Can the James Webb Space Telescope detect isolated population III stars? (2023)

Department of Astronomy, Stockholms University
  Erik Zackrisson
Department of Astronomy, Stockholms University
  Pat Scott
Department of Physics, McGill University


Isolated population III stars are postulated to exist at approximately z=10-30 and may attain masses up to a few hundred solar masses. The James Webb Space telescope (JWST) is the next large space based infrared telescope and is scheduled for launch in 2014. Using a 6.5 meter primary mirror, it will probably be able to detect some of the first galaxies forming in the early Universe. A natural question is whether it will also be able to see any isolated population III stars. Here, we calculate the apparent broadband AB-magnitudes for 300 M population III stars in JWST filters at z=10-20. Our calculations are based on realistic stellar atmospheres and take into account the potential flux contribution from the surrounding HII region. The gravitational magnification boost achieved when pointing JWST through a foreground galaxy cluster is also considered. Using this machinery, we derive the conditions required for JWST to be able to detect population III stars in isolation. We find that a detection of individual population III stars with JWST is unlikely at these redshifts. However, the main problem is not necessarily that these stars are too faint, once gravitational lensing is taken into account, but that their surface number densities are too low.

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1 Introduction

Both theoretical arguments and numerical simulations, reviewed in [1], strongly support the notion that population III stars were very massive, significantly more so than the population I and population II stars that formed later on. When stars form in metal enriched gas, the Jeans mass is lower, which leads to fragmentation and thus lower masses. Lacking metals, a chemically unenriched cloud does not fragment in the same way and higher stellar masses are therefore possible. It has been argued that two different classes may have existed: population III.1 and population III.2. Population III.1 stars formed in dark matter minihalos of mass 105-106 M at z=10-30. As described in [2], probably only one star, with an average mass of 100 M were produced in every subhalo. This follows as the massive star that is formed emits a lot of UV radiation which destroys the molecular hydrogen in the parent cloud, preventing further cooling and star formation. Population III.2 stars then form due to HD cooling with an average mass of 10 M. Even though recent simulations indicate a more complex scenario, see [3] and [4], we will for simplicity assume that only one heavy population III.1 star is formed per halo. As we will argue, a flux boost due to gravitational lensing by a foreground galaxy cluster will be necessary to detect such stars. To assess the required properties of the lens in order to see on average one population III.1 star per survey field, we will in general use the most optimistic parameters for the calculations. Although debatable, it has become standard practice to assume a mass range of 60 M to 300 M for such stars, (e.g. [2] and [5]). Here, we will explore the most optimistic scenario possible, and therefore adopt 300 M for our population III.1 stars.

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The spectral energy density of a primordial star has previously been investigated by Bromm et al [6], with the result that isolated population III stars were deemed to be too faint for detection with the James Webb Space telescope ([7] and [8]). Even though the possibility of gravitational lensing has been briefly mentioned in [7] it has not been investigated in detail. However, gravitational lensing seems to offer the only plausible route to direct detection of isolated population III stars before they explode as supernovae (e.g. [9]).

2 Modelling the spectra of Population III stars

The population III properties derived in [10] have been used as the basis for our magnitude calculations. Here, we adopt the main sequence properties of these stars and thereby neglect the star emitting less ionizing flux when aging. We have used realistic stellar atmospheres and have also taken into account the potential flux contribution from the surrounding HII region. To model the atmosphere we have used the publicly available TLUSTY code, see [11]. This code computes 1D, non-LTE, plane-parallel stellar model atmospheres and spectra, given a certain input stellar composition, surface temperature and gravity.

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The observed flux from a population III star probably originates mostly from the HII region that is created around it. To model this, we have used the publicly available photoionization code Cloudy [12]. We use this to calculate the spectrum from spherically symmetric HII regions around these stars. Both the nebular continuum and emission lines are predicted. This procedure results in an optimistically bright emission spectrum, since real nebulae experience feedback effects that could give rise to holes in the HII region. This exposes the star underneath and the spectrum emerging from the stellar atmosphere. The region could also break out of the gravitational well of the host halo if the feedback is strong enough. As described in [13], this dillutes the nebular flux and exposes more of the purely stellar spectrum.

Because of likely Lyα absorption in the neutral IGM at z>6, the spectra have both the continuum intensity at wavelengths shorter than the Lyα and the Lyα line set to zero. At high redshift this has a huge impact on the magnitudes since this effect will be redshifted into the filter we are using, as described below.

