A DARK COSMIC WEB THAT TIES THE UNIVERSE TOGETHER

After counting all the normal, luminous matter in the obvious places of the universe (galaxies, clusters of galaxies and the intergalactic medium) about half of it is still missing. So not only is 85% of the matter in the universe made up of an unknown, invisible substance dubbed dark matter, we can't even find all the small amount of normal matter that should be there.

This is known as the "missing baryons" problem. Baryons are particles that emit or absorb light, like protons, neutrons or electrons, which make up the matter we see around us. The baryons unaccounted for are thought to be hidden in filamentary structures permeating the entire universe, also known as "the cosmic web".

The universe is permeated by a vast, invisible web, its tendrils weaving through space. But despite organizing the matter we see in space, this dark web is invisible. That's because it is made up of dark matter, which exerts a gravitational pull but emits no light. 

That is, the web was invisible until now. For the first time, researchers have illuminated some of the darkest corners of the universe. Now a new study, published in arXiv, offers a better view that will enable us to help map what it looks like.

A long time ago, the universe was hotter, smaller and denser than it is now. There wasn't much variation in density from place to place. space was much more cramped overall and no matter where you went, things were pretty much the same.

But there were tiny, random differences in density. Those nuggets had slightly more gravitational pull than their surrounding neighbourhood, so matter tended to flow into them and made them bigger. 

In this way,  they developed an even stronger gravitational influence which helped them pull more matter in and so on and so on for billions of years. Simultaneously, as the nuggets grew, the spaces between them emptied out. Eventually, the dense patches grew to become the first stars, galaxies and clusters, while the spaces between them became the great cosmic voids. 

The vast majority of matter in our universe is dark; it does not interact with light or with any of the normal matter. As a result, much of the cosmic web is completely invisible to us.

Now we can easily spot the great cosmic voids because there are no galaxies to illuminate these spaces as we know there is no matter there. It’s just truly empty space. But the grandeur of the cosmic web lies in the delicate lines of the filaments themselves. Stretching for millions of light-years, these thin tendrils of galaxies act like great cosmic freeways crossing black voids, connecting bright urban clusters.

Those filaments in the cosmic web are the hardest part of the web to study. They have some galaxies but not a lot. And they have all sorts of lengths and orientations; in comparison, the clusters and voids are geometric child's play. So, even though we've known of the existence of filaments, through computer simulations, for decades, we have had a hard time actually, you know, seeing them.

Recently, a team of astronomers made a major advancement in mapping our cosmic web, publishing their results at the arXiv database. First, they took a catalogue of luminous red galaxies (LRGs) from the Baryon Oscillation Spectroscopic Survey (BOSS) survey. LRGs are massive beasts of galaxies, and they tend to sit in the centres of dense blobs of dark matter. And if the LRGs sit in the densest regions, then lines connecting them should be made of the more delicate filaments.

But staring at the space between two LRGs isn't going to be productive; there isn't a lot of stuff there. So, the team took thousands of pairs of LRGs, realigned them and stacked them on top of each other to make a composite image.

Using this stacked image, the scientists counted all the galaxies that they could see, adding up their total light contribution. This allowed researchers to measure how much normal matter made up the filaments between the LRGs. Next, the researchers looked at the galaxies behind the filaments, and specifically, at their shapes.

As light from those background galaxies pierced the intervening filaments, the gravity from the dark matter in those filaments gently nudged the light, ever so slightly shifting the images of those galaxies. By measuring the shear (the amount of shifting), the team was able to estimate the amount of dark matter in the filaments.

That measure lined up with theoretical predictions (another point for the existence of dark matter). The scientists also confirmed that the filaments weren't entirely dark. For every 351 suns' worth of mass in the filaments, there was 1 suns' worth of light output.

It's a crude map of the filaments, but it's the first, and it definitely shows that while our cosmic web is mostly dark, it's not completely black. This will help reveal more mystery surrounding the cosmic web and provide us with a definitive census of the matter in the universe.

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NASA’s James Webb Space Telescope

Reaching a major milestone, engineers have successfully connected the two halves of NASA’s James Webb Space Telescope for the first time at Northrop Grumman’s facilities in Redondo Beach, California. Once it reaches space, NASA's most powerful and complex space telescope will explore the cosmos using infrared light, from planets and moons within our solar system to the most ancient and distant galaxies.

