large scale universe


Cosmic superclusters, the Universe’s largest structures, don’t actually exist

“The idea of a supercluster and the name for ours, “Laniakea,” will persist for a long time. But just because we named it doesn’t make it real. Billions of years from now, all the different components will simply be strewn farther and farther apart from one another, and in the farthest futures of our imaginings, they’ll disappear from our view and reach entirely.”

Galaxies don’t just exist in isolation in our Universe, but are often found bound together as a part of even grander structures. Our own Milky Way is bound in a galactic group (our local group), nearby are larger groups and galaxy clusters, and on still larger scales, cosmic superclusters appear to encompass as many as 100,000 individual galaxies. Yet it isn’t sufficient to simply see what appears to be a collection and draw an imaginary line around it. You can’t just give something a name and proclaim that it’s meaningful because you defined it. Instead, for a collection of objects in space, they need to be gravitationally bound together and connected. Thanks to dark energy, these superclusters aren’t.

Over billions of years, the galaxies in even our own Local Group will separate from the other clusters and groups nearby, and we’ll never wind up with a bound supercluster. Not here, and not anywhere in the Universe.


Astronomers with the Sloan Digital Sky Survey (SDSS) have created the first map of the large-scale structure of the universe based entirely on the positions of quasars. Quasars are the incredibly bright and distant points of light powered by supermassive black holes.

“Because quasars are so bright, we can see them all the way across the universe,” said Ashley Ross of the Ohio State University, the co-leader of the study. “That makes them the ideal objects to use to make the biggest map yet.”

The amazing brightness of quasars is due to the supermassive black holes found at their centers. As matter and energy fall into a quasar’s black hole, they heat up to incredible temperatures and begin to glow. It is this bright glow that is detected by a dedicated 2.5-meter telescope here on Earth.

“These quasars are so far away that their light left them when the universe was between three and seven billion years old, long before the Earth even existed,” said Gongbo Zhao from the National Astronomical Observatories of Chinese Academy of Sciences, the study’s other co-leader.

To make their map, scientists used the Sloan Foundation Telescope to observe an unprecedented number of quasars. During the first two years of the SDSS’s Extended Baryon Oscillation Spectroscopic Survey (eBOSS), astronomers measured accurate three-dimensional positions for more than 147,000 quasars.

The telescope’s observations gave the team the quasars’ distances, which they used to create a three-dimensional map of where the quasars are. But to use the map to understand the expansion history of the universe, they had to go a step further, using a clever technique involving studying “baryon acoustic oscillations” (BAOs). BAOs are the present-day imprint of sound waves which travelled through the early universe, when it was much hotter and denser than the universe we see today. But when the universe was 380,000 years old, conditions changed suddenly and the sound waves became “frozen” in place. These frozen waves are left imprinted in the three-dimensional structure of the universe we see today.

The good news about these frozen waves – the original baryon acoustic oscillations – is that the process that produced them is simple. Thus, we have a good understanding of what BAOs must have looked like at that ancient time. When we look at the three-dimensional structure of the universe today, it contains these same BAOs grown out to a huge scale by the expansion of the universe. The observed size of the BAO can be used as a “standard ruler” to measure distances. Just as by using the apparent angle of a meter stick viewed from the other side of a football field, you can estimate the length of the field. “You have meters for small units of length, kilometres or miles for distances between cities, and we have the BAO scale for distances between galaxies and quasars in cosmology,” explained Pauline Zarrouk, a PhD student at the Irfu/CEA, University Paris-Saclay, who measured the projected BAO scale.

Astronomers from the SDSS have previously used the BAO technique on nearby galaxies and then on intergalactic gas distributions to push this analysis farther and farther back in time. The current results cover a range of times where they have never been observed before, measuring the conditions when the universe more than two billion years before the Earth formed.

The results of the new study confirm the standard model of cosmology that researchers have built over the last twenty years. In this standard model, the universe follows the predictions of Einstein’s general theory of relativity – but includes components whose effects we can measure, but whose causes we do not understand. Along with the ordinary matter that makes up stars and galaxies, the universe includes dark matter – invisible yet still affected by gravity – and a mysterious component called “dark energy.” Dark energy is the dominant component at the present time, and it has special properties that cause the expansion of the universe to speed up.

