Deep-sky survey seeks to answer some of astronomy’s most pressing questions.
When our universe was very young, it was a dark place filled with a neutral and opaque gas. How that gas became transparent is something that scientists have been trying to understand for a long time. Many believe that change involved the first generation of extremely massive, luminous and hot stars to form after the big bang. Soon, through the power of NASA’s James Webb Space Telescope, astronomers may come closer to answering that question.
By peering deep into the universe, Webb will actually look back in time. A large, ambitious, deep-sky survey totaling nearly 800 hours of observing time will trace the formation and evolution of the first galaxies in what is possibly the cosmos’ busiest star-forming period. Other open questions this survey will address are how rapidly galaxies form and assemble, and how quickly and where they form their stars. Also, scientists know that supermassive black holes were already in place less than 1 billion years after the big bang. With Webb, they hope to detect the primeval seeds of these monsters.
A spectacular firestorm of star birth suddenly lit up the heavens and populated the first galaxies when the universe was less than five percent of its current age. This fiery flurry—possibly the cosmos’ busiest star-forming period—occurred just a few hundred million years after the big bang. Soon, through the power of NASA’s James Webb Space Telescope (JWST), astronomers will look back to that raucous, early period in a deep-sky survey to trace the formation and evolution of the first galaxies.
Called JADES—the JWST Advanced Deep Extragalactic Survey—this large, ambitious survey totals nearly 800 hours of observing time. The survey takes advantage of Webb’s sensitivity to infrared light, which has longer wavelengths than visible light and is invisible to the human eye.
“Galaxies, we think, begin building up in the first billion years after the big bang, and sort of reach adolescence at 1 to 2 billion years. We’re trying to investigate those early periods,” explained JADES teammate Daniel Eisenstein, a professor of astronomy at Harvard University. “We must do this with an infrared-optimized telescope because the expansion of the universe causes light to increase in wavelength as it traverses the vast distance to reach us. So even though the stars are emitting light primarily in optical and ultraviolet wavelengths, that light is shifted quite relentlessly out into the infrared. Only Webb can get to the depth and sensitivity that’s needed to study these early galaxies.”
The JADES survey is a collaboration of two Webb instrument teams granted Guaranteed Time Observations: the Near Infrared Camera (NIRCam) and the Near Infrared Spectrograph (NIRSpec) teams. The program combines the imaging of NIRCam and the spectroscopic capabilities of NIRSpec with Webb’s Mid-Infrared Instrument (MIRI), which boasts both a camera and a spectrograph. Through the use of coordinated, parallel observations, the JADES team will get the best out of all three instruments.
Scientists will then combine Webb’s results with the deepest data from NASA’s Hubble Space Telescope, NASA’s Chandra X-ray Observatory, and the ground-based Atacama Large Millimeter/submillimeter Array and Jansky Very Large Array radio telescopes to produce an unprecedented view of the universe’s very earliest galaxies. By studying galaxies across all these wavelengths, scientists will get a complete picture, allowing them to analyze the light of the galaxies’ stars, the dust and the interstellar medium, and the supermassive black holes that are thought to reside within these galaxies.
Studying Familiar Fields
The team chose two, previously well-studied fields from the Great Observatories Origins Deep Survey (GOODS) for their observations. GOODS united extremely deep observations from NASA’s Spitzer, Hubble, and Chandra, as well as ESA’s Herschel and XMM-Newton space telescopes, and from the most powerful ground-based facilities to survey the faintest light then detectable in the distant universe across the electromagnetic spectrum. The survey covered two large fields, GOODS-North and GOODS-South, which are located in the northern constellation Ursa Major and the southern constellation Fornax, respectively. GOODS-South also contains the Hubble Ultra Deep Field, which is to this day the deepest, most sensitive image of the sky ever taken with Hubble. Now, looking at the same areas, Webb will go even deeper.
