Universe Simulations Show Webb Telescope Can Reveal Distant Galaxies Hidden in Quasars’ Glare

High Redshift Quasar and Companion Galaxy

This artist’s illustration portrays two galaxies that existed in the first billion years of the universe. The larger galaxy at left hosts a brilliant quasar at its center, whose glow is powered by hot matter surrounding a supermassive black hole. Scientists calculate that the resolution and infrared sensitivity of NASA’s upcoming James Webb Space Telescope will allow it to detect a dusty host galaxy like this despite the quasar’s searchlight beam. Credit: J. Olmsted (STScI)

Webb observations will seek dusty galaxies from the first billion years of the universe.

The brightest objects in the distant, young universe are quasars. These cosmic beacons are powered by supermassive black holes consuming material at a ferocious rate. Quasars are so bright that they can outshine their entire host galaxy, making it difficult to study those galaxies and compare them to galaxies without quasars.

A new theoretical study examines how well NASA’s upcoming James Webb Space Telescope, slated for launch in 2021, will be able to separate the light of host galaxies from the bright central quasar. The researchers find that Webb could detect host galaxies that existed just 1 billion years after the big bang.

This video zooms into a highly detailed simulation of the universe called BlueTides. Much like the iconic Powers of Ten video, each step covers a distance 10 times smaller than the previous one. The first frame spans about 200 million light-years while the fourth and final frame spans only 200,000 light-years and contains two galaxies. Researchers used this simulation to investigate the properties of galaxies that contain quasars – bright galactic cores powered by accreting supermassive black holes. Credit: Y. Ni (Carnegie Mellon University) and L. Hustak (STScI)

Quasars are the brightest objects in the universe and among the most energetic. They outshine entire galaxies of billions of stars. A supermassive black hole lies at the heart of every quasar, but not every black hole is a quasar. Only the black holes that are feeding most voraciously can power a quasar. Material falling into the supermassive black hole heats up and causes a quasar to shine across the universe like a lighthouse beacon.  

Although quasars are known to reside at the centers of galaxies, it’s been difficult to tell what those galaxies are like and how they compare to galaxies without quasars. The challenge is that the quasar’s glare makes it difficult or impossible to tease out the light of the surrounding host galaxy. It’s like looking directly into a car headlight and trying to figure out what kind of automobile it is attached to.

A new study[1] suggests that NASA’s James Webb Space Telescope, set to launch in 2021, will be able to reveal the host galaxies of some distant quasars despite their small sizes and obscuring dust.

Simulated Infrared Images From Webb and Hubble

These simulated images show how a quasar and its host galaxy would appear to NASA’s upcoming James Webb Space Telescope (top) and Hubble Space Telescope (bottom) at infrared wavelengths of 1.5 and 1.6 microns, respectively. Webb’s larger mirror will provide more than 4 times the resolution, enabling astronomers to separate the galaxy’s light from the overwhelming light of the central quasar. The individual images span about 2 arcseconds on the sky, which represents a distance of 36,000 light-years at a redshift of 7. Credit: M. Marshall (University of Melbourne)

“We want to know what kind of galaxies these quasars live in. That can help us answer questions like: How can black holes grow so big so fast? Is there a relationship between the mass of the galaxy and the mass of the black hole, like we see in the nearby universe?” said lead author Madeline Marshall of the University of Melbourne in Australia, who conducted her work within the ARC Centre of Excellence in All Sky Astrophysics in 3 Dimensions.

Answering these questions is challenging for a number of reasons. In particular, the more distant a galaxy is, the more its light has been stretched to longer wavelengths by the expansion of the universe. As a result, ultraviolet light from the black hole’s accretion disk or the galaxy’s young stars gets shifted to infrared wavelengths.

In a recent study[2], astronomers used the near-infrared capabilities of NASA’s Hubble Space Telescope to study known quasars in hopes of spotting the surrounding glow of their host galaxies, without significant detections. This suggests that dust within the galaxies is obscuring the light of their stars. Webb’s infrared detectors will be able to peer through the dust and uncover the hidden galaxies.

“Hubble simply doesn’t go far enough into the infrared to see the host galaxies. This is where Webb will really excel,” said Rogier Windhorst of Arizona State University in Tempe, a co-author on the Hubble study.