To combine both halves of Webb, engineers carefully lifted the Webb telescope (which includes the mirrors and science instruments) above the already-combined sun shield and spacecraft using a crane. Team members slowly guided the telescope into place, ensuring that all primary points of contact were perfectly aligned and seated properly. The observatory has been mechanically connected; the next steps will be to electrically connect the halves and then test the electrical connections. 

“The assembly of the telescope and its scientific instruments, sun shield and the spacecraft into one observatory represents an incredible achievement by the entire Webb team,” said Bill Ochs, Webb project manager for NASA Goddard Space Flight Center in Greenbelt, Maryland.  “This milestone symbolizes the efforts of thousands of dedicated individuals for over more than 20 years across NASA, the European Space Agency, the Canadian Space Agency, Northrop Grumman, and the rest of our industrial and academic partners.”

Next up for Webb testing, engineers will fully deploy the intricate five-layer sun shield, which is designed to keep Webb's mirrors and scientific instruments cold by blocking infrared light from the Earth, Moon and Sun. The ability of the sunshield to deploy to its correct shape is critical to mission success.

“This is an exciting time to now see all Webb’s parts finally joined together into a single observatory for the very first time,” said Gregory Robinson, the Webb program director at NASA Headquarters. “The engineering team has accomplished a huge step forward and soon we will be able to see incredible new views of our amazing universe.”

Both of the telescope’s major components have been tested individually through all of the environments they would encounter during a rocket ride and orbiting mission a million miles away from Earth. Now that Webb is a fully assembled observatory, it will go through additional environmental and deployment testing to ensure mission success. The spacecraft is scheduled to launch in 2021.

Webb will be the world's premier space science observatory. It will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international project led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.

The James Webb Space Telescope (sometimes called JWST or Webb) will be a large infrared telescope with a 6.5-meter primary mirror.  The telescope will be launched on an Ariane 5 rocket from French Guiana in 2021.

Webb will be the premier observatory of the next decade, serving thousands of astronomers worldwide. It will study every phase in the history of our Universe, ranging from the first luminous glows after the Big Bang, to the formation of solar systems capable of supporting life on planets like Earth, to the evolution of our own Solar System.

Several innovative technologies have been developed for Webb. These include a primary mirror made of 18 separate segments that unfold and adjust to shape after launch. The mirrors are made of ultra-lightweight beryllium. Webb’s biggest feature is a tennis court-sized five-layer sunshield that attenuates heat from the Sun more than a million times. The telescope’s four instruments - cameras and spectrometers - have detectors that are able to record extremely faint signals. One instrument (NIRSpec) has programmable micro shutters, which enable observation up to 100 objects simultaneously. Webb also has a cryocooler for cooling the mid-infrared detectors of another instrument (MIRI) to a very cold 7 K so they can work.

Webb is an international collaboration between NASA, the European Space Agency (ESA), and the Canadian Space Agency (CSA). The NASA Goddard Space Flight Center is managing the development effort. The main industrial partner is Northrop Grumman; the Space Telescope Science Institute will operate Webb after launch.

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Two Supermassive Black Holes On A Collision Course

Supermassive black holes are thought to be at the centre of most galaxies, and they are huge. The Milky Way’s own supermassive black hole, Sagittarius A*, is about 4 million times the mass of our sun. But scientists have just spotted two absolute behemoths, that dwarf Sagittarius A*, and they are on a collision course. It’s the first time such massive black holes have been spotted this close together, and it could help us detect a hum of gravitational background noise. 

Of course “close” is a relative term and in this particular instance when scientists say close, they mean about 1,400 light-years apart. The black holes are located about 2.5 billion light-years from us, so since the light from them took 2.5 billion years to reach us, we are observing them as they were 2.5 billion years ago.

Coincidentally, the scientists who discovered them estimate that that’s about how long it will take before they collide. They could be merging with each other right now, unleashing huge gravitational waves millions of times more powerful than those previously detected by LIGO and Virgo. Of course, because of how far away they are, the waves won’t reach us for 2.5 billion years.

That is if they happen at all. We have observed stellar-mass black holes merging, but we are not sure if their supermassive counterparts can join forces by merging too. It seems odd, these things each have an incredible gravitational pull, why wouldn’t they run head-on into each other?

Right now the thinking is when galaxies merge, their supermassive black holes begin to orbit each other. As they do, dust and stars in between them sap some of their energy, causing their orbits to tighten. But as they get closer, that region of space between them shrinks, until theoretically there’s no way to lose more energy.