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3 JWST broadband fluxes of population III stars

Figure 1 shows the predicted AB-magnitude in the JWST NIRCam/F200W filter for our 300 M star. This instrument/filter have been selected to optimize the probability of detecting the star through deep imaging. The NIRCam/F200W filter has its main transmission between 17,500 Å and 22,500 Å. This means that the redshifted Lyα (1216 Å) absorption starts affecting the magnitudes at approximately z=15. For objects at z=18 it has absorbed most of the spectrum entering the filter. The effect from Lyα absorption can be seen as the sharp increase of magnitudes in this redshift interval. With a very optimistic scenario of a 100 hour exposure, a detection limit of m200=31.68 can be reached at 5σ. Since the flux of a 300 M star is predicted to be m200¿37 magnitude, a flux boost due to gravitational lensing is required for a detection to be feasible. The gravitational lens magnification required for this has been plotted as a function of z in figure 2. At z=10, a magnification of 160 is required to detect this object. At higher redshift, the required magnification becomes even greater.

Can the James Webb Space Telescope detect isolated population III stars? (1)
Can the James Webb Space Telescope detect isolated population III stars? (2)

Using the Trenti and Stiavelli models [5], the number of stars per square arcmin and redshift can be calculated. Here, we have adopted the no Lyman-Werner scenario, since this results in the most optimistic prospects for detecting isolated population III stars at z¡15. The magnified area required for detecting on average one population III star of 300 M can be seen in figure 3. In this graph we have also used the very unrealistic assumption that all stars attain the mass of 300 M. In reality just a fraction will be, and the area should increase accordingly. The area is moreover calculated with the assumption that it has exactly the required magnification. In a real lens, the magnification will generally be higher in certain regions. This means that less area is covered in the source plane, and that a larger area is required in the lens plane. The area actually decreases from z=10 to z=12, where an area of about 0.15 square arcmin is needed, simply because the models predict more stars at this epoch. The area at redshift 12 corresponds to a magnification of 200. For comparison, the gravitational lens with the greatest known Einstein radius (MACS J0717.5+3745 at z=0.546, [14]) has a magnification of 100-300 (average 160) in an area of 0.3 square arcmin at redshift 6-20 (see [15]). While this is in the right ballpark to allow 300 M population III stars to be detected, this requires that a number of desperately unlikely conditions are met, as we discuss below.

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Can the James Webb Space Telescope detect isolated population III stars? (3)

4 Discussion

Even though the calculations presented in section 3 would suggest that population III stars might be detectable when viewed through a powerful gravitational lens, this only holds true if the most optimistic assumptions possible are adopted. Hence, no matter how one twists and turns, the prospects of detecting isolated population III stars in the foreseeable future appear bleak. However, contrary to previous claims, [7] and [8], the problem is not necessarily that population III stars are too faint for detection, since the magnification of a lens may actually lift them above the JWST detection threshold. The main obstacle is instead that the surface number densities for a sufficiently massive population III star is likely to be too low.

We have calculated the AB-magnitudes for population III stars using realistic models for the atmosphere and the HII region. However, our results are admittedly based on a number of simplifications, most of them made in the direction that would improve the prospects of detection. The spherically symmetric HII region that we have assumed is likely overestimating the flux, as there probably will be holes in the nebula. Recieving a 100h exposure time for a lensed field is probably overly optimistic so in reality the detection limit would be lower. The model selected is the model with highest SFR among the Trenti and Stiavelli models, thereby giving an overly generous estimate of the number of stars in a given area of the sky. The magnification is assumed to be exactly the magnification needed for observation. Finally our strategy of assuming that all population III stars attains masses of 300 M probably overestimates the probability of detection. The only possibly pessimistic assumption is that of a negligible Lyα emission line.

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Can the James Webb Space Telescope detect isolated population III stars? ›

Our calculations are based on realistic stellar atmospheres and take into account the potential flux contribution from the surrounding HII region. We find that unlensed population III stars are beyond the reach of JWST, and that even lensed population III stars will be extremely difficult to detect.

Can we see population 3 stars? ›

Their destruction suggests that no galactic high-mass population III stars should be observable. However, some population III stars might be seen in high-redshift galaxies whose light originated during the earlier history of the universe.

Can Webb see individual stars in other galaxies? ›

Thanks to the suite of complementary instruments aboard Webb, the telescope can simultaneously pick up details of individual stars in these galaxies, see the cold dust and gas fueling star formation within these galaxies and – most remarkably – block out the stars, gas and dust to see the material swirling around the ...

What does the James Webb Space Telescope primarily detect? ›

And it is with infrared light that we can see stars and planetary systems forming inside clouds of dust that are opaque to visible light. The primary goals of Webb are to study galaxy, star and planet formation in the universe.