To determine what Webb is expected to see, the team used a state-of-the-art computer simulation called BlueTides, developed by a team led by Tiziana Di Matteo at Carnegie Mellon University in Pittsburgh, Pennsylvania.

“BlueTides is designed to study the formation and evolution of galaxies and quasars in the first billion years of the universe’s history. Its large cosmic volume and high spatial resolution enables us to study those rare quasar hosts on a statistical basis,” said Yueying Ni of Carnegie Mellon University, who ran the BlueTides simulation. BlueTides provides good agreement with current observations and allows astronomers to predict what Webb should see.

The team found that the galaxies hosting quasars tended to be smaller than average, spanning only about 1/30 the diameter of the Milky Way despite containing almost as much mass as our galaxy. “The host galaxies are surprisingly tiny compared to the average galaxy at that point in time,” said Marshall.

The galaxies in the simulation also tended to be forming stars rapidly, up to 600 times faster than the current star formation rate in the Milky Way. “We found that these systems grow very fast. They’re like precocious children – they do everything early on,” explained co-author Di Matteo.

The team then used these simulations to determine what Webb’s cameras would see if the observatory studied these distant systems. They found that distinguishing the host galaxy from the quasar would be possible, although still challenging due to the galaxy’s small size on the sky.

“Webb will open up the opportunity to observe these very distant host galaxies for the first time,” said Marshall.

They also considered what Webb’s spectrographs could glean from these systems. Spectral studies, which split incoming light into its component colors or wavelengths, would be able to reveal the chemical composition of the dust in these systems. Learning how much heavy elements they contain could help astronomers understand their star formation histories, since most of the chemical elements are produced in stars.

Webb also could determine whether the host galaxies are isolated or not. The Hubble study found that most of the quasars had detectable companion galaxies, but could not determine whether those galaxies were actually nearby or whether they are chance superpositions. Webb’s spectral capabilities will allow astronomers to measure the redshifts, and hence distances, of those apparent companion galaxies to determine if they are at the same distance as the quasar.

Ultimately, Webb’s observations should provide new insights into these extreme systems. Astronomers still struggle to understand how a black hole could grow to weigh a billion times as much as our Sun in just a billion years. “These big black holes shouldn’t exist so early because there hasn’t been enough time for them to grow so massive,” said co-author Stuart Wyithe of the University of Melbourne.

Future quasar studies will also be fueled by synergies among multiple upcoming observatories. Infrared surveys with the European Space Agency’s Euclid mission, as well as the ground-based Vera C. Rubin Observatory, a National Science Foundation/Department of Energy facility currently under construction on Cerro Pachón in Chile’s Atacama Desert. Both observatories will significantly increase the number of known distant quasars. Those newfound quasars will then be examined by Hubble and Webb to gain new understandings of the universe’s formative years.


  1. “The host galaxies of z = 7 quasars: predictions from the BlueTides simulation” by Madeline A Marshall, Yueying Ni, Tiziana Di Matteo, J Stuart B Wyithe, Stephen Wilkins, Rupert A C Croft and Jussi K Kuusisto, 5 October 2020, Monthly Notices of the Royal Astronomical Society.
    DOI: 10.1093/mnras/staa2982
  2. “Limits to Rest-frame Ultraviolet Emission from Far-infrared-luminous z sime 6 Quasar Hosts” by M. A. Marshall, M. Mechtley, R. A. Windhorst, S. H. Cohen, R. A. Jansen, L. Jiang, V. R. Jones, J. S. B. Wyithe1, X. Fan, N. P. Hathi, K. Jahnke, W. C. Keel, A. M. Koekemoer, V. Marian, K. Ren, J. Robinson, H. J. A. Röttgering, R. E. Ryan Jr., E. Scannapieco, D. P. Schneider, G. Schneider, B. M. Smith and H. Yan, 27 August 2020, The Astrophysical Journal.
    DOI: 10.3847/1538-4357/abaa4c

The Bluetides simulation (project PI: Tiziana Di Matteo at Carnegie Mellon University) was run at the Blue Waters sustained-petascale computing facility, which is supported by the National Science Foundation.

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.