“Our results are consistent with Einstein’s theory of general relativity,” said Hector Gil-Marin, a researcher from the Laboratoire de Physique Nucléaire et de hautes Énergies in Paris who undertook key parts of the analysis. “We now have BAO measurements covering a range of cosmological distances, and they all point to the same thing: the simple model matches the observations very well.”

Even though we understand how gravity works, we still do not understand everything – there is still the question of what exactly dark energy is. “We would like to understand dark energy further,” said Will Percival from the University of Portsmouth, who is the eBOSS survey scientist. “Surveys like eBOSS are helping us to build up our understanding of how dark energy fits into the story of the universe.”

The eBOSS experiment is still continuing, using the Sloan Telescope at Apache Point Observatory in New Mexico, USA. As astronomers with eBOSS observe more quasars and nearby galaxies, the size of their map will continue to increase. After eBOSS is complete, a new generation of sky surveys will begin, including the Dark Energy Spectroscopic Instrument (DESI) and the European Space Agency Euclid satellite mission. These will increase the fidelity of the maps by a factor of ten compared with eBOSS, revealing the universe and dark energy in unprecedented detail.

IMAGE….A slice through largest-ever three-dimensional map of the universe. Earth is at the left, and distances to galaxies and quasars are labeled by the lookback time to the objects (lookback time means how long the light from an object has been traveling to reach us here on Earth). The locations of quasars (galaxies with supermassive black holes) are shown by the red dots, and nearer galaxies mapped by SDSS are also shown (yellow). The right-hand edge of the map is the limit of the observable Universe, from which we see the cosmic microwave background (CMB) – the light “left over” from the Big Bang. The bulk of the empty space in between the quasars and the edge of the observable universe are from the “dark ages,” prior to the formation of most stars, galaxies, or quasars. Credit: Anand Raichoor (Ecole Polytechnique Federale de Lausanne, Switzerland) and the SDSS Collaboration


How Does Earth Move Through Space? Now We Know, On Every Scale

“Ask a scientist for our cosmic address, and you’ll get quite a mouthful. Here we are, on planet Earth, which spins on its axis and revolves around the Sun, which orbits in an ellipse around the center of the Milky Way, which is being pulled towards Andromeda within our local group, which is being pushed around inside our cosmic supercluster, Laniakea, by galactic groups, clusters, and cosmic voids, which itself lies in the KBC void amidst the large-scale structure of the Universe. After decades of research, science has finally put together the complete picture, and can quantify exactly how fast we’re moving through space, on every scale.”

It’s hard to believe, but despite being at rest here on the surface of Earth, we’re actually hurtling through the Universe in a variety of impressive ways. The Earth spins on its axis, giving someone at the equator a speed of some 1700 km/hr. Yet at even faster speeds, the Earth orbits the Sun, the Sun moves through the Milky Way, and there’s a great cosmic motion that applied to the Milky Way galaxy beyond even that. For a long time, we’ve been able to measure the total effect of all these motions, summed up, by measuring our motion relative to the cosmic microwave background: the leftover glow from the Big Bang. But it’s only very, very recently that we’ve identified the source of all the gravitational causes of this motion. While we’ve known of stars, galaxies, and the large-scale structure of where matter is, it’s new that we’ve quantified the effects of these great cosmic voids.

By combining everything together, we can finally explain the grand total of all of our cosmic motion through the Universe. Come get the full, complete story at last!

Study reveals substantial evidence of holographic universe

A UK, Canadian and Italian study has provided what researchers believe is the first observational evidence that our universe could be a vast and complex hologram.

Theoretical physicists and astrophysicists, investigating irregularities in the cosmic microwave background (the ‘afterglow’ of the Big Bang), have found there is substantial evidence supporting a holographic explanation of the universe – in fact, as much as there is for the traditional explanation of these irregularities using the theory of cosmic inflation.

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The Huge-LQG (Large Quasar Group)

The Huge-LQG is a possible structure that could be one of the largest in the known universe. Having originally been identified as the largest, the Hercules-Corona Borealis Great Wall is bigger at 10 billion light years.