What will the Webb telescope be able to detect that the Hubble telescope could not? ›

Webb will primarily look at the Universe in the infrared, while Hubble studies it primarily at optical and ultraviolet wavelengths (though it has some infrared capability). Webb also has a much bigger mirror than Hubble.

Who discovered population 3 stars? ›

Stars observed in galaxies were originally divided into two populations by Walter Baade in the 1940s.

How long did population III stars last? ›

(More massive stars burn through their available fuel more quickly.) As such, Population III stars wouldn't have lasted long in the history of the universe — perhaps a few hundred million years as the last pockets of primordial gas dissipated.

Can the James Webb telescope see other universes? ›

Webb is telling us more about the atmospheres of extrasolar planets, and perhaps will even find the building blocks of life elsewhere in the universe. In addition to other planetary systems, Webb is also studying objects within our own Solar System.

Can the James Webb telescope see the Andromeda Galaxy? ›

James Webb Telescope spent hours observing Andromeda Galaxy on August 19, 2022. NIRCam Imaging instrument was used to study and collect data on Andromeda Galaxy.

Can James Webb see the first stars? ›

Webb is a powerful time machine with infrared vision that is peering back over 13.5 billion years to see the first stars and galaxies forming out of the darkness of the early universe.

What are the limitations of the James Webb telescope? ›

The key limiting constraint is that the telescope needs its thrusters to keep itself in orbit; those thrusters have enough propellant to last 10 years. Moreover, the observatory's design and its distance from Earth mean that JWST cannot be repaired or upgraded, as Hubble was.

What are 5 key facts about the James Webb telescope? ›

Key Facts
Launch Date:December 25, 2021 07:20am EST ( 2021-12-25 12:20 GMT/UTC)
Mission Duration5 - 10 years
Total payload mass:Approx 6200 kg, including observatory, on-orbit consumables and launch vehicle adaptor.
Diameter of primary Mirror:6.5 m (21.3 ft) approximately
Clear aperture of primary Mirror:25 m2
13 more rows

Are Webb images real? ›

Of course they were real! Were they exactly as Webb captured them in one single image, like you taking a photo with your phone? No—not at all. Webb is designed to be sensitive to light that we cannot see.

Is the James Webb telescope seeing things that aren t there? ›

In a new study, an international team of astrophysicists has discovered several mysterious objects hiding in images from the James Webb Space Telescope: six potential galaxies that emerged so early in the universe's history and are so massive they should not be possible under current cosmological theory.

What is the farthest object detected by the James Webb telescope? ›

Astronomers have used the James Webb Space Telescope (JWST) to spot the most distant galaxy cluster ever found, located nearly 30 billion light years away.

How James Webb will reveal what Hubble missed? ›

NASA's James Webb Space Telescope, fortunately, will overcome Hubble's many impediments. With a larger aperture, cooler temperatures, and wavelength sensitivity ~15 times as long as Hubble's, Webb will shatter these cosmic records. More distant, more obscured, and intrinsically fainter galaxies will all be revealed.

How big were population III stars? ›

We now know that Pop III stars were much more massive than present-day stars, ranging up to over a hundred times the mass of the Sun.

What temperature are population III stars? ›

Pop III massive stars with M ≳ 10 M keep the central temperature as high as Tc ∼ (1.0–1.5) × 108 K through the main sequence. The stellar luminosity is of the order of ∼106–107L.

How old are population 1 stars? ›

Population I consists of younger stars, clusters, and associations—i.e., those that formed about 1,000,000 to 1,000,000,000 years ago. Certain stars, such as the very hot blue-white O and B types (some of which are less than 1,000,000 years old), are designated as extreme Population I objects.

What year did the population pass 3 billion? ›

The UN estimated that the world population reached one billion for the first time in 1804. It was another 123 years before it reached two billion in 1927, but it took only 33 years to reach three billion in 1960.

What year did the population reach 3 billion? ›

World population did not reach one billion until 1804. It took 123 years to reach 2 billion in 1927, 33 years to reach 3 billion in 1960, 14 years to reach 4 billion in 1974 and 13 years to reach 5 billion in 1987.

When did the world population triple? ›

In 1955, there were 2.8 billion people on Earth.

What is the oldest object in the universe? ›

HD 140283 had a higher than predicted oxygen-to-iron ratio and, since oxygen was not abundant in the universe for a few million years, it pointed again to a lower age for the star. As a result of all of this work, Bond and his collaborators estimated HD 140283's age to be 14.46 billion years.

