Space

JWST Unfolds the Universe: Distant Galaxies & Cosmic Cliffs

Last week, the first full colour images of the universe, as seen by the new James Webb Space telescope (the successful launch of which was the astronomy community’s collective Christmas present last year!), were published- leaving everyone in awe of both the universe’s beauty, and of the new era of science it ushers in. If you were wondering what the significance of all the images were, or how they were taken… read on! So without further ado, let’s take a look through a few of JWST’s first photos!

Deep Sky, Deep Time

This was the first image to be released, of the galaxy cluster SMACS 0723 and is a fantastic example of why JWST is so special:

Immediately clear is just how much more detailed than previously possible the image is, as the most distant galaxies are now far more than just blurry smudges in the background, but have distinguishable features, making them useful targets in their own right. One of these such galaxies in the background was found to be 13.1 billion years old, and a full spectrum was taken, allowing the identification of different elements it contains. Tracking how this changes over time by measuring galaxies of different ages (as determined by calculating the redshift- how much known lines in the spectrum have shifted compared to lab spectra) will help scientists understand how galaxies evolve!


Some quick tips for interpreting the images:

  • Individual stars are probably within our own galaxy, and have the characteristic diffraction pattern of 8 spokes. This is like a fingerprint of the observing equipment- the mirrors of JWST are hexagonal, hence the 6 main spokes, and the horizontal line is caused by the supports of the secondary mirror.
  • Its a false colour image, but this doesn’t make it any less real- JWST detects wavelengths longer than the human eyesight can see, in the infrared. But by using filters to only let certain wavelengths through, the data can be processed so that the longer wavelengths appear red, and the shorter ones blue.

As well as revealing the composition of the earliest galaxies (helping to uncover the intricacies of galaxy evolution), the spectrograph NIRISS also proved useful in confirming the identity of galaxies in the image. As the central galaxy cluster (and its associated dark matter) is so massive, it’s gravitational pull causes light to bend around it, forming the distorted, arc-shaped features seen around it. Due to the nature of this process, known as gravitational lensing, multiple images of the same galaxy can appear, and JWST has been able to confirm this by comparing the spectra of the galaxies.

Although this in itself isn’t completely ground-breaking, as gravitational lensing is frequently observed, it is a reminder of the genius of Einstein’s predictions, and as we will come to expect from JWST, the resolution obtained is just astounding! The lensing effect of this cluster is also very useful as it magnifies the distant galaxies, so more features can be observed, allowing us insights into how the first galaxies formed, as they are imaged as they were over 13 billion years ago!

One of my favourite areas of the photo is close to the bottom, where there is a series of interesting looking galaxies next to a foreground star (with the characteristic 6 spoked diffraction pattern that will become a distinguishing feature of JWST images), as well as a diffuse galaxy with visible star clusters beneath it, and a lensed galaxy with structures still discernible above it.

This also shines a light on just how rich every image from JWST will be: the diversity of objects in just this small area of the image is astounding, and as the spectra of all the bodies in the field are determined, not only the principal target, unexpected discoveries may be frequent with each data release.

And this is just scratching the surface of what JWST will be able to capture in the deep field- it took Hubble about 13 days to capture its SMACS 0723 image, but JWST took just 12.5 hours… imagine what it could reveal with longer exposures! Another way to think about it is that the original Hubble Deep Field image had a diameter roughly 1/13th of the moon, and imaged roughly 3000 galaxies over 10 days, but the SMACS 0723 may depict many more galaxies than this, in an area the same as covered by a grain of sand held at arms-length.

View the full size JWST image here to zoom in!


Through the Dust to Climb Cosmic Cliffs

The beauty of the infrared is twofold- it can reveal the galaxies so distant their light has been stretched beyond the visible part of the spectrum as the universe expanded, as discussed above, but it can also can allow us to peer through the dust clouds of star-forming regions (which blocks visible light), revealing the genesis of new solar systems, previously hidden from view.

This can be seen in the new image of the Carina Nebula, a favourite target for amateur astronomers as well as JWST’s predecessors, but as expected, is now imaged in unprecedented detail. As well as new stars, the actual structure of the dust clouds can be resolved, revealing how the ‘pulling’ forces of gravity and ‘pushing’ forces of stellar winds (the high energy streams of ionised gas & dust) and ultraviolet radiation emitted from young stars interact to encourage yet more star formation. This is seen on large and small (well, smaller, the pillars alone are over 7 light years tall- double the distance to our nearest star, Proxima Centauri) scales, in the fine structure of the cloud and the cosmic cliffs themselves, formed at the edge of an expanding cavity created by the pressure of radiation from the massive, extremely hot young stars found above the image in the centre of the cavity.

The NIRCam image is truly stunning, but the MIRI data shows more clearly the infant planetary systems (the pink/red stars shining through the dust). That’s the beauty of having multiple instruments aboard Webb, as the interesting features identifiable in the high resolution NIRCam image can be traced to their sources in the MIRI image, allowing for greater knowledge of the conditions of these systems and how they form, which, therefore, leads to a deeper understanding of our own history.

Find the full size composite image here, and NIRCam image here.


NIRCam, NIRSpec, MIRI… What’s the difference?

JWST is an infrared telescope, meaning it mainly detects light which has a longer wavelength than what our eyes can detect, and tends to be associated with heat, although JWST will also detect infra-red light which was initially emitted at shorter wavelengths, but has been stretched and redshifted into the infrared as the universe expanded. The exact range for Webb is 0.6-28 micrometres, which spans from the orange/red end of visible light, to the mid-infrared. But different instruments are needed to cover different parts of this range.

The instruments are within the ISIM, and the mirrors work to focus light onto them!

MIRI (developed in part by the UK ATC in Edinburgh!) detects the mid-infrared (unsurprisingly, as it’s name literally stands for the Mid InfraRed Instrument), from 5 to 28 micrometres, and consists of both a camera (to take a photo of the target) and a spectrograph (to tell us what the target is made of). As it detects longer wavelength light, MIRI is useful for detecting very distant galaxies, whose light has been extremely stretched and redshifted, as well as the cooler (relatively, in terms of temperature) objects of the universe such as distant young planetary systems & stars, or objects within our own solar system! MIRI is also the most high maintenance instrument, as it requires the temperature to remain close to absolute zero (~7 Kelvin/ -267°C)

MIRI

NIRCam, then, detects the shorter wavelengths of the Near-Infrared (shocking I know), as well as some visible light, from 0.6 to 5 micrometres. This is very much a jack of all trades instrument, peering through dust to capture the universe’s earliest galaxies, newly forming stars, planets and objects in our own solar system, and much more!

Most images you will see will be composites of the MIRI and NIRCam data combined, as this produces the most detailed, rich photos, but they aren’t the only instruments aboard Webb. In fact, the most interesting science is (in my opinion, as a fan of planetary science) will come from the spectrographs. MIRI has this built in, but at a much lower resolution than what is possible with the specialised NIRSpec and NIRISS. The former is behind an innovative micro-shutter array, allowing it to measure the spectra of 100 objects simultaneously to high resolution, as mentioned above, by opening/shutting doors to particular parts of the telescope field of view. NIRISS is a more specialised spectrograph, for exoplanet detection and characterisation, eg. by transit spectroscopy- splitting the light that has passed through the planet’s atmosphere when it passes between us and it’s star.

For more on exoplanets, and the rest of the first JWST images, come back tomorrow for my next blog post! Make sure you’ve signed up for updates using the follow blog box in the sidebar 🙂

Further Reading/Good Articles I found not referenced in text

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