The two black holes find themselves stably orbiting each other but never getting closer. Some studies suggest that happens at about 1 parsec, or roughly 3.2 light-years distance, so it’s known as the final parsec problem. But all that is theoretical, and we’re lacking more observational data.

It’s possible our predictions are wrong and black holes of this size do merge instead of stalling out a parsec apart. Unfortunately, black hole pairs are very hard to spot. Remember how we mentioned earlier this is the closest we have seen two this big and they’re 1,400 light-years away from each other?

Because 1 parsec is way too close for us to distinguish two supermassive black holes apart. And now that we have found these two, it’s not like we can wait around 2.5 billion years to see if they merge. we will probably be dead by then. But since we have spotted these two, we can start to guess how common merging supermassive black holes would be. 

Based on their findings the scientists estimate that optimistically there are 112 black holes whose gravitational waves we can detect from Earth. This would make a kind of constant hum, the scientists likened this gravitational background noise to a chorus of chirping crickets. 

Normally it’d be impossible to distinguish one cricket from another. But if there’s no final parsec problem and they can merge, it should create a massive chirp at the moment they collide. When that happens, the waves will be at frequencies outside what LIGO and Virgo can detect. So instead, scientists will have to keep a close eye on pulsars, special stars that send out radio waves at regular intervals.

If a supermassive merger stretches or compresses the space between us and a pulsar, the rhythm will appear to be thrown off. These frequency changes are so small, just tens to hundreds of Nanohertz, it will require close to a decade of observation to spot the weak signal hiding in the noise. 

They are searching for more pairs of black holes to refine their prediction further, but it’s possible we never detect a merger and the final parsec problem is insurmountable after all. And while LIGO can’t detect supermassive mergers, it was recently upgraded, making it 40% more sensitive as it continues its hunt for merging stellar-mass black holes.

Source:-  The Astrophysical Journal Letters :- http://bit.ly/2z6YfJx

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Did The Big Bang Created All The Elements In Periodic Table?

My absolute favourite fact in the universe is that we are made of dead stars. And that's literally true. The atoms in our bodies were actually created inside the cause of stars that then exploded and died or unravelled into space. And so the question about the periodic table is very interesting. What was the periodic table like at the beginning of the universe, the moment of the Big Bang?

Well, one thing Astronomers say is that it was a lot simpler. The Big Bang, when it went off, produced basically three elements. Almost everything was hydrogen. There was a little bit of helium, and a tiny, tiny little smattering of lithium as well. So those three elements were around just a couple of minutes after the formation of the universe, but nothing else.

And that's actually not a theory. That's actually something we can observe. One of the wonderful things about being an astronomer is, as you look out into space, farther and farther away, the light has taken longer to get to you. And the farthest we can see is actually back to a time only about 400,000 years after the Big Bang.

At that time, there was nothing but very hot hydrogen gas, and a little bit of helium and lithium as well. So everything larger than that, every atom more complex had to be formed inside a star. Over time, stars like the sun are pretty good, over the life cycle, at producing things like carbon and oxygen. They don't really get much more far off the periodic table than that. 

If you want to go any farther than the element, iron, you actually need a very violent explosion, a supernova explosion. The cores of very massive stars and by that, I mean stars that are 10, 20, maybe even as much as 50 times the mass of the sun, their cores are much hotter, because the gravity crushes things down and the temperature goes up many, many millions of degrees hotter than inside the sun. So these stars can actually form bigger and bigger atoms.

The hotter the temperature, the denser the core, the more you can ram things together and actually, form bigger and bigger atoms over time. But there's a very special thing that happens when you get to the atom, iron. And it's something you have actually heard about but you may never have thought of.

When people think about getting energy out of a nuclear reaction-- you've heard about fusion reactions. So like a fusion bomb, actually, takes hydrogen, fuses it together to make helium and that creates energy. The sun also runs on that particular reaction, fusing hydrogen together.

Then you also heard that there's something called fission. And this is how, say, a uranium bomb would work. A uranium nucleus has many, many particles inside it you actually get energy out of breaking it up and forming two smaller nuclei that are actually a bit denser and they hold together better. And so you get energy out of breaking them apart.

So, the element, iron, is exactly halfway between those two processes. So you have been getting energy by fusing things together until you get to iron. And iron is the first nucleus where you don't get any energy out of fusing. From anything bigger, now, you get energy out of ripping apart, fission. 

