European Space Agency (ESA) by a consortium of European companies led by Airbus Defence and Space (ADS) with NASA’s Goddard Space Flight Center providing its detector and micro-shutter subsystems. Credit: NASA, ESA, CSA, and STScI

Astronomy is motivated by great questions, and none are bigger than how the first stars and galaxies formed, eventually giving rise to our own existence. The answers are buried in a faraway cosmos, so far away that light traveled billions of years to reach us, delivering images of the earliest galaxies forming. This early epoch, only 200 million years after the Big Bang, is beyond the reach of prior telescopes, which were already amazing. It is currently visible thanks to the NASA/ESA/CSA James Webb Space Telescope. Even the best space telescope is only as good as the instruments attached to it, which is where the NIRSpec instrument, one of Europe's contributions to the Webb project, comes in.

According to Pierre Ferruit, former ESA Webb Project Scientist, the ambition of the scientists comes first in any instrument design. NIRSpec was formed by studying the development of the earliest stars and galaxies.

Webb's Near-Infrared Spectrograph is abbreviated as NIRSpec. Its duty is to separate the infrared light captured by Webb into its constituent wavelengths in order to create a spectrum. Astronomers may learn a lot about an object's physical features and chemical makeup by observing how its brightness fluctuates across different wavelengths. This was difficult to achieve before Webb and NIRSpec for the most distant galaxies.

According to ESA astronomer Giovanna Giardino, "now that we can accomplish this, a tremendous avenue is opening up for us." We can now examine distant galaxies, in the same manner, we study nearby things.

The data will allow scientists to trace the evolution of galaxies from the very early phases of the universe to the things we see around us today. NIRSpec has evolved under the direction of ESA, with Airbus Defense and Space Germany serving as the main contractor. Airbus organized a team of seventy workers from its Ottobrunn and Friedrichshafen, Germany, and Toulouse, France, facilities. They were also helped by NASA and 17 European subcontractors. Early on, the team determined that the best approach to achieve success was to simplify everything.

According to Ralf Ehrenwinkler, Head of the NIRSpec Program at Airbus, the design of NIRSpec is rather straightforward.

By keeping things basic in terms of how light is channeled through the instrument, the team was able to focus on the groundbreaking elements of the instrument. Among these was the requirement to efficiently record spectra from several objects at the same time, which had never been done in space previously. The ambition to investigate the far cosmos, where galaxies are so faint, immediately demanded this one-of-a-kind capacity. To piece together a complete picture of our early origins, we would need to witness thousands of them.

The iconic Hubble Deep Field provided our first sight of this area in 1995. Hubble took advantage of its unobstructed vision of the universe by staring at a single area of sky for 10 days starting on December 18. The chosen spot was hardly larger than a speck, around one-fourth of the size of the entire sky. Nonetheless, Hubble discovered over 3000 previously unknown objects, the majority of which were infant galaxies billions of light-years away. Similar deep-field photos may now be collected in hours rather than days, thanks to Webb's enormous 6.5-meter mirror, and NIRSpec can capture their spectra. However, with so many galaxies to record, it would be absolutely unworkable if NIRSpec could only acquire one spectrum at a time. So the team had to figure out how to accomplish it for several items at the same time. They were a huge success.

According to Maurice Te Plate, ESA's NIRSpec Systems Engineer, "we're able to gather spectra for up to 200 objects at a moment, it's a game changer."

NIRSpec employs a revolutionary gadget known as a micro-shutter array to accomplish this astounding feat of multitasking. It is made and provided by NASA's Goddard Space Flight Center in Greenbelt, Maryland, USA, and is made up of around a quarter million small autonomous shutters. Each one measures only 80 by 180 micrometers. They may be operated independently to open and close as needed.

This galaxy emitted its light 13.1 billion years ago. It was captured by Webb’s microshutter array, part of its Near-Infrared Spectrograph (NIRSpec). This instrument is so sensitive that it can observe the light of individual galaxies that existed in the very early Universe. This will prove transformational for research. Webb’s capabilities have allowed scientists to observe spectra of galaxies this far away for the first time. When researchers stretch out the light of an individual galaxy into a spectrum, like the graph shown above, they can learn about the chemical composition, temperature, and density of the galaxy’s ionized gas. For example, this galaxy’s spectrum will reveal the properties of its gas, which will indicate how its stars are forming and how much dust it contains. These data are rich – and have never before been detected from this far away at this quality. As astronomers begin analyzing Webb’s data, we will learn an incredible amount about galaxies that existed all across cosmic time – and how they compare to the beautiful spiral and elliptical galaxies in the nearby Universe. Want to capture your own spectra with Webb’s microshutter array? Learn how scientists use the instrument by “taking” your own observations in this interactive and analyze the spectra it returns. NIRSpec was built for the European Space Agency (ESA) by a consortium of European companies led by Airbus Defence and Space (ADS) with NASA’s Goddard Space Flight Center providing its detector and micro-shutter subsystems. Credit: NASA, ESA, CSA, and STScI

This tackles one of the most difficult challenges in obtaining spectra from the far universe: if the spectra of nearby objects, stars, and less distant galaxies are not masked, they interfere with the fainter ones.

According to Maurice, we only leave the ones that are over fascinating items open, while the others are all closed. As a result, only light from the specified targets enters the spectrograph optics to be evaluated.

NIRSpec is meant to look at celestial objects considerably closer to home, such as exoplanets, as well as the distant universe. The atmospheres of these worlds absorb part of the infrared light that flows through them from their parent star. NIRSpec searches for the minuscule quantities of light that are absent at certain wavelengths by gathering the star's radiation and separating it into a spectrum. They can then determine which compounds are present in the planet's atmosphere and extract more information about physical conditions.

