The above montage shows six recent images of ‘potentially’ massive galaxies photographed by the James Webb space telescope, going back to epochs around 600 million years after the universe began.
If the six red dots are confirmed to indeed be large galactic structures, these examples contradict almost all known models of galaxy formation from the early history of the universe and would suggest stellar masses over 100 times greater than previously predicted in this early period. Existing models of galaxy formation predict large galaxies would require several billion years to form, so if true these findings will require extensive revisions to our understanding of the large structure evolution of the universe.
Truth told we still know very little about the formation of galaxies. Their evolution is still shrouded in deep mystery, for example what forms the large bars we see in the centre of most mature spiral galaxies, including our own Milky Way?
And of course their rotational dynamics have lead to the conclusion that clouds of invisible matter must surround them in giant halos (dark matter).
Our next stargazing and storytelling session at Abriachan Forest will be on New Moon (Jan 21st) and we welcome back Glasgow Science Centre astronomer Steve Owens to guide us under the stars (or present a backup indoor talk on the planets). Our guest campfire storyteller Fiona Macdonald should also be in attendance.
If you booked for the cancelled December event your tickets will carry over and will be valid for the Jan event.
If you missed out on the last few events we have a February and March events planned so stay tuned. The February tickets links and event details will go up in the next week.
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.
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).
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.
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.
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.
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.
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 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.
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!
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.