The Huge-LQG consists of 73 quasars, a quasar being a class of active galactic nuclei is essentially a superheated region of gas and dust that surrounds a supermassive black hole typically being 10-10,000 times the size of the Schwarzschild radius of the black hole. The existence of this structure defies Einstein’s cosmological principal which states that at large scales, the universe is approximately homogenous (meaning that the fluctuation in matter density throughout space can be considered small). It’s around 9 billion light years away from us, has a length of 1.24 gigaparsecs which is 4.0443 billion light years and a solar mass of 6.1 quintillion (that’s 6.1 quintillion times the mass of our sun and our sun is approximately 2 nonillion kg’s)!

On April 24, 1990, the Hubble Space Telescope was launched into orbit.

“No matter what Hubble reveals — planets, dense star fields, colorful interstellar nebulae, deadly black holes, graceful colliding galaxies, the large-scale structure of the Universe — each image establishes your own private vista on the cosmos.” - Neil deGrasse Tyson

Astronomers discover mysterious alignment of black holes

Deep radio imaging by researchers in the University of Cape Town and University of the Western Cape, in South Africa, has revealed that supermassive black holes in a region of the distant universe are all spinning out radio jets in the same direction – most likely a result of primordial mass fluctuations in the early universe. The astronomers publish their results in a new paper in Monthly Notices of the Royal Astronomical Society.

The new result is the discovery – for the first time – of an alignment of the jets of galaxies over a large volume of space, a finding made possible by a three-year deep radio imaging survey of the radio waves coming from a region called ELAIS-N1 using the Giant Metrewave Radio Telescope (GMRT).

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Why Dark Matter?

“Thanks to the power of gravitational lensing, where intervening mass acts like a lens to background light, distorting and magnifying it, we were able to reconstruct the mass. Lo and behold, it appeared (in blue) well-separated from where the X-rays and therefore the gas (in pink) was. And when we reconstructed how much of that mass is present in the form of dark matter, we find that it’s almost all of it. Again, normal matter, even if we change the laws of gravity, can’t account for these observations. Fast-forward to the present day, and we’ve found a great number of these colliding clusters that all show the same separation between the X-ray emitting normal matter and the mass, present in the form of dark matter.”

When we look out at the Solar System, the Sun dominates in terms of both light and mass. Responsible for nearly 100% of the light and for 99.8% of the mass, it stands to reason that stars would account for the vast majority of mass in the Universe. Yet when we apply what we observe of light and stars to structures like galaxies, clusters, and the large-scale structure of the Universe, not only do stars not get us there, but all the known forms of matter, including gas, dust, plasma and black holes, don’t get us there either. In order to account for the full suite of observations as astronomers’ and cosmologists’ disposal, there has to be something more to the Universe, outmassing normal matter by a 5-to-1 ratio, than all forms of normal matter can explain. At this point in time, the only explanation that nabs them all is dark matter.


Is Dark Matter Required For Life To Exist?

“Dark matter is the most mysterious, non-interacting substance in the Universe. Its gravitational effects are necessary to explain the rotation of galaxies, the motions of clusters, and the largest scale-structure in the entire Universe. But on smaller scales, it’s too sparse and diffuse to impact the motion of the Solar System, the matter here on Earth, or the origin and evolution of humans in any meaningful way. Yet the gravity that dark matter provides is an absolute necessity for allowing our galaxy to hold onto the raw ingredients that made life like us and planets like Earth possible at all. Without dark matter, the Universe would likely have no signs of life at all.”

Making up some 85% of the mass in our Universe, dark matter is necessary to explain the motions of individual galaxies, the grouping and clustering of assemblies of galaxies, the large-scale structure of the Universe and more. But on a much closer-to-home level, dark matter may be absolutely essential to the origin of life, too! Without dark matter, supernova explosions and starburst events would still create copious amounts of heavy elements, driven outwards by winds and the force of the explosions. But it’s the extra gravity of the dark matter that prevents most of this material from escaping, and allows it to take part in the formation of future generations of stars, to participate in rocky planet formation, and to deliver the ingredients necessary for life.

Go get the whole, detailed story today, and find out why life needs dark matter to exist after all!