According to Giovanna, "we can now observe the signatures of several critical chemicals in the atmospheres of exoplanets that were not visible from the ground or with space instruments prior to NIRSpec."

NIRSpec expands astronomers' skills. It may, for example, break bigger objects like galaxies and nebulae into 30 slices and detect a spectrum for each slice in a single shot. The resultant maps of physical circumstances and chemistry are critical to understanding the birth and death of stars, as well as the operation of galaxies.

A transmission spectrum of the hot gas giant exoplanet WASP-39 b, captured by Webb’s Near-Infrared Spectrograph (NIRSpec) on 10 July 2022, reveals the first definitive evidence for carbon dioxide in the atmosphere of a planet outside the Solar System. This is the first detailed transmission spectrum ever captured that covers wavelengths between 3 and 5.5 microns. A transmission spectrum is made by comparing starlight filtered through a planet’s atmosphere as it moves in front of the star, to the unfiltered starlight detected when the planet is beside the star. Each of the 95 data points (white circles) on this graph represents the amount of a specific wavelength of light that is blocked by the planet and absorbed by its atmosphere. This spectrum was made by measuring the change in brightness of each wavelength over time as the planet transited its star. The planet’s atmosphere absorbs some wavelengths more than others. Wavelengths absorbed by the atmosphere appear as peaks in the transmission spectrum. The hill centred around 4.3 microns represents the light absorbed by carbon dioxide. The grey lines extending above and below each data point are error bars that show the uncertainty of each measurement, or the reasonable range of possible values. For a single observation, the error on these measurements is extremely small. The blue line is a best-fit model that takes into account the data, the known properties of WASP-39 b and its star (e.g., size, mass, temperature), and the assumed characteristics of the atmosphere. Researchers can vary the parameters in the model — changing unknown characteristics like cloud height in the atmosphere and abundances of various gases — to get a better fit and further understand what the atmosphere is really like. The model shown here assumes that the planet is made primarily of hydrogen and helium with small amounts of water and carbon dioxide, with a thin veil of clouds. The observation was made using the NIRSpec PRISM bright object time-series mode, which involves using a prism to spread out light from a single bright object (like the star WASP-39) and measuring the brightness of each wavelength at set intervals of time. WASP-39 b is a hot gas giant exoplanet that orbits a Sun-like star roughly 700 light-years away, in the constellation Virgo. The planet orbits extremely close to its star (less than 1/20 of the distance between Earth and the Sun) and completes one orbit in just over four Earth-days. The planet’s discovery, based on ground-based observations, was announced in 2011. The star, WASP-39, is roughly the same size, mass, temperature, and colour as the Sun. The background illustration of WASP-39 b and its star is based on current understanding of the planet from Webb spectroscopy and previous ground- and space-based observations. Webb has not captured a direct image of the planet or its atmosphere. NIRSpec was built for the European Space Agency (ESA) by a consortium of European companies led by Airbus Defence and Space (ADS) with NASA’s Goddard Space Flight Centre providing its detector and micro-shutter subsystems. Credit: NASA, ESA, CSA, and L. Hustak (STScI). Science: The JWST Transiting Exoplanet Community Early Release Science Team

To work in the near-infrared, NIRSpec and much of Webb must operate at a temperature of 40 Kelvin (-233°C), which is maintained by Webb's characteristic sun cover. When it comes to developing exact scientific instruments, this creates a significant obstacle. When cooled, different materials shrink at varying rates, causing minor distortions in the instrument that impact its accuracy.

According to Ralf, this was the most difficult aspect, which is why Airbus opted to manufacture this instrument mostly out of silicon carbide. Silicon carbide is used for the base plate, the majority of the structures, and the mirrors.

Silicon carbide is a ceramic substance that is exceptionally stable at low temperatures while being difficult to deal with. Thermal distortions might be minimized by creating the majority of the instrument out of it. However, it necessitated being totally confident of the design before beginning production. NIRSpec originated as a block of silicon carbide in the so-called green state, which is soft and workable. NIRSpec was then machined into shape in the same manner that a sculptor shapes stone. All of the holes and channels were drilled, and once completed, it was placed in a furnace to be "sintered." This hardens the material and makes it incredibly difficult to manufacture. As a result, the team had to be absolutely convinced of the design before beginning production.

Working in silicon carbide was a challenge, according to Maurice, and I'm quite happy that we were able to complete it.

Working with the material has now become something of a European specialty, thanks in part to their success. The success of NIRSpec was brought home to the crew when the first photographs and data were returned to Earth.

Ralf stated, "I'm an engineer, not a scientist." So I'm relieved to see that all of the telemetries is green and NIRSpec is operational. But I will say that when the initial photographs were released, I was in Baltimore with around 200 other individuals. We were all overcome with emotion.

And now that the evidence is pouring in, many others are feeling the same way.

Pierre stated, "I am astounded by the quality of the spectra that we are obtaining." I can tell that the observers are pleased with the data as well. That, in my opinion, is why we created NIRSpec. I believe this is shared by the entire crew. It feels amazing now that NIRSpec is delivering.

Once the painstaking data analyses are completed, we will have new answers to those extraordinary questions that are so important to understanding our own existence: how the first galaxies and stars formed in our universe, and how frequently planets orbiting other stars offer conditions conducive to life as we know it. It is exactly what NIRSpec was designed to do: provide multiple windows to examine huge topics.