Dark Sky December at Abriachan

Join me on December 17th up at Abriachan Forest (a Dark Sky Discovery site) for an evening of stargazing and storytelling under Moonless dark skies.

If conditions are clear I’ll guide you under Abriachan’s Milky Way class dark skies (with a backup indoor astronomy presentation if clouds roll in).

Meanwhile we welcome our first guest storyteller of the season. Local gael Fiona Macdonald will lead the campfire storytelling section of the evening with tales steeped in Highland folklore.

Due to site and classroom capacity, booking via Eventbrite is essential. Admission is free for under 16s with accompanying adults but please inform Abriachan of any large booking requests.

For driections to the forest classroom please follow directions to Abriachan Forest Classroom here: https://www.abriachan.org.uk/environment/

Tickets are available on Eventbrite here.

Our Supermassive Black Hole – Sagittarius A

Sagittarius A – as imaged by the team at the Event Horizon Telescope.

Imagine taking over 4 million copies of our Sun and cramming the combined mass into a region of space no bigger than the orbit of Mercury.

That’s Sagittarius A, the supermassive black hole at the centre of our own Milky Way galaxy. Evidence for Sagittarius A has been growing since the 1970s but now in 2022 the team at the Event Horizon Telescope have actually imaged it.

The term ‘supermassive’ when attributed to black holes is very misleading as black holes are incredibly low volume but dense regions of space. To give you a feel for this, if you took our Moon and somehow compressed it into a black hole, the resulting anomaly would have a diameter of 0.2 millimetres! That’s probably less than the size of a single pixel on the screen you’re reading this article on.

As black holes grow they can devour more mass and will slowly get bigger with the event horizon radius r defined by the famous Schwarzschild equation:

r = 2GM/c^2

In this equation G is the universal gravitational constant, c is the speed of light and M is the mass of the black hole. This is a simple linear relationship, so for example doubling the mass of a black hole will double its radius.

The bright central region of our Milky Way galaxy where Sagittarius A is located. Telescopes of the Atacama Large Millimeter/submillimeter Array in the foreground. Credit: EHT Collaboration

Given the relatively small volumes and areas of space involved, detecting even the most massive black holes in challenging to say the least. Sagittarius A, despite containing millions of solar masses, occupies a volume smaller than a single star in its giant phase of evolution. This gets compounded by the incredible distances involved. The centre of our Milky Way where Sagittarius A is located is a staggering 26,000 light years away. How then did the team capture the image?

The key was using multiple detectors spread across the planet, effectively constructing an Earth sized telescope. The data collected from these widely spaced arrays was then gathered together, producing many terabytes of data, and processed by banks of supercomputers called ‘correlators’. The final image was constructed using advanced algorithmic and statistical imaging techniques.

EVT’s detectors are spread around the planet effectively creating an Earth sized detection aperture.

Clearly by their nature black holes do not allow any light to escape so what we see in the final image is the infrared signature of super-heated gas rotating close to the black hole.  Black holes therefore reveal themselves by their indirect influence on nearby objects rather than direct observation.

Indeed, Sagittarius A’s existence was originally inferred by its influence on nearby stars, which are being thrown about at fantastically high speeds due to its intense gravitational influence. Fast enough for us to produce time lapse images over several years (see animation below).

Time-lapse from the ESO’s Very Large Telescope in Chile shows stars orbiting close to Sagittarius A over a 20 year detection period. 

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.

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.

January 2022 Star Stories at Abriachan Forest

The brilliant stars of Orion shining down over Abriachan Forest.

Many thanks to everyone who made it up to Abriachan Forest for our Burns stargazing event on Saturday. Big thanks to Jim for his excellent Haggis address and the Abriachan team for the delicious Burns supper fare.

Skies were a little patchy but we did see good naked eye views towards the south and the main focus of the evening talk – the mighty Orion constellation.

After observing Orion we headed inside to explore some of the amazing deep sky objects hidden within this giant of the night sky, like the beautiful Horsehead and Flame nebulae, part of the enormous star forming Orion Molecular Cloud Complex.

This region contains areas of dark, emissive and reflection nebulosity, with hot young stars blasting intense radiation into the hydrogen clouds producing the distinctive red areas due to ionisation.

At this scale the extent of our solar system (out to Neptune) would be one 10,000th of the width of the picture you see below on the right – less than a single pixel element within the image!

The Horsehead nebula sits close to the left most belt star in Orion, Almitak

Ticket links will go up very shortly for our February and March guest speaker Star Stories events with Martin Hendry and Catherine Heymans. I hope to see you all there.

Star Stories Astronomy Guest Speakers

Astronomer Royal for Scotland, Catherine Haymens, will visit Abriachan Forest in March 2022.

I’m delighted to confirm our guest speakers for the 2022 Star Stories programme. Following a ‘Stargazing Burns’ event on January 27th we’ll have a dark sky event in February with guest speaker Martin Hendry, Professor of Gravitational Astrophysics and Cosmology at the University of Glasgow. Martin is a regular visitor to the forest and will be updating us on the latest discoveries on dark matter and dark energy followed by naked eye and binocular stargazing under Abriachan’s Milky Way class dark skies.

Then in March we’re very excited to welcome Scotland’s new Astronomer Royal, Catherine Haymens. Catherine will be joining us on March 14th for a special Moon night with a talk all about the Moons of our solar system. This will be followed by a live Moon observing session and Q&A. Catherine is Professor of Astrophysics and a European Research Council Fellow at the University of Edinburgh. She’s also director of the German Centre for Cosmological Lensing at the Ruhr-University Bochum.

Where possible, and understandably, all events will be setup for outdoor learning so please bring plenty of warm clothes and wrap up. Storytelling and other family friendly activities will also be delivered by the Abriachan team and guests. Ticket links will go live about 4 weeks prior to each event. Please follow my Facebook page for the latest.

Meanwhile the November 27th event has now sold out. This will be a dark sky evening with stargazing or astronomy talk presented by yours truly. Best selling author John Burns is our guest storyteller in November.

M13 The Great Hercules Globular Cluster

The Great Hercules Globular Cluster – M13

I hope you enjoy this conversational deep dive into the great globular cluster in Hercules. Joining me once again is Steve Owens, astronomer at Glasgow Science Centre and author of Stargazing For Dummies.

In this video podcast we discuss:

1. Finding M13 and what to expect when observing.
2. The physical scale and composition of this vast cluster.
3. What the night sky might look like from within M13.
4. Could life emerge and survive within these ancient and densely packed stellar environments.
5. What can globular clusters tell us about our position within our own Milky Way.

Music by Rising Galaxy, Cosmicleaf Records , Spain.