Meredith is a Postdoctoral Researcher in the Department of Astronomy at the University of Washington. She writes software to prepare for the coming onslaught of data from the Large Synoptic Survey Telescope and studies weird binary stars. She is also the lead organizer of the ComSciCon-Pacific Northwest workshop for STEM graduate students in Seattle this March. Meredith holds degrees in physics and astronomy from Harvey Mudd College, San Diego State University, and New Mexico State University. When she’s not science-ing or telling people all about it, she plays viola, volunteers at summer camp, and advocates for more equity and less light pollution.
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Clearly I need to learn to be more specific when I write these articles. Everything time I open my mouth, I need to prepare for the collective imagination of the viewers.
We did a whole article about the biggest things in the Universe, and identified superclusters of galaxies as the best candidate. Well, the part of superclusters actually gravitationally bound enough to eventually merge together in the future. But you had other ideas, including dark energy, or the Universe itself as the biggest thing. Even love? Aww.
One intriguing suggestion, though, is the idea of the vast cosmic voids between galaxies. Hmm, is the absence of something a thing? Whoa, time to go to art school and talk about negative space.
Ah well, who cares? It’s a super interesting topic, so let’s go ahead and talk about voids.
When most people imagine the expansion of the Universe after the Big Bang, they probably envision an equally spaced smattering of galaxies zipping away from one another. And that’s pretty accurate at the smallest scales.
Credit: NASA, ESA, and E. Hallman (University of Colorado, Boulder)
But at the largest scales, like when you can see billions of light-years in a cube that fits on your computer screen, then a larger structure starts to take shape.
It looks less like an explosion, and more like a tasty tasty sponge cake, with huge filaments, walls, and the vast gaps in between. The gaps, the voids, the supervoids, are the point of today’s article, but to understand the gaps, we’ve got to understand why the Universe is clumped up the way it is.
Run the Universe clock backwards, all the way to the beginning, to a fraction of a second after the Big Bang. When the entire cosmos was compressed down into a tiny region of superheated plasma.
Although it was mostly uniform in density, there were slight variations – quantum fluctuations in spacetime itself. And as the Universe expanded, those differences were magnified. What started out as tiny differences in the density of matter at the smallest scale, turned into regions of higher and lower density of matter in the Universe.
Here we are, 13.8 billion years after the Big Bang, and we can see how the microscopic variations at the beginning of time were magnified to the largest scales. Instead of individual galaxies, we see huge walls containing thousands of galaxies; filaments of galaxies connect in nodes. These structures are huge; hundreds of millions of light-years across, containing thousands of galaxies. But the gaps, the voids, between these clusters can be even larger.
Astronomers first started thinking about these voids back in the 1970s, when the first large-scale surveys of the Universe were made. By measuring the redshift of galaxies, and determining how fast they were speeding away from us, astronomers started to realize that the distribution of galaxies wasn’t even.
Red-shifted galaxies. Credit: ESO
Some galaxies were relatively close, but then there were huge gaps in distance, and then another cluster of galaxies collected together.
Over the last few decades, astronomers have built sophisticated 3-dimensional models that map out the Universe in the largest scales. The Sloan Digital Sky Survey, updated in 2009, has provided the most accurate map so far. The Large Synoptic Survey Telescope, destined for first light in a few years will take this to the next level.
The largest void that we currently know of is known as the Giant Void (original, I know), and it’s located about 1.5 billion light-year away. It has a diameter of 1 billion to 1.3 billion light-years across.
To be fair, these regions aren’t really completely empty. They just have less density than the regions with galaxies. In general, they’ve got about a tenth the density of matter that’s average for the Universe.
Galaxy MCG+01-02-015 is so isolated that if our galaxy, the Milky Way, were to be situated in the same way, we would not have known of the existence of other galaxies until the 1960s Credit: ESA/Hubble & NASA and N. Gorin (STScI). Acknowledgement: Judy Schmidt
Which means that there’s still gas and dust in these regions, as well as dark matter. There will still be stars and galaxies out in the middle of those voids. Even the Giant Void has 17 separate galaxy clusters inside it.
You might imagine continuing to scale outward. Maybe you’re wondering if the this spongy distribution of matter is actually just the next step to an even larger structure, and so on, and so on. But it isn’t. In fact, astronomers call this “the End of Greatness”, because it doesn’t seem like there’s any larger structure to the Universe.
As the expansion of the Universe continues, these voids are going to get even larger. The walls and filaments connecting clusters of galaxies will stretch and break. The voids will merge with each other, and only gravitationally bound galaxy clusters will remain as islands, adrift in the expanding emptiness.
The full scale of the observable Universe is truly mind boggling. We’re here in this tiny corner of the Local Group, which is part of the Virgo Supercluster, which is perched on the precipice of vast cosmic voids. So much to explore, so let’s get to work.
Artistic impression of a star going supernova, casting its chemically enriched contents into the universe. Credit: NASA/Swift/Skyworks Digital/Dana Berry
We’ve written quite a few articles on what happens when massive stars fail as supernovae. Here’s a quick recap.