So iron is what sets off a supernova explosion. When a star tries to fuse iron together, it absorbs energy. And that's not great for the star. The core collapses. And that huge collapse creates this giant wave of heat and the formation of many, many new elements after that. So anything heavier than iron has to be created in a supernova explosion.

Now, there are some elements, heavier still, that even supernova energies don't really get up quite high enough to make. And this is something we only found out recently, in the last couple of years. Elements like gold, platinum, bismuth and all the big things, like uranium and all of the really large atoms; they have to be formed by something that seems almost preposterous, but we have observed this happening-- two neutron stars colliding.

So neutron stars are the cores of dead stars. They are super-compressed. The density of a neutron star is about a Mount Everest worth of mass in every square centimetre. So think about crushing Mount Everest into a little cube. The entire star, which is only about 10 miles across, is actually that density. And that means you have a tremendous amount of nuclear components neutrons, protons really close together. And two neutron stars collide.

When that happens, you make all of these very heavy elements up, like gold, and platinum, uranium and all the big stuff. And again, this is not something that we just know theoretically. We actually have observed this happening. Recently, we observed two neutron stars colliding. And in that single explosion, 10,000 times the mass of the Earth in gold came out of that explosion. It was tremendous. So, we definitely know where those atoms come from now. We observed that happening. 

So to recap, at the beginning of the universe, you had three elements mostly hydrogen, a little bit of helium, a tiny bit of lithium. Now we have the entire periodic table. And a lot of those are formed in stars like the sun. Anything past iron has to be formed much more violently, in a supernova explosion or in the case of very large atoms, two colliding neutron stars. And over billions of years, we have filled out the periodic table that way.

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Problem With Uranus

Suppose you are standing at the North Pole of Uranus, by the way, you can't you would sink right in, But if you could you would see the Sun appear on the horizon circle higher and higher for 21 years. Then circle back down to the horizon over the course of another 21 years. Once the Sun went below the horizon, you would experience another 42 years of darkness before the Sun appeared again now that's a long wait. But why does this happen? 

It all started with something huge that smashed Uranus some 1 billion years ago and locked it over on its side. While the other planets looked like spinning tops as they revolve around the Sun Uranus is flipped on its side and appears to be rolling around the Sun. This has a weird and dramatic effect on the seasons on Uranus.

Uranus like Earth has four seasons, however, the seasons on earth and Uranus are very different. It takes Earth 365 days to orbit around the Sun, but it takes Uranus the equivalent of 84 years here on earth. So 1 Uranus year is 84 earth years long and each season on Uranus lasts 21 earthly years. But it's the tilt of the planet that makes this season weird.

It's unusual seasons just as Earth's seasons are caused by planet’s own tilt on its axis, but the tilt of our planet is very different. Earth's axis is tilted 23.5 degrees from the plane of its orbit around the Sun whereas with respect to its orbit the axis of Uranus is tilted at an angle of 98 degrees.

During the summer earth has a Midnight Sun at its poles and a long polar night in winter, but those dark and bright times at Earth's poles only affect a smaller part of our planet and don't last nearly as long as they do on Uranus. During Uranus's winter/summer season the winter side of the planet doesn't see the Sun at all for 21 long years. Meanwhile, the summer side of the planet has continuous daylight. 

However, during its spring and fall seasons, Uranus is oriented in its orbit so that sunlight strikes its equatorial region, which drastically affects the lengths of its days. Uranus spins on its axis about every 17 hours and 14 minutes making that the length of its day and night. Day and night cycle so for much of the planet where there had once been a continuous day or continuous night lasting decades on an earthly scale. Now there is a relatively rapid change between day and night all depending solely on the seasons. 

You can at last think of Uranus as one of the weirdest planets of the solar system and also, of course, the one with the funniest name.

Also Read:- Discovery Of Twelve New Moons Orbiting Jupiter

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Mystery Around Hypatia Stone

From snazzy banded agates to volcanic elephants, there are some pretty weird rocks out there. But the weirdest ones geologists find might be those that fall from space. One of them called the Hypatia stone, it might be, the strangest of them all. In fact, all signs currently suggest that this rock’s origin story is older than the solar system itself and if it is not well, we are going to have to rethink what we know about our cosmic neighbourhood.

The Hypatia stone was found in 1996 by a geologist in the southwest Egyptian Sahara. It is named after the first female astronomer and mathematician who managed to make the history books.