“We chose these fields because they have such a great wealth of supporting information. They’ve been studied at many other wavelengths, so they were the logical ones to do,” said Marcia Rieke, who co-leads the JADES Team with Pierre Ferruit of the European Space Agency (ESA). Rieke is also the principal investigator on Webb’s NIRCam instrument and a professor of astronomy at the University of Arizona.
The team is also observing the two widely separated fields to study the differences between the number of galaxies at different distances in one field, as compared with the other.
Seeing the Formation of Galaxies, Stars and Black Holes
How rapidly galaxies form and assemble, and how quickly and where they form their stars are still open questions. Several ambitious goals of the JADES program include understanding the distribution of stellar mass in infant galaxies, as well as stellar luminosity, star-formation rates, and stellar age, size and composition. JADES will also analyze galaxies’ nuclear activity, determine galaxy structure, and map gas movement over a wide range of distances.
Another goal of the program is understanding the properties of the first generation of black holes. Scientists have measured a tight relationship between the mass of a galaxy’s central black hole and the mass of that galaxy’s bulge, but how that occurs is currently only the stuff of models and speculation. The JADES team hopes to illuminate the nature of this relationship.
Scientists know these supermassive black holes were already in place with billions of solar masses less than 1 billion years after the big bang, which is less than 10 percent of the universe’s current age. But how such enormous black holes came about so early in the universe is very difficult to understand.
“We hope to detect the primeval seeds of these monster black holes, the smaller black holes that formed soon after the big bang, and to understand what were their masses, how they were accreting mass, and where they were located,” explained JADES teammate Roberto Maiolino, a member of ESA’s NIRSpec Instrument Science Team and a professor of experimental astrophysics at the University of Cambridge in the United Kingdom. “For a long time, Webb will be the only facility to possibly detect and understand the processes that later on resulted in these monsters that were already created in the early universe.”
Seeking the First Stars
Another mystery involves the gas between the galaxies, which astronomers know today is highly ionized and transparent. But in the first million years, it was not ionized—it was neutral gas that was opaque. How the transition from neutral to ionized gas—from opaque to transparent—occurred is something that scientists have been trying to understand for a long time.
“This transition is a fundamental phase change in the nature of the universe,” said JADES teammate Andrew Bunker, another member of the ESA NIRSpec Instrument Science Team and a professor of astrophysics at the University of Oxford in the United Kingdom. “We want to understand what caused it. It could be that it’s the light from very early galaxies and the first burst of star formation.”
The JADES team hopes to discover this first population of extremely massive, luminous and hot stars to form after the big bang. “That’s kind of one of the Holy Grails, to find the so-called Population III stars that formed from the hydrogen and helium of the big bang,” explained Bunker. “People have been trying to do this for many decades and results have been inconclusive so far.”
The extremely distant targets of the JADES team appear very small and faint, and their light is often completely shifted beyond optical wavelengths. For these reasons, these objects can only be observed with superlative infrared capability of a large, cold telescope. Webb was built specifically for this purpose; this was one of the major science cases driving its design.
Because of Webb’s sheer size, it will have spatial resolution in the infrared similar to what astronomers have enjoyed with Hubble. Webb will give them a much clearer view at long wavelengths than they have ever had before.
Webb’s ability to get simultaneous spectra of multiple objects at infrared wavelengths is another critical aspect of the JADES program. NIRSpec will be able to target more than 100 galaxies at one time, taking a spectrum of each.
Webb’s much larger collecting area, its ability to observe fainter galaxies, and its capacity to simultaneously study multiple objects in a way that scientists have not been able to do before make ambitious, large surveys such as JADES possible for the first time.
“We tend to talk about projects like this in the context of theories and models that we have right now,” said Rieke. “But I’m hoping that with Webb we’ll find something that we haven’t suspected at all—that there will be some new surprise—and that will be great fun!”
The James Webb Space Telescope will be the world’s premier space science observatory when it launches in 2021. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.