Ask Ethan: Is this actually a hole in the Universe?

“What do you do about people and entities who actively harm the amount of knowledge that the general populace has in the world? After all, the opposite of knowledge isn’t ignorance, but rather misinformation posing as knowledge.”

There are plenty of scientific myths that go around, including many that were generated recently by so-called science communicators that actively harm public knowledge. One of them was a now-famous image of a dark nebula silhouetted against a star field, claiming that this was a hole in the Universe a billion light years across with no matter in it. Not only is the image itself a completely different picture – that of a tiny molecular gas cloud just 500 light years away – but the study that led to the conclusion of a “hole in the Universe” has that as only one of many possible interpretations. Far more likely is that we’re simply looking at a large, underdense region that’s well within the range of what’s normal and expected for our Universe.

Go get the full story on this week’s Ask Ethan!


Ask Ethan: How Do We Know The Universe Is 13.8 Billion Years Old?

“You’ve heard the story before: the Universe began with the Big Bang 13.8 billion years ago, and formed atoms, stars, galaxies, and eventually planets with the right ingredients for life. Looking at distant locations in the Universe is also looking back in time, and somehow, through the power of physics and astronomy, we’ve figured out not only how the Universe began, but its age. But how do we know how old the Universe is? That what Thys Hauptfleisch wants to know for this week’s Ask Ethan:

Ethan, how was the 13.8 billion years calculated? (In English please!)”

There’s a unique relationship between everything that exists in the Universe today – the stars and galaxies, the large-scale structure, the leftover glow from the Big Bang, the expansion rate, etc. – and the amount of time that’s passed since it all began. When it comes to our Universe, there really was a day without a yesterday, but how do we know exactly how much time has passed between then and now? There are two ways: one complex and one simple. The complex way is to determine all the matter and energy components making up the Universe, to measure how the Universe has expanded over the entirety of its cosmic history, and then, in the context of the Big Bang, to deduce how old the Universe must be. The other is to understand stars, measure them, and determine how old the oldest ones are.

The complex answer is more accurate, but more importantly, they both agree with each other. Get the details on this week’s Ask Ethan!


The early Universe’s most massive galaxy cluster revealed

“Discovered by Spitzer, it was rediscovered in archival Chandra data, and then reimaged for 28 hours. Also captured by Hubble, this cluster may, by today, be the most massive one in the visible Universe.”

13.8 billion years ago, the Universe as we know it was born with no stars, no clusters and no galaxies. But over time, gravitation has built up all sorts of complex structures, with the largest galaxy cluster today, El Gordo, weighing in at 3 quadrillion Suns. But back when the Universe was just a quarter of its present age, the cluster IDCS J1426.5+3508 already has a mass of 500 trillion Suns, a mass that’s been measured by three different methods. By time we fast-forward to today, this cluster is probably the most massive one contained within our visible Universe.


Joel Primack: Dark Matter Reveals the Structure of the Universe

We know that the dark matter has to be pretty cold - moving so slowly that its motion hardly matters - and that allows us to predict in great detail the large scale structure of the universe.

Directed / Produced by Jonathan Fowler, Elizabeth Rodd, and Dillon Fitton

via Big Think.


Throwback Thursday: The Little Bit Of Dark Matter We Know

“While large-scale structure tells us that the vast majority of the dark matter must be either cold or warm, we know that there is a tiny bit of hot dark matter, and that’s in fact what the neutrinos are! So while the large scale structure in the Universe agrees […] with cold dark matter […] we know that there’s a tiny mix — between 0.55% and 1.6% — of Hot Dark Matter, in the form of neutrinos, thrown in there!”

When Fritz Zwicky first calculated what the mass of a galaxy cluster needed to be to keep its galaxies moving at the observed speeds and compared it with the masses due to the starlight he saw, there was a huge discrepancy. The amount of gravity in the Universe, when compared to the amount of visible matter, didn’t match. Adding up all the known sources of normal matter didn’t quite get us there, either: only one-sixth of the matter can be made of protons, neutrons and electrons. The other 83% or so must be some form of dark matter, which is yet undiscovered. Well, except for around 1% of it, which we actually know must be in the form of neutrinos.