The stone was discovered in fragments no bigger than a centimetre across and in total, the pieces added up to a volume only about 20 cubic centimetres. Technically, it isn’t considered a meteorite, because the Meteoritical Society requires 20% of a rock’s original mass to be present to earn that title. And scientists have chipped this thing apart and sent pieces to so many labs that it no longer fits the bill.

But it’s definitely from space. When its extraterrestrial origins were confirmed in 2013, scientists assumed it was the very first comet nucleus or the rocky, central part of a comet, to be found on Earth. But its story is a bit more complicated and interesting.

First, exactly when the stone struck our planet is hard to pin down. It was found in an area of the Sahara which is full of these special rocks called Libyan Desert Glass, which are believed to have been created by a meteorite impact 28 million years ago. But the relationship between the Hypatia stone and this glass is far from certain. We are also not positive how big this rock was when it initially entered Earth’s atmosphere.

Based on its amount of a certain type of neon, we think it could not have been more than several meters in diameter. Or if it were bigger, the Hypatia stone itself had to have come from the upper few meters. These basic details are important to figure out, but what’s really strange about the Hypatia stone is what researchers discovered once they started analysing its composition. Because from what we can tell, Hypatia’s chemical makeup isn’t just out of this world.

It’s out of the entire solar system! See, everything in our neighbourhood formed out of the same cloud of dust and gas. And since astronomers believe that the cloud was relatively homogeneous, the rocky bits that formed should all have roughly the same chemical makeup.

But in 2015, scientists revealed that the Hypatia stone is different. It has a composition unlike any other solar system object studied in a lab. For example, its amount of the isotope nitrogen-15, a type of nitrogen with an extra neutron, was way off for it to be from a standard Comet.

Astronomers also found a type of xenon that’s created when one iodine isotope, one that predates the solar system, undergoes radioactive decay. So something about this thing totally isn’t normal. And in 2018, we got an even deeper analysis.

In February 2018, a team of astronomers announced that they would identify two separate, yet intermingled, matrices in the Hypatia stone, kinda like finding two different batters in the same cake. The matrices themselves had to have formed when the solar system did because Hypatia needed a cloud of dense interstellar dust to form. But they had the opposite composition of carbon and silicon that common meteorites do.

The ones we normally see, called chondritic meteorites, are low in carbon and high in silicon, but Hypatia has lots of carbon and basically no silicon. So again, not normal. But what was even more surprising about this analysis is that one of those matrices was also chock-full of deposits or inclusions. And each of them likely existed before the entire solar system! This includes moissanite grains, which are commonly a small part of some meteorites but are considered to be mostly pre-solar.

They also found a nugget of pure metallic aluminium in Hypatia, which is super rare in solar system rocks. And there were also a lot of these organic molecules called polycyclic aromatic hydrocarbons or PAHs, which are a big part of interstellar dust. PAHs are also inside certain comets and asteroids, so finding them in the Hypatia stone wasn’t unusual, but the abundance of them was. Conveniently, these PAHs were also a big reason we are able to study the stone today.

Many of them were turned into a crust of tiny diamonds, likely when Hypatia crashed into the Earth, and they protected and preserved the inside of the rock for millions of years. But that doesn’t explain where they came from. And there were other compounds found that haven’t been observed in any studied space rock, too. So the Hypatia stone is still completely unique.

At least as far as we know. Although it’s a pretty compelling case, we will still need further analysis of certain isotopes before we can definitively say that parts of this rock existed before the Sun. But the exciting news is, the authors of that 2018 paper hope to get that research out ASAP.

So, even if Hypatia turns out not to be pre-solar, that might be even weirder. That would imply that the early solar system wasn’t homogeneous after all, despite the generally accepted view. So we would have to change the way we think about our neighbourhood’s history.

Based on what we know so far, astronomers can at least tell that the stone had to have formed in a super cold environment, one below about -200°C. So if it is from around here after all, that likely means Hypatia had to have formed out in the Kuiper Belt where Pluto lives, or even farther away, like in the distant, mysterious Oort cloud.

We don’t actually know a lot about the composition of all the bodies that far out there, so it could totally turn out that there are other Hypatia-like space rocks. Mostly, all this means means we just have to keep looking. But no matter what the answer to this mystery is going to a cool one.

Also Read:-Pulsed Plasma Thrusters

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Let's Understand Black Hole

Black holes are among the most fascinating objects in our universe and also the most mysterious. A black hole is a region in space where the force of gravity is so strong not even light the fastest known entity in our universe can escape. 

The boundary of A black hole is called the event horizon a point of no return beyond which we truly can not see. When something crosses the event horizon it collapses into the black hole's singularity an infinitely small infinitely dense point for space-time and the laws of physics no longer apply.

Scientists have theorized several different types of black holes with stellar and supermassive black holes being the most common. Stellar black holes form when massive stars die and collapse the roughly 10 to 20 times the mass of our Sun and scattered throughout the universe. There could be millions of these Stellar black holes in the Milky Way alone. 

Supermassive black holes are giants by comparison measuring millions even billions of times more massive than our Sun. Scientists can only guess how they form but we do know they exist at the centre of just about every large galaxy including our own. Sagittarius a the supermassive black hole at the centre of the Milky Way has a mass of roughly 4 million Suns and has a diameter about the distance between the earth and our Sun.

Because black holes are invisible the only way for scientists to detect and study them is to observe their effect on nearby matter. This includes accretion disks, a disk of particles that form when gases and dust fall toward a black hole. And quasars Jets of particles that blast out of supermassive black holes.

Black holes remained largely unknown until the 20th century. In 1916 using Einstein's general theory of relativity a German physicist named Karl Schwarzschild calculated that any mass can become a black hole if it were compressed tightly enough. But it wasn't until 1971 when theory became reality. Astronomers studying the constellation Cygnus discovered the first black hole. 

An untold number of black holes are scattered throughout the universe, Constantly warping space and time altering entire galaxies. And endlessly inspiring both scientists and our collective imagination

Also Read:- Can Gravity Beat Dark Energy?

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Can Gravity Beat Dark Energy?

Although it might not seem obvious when you look at the night sky, but we live in a universe that is expanding faster by the instant. Every day, stars fall over the horizon of what we can see, as the space between us stretches faster than their light can reach us. And we can never know what exists past that horizon. So you might imagine or you might have heard about, a far-off future, where space is stretching faster and faster and where all of the stars and galaxies are over that edge. A future where Earth will be left with a dark, empty sky. But luckily for us, or, at least, for hypothetical future earthlings, that’s not actually the case. Because the universe is expanding but not all of it.

We have known that the universe is expanding since the 1920s, but we only discovered that the expansion is accelerating in the 1990s, thanks to the Hubble Space Telescope. Hubble was the first tool to measure really precise distances to supernovas out near the edge of the observable universe. And it showed us that out there, ancient galaxies and the supernovas in them are zooming away from us faster than anywhere else. In fact, astronomers realized that they were flying away even faster than expected. Which, at first, didn’t make sense.

At the time, we thought the universe was dominated by gravity, which pulls things together. So seeing everything accelerate apart was weird. It would kind of be like if you kicked a ball uphill and saw it speed up instead of coming back down to you. Because of this, scientists concluded that there had to be something else going on, something pushing these galaxies apart. They came to call that thing dark energy. Decades later, dark energy is still really mysterious and there is a lot we don’t understand about it.

One explanation is that it’s a property of empty space. This means that space itself, with no stuff in it at all, has dark energy. And that energy pushes space apart, creating new space, which in turn has dark energy, which pushes space apart, creating new space, which in turn has dark energy, which You get it. If dark energy is a property of space, that also means you can’t dilute it. Its density will always be the same, no matter how much space expands.

Of course, that density is also pretty small. If you borrow Einstein’s “E=mc2” trick and express energy as mass, it is equivalent to about one grain of sand in a space the size of the entire Earth. But if you average that over the whole universe, which is mostly empty space, there is more dark energy than anything else. So it dominates and the universe as a whole expands. That’s why the most ancient galaxies are also moving away faster than before.

It has taken a long time for their light to reach us, so the universe has had more time to stretch. Now, this might all make dark energy seem super strong. After all, it makes up more than two-thirds of all the stuff in the universe and it’s pushing apart entire galaxies. But it is only powerful because there is a lot of it.

Within small spaces, especially those full of planets and stars, dark energy is actually pretty weak. Like, the gravity between the Sun and the Earth or the Earth and the Moon is more than enough to overpower the repulsive dark energy between them. In fact, most of the universe’s mass is concentrated in galaxy clusters and these pockets of matter are completely immune to dark energy. They are simply not expanding. 

It doesn’t mean the expansion is negligible, like how technically your gravity pulls ever-so-slightly on Earth but it is not enough to actually notice. It means that, as far as we know, dark energy is truly not stretching our galaxy at all. This is because it’s not a force like gravity, so it works a little differently.

To understand how, think about pushing on a heavy door. If you push lightly, it won’t open. Push a little harder and it still won’t. But if you push hard enough, once you cross a certain threshold of pushing, it will open. That door is gravity and within a galaxy, there’s just not enough dark energy to push it open. 

In other words, gravity is too strong. So our galaxy will never expand, because if it can’t stretch even a little, then it can’t create more space. And that means the amount of dark energy inside will never grow. Of course, this isn’t something we have been able to directly observe, like by looking at other galaxies. But multiple observations have shown us what dark energy is like and they all suggest this should be true.

Eventually, in the really distant future, fewer and fewer galaxies will be visible from Earth. And in 100 billion years or so deep space will be almost empty. But if Earth were still around by then, which, admittedly, is pretty unlikely, we would still have a beautiful night sky. Even as the universe stretches, the glow of our galaxy will still be overhead and we will have stars, constellations and even a handful of galaxies bound by gravity to ours. All because dark energy just can’t get a foothold around here. Of course, this will only last until the heat death of the universe but that’s another story.

Also Read:- The Big Rip Due To Dark Energy

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The Big Rip Due To Dark Energy

Even though nobody else will be around to see it, scientists are fascinated by the end of the universe. It is kind of like the Big Bang there's just something so interesting about knowing where your atoms came from and where they are ultimately going to go in billions of years. Right now, there are a few ideas about how everything could end, where everything is spread so thin that activity basically stops.

Except, based on the results from a paper published in Nature Astronomy, that might not actually be true. Instead, there is a chance that everything in existence will eventually be ripped apart. And it would all be thanks to dark energy. Scientists think it makes up about 70% of the stuff in the universe and that it is the reason the expansion of the universe is accelerating. But there is a lot they are still figuring out.

Some of their research into dark energy has involved tools called standard candles. Standard candles are objects or events of known brightness that are used to measure distance in the far-off universe. Essentially, if you know how bright something should be up close, then how bright it actually looks indicates how far away it is.

For decades, the most important standard candle has been a special kind of exploding star called a type a supernova. These events always have the same brightness and in the 1990s, they allowed scientists to discover that the universe’s rate of expansion was accelerating. But what is really important for this recent study is that all the estimates provided by type 1a supernovas also indicate that the density of dark energy is fixed.

There is a lot of math involved, but this fact is a big reason they believe the Big Freeze is most likely. The problem is, you can only see so far with any given candle before it gets too dim and type 1a can’t take us back to the beginning of the universe. Because light can only move so fast, looking deep into space is like looking back in time. And these supernovas only allow us to see what things were like 4.5 billion years or so after the Big Bang.

Admittedly, there are some data sources like one called the Cosmic Microwave Background, that can tell us what things were like around 400 thousand years after the Big Bang. But that Background actually seems to disagree with what supernovas say about the expansion rate, which has had astronomers debating different options for years. There is also been a 4-billion-year gap between the two data sources, so it has been hard to figure out what’s going on.

That’s where last week’s news comes in. In their paper, a pair of astronomers proposed a new kind of standard candle, one that can let us peer back to that sweet spot just 1-2 billion years after the Big Bang. Their idea relies on quasars, rapidly-growing black holes that are among the universe’s brightest objects. Although quasars vary a lot in brightness, the authors claim that the ratio of ultraviolet brightness to X-ray brightness is not only more predictable but also reliable enough to indicate a quasar’s distance.

They point out that, at distances where both type 1a supernovas and quasars are visible, they provide comparable results, too. But the key is, farther from Earth, and further back in time, only quasars are visible. And after looking at some of those super-distant objects, the authors claim to have made a surprising observation: In the first couple billion years after the Big Bang, the growth rate of the universe didn’t match the predictions made by the supernova-based models. Back then, things seemed to be getting bigger more slowly than expected.

That implies that the amount of dark energy driving that expansion hasn’t been constant after all. Instead, it has been increasing over time. It sounds like a wild idea, but it would help explain why there isn’t a perfect match between the expansion rate we see from supernovas and that of Cosmic Microwave Background. So it is not like there is no foundation for it. But still, before they rewrite your Astronomy textbook, it is important to remember two things. One, these results will need a lot of confirmation before they are accepted into the mainstream theory. And two, scientists have effectively no clue what dark energy actually is.

So it is not even worth asking questions like what would be generating more and more of it, because we don’t even know what IT is. But if these results are true, there is one thing we do know, instead of ending in the Big Freeze, the universe would eventually end in the so-called Big Rip, where ever-increasing dark energy tears apart every particle until there’s nothing left and no one to see it. But the assumption is that it’s not such a big deal, because there is no way we would be around by then.