7 Comments on "Universe Simulations Show Webb Telescope Can Reveal Distant Galaxies Hidden in Quasars’ Glare"

  1. … and since the Universe is hot and outside of that area is cold, and since cold is getting from hot, would that add to the speed of spreading Universe…

  2. Torbjörn Larsson | October 17, 2020 at 3:32 pm | Reply

    “… and since the Universe is hot and outside of that area is cold, and since cold is getting from hot, would that add to the speed of spreading Universe…”

    The universe is ~3 K as observed in the cosmic background spectra, the now low background temperature set by the expansion since the hot big bang.

    The expansion rate is set by the inner state of the universe, with the inflation era, the radiation dominated era at the start of the hot big bang, the matter dominated era and now recently the vacuum (dark) energy dominated era each have its own expansion rate behavior [“Scale factor(cosmology) @ Wikipedia]. The fluctuations from homogeneity and isotropy was set to 1 part per 100,000 from inflation quantum fluctuations onto the early hot big bang as observed in the cosmic background spectra, with later gravitational condensation of the cosmic filament web as seen in cosmological simulations such as Blue Tides over cosmological time – it isn’t many orders of magnitude difference. Based on that context I don’t think there would be much inhomogeneity in universe expansion rate – and specifically models don’t look at that much. IIRC it has been shown that the local void of ~1 % underdensity cannot explain ~10 % tension in Hubble rates between mostly the set of low-z observations and mostly the set of high-z integrative (multiset data) observations.

  3. Torbjörn Larsson | October 17, 2020 at 3:36 pm | Reply

    [“Scale factor(cosmology) @ Wikipedia] – [“Scale factor(cosmology)” @ Wikipedia].

    Also, if “he Universe is hot and outside of that area is cold” is somehow to be taken to mean outside the universe it is impossible – the universe has no outside (as it is all there is, implicitly so classically and explicitly so in modern general relativistic models).

  4. … yeah, mr Torbjörn Larsson…
    … The nothing is spreading to a nothing with unknown dark energy and unknown part of dark matter…
    … one might consider that small energy that springs into our universe from nowhere…
    So! Let’s stop for a second.
    The Universe comes from nothing, and it is spreading into nothing with the help of nothing and it is kept together by nothing…

  5. … I wish I was more careful at my theology classes way back, that explanation makes more sense, though…

  6. Torbjörn Larsson | October 18, 2020 at 12:50 pm | Reply

    “The Universe comes from nothing, and it is spreading into nothing with the help of nothing and it is kept together by nothing…”.

    The concept of “nothing” isn’t science, it cannot be defined in a testable way and all we ever see is “something”. On such an unfactual basis, yes, I can see how superstition instead of observable facts may befuddle.

    But if we continue to look at the facts, we now know enough of cosmology to observe that the observable universe is a volume in a much larger universe that can be described by general relativity and is undergoing an expansion process [which I gave references to]. A general relativistic universe do not “spread into nothing”, it is a self contained description of an expansion (scale factor). Else you go back to pre-big bang cosmology which erroneosuly believed there was an ‘explosion’ from ‘an origin’.

    Moreover space is on average flat over sufficiently large volumes, which in general relativity translates to an average zero energy density – positive energies such as from matter is balanced by negative energies such as from potential energies.

    So no “small energy” but zroe energy total. But a zero energy universe is not ‘nothing’ – I have already referenced what contents dominate it during differen eras – but its expansion is adiabatic and free, meaning it is a spontaneous process. We can tell from the zero energy density condition what is natural and what is magic – re theology that said we could not – and the universe and how it behaves is entirely natural. Do not confuse zero energy with no content.

    Speaking of contents, I don’t think cosmologists would say that dark energy or dark matter are unknown – they are known from their observed properties (as vacuum energy domination today’s universe expansion and as cold dark matter gravitationally interacting particles). But they are rather not known in all their properties – good enough to do cosmology, but not good enough to study in particle accelerators. C.f. how neutrinos took decades before more detailed observation – and we still do not know enough to say if they were solely responsible for matter/antimatter symmetry breaking during the hot big bang.

  7. Torbjörn Larsson | October 18, 2020 at 12:51 pm | Reply

    “zroe energy” – zero energy.

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