Presidents’ Articles

Large Scale Structure of the Universe

From our vantage point on Earth we can only easily see a few 10’s of thousands of light-years into the Universe, with the unaided eye.

However using modern Telescopes we can see Galaxies on a far grander vista, from our Local Group – up to distances of a few 10’s of millions of Light years, to Galaxy Clusters, at distances of anything from 100’s of millions to more than 10 billion Light years away.

 Whilst the Universe is thought to have started off as a point source, the effect of Dark Matter did – it seems – created tiny fluctuations in the density of the early Universe that have now evolved into some of the largest organised structures in our Universe today.

 The study of these large scale structures is providing a window how the Universe grew during its first billion years or so, and also how it might evolve billions or even trillions of years into the future, principally caused by the influence of Dark Energy.

 So what has been discovered about these large scale structures and what insight might it provide about the future of our Universe.

 Large-scale structure of the Universe – Simple English Wikipedia, the free encyclopedia

Firstly the basics. Galaxies exist in isolation on small scales [<=1 million Ly apart], however on larger scales [10-100 million Ly] they form groups of from a few galaxies – for example our Local Group comprising the Milky Way, M31 and M33 as well as a number of smaller galaxies such as the LMC and SMC as well as a multitude of Dwarf Galaxies [profiled in a previous Newsletter article] ; to much larger – often interacting – galaxy clusters – such as Stephan’s Quintet and up to clusters of hundreds of galaxies – for example The Virgo or Perseus Clusters of galaxies.

From our point of view it is – relatively – easy to see these groups and how they have already, currently are or likely will interact in the future.

Recent research  Huge ring of galaxies challenges thinking on cosmos – BBC News is now challenging our existing ideas about these larger structures.

The Ring Structure is around 1.5 billion Ly in diameter and contains a mixture of discrete galaxies strung together – like a string of Pearls – with larger galaxy clusters, comprising many 10’s, 100’s or 1000’s of members.

The appearance of this structure is contrary to our existing ideas of the Cosmological Principle Cosmological Principle | Definition, Implications & Examples – Video & Lesson Transcript | Study.com . This basically says that on a large enough scale, the view of the Universe is Isotropic – the  same laws apply to every point in the Universe –  and homogeneous – the same evidence is available from any viewpoint, for all observers.

 However there are some major problems with both of these ideas:

  1. Isotropy – the Cosmic Microwave Background  is ‘lumpy’ even on the largest scale but has the smallest variations – see ESA – Planck
  2. There are a number of observations that go against homogeneity:

a) the Clowes-Campusano LQG structure which is ~550 MLy long THE CLOWES–CAMPUSANO LARGE QUASAR GROUP SURVEY. I. GALEX SELECTED SAMPLE OF LYMAN BREAK GALAXIES AT z ∼ 1 – IOPscience

b) The Sloane Great Wall – discovered during the  Sloane Digital Sky Survey – which is ~1.5GLy long Imagine the Universe! (nasa.gov)

c) U1.11 – A massive cluster of Quasars which is ~2GLy in size U1.11 – Wikipedia

d) The Huge LQG – which appears more than 2x the predicted maximum size of any Galaxy Cluster or String Large quasar group – Wikipedia

e) The Hercules – Corona Borealis Great Wall which is ~ 7-10GLy in size Hercules-Corona Borealis Great Wall: The Biggest Thing In Universe (scienceabc.com)   .

f) In 2020 a 4.9σ [~the chance of being incorrect is ~1 in 3.5 million] conflict was found between the kinematic explanation of the CMB dipole and the measurement of the dipole in the angular distribution of a flux-limited, all-sky sample of 1.36 million quasars

g) 2021 –  a Galaxy structure – the Giant Arc – was located that is 3.6 GLy in size containing many galaxies, galaxy clusters, gas and dust – at a distance of ~10GLy .

Discovery of a Giant Arc in distant space adds to challenges to basic assumptions about the Universe – UCLan

Since the Universe came about there have been a number of epochs where different forces held court:

  1. Approx 1-3Gy@BB   Era of Radiation The Early Universe (uoregon.edu) – where the CMB structured the Universe
    1. Approx 4 to 8 Gy@BB           Era of Matter Astronomy Lecture Number 26 (njit.edu) – where the rate of expansion of the Universe slowed as matter was created and Gravity held sway
    1. Approx 8Gy to present day     Era of Dark Energy The Universe is already in its sixth and final era – Big Think – accelerating expansion caused by an – as yet unidentified source of energy – which may be Vacuum Energy Vacuum energy – Wikipedia in nature

Each of these have sculpted our Universe in different ways. Radiation created the scaffolding on which matter was deposited. The Matter then created the vertices on which Dark Energy began to push the Universe apart.

There are some other projects currently ongoing to find out more about the way these three epochs have created the Universe we see today:

The Dark Energy Survey Large-Scale Structure – The Dark Energy Survey aims to map out how the structure of the Universe has moulded what we see. By looking back over specific timelines it is trying to understand how the large scale structure of the Universe evolved, under the influence of gravity.

Using data from SDSS Sloan Digital Sky Survey – Wikipedia and Sloan Digital Sky Survey-V: Pioneering Panoptic Spectroscopy – SDSS-V , data is being used to see if – when viewing at larger Z-values – whether – or not – the Universe appears differently. Moreover – if it does look differently – can we work out what caused that, if it was not due to gravity alone. This will pin down more precisely the timing of any change in Epoch as described above .

Fundamental to this investigation is a study to locate when – and how – the 4 fundamental forces in the Universe ‘budded off’ from each other.

By this theory the Universe can be segmented into distinct zones – in time:

This is one of the hottest topics in Cosmology at the moment and it may be quite a while before any significant conclusions arise.