Reference:- Quasars as standard candles
Also Read:- Let's Understand Wormholes

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Let's Understand Wormholes

Whether it’s Star Trek, Stargate or Babylon 5 wormholes have been showing up in science fiction for a long time. They are just a super convenient tunnel to another part of the universe, a way for sci-fi writers to send their characters across huge distances in the blink of an eye. And it turns out that they are not just science fiction: wormholes could really exist. But if they do, they are much weirder than anything we could make up.

In physics, a wormhole is known as an Einstein-Rosen bridge. It is named after Albert Einstein and another physicist, Nathan Rosen. They came up with the idea together in 1935 and showed that according to the general theory of relativity, wormholes are a definite possibility. A wormhole acts like a tunnel between two different points in spacetime, which is just the continuum of space and time that makes up the fabric of the universe.

According to general relativity, gravity works by bending spacetime. Planets and Stars act like a weight in the fabric of the universe, creating a curve. It can be kind of hard to picture what spacetime is, let alone what it would mean for it to bend, so physicists often talk about it by using weights on a stretched bedsheet as an analogy. Earth would be like a big bowling ball making a big dip in the sheet and when something gets too close to the planet and it’s pulled in by the gravity, it’s like it’s falling into that dip in the sheet. 

But if spacetime can be curved, it can also be twisted and shaped in other ways, like by connecting two different places with a tunnel. It’s kind of like poking two holes into that bedsheet, folding it over and then stretching the fabric so that the edges of the holes can get together and you just sew them into a tunnel. That’s a wormhole in a bedsheet. But because wormholes don’t seem to violate the laws of physics does not mean that they actually exist; they are just technically possible. And unfortunately, we haven’t yet detected any and we aren’t even sure how they would form.

If wormholes do exist, one reason we might not have spotted them is that they could be hiding behind black holes. A black hole is what happens when there is so much mass squeezed into an object that it ends up with such a strong force of gravity that even light can’t escape its pull. Once you get too close to a black hole, you are toast: there is no escaping from being smashed into oblivion. In the bedsheet model, black holes and wormholes look very similar, they both have a steep falloff that seems to go on forever. Except, with a wormhole, the steep drop actually leads somewhere.

According to general relativity, wormholes could have black holes at each end, meaning that after diving into a black hole on one end, the energy that was once your body could get spewed out somewhere totally different in the universe. Of course, you would not survive that trip. All that would be left is radiation and subatomic particles. Then there are white holes, which are the opposite of black holes: They spew out matters with such force that it would be impossible to enter them. If black holes are infinite weights on a bedsheet, white holes would be like hills: objects pushing up on the bedsheet.

Like wormholes, these are a thing that could exist, the math does check out, we are just not sure how they would form. But we know that if they exist, they could be found at either end of a wormhole, too. So, maybe if there was a black hole at one end of the wormhole and a white hole at the other, we could go in the black hole end and be blasted out the white hole end, Maybe. But you would still probably be crushed by the black hole in the process. Not to mention it would definitely be a one-way trip.

There are a few other problems with wormholes. For one thing, they would probably be dangerous. Sudden unexpected collapse, weird exotic particles, a ton of radiation. In fact, travelling through a wormhole could instantly collapse it, because they would probably be unstable. And then there is the fact that wormholes might not be a shortcut at all. A random wormhole could easily be a longer-than-normal path. Size is also a problem. A real-life wormhole could be too small for us to travel through. Not to mention the travel time, which could be millions or billions of years, making some wormholes pretty useless.

So, that’s a lot of problems. The biggest hope actually comes from how little we know. A lot of this depends on physics that we haven’t quite worked out yet or on facts about our universe’s history and geometry that we just don’t know for sure. Once we have all that figured out, the final barrier would be technology and opportunity. Right now, we definitely don’t know how to make a wormhole and we would have to be super lucky to find one that is useful to us if they exist at all.

So, it’s pretty clear that we won’t be sliding through any wormholes anytime soon. But we know that they could be out there, hiding in some of the most extreme places in the universe. And who knows? Maybe our ideas about wormholes will be totally different in the future. People living just a few hundred years ago couldn’t have even imagined particle accelerators or internet. Until we find one or build one Let's will keep exploring the universe.

Also Read:- Let's Understand Naked Singularities

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