A star with more than 8 times the mass of the Sun runs out of usable fuel in its core and collapses in on itself. The enormous amount of matter falling inward creates a dense remnant, like a neutron star or a black hole. Oh, and an insanely powerful explosion, visible billions of light-years away.
There are a few other classes of supernovae, but that’s the main way they go out.
But it turns out some supernovae just don’t bring their A-game. Instead hitting the ball out of the park, they choke up at the last minute.
They’re failures. They’ll never amount to anything. They’re a complete and utter disappointment to me and your mother. Oh wait, we were talking about stars, right.
So, how does a supernova fail?
In this artist’s conception, a supernova explosion is about to obliterate an orbiting Saturn-like planet. Credit: David A. Aguilar (CfA)
In a regular core collapse supernova, the infalling material pushes the star denser and denser until it reaches the density of 5 billion tons per teaspoon of matter. The black hole forms, and a shockwave ripples outward creating the supernova.
It turns out that the density and energy of the shockwave on its own isn’t enough to actually generate the supernova, and overcome the gravitational force pulling it inward. Instead, it’s believed that neutrinos created at the core pile up behind the shockwave, and give it the push it needs to blast outward into space.
In some cases, though, it’s believed that this additional energy doesn’t show up. Instead of rebounding from the core of the star, the black hole just gobbles it all up. In a fraction of a second, the star is just… gone.
According to astronomers, it might be the case that 1/3rd of all core collapse supernovae die this way, which means that a third of the supergiant stars are just disappearing from the sky. They’re there, and then a moment later, they’re not there.
And this is all that remains. Image Credit: NASA
Seriously, imagine the forces and energy it must take to swallow an entire red supergiant star whole. Black holes are scary.
Astronomers have gone looking for these things, and they’ve actually been pretty tricky to find. It’s like one of those puzzles where you try to figure out what’s missing from a picture. They studied images of galaxies taken by the Hubble Space Telescope, looking for bright supergiant stars which disappeared. In one survey, studying a large group of galaxies, they only turned up a single candidate.
But they only surveyed a handful of galaxies. To really get serious about searching for them, they’ll need better tools, like the Large Synoptic Survey Telescope due for first light in just a few years. This amazing instrument will survey the entire sky every few nights, searching for anything that changes. It’ll find asteroids, comets, variable stars, supernovae, and now, supergiant stars that just disappeared.
We’ve talked about failed supernovae. Now let’s take a few moments and talk about the complete opposite: super successful supernovae.
When a star with more than 8 times the mass of the Sun explodes as a supernova, it leaves behind a remnant. For the lower mass star explosions, they leave behind a neutron star. If it’s a higher mass star, they leave behind a black hole.
But for the largest explosions, where the star had more than 130 times the mass of the Sun, the supernova is so powerful, so complete, there’s no remnant behind. There’s an enormous explosion, and the star is just gone.
No black hole ever forms.
Artist’s impression of a supernova explosion which involves the destruction of a massive supergiant star. Credit: ESO
Astronomers call them pair instability supernovae. In a regular core collapse supernova, the layers of the star collapse inward, producing the highly dense remnant. But in these monster stars, the core is pumping out such energetic gamma radiation that it generates antimatter in the core. The star explodes so quickly, with so much energy, it totally overpowers the gravity pulling it inward.
In a moment, the star is completely and utterly gone, just expanding waves of energy and particles.
Only a few of these supernovae have ever been observed, and they might explain some hypernovae and gamma ray bursts, the most powerful explosions in the Universe.
Beyond 250 times the mass of the Sun, however, gravity takes over again, and you get enormous black holes.
As always, the Universe behaves more strangely than we ever thought possible. Some supernova fail, completely imploding as a black hole. And others detonate entirely, leaving no remnant behind. Trust the Universe to keep mixing it up on us.
If you follow some of my other shows, like Astronomy Cast and the Weekly Space Hangout. Of course you do, what a ridiculous thing to say… “if”. Anyway, since you follow those other shows, you know I’m currently obsessed with an upcoming observatory called the Large Synoptic Survey Telescope.
Obsessions are best when they’re shared. So today, I invite you to become as obsessed as I am about the LSST.
In the past, astronomers focused on building bigger telescopes at more remote locations so they could peer more deeply into the past, to resolve the faintest objects, to see right to the edge of the observable Universe.
But there’s a whole other dimension to the Universe: time. And by taking advantage of time, astronomers have made some of the most momentous discoveries in the history of astronomy.
The Large Synoptic Survey Telescope is all about time. Watching the sky over and over, night after night, watching for anything that changes.
Credit: Large Synoptic Survey Telescope (CC-SA 4.0)
First, let’s talk about some of the kinds of discoveries that can be made when you’re watching the sky for changes.
Perhaps the best example of this is the Mira Variable. These are red giants at the very end of their stellar evolution, almost out of usable hydrogen to burn in their cores. As their stellar flame flickers out, the light pressure can no longer hold against the gravity pulling the star inward. The star compresses in on itself, raising the temperature and pressure, allowing more fusion. It flