Everybody was waiting for the big day, July 12th when the initial images from the James Webb Space Telescope would be released to the public. They are stunning. Poring over magnified close-ups of them, I’ve entered a locked room of sublime, never-before-seen sights, a step closer to the beginning of creation – maybe just one more door to go [1]. Some say they have trouble getting their minds around what these images mean in the context of things they’re familiar with: a sense of being simultaneously “overwhelmed and exalted. [2]”
It’s hard for example to get your mind around the JWST image of Stefan’s Quintet [3]. As an amateur astronomer I’ve looked at SQ in all manner of telescopes for many years. Through my 18” inch reflecting telescope, they looked like ghostly wisps of galactic light hanging in space, collectively rather faint at about 12.5 magnitude [4]. Such things seem to exist in a realm beyond time. And in a way that’s true. Four of them, listed as NGC 7317, 7318A, 7318B, 7319, range between 275 and 325 million light years distant, all interacting gravitationally, while a fifth, NGC 7320, is actually a foreground object (on the left side of the picture) almost a mere 40 million light years away [5]. Here's a finder chart for the galaxies in the image (aligned a bit more clockwise than the JWST picture above; NGC 7320C, discussed below, is not in the JWST picture) :
To put these distances in perspective, the light from the four interacting members of Stefan’s Quintet left their neighborhood near the beginning of earth’s Permian period when the landmass of our world was concentrated in the supercontinent Pangaea. The light that JWST captured from NGC 7320, the bigger, flatter, splashier galaxy on the bottom of the image, departed that galaxy when the prehensile-tailed New World Monkeys were evolving as a separate lineage here on earth.
The detail in the images is certainly unlike any I’ve seen in any astronomical picture in my lifetime. They are better than the sharpest images I’ve ever seen from any telescope on earth or in space [6]. Just compare the amazing jellyfish-like detail of JWST’s NGC 7320 with this quite excellent optical image taken with the 3.58-meter Canada-France-Hawaii Telescope on Mauna Kea in Hawaii.
I’m used to seeing mosaic images of large field objects, but this is a new kind of mosaic. The Stefan’s Quintet image is a composite from Webb’s Near-Infrared Camera (NIRCam) and its Mid-Infrared Instrument (MIRI) and contains over 150 million pixels from about 1,000 separate image files. Here is NASA’s vivid description:
Webb shows never-before-seen details in this galaxy group. Sparkling clusters of millions of young stars and starburst regions of fresh star birth grace the image. Sweeping tails of gas, dust and stars are being pulled from several of the galaxies due to gravitational interactions. Most dramatically, Webb’s MIRI instrument captures huge shock waves as one of the galaxies, NGC 7318B, smashes through the cluster. These regions surrounding the central pair of galaxies are shown in the colors red and gold.
When I was growing up, photographs taken from the Carnegie Institution’s big 200” telescope on Mt. Palomar were the main big thing, ultimately overtaken, instrument-wise, by the wave of giant telescopes all over the world, and those by the glorious images taken from above our watery atmosphere by the Hubble Space Telescope (HST), and now Hubble overtaken by JWST at the far-out L2 point. That point, a million and a half kilometers out from the earth, where all is dark and cool and noise free, is the perfect place for JWST, a telescope designed mainly to look for things in the infrared portion of the spectrum. It’s the ideal instrument there because one of its missions is to learn about the early time in the universe’s history when galaxies were forming. Because of the extreme redshift of distant galaxies, they all appear in the infrared.
To put this into context and see how far we have come in the short space of a few decades, consider the barred spiral galaxy NGC 7479 in the constellation of Pegasus. The NASA Atlas of Galaxies put together in the late 1980s by Allan Sandage and John Bedke as part of the Hubble Key Project [7], listed NGC 7479 as its fastest galaxy for investigation by the HST, 114 million light years away and receding at 2,630 km/s. The JWST’s galaxy images, as we’ll shortly discuss, are of galaxies receding at many more thousands of kilometers per second and lying many hundreds of millions to billions of light years away.
In Search of High Z
Think of a one-way time machine with a big Z marked on the dial. Turning the knob to a given Z tells you how far back in time you want to go. The greater the Z the farther back you go in time. There is only one limitation: can’t go back farther than the age of the universe.
This sounds like science fiction but actually Z is a real number used by astronomers all the time to describe the redshift of an object. Let’s see what we mean.
Galaxies are moving away from us with increasing velocity the farther away from us they are, and their spectra are red-shifted – meaning that spectral lines, which represent various elements in the source, like hydrogen and helium, are displaced to a longer wavelength, hence toward the red. You may recall from my blog, Fast Stars and Hotrod Galaxies ~ Vesto Slipher’s Historic Discovery of Galactic Redshifts, that because of the expansion of the universe, redshift is a linear function of the galaxy’s velocity: the greater the recession velocity from us, the greater the shift in the spectral lines.
Similarly, the greater the redshift, the farther back one sees in time. Because light is finite, and it takes a very long time for the light from distant objects to reach us. It takes a year for an object one light-year away to reach us [8]. It takes 100 million years for the photons from a galaxy 100 million light years away to reach us. And if we want to go back in time to as near as we can get to the beginning of the universe, over13 billion years ago, we have to look back in space by that many light years. No telescope has ever seen an object that many light years away, that far back in time. No one has seen the dawn of galaxies near the beginning of creation. But JWST aims to get close. It is designed to turn the Z dial higher than any instrument has ever done before.
Let’s look at the quantitative meaning of Z. It represents the amount of shift in the spectral line caused by the galaxy’s speed of recession:
If for example the 500 nm line in a galaxy’s spectrum (the λ in the equation) is shifted toward the red by 15 nm (the Δλ in the equation), Z would equal .03 or 3% [9]. This implies a recession velocity of 3% of the speed of light (about 3,000 km per second) or 9,000 km/s. Multiplying by the speed of light will give you the velocity:
In the case of NGC 7320 in Stephan’s Quintet, its Z is .00267 and its cz recession velocity v is therefore about 800 km/s. Its distance can be calculated by dividing the velocity by the Hubble Constant, H, which has now converged on 67.8 kilometers per second per megaparsec, abbreviated km/s/Mpc [10]. (The “megaparsec” is just another convenient unit of big distance, equal to 3.26 million light years.)
This yields a distance of about 12 Mpc or about 39 million light years, not all that distant, as galaxies go. It should not really be considered part of the actual, physical grouping since it is a foreground object.
But the other galaxies in the quintet, being much farther away, are another story. The ‘quartet’ of NGC 7317, 7318A/B, and 7319 are in a great interacting tangle of gravity and motion. NGC 7317, with a redshift Z of .0220 recedes at about 6,599 km/s, at a distance of 317 million light years. It is the B that is smashing into A. NGC 7318A/B together have a redshift of about .0207 and velocity of about 6,203 km/s, for an average distance of nearly 300 million light years. NGC 7319 has a redshift of .0225, indicating a recession speed of 6,747 km/s, yielding a distance of about 324 million light years. A nearby galaxy, NGC 7320C, is not part of the Hickson Compact Group known as Stefan’s Quintet yet is shares approximate redshift (.0199) and distance (288 million light years) with the Quintet.
Toward the Edge
Let’s leave our sojourn with Stefan’s Quintet and see what else JWST is capable of probing as it searches vastly farther into space, pushing the Z dial toward the beginnings of our universe. Here, at the very frontier of human knowledge, we enter a truly strange realm. Below is JWST's first deep field image that is worth pondering over. You, me, and the rest of the human race have never seen anything like this before.
This is a near-infrared picture of galaxy cluster SMACS 0723. You can see myriad galaxies in this spectacular image. The bright, white galaxies are part of a foreground cluster dominated by a big elliptical galaxy in the center. You may be puzzled by the little orange tadpole-shaped things that seem to encircle the elliptical galaxy. They are also galaxies, but they're much farther away than the bright ones. JWST can image them because of the phenomena of gravitational lensing.
Lensing? What's that? you say. It's just a "spacetime telescope," the astronomer answers. More science fiction, right? No, it really does work. As a consequence of Einstein’s General Theory of Relativity, mass bends light. (Einstein's idea was proved by A.S. Eddington's photographs of the solar eclipse of 1919, showing that the mass of the sun did minutely divert the light from nearby stars from their paths.) So if a thing can bend – refract – light, it can act as a lens.
The cluster of foreground galaxies contains enormous mass that bends the light emanating from the more distant galaxies behind the cluster. The mass of the cluster thus acts like a colossal lens, magnifying and refracting but with a lens unlike any you've ever experienced: this one's made of gravitationally warped spacetime, not glass. There is distortion – like looking at your friend’s face through the bottom of a bottle. Some of them appear mirrored with its match on the other side. The more distant the galaxies thus appear as little orange arcs circling the brighter clustered galaxies in the foreground. Hard to fathom, but those arcs are actually the squished-out and bent images of immensely high-Z galaxies, whose spectra, amazingly, can be analyzed.
Here is one of NASA's analyses of four of the distant lensed galaxies in the picture:
JWST’s near-infrared spectrograph instrument (NIRSpec) examined 48 galaxies in SMACS 0723, using tiny little microshutters (it has 248,000 of them!) that can be opened or shut individually to take the spectra of single galaxies in a cluttered picture. The shot above illustrates how the spectral lines for hydrogen and ionized oxygen have red-shifted in the selected galaxies, revealing their distances to be 11.3, 12.6, 13.0 and 13.1 billion light years. While there are only four galaxies in this demonstration picture, JWST could use its microshutters to simultaneously take the spectra of up to 250 separate objects.
Finally, in the graphs below, NASA plotted the light gathered from three (unidentified) high-redshift spiral galaxies. Each shows how far the light from each galaxy has shifted due to the expansion of the universe. These show Zs (redshift numbers) of 10, 11, and 12, representing distances of 13.2, 13.3 and 13.4 billion light years away, with “ages” respectively, from the Big Bang of 480, 420, and 370 billion years. A redshift of 12 suggests a velocity of recession of 36,000 km/s! It is phenomenal that we are even thinking about studying these "young" galaxies born so soon (relatively speaking!) after the creation of the universe. They are young, but oh so incredibly old. Try to get your mind wrapped around that idea for a while . . .
NOTES [1] The JWST images can be seen at https://webbtelescope.org/news/first-images . They can be downloaded in a variety of resolutions and enlarged and inspected in awesome detail. This article focuses just on galaxies. The other pictures there are no less stunning. [2] The writer Robert Doran described the psychological experience of being simultaneously "overwhelmed and exalted" as the definition of the sublime. Doran, R., The Theory of the Sublime from Longinus to Kant (Cambridge: Cambridge University Press, 2015). That is, being blown away and yet feeling vaguely uneasy; a heightened awareness of one’s inability to fully comprehend the vastness of what one is experiencing. [3] For JWST’s Stephan’s Quintet images, go to https://webbtelescope.org/contents/media/images/2022/034/01G7DA5ADA2WDSK1JJPQ0PTG4A [4] Stefan’s Quintet is about half a degree south of NGC 7331, a spectacular barred spiral galaxy in the constellation of Pegasus. [5] NGC stands for New General Catalog. The group is also known as Arp 319 and Hickson Compact Group 92 (HCG 92). Distances derived from the NASA/IPAC Extragalactic Database, http://ned.ipac.caltech.edu/byname?objname=NGC+7320&hconst=67.8&omegam=0.308&omegav=0.692&wmap=4&corr_z=1. An interesting older paper on each member of Stephan’s Quintet can be read at https://articles.adsabs.harvard.edu/pdf/1998A%26A...334..473M . Stephan’s Quintet has historically been the focus of intense study on the nature of the redshift. [6] See for example, the various images on NGC 7320 on the Images tab in the NASA/IPAC Extragalactic Database: http://ned.ipac.caltech.edu/byname?objname=NGC+7320&hconst=67.8&omegam=0.308&omegav=0.692&wmap=4&corr_z=1 . The JWST images are false color images, monochromatic inputs sorted by wavelength and mapped to a chosen color palette. [7] The authors were then both affiliated with the Space Telescope Science Institute. Their Atlas was for the purpose of studying the best targets for HST in determining the value of the cosmological distance scale known as the Hubble Constant. The Hubble Key Project, one of the primary missions of the Hubble Space Telescope, was the effort to determine the most accurate value ever for the Hubble Constant, a kind of Holy Grail of cosmology. The final result of that effort as of 2001 is reported at: https://iopscience.iop.org/article/10.1086/320638/pdf. That 2001 value, 72 km/s/Mpc (with error bars), has since come down to 67.8 km/s/Mpc. [8] This is the definition of the light year. It is almost 6 trillion miles, and is also 63,421 astronomical units, th au being the mean distance between the earth and the sun.
[9] Nanometers are indicated by the abbreviation nm. They are billionths of a meter. An Ångström is a tenth of a nanometer. Thus, 500 nm equals 5000 Å. [10] Astronomers have labored for a century to nail down the precise value of H. (See note 7.) The 67.8 km/s/Mpc value for H used here is the same as in the NASA/IPAC Extragalactic Database, http://ned.ipac.caltech.edu/.
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