Earendel – The Most Distant Star Detected

The star Earendel is located at the point of the arrow in the image above, surrounded by the light from diffuse and distant galaxies.

The NASA Hubble space telescope has imaged the most distant star ever detected at a staggering 12.9 billion light years away. The light captured from Earendel (dubbed the ‘Morning Star’) is a snapshot from an epoch when the universe was only 1 billion years old, making it significantly older than the previous furthest star detected by Hubble in 2018. (That star was dated to 4 billion year after the big bang).

Normally stars at such immense distances would be undetectable, but its discovery was aided by the gravitational distortion from distant galaxy clusters, magnifying the star and its host galaxy in a phenomena called ‘gravitational lensing.

An example of a distant galaxy, revealed by the distortion of space (and therefore light) near a closer area of high mass, in the form of a galaxy cluster.

Gravitational lensing is analogous to the refraction of light from a glass lens, magnifying and revealing objects that would normally be occulted by closer structures by the bending of space near areas of high mass – like galaxy clusters. Sometimes duplicate images of the same object can be seen, creating copies of the object along symmetrical arcs. The image below illustrates this effect on a star cluster which appears either side of Earendel.

A closer image of Earendel with a mirrored image of a nearby star cluster created by gravitational lensing

You might wonder how immense distances like this can be calculated given the complexity and uncertainty in pin pointing the distance to relatively close stars, let alone objects billions of light years away?

The principle tool used to measure these vast distances is an object’s spectral redshift – a measure of how much its light rays have been stretched (made longer) due to the fabric of space itself being stretched the further away we observe. Larger redshifts indicate objects that are further away – a relationship first accurately established by Edwin Hubble when cataloging the spectra from many distant galaxies.

A measured spectra shifted towards the red end of the spectra, signalling longer wavelengths and higher recessional speeds.

Given the redshift of an object we can calculate its recessional speed (related to the global expansion of the universe) and from this its distance can be determined using the Hubble’s constant Ho. These calculations can be set out very simply:

V (recessional speed) = Red-shift x Speed of Light

In the case of Earendel the detected redshift from its spectra was 6.2. Therefore:

V (Earendel) = 6.2 x 300 million m/s = 1860 million m/s.

It’s important to note that this speed is faster than the speed of light! How can this be? Well this is actually a measure of the speed that space itself is expanding. Light cannot travel faster than 300 million m/s – our cosmological speed limit – but there is no limit on the rate at which the fabric of space can expand. In fact for general relativity to work space must be permitted to expand at potentially unlimited rates.

From the recessional speed we then use Hubble’s law to find the distance to the star:

D (distance) = V (recessional velocity) / H0 (Hubble’s constant)

This gives our published distance to Earendel of 12.9 billion light years! A staggering distance taking us back to the earliest period of star formation when the abundance of atomic elements in the universe was very different to today.

We believe the very first population of stars emerged around 100 to 250 million years after the big bang, so Earendel formed only a few hundred million yeas after this. The new James Webb telescope will likely continue to study Earendel in the infrared, at longer wavelengths, potentially revealing the star’s temperature and luminosity and therefore its stellar classification.

James Webb – First Fully Aligned Image

Fine phasing of James Webb’s honeycomb mirror segments is now complete, revealing this first fully aligned image of star 2MASS J17554042+6551277 via the telescope’s NIRCam sensor.

This test image has exceeded NASAs expectations in terms of resolving power and clarity. You can even see well defined distant spiral galaxies in the background.

Unlike the Hubble space telescope the wavelengths of light gathered here is around 2 microns, within the infrared band of the electromagnetic spectrum (the region Webb has been designed to observe). These are wavelengths longer than the human eye can detect but ideal for revealing the evolutionary structure and morphology of stars and distant galaxies.

The Webb team will now continue with calibration of the on-board spectrographs, completing the full scientific instrument setup.

This process is expected to take several more months, but so far so good.

Why do we See what we See?

The western highlands of Scotland, bathed in the visible light of our home star.

When we think about the vast array of electromagnetic radiation all around us – from Gamma rays, X-rays , UV, Microwaves and Radio waves – a natural question to ask is why do human eyes see in a very narrow band we call ‘visible light’?

The answer is undoubtably tied to the energy output of our nearest star – the Sun. Its peak radiation just happens to be at this ‘visible’ band of radiation. I’ve illustrated this below with a black body radiation profile of our Sun.

Our eyes have therefore evolved to ‘see’ this particular narrow range of otherwise insignificant wavelengths. There’s nothing inherently important about visible light – in fact it makes up a tiny 0.0035 percent of the entire electromagnetic spectrum.

Understanding this makes me wonder about the potential sensory apparatus of life that might have evolved elsewhere in the universe. Other stars with different stellar classifications to our Sun have different peak radiation profiles.

If we had evolved next to a source of intense gamma rays for instance, we would very likely be completely blind to visible light but adept at observing small granular differences in the intensity of gamma radiation.

The Final Evolution of our Sun – illustrated by Adolf Shaller

I wanted to share some images with you that had me transfixed when I was a young boy (and still do to this day). I recall first seeing them in a hardback book of my father’s called Cosmos (which presumably accompanied the TV series that was being broadcast at the time).

The images depict the fate of our planet as the Sun transitions into a red giant star, at the very end of its life, some 4-5 billion years from now.

As the temperature of the Sun slowly increases, the oceans recede and our precious atmosphere is stripped away. Eventually the whole horizon is overwhelmed by the Sun in a bloated distended form, with the final image showing the Earth completely barren and parched.

I remember wondering at the time – where would all the people and animals be? Would we perish or find some new star to call our home? I think it was the first moment I glimpsed the immensity of stellar time scales and how tiny human lives and endeavours appeared to be next to these vast physical processes.

This is still what fascinates me most about astronomy and cosmology, and it’s amazing how something as natural and simple as looking up at the stars is a gateway into these incredible realms of the imagination.

Anyway here are the images, including their original captions. I was also pleased to find out that Adolf Shaller is still producing amazing art. Try an image search on Google with his name and enjoy.

‘The last perfect day’
‘The waters recede and most life is extinguished as the sun starts to swell and its luminosity rises.’
‘The oceans have evaporated and the atmosphere has escaped into space’
‘The sun, now a red giant, fills the sky over a dead planet. As we see in the next section, the red giant will eventually throw off its outer layers and become a white dwarf.’

‘Not too hot and not too cold’

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The Goldilocks zone around three different type of stars

The Goldilocks Zone.  The above image is a great illustration of the relative size of the habitable zone around different types of star, with stars like our Sun at the bottom.

Even very dim M class dwarf stars (pictured top) could harbour planets with liquid water – the planets would just need to be situated much closer in. These stars can have very active magnetic fields however, frequently throwing harmful radiation out towards any orbiting planets.  M class stars are also extremely stable, some destined to burn for over 100 billions years, much longer than our Sun which has around 4 billion years of fuel left.

In the middle we see the K class dwarf stars. These will also out live our Sun (by a factor of 4), have nice wide zones of habitation, and much less magnetic activity than the M class stars.  Potentially these K class stars are the ideal incubators for the slow evolution of life, and there’s plenty of them. Nearly 13% of stars in our galaxy are K class red dwarfs.  That’s approximately 26 billion in our galaxy alone! 

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An artist’s impression of a rocky world orbiting a red dwarf star, like the M and K class stars mentioned above.

Solstice Sunsets

Video from the shores of Bunchrew looking over Ben Wyvis, panning from the north west to north east

The sunsets in the Highlands of Scotland are some of the best in the world when conditions are right, especially around the solstice when the setting Sun grazes just 8 degree below the northern horizon producing mesmerising night long sky glow.

On June 22nd I camped out at the Bunchrew shoreline with my daughter Violet and managed to capture some video and still images of the sunset looking north towards Ben Wyvis.  Footage captured around 10.45pm.

 

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Venus Morning Star

The planet Venus is a brilliant morning star at the moment. Catch it rising in the south east ahead of the Sun between 5.30am and 7.30am.

With keen eyesight and binoculars you should be able to discern Venus’s phase, currently a beautiful crescent. A telescope will make this much clearer as demonstrated by this video footage I shot last year, when Venus was ‘the evening star’.

Over the month of November Venus will get brighter as its phase waxes from a thin crescent to a 25% illuminated disc at month end.  Despite this brightening Venus is actually travelling away from us and after December 2nd its brightness will begin to diminish as it pulls further away from earth and its disc size shrinks .

Once Venus passes behind the Sun it will eventually reappear as an evening star around mid August 2019.

Clear skies!

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