How can Webb see back in time? ›

Using its infrared-sensing instruments, the telescope can peer past dusty regions of space to study light that was emitted more than 13 billion years ago by the most ancient stars and galaxies in the universe.

How can we see light from 13 billion years ago? ›

We know that light takes time to travel, so that if we observe an object that is 13 billion light years away, then that light has been traveling towards us for 13 billion years. Essentially, we are seeing that object as it appeared 13 billion years ago.

Can you see the Milky Way from James Webb telescope? ›

The James Webb Space Telescope has peered inside one of the oldest star clusters of our Milky Way galaxy, revealing a region of our galactic halo teeming with brilliant stars.

How many galaxies can Webb see? ›

The James Webb Space Telescope, the new preeminent observatory in the sky, saw about 25,000 galaxies in that single image, dramatically surpassing the nearly 10,000 shown in the Hubble Space Telescope's Ultra Deep Field Survey(opens in a new tab).

What is the oldest star seen by Webb Telescope? ›

That star, named Icarus, existed when the universe was about four billion years old, or about 30% of its current age.

Can the James Webb Telescope see black holes? ›

The James Webb Space Telescope has spotted the earliest known black hole in the universe, and astronomers think even earlier ones could have swarmed the young cosmos.

Who created dark matter? ›

The term dark matter was coined in 1933 by Fritz Zwicky of the California Institute of Technology to describe the unseen matter that must dominate one feature of the universe—the Coma Galaxy Cluster.

What happens when James Webb runs out of fuel? ›

It's not coming back to Earth, that's for sure. When it finally runs out of fuel (in about 20 years) - it'll no longer be able to maintain it's orbit around L2 and because L2 is an “unstable equilibrium” point - JWST will drift away from there at increasing speed.

How many points of failure did the James Webb telescope have? ›

Then, success. July 17, 2022 8:56 a.m. Some of the expanse captured by the James Webb telescope.

How far can the James Webb telescope see in light years? ›

Webb has the capacity to look 13.6 billion light years distant—which will be the farthest we've ever seen into space. This image of the galactic cluster known as SMACS 0723 contains thousands of galaxies, some of which are as far away as 13.1 billion light years. (A single light year is just under 6 trillion miles.)

Can James Webb be refuelled? ›

Theoretically possible, but not planned. Refuelling in the sense of replacing expended fuel in the propulsion system is possible in theory.

How much gold is on the James Webb telescope? ›

Although the Webb mirrors are rather large (the primary mirror has a total diameter of approximately 6.5 m), the thin gold layer weighs in at a mere 48.25 g.

How many megapixels is the James Webb Space Telescope? ›

There are two sensors, each of 4 megapixels. MIRI (Mid-Infrared Instrument) measures the mid-to-long-infrared wavelength range from 5 to 27 μm. It contains both a mid-infrared camera and an imaging spectrometer.

Is there a color in space? ›

If we add up all the light coming from galaxies (and the stars within them), and from all the clouds of gas and dust in the Universe, we'd end up with a colour very close to white, but actually a little bit 'beige'.

How old are Webb images? ›

The faintest objects in this Webb image are some 13.1 billion years old, Rigby said.

Are the Webb photos altered? ›

The James Webb Space Telescope images aren't faked.

How far back in time can we see? ›

We can see light from 13.8 billion years ago, although it is not star light – there were no stars then. The furthest light we can see is the cosmic microwave background (CMB), which is the light left over from the Big Bang, forming at just 380,000 years after our cosmic birth.

Can we see Earth in the past? ›

The past no longer exists, so no one can directly look at it. Instead, the telescopes are looking at the present-time pattern of a beam of light. Since the beam of light has been traveling through the mostly-empty vacuum of space for millions of years, it has been largely undisturbed.

Can the James Webb telescope see the flag on the moon? ›

No, it is not possible for a telescope to see the flags on the Moon. The flags are only 121 centimeters (4 ft) long and the average home telescope can only see objects larger than 1.5 kilometers (0.9 mi). Even the Hubble or the James Webb aren't big enough to reach that level of magnification.

What is the oldest galaxy found by James Webb? ›

Additionally, the James Webb Space Telescope confirmed the existence of another galaxy named JADES-GS-z10-0, which was first observed by the Hubble Space Telescope and dates back to 450 million years after the Big Bang.

What is the most isolated galaxy? ›

One remarkable example is the galaxy MCG+01-02-015, which is the only one around for some 100 million light-years in all directions. It's the loneliest galaxy in the known Universe, and we can scientifically predict its ultimate fate.

What is the farthest point humans have seen in the universe? ›

GN-z11 is a high-redshift galaxy found in the constellation Ursa Major. It is among the farthest known galaxies from Earth ever discovered. The 2015 discovery was published in a 2016 paper headed by Pascal Oesch and Gabriel Brammer (Cosmic Dawn Center).

How much of the sky can Webb see? ›

How much of the sky can Webb see? Over the course of six months, as Webb orbits the Sun with Earth, it has the ability to observe almost any point in the sky. Webb's field of regard is limited to a 50-degree swath of the celestial sphere: About 39% of the sky is potentially visible to Webb at any given time.

What did James Webb reveal? ›

WASP-96b (spectrum): Webb's detailed observation of this hot, puffy planet outside our solar system reveals the clear signature of water, along with evidence of haze and clouds that previous studies of this planet did not detect.

How does Webb send images back? ›

Radio and television signals emanating from Earth have even traveled outside our solar system. The James Webb Space Telescope is equipped with a high-frequency radio transmitter that can send information it has gathered, including images, toward Earth.

Why do I see 3 stars? ›

The three stars in a row are often referred to as Orion's Belt, and their spiritual meaning varies depending on the culture and context. Some people believe that seeing these stars is a sign of protection or guidance from the universe, while others view them as a symbol of power and strength.

How many stars are visible to humans? ›

An extremely, yep, tiny little percentage. There are only about 5,000 stars visible to the naked, average, human eye, MinutePhysics points out. And, because the Earth itself gets in the way, you can only see about a half of those from where you stand.

Where can Population I stars be found? ›

All known Population I members occur near and in the arms of the Milky Way system and other spiral galaxies. They also have been detected in some young irregular galaxies (e.g., the Magellanic Clouds).

How many stars can you see in a city? ›

Depending on the specific viewing location that could be just 300 to 450 stars. If 4 were the magnitude limit globally, the total number of visible stars worldwide would be ~500. From the core of a large city, you may only be able to see stars of magnitude 1 or brighter, for a total of maybe half a dozen stars.

When you see 3 stars in a row? ›

Seemingly arranged in a completely straight line, these stars look like the hunter's belt. Thus the name, “Orion's belt.” This belt is what makes Orion so easy to locate in the night sky. Just look for three stars closely together in a straight line and voila, you've located Orion constellation.

What 3 stars are in a line? ›

One of the most recognizable constellations in the sky is Orion, the Hunter. Among Orion's best-known features is the “belt,” consisting of three bright stars in a line, each of which can be seen without a telescope. The westernmost star in Orion's belt is known officially as Delta Orionis.

What are 3 stars in a row called? ›

Orion's Belt or the Belt of Orion, also known as the Three Kings or Three Sisters, is an asterism in the constellation Orion. It consists of the three bright stars Alnitak, Alnilam and Mintaka.

How many stars are there in heaven? ›

To answer the question, "How many stars in the sky?" The total comes to 9,096 stars visible across the entire sky. Both hemispheres. Since we can only see half the celestial sphere at any moment, we necessarily divide that number by two to arrive at 4,548 stars (give or take depending on the season).

What is the largest known star? ›

The biggest star in the universe (that we know of), UY Scuti is a variable hypergiant with a radius around 1,700 times larger than the radius of the sun. To put that in perspective, the volume of almost 5 billion suns could fit inside a sphere the size of UY Scuti.

How many galaxies can we see with your naked eyes? ›

The nearby Andromeda Galaxy, also called M31, is bright enough to be seen by the naked eye on dark, moonless nights. The Andromeda Galaxy is the only other (besides the Milky Way) spiral galaxy we can see with the naked eye.

Are population 1 stars hot? ›

Population I stars include the sun and tend to be luminous, hot and young, concentrated in the disks of spiral galaxies. They are particularly found in the spiral arms.

Where are 90% of stars found? ›

About 90% of the stars lie on the main sequence. Only about 10% of the stars are white dwarfs, and fewer than 1% are giants or supergiants.

Can human eyes see Milky Way? ›

From Earth, it can be seen as a hazy form of stars in the night sky that the naked eye can barely notice. You can see the Milky Way all year, no matter where you are in the world. It's visible as long as the sky is clear and there's minimal light pollution.

What blocks the stars? ›

In addition to all the stars in space, there is a lot of other matter, called dark matter, between us and the stars that can block starlight. This dark matter can include nebulae which are clouds of gas, interstellar dust or planets.

Are the stars we see no longer exist? ›

Because stars are so far away, it takes years for their light to reach us. Therefore, when you look at a star, you are actually seeing what it looked like years ago. It is entirely possible that some of the stars you see tonight do not actually exist anymore. Public Domain Image, source: NASA.


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