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.

The Physics of Visible Star Light

Globular cluster NGC 6717. The colour of light from the stars is a general indicator of surface temperature.

The colour of a star tells us how hot it burns. From the dull red of Arcturus to the brilliant blue of Rigel, you can actually see these subtle colour differences with your own eyes when looking up at the night sky.

Just like an iron cast into the blacksmith’s forge, which slowly changes from red to white hot, stars emit light at different frequencies depending on their overall luminosity and energy output.

The same relationship between colour and temperature is noted when metal objects are heated.

The Planck-Einstein equation E = hf is a basic way of understanding this. E is energy, f is frequency and h is the famous Planck’s constant. Higher frequency light (blue) is more energetic than lower frequency light (red) and therefore hotter and more luminous stars tend to appear more blue. Meanwhile cooler stars whose external atmospheric envelopes has expanded (red giants like Betelgeuse) appear redder.

A simple way to highlight the colour of star light is to take your smartphone camera or DSLR and manually defocus it on a target star. This will emphasise the colour and you can even produce beautiful star trails like the one below by taking a movie or long exposure star trail.

Star trail image credit – Amanda Cross

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.

Tales of the Moon with Catherine Heymans

Stargazing and Moon Observing with Scotland’s Astronomer Royal Catherine Heymans.

Join me up at Abriachan Forest (a Dark Sky Discovery site) for an evening of stargazing, Moon observing and astronomy with our special guest Scotland’s astronomer royal Catherine Heymans.

If skies are clear Catherine and local astronomer Stephen Mackintosh will host an outdoor Moon observing session with binoculars and telescope. Following this Catherine will present her indoor guest talk titled “Do Look up! Space Rocks and Killer Asteroids”

Refreshments provided plus binoculars for stargazing. Under 16s with accompanying adults go free. 

Catherine Heymans is the Astronomer Royal for Scotland and Professor of Astrophysics at the University of Edinburgh. She’s also director of the German Centre for Cosmological Lensing at the Ruhr-University Bochum. She is an experienced science communicator, visiting schools across Scotland, in addition to art, music, comedy, philosophy and science festivals.

Tickets are available via Eventbrite or my Facebook page.

James Webb First Light

Here is the first ever image processed from the James Webb space telescope’s primary mirror. It shows copies of a distant star HD 84406, individually imaged through Webb’s 18 honey-comb like mirror segments.

This is part of the primary mirror alignment phase. A bit like the process backyard observers go through when we collimate our telescopes.

Over the next several weeks these individual points will converge to form a single image of the star, completing the alignment process and ensuring all components of the 6.5 meter primary mirror are working as one.

You can see the gold plated hexagonal components of the primary mirror in this second picture, which is a selfie the telescope took of its main mirror from outer space.

The astrophysical community awaits Webb’s first active mission pictures which I understand will be images of three of the largest low-albedo asteroids, as well as Jupiter’s red spot and Neptune’s southern polar vortex.

Orion Nebula Telescopic Livestream

I hope you enjoy my short livestream of the Orion nebula – the closest region of massive star formation to our Sun. Roughly 1,300 light years away in the sword of the constellation Orion, the nebula is visible naked eye or in binoculars or telescope.

This live stream was originally streamed from my Facebook page and later archived on my YouTube channel. The stream was filmed using a 200mm telescope and 32mm eyepiece.

Tales of Dark Matter

All the light we see from distant stars and galaxies is made from visible matter, yet evidence from the rotational speeds of other galaxies suggests dark matter outweighs visible matter on a ratio six to one. Image: ‘Our galaxy Over Achnasheen’, Stephen Mackintosh

Join me up at Abriachan Forest (a Dark Sky Discovery site) for an evening of stargazing and astronomy on February 25th with our first guest speaker of the 2022 season – Professor Martin Hendry.

If skies are clear Martin and myself will host an outdoor stargazing session, discussion and Q&A under the stars. Following this Martin will present his indoor guest talk on the very latest discoveries in cosmology, concentrating on the elusive nature of dark matter and dark energy.

Refreshments provided plus binoculars for stargazing. Under 16s with accompanying adults go free. Tickets can be booked via Eventbrite here or you can reserve directly from my Facebook page here.

Martin speaking at the Science on Stage Festival

Martin Hendry is Professor of Gravitational Astrophysics and Cosmology at the University of Glasgow and is a passionate advocate for STEM education and science engagement with schools and public audiences. He is the author of more than 200 scientific articles and is a senior member of the LIGO Scientific Collaboration, the global team of more than 1400 scientists which made the first-ever detection of gravitational waves – a discovery awarded the 2017 Nobel Prize for Physics. Martin is a Fellow of the Institute of Physics and the Royal Society of Edinburgh and is currently a Trustee of the IOP and the James Clerk Maxwell Foundation. In 2015 he was awarded an MBE for services to the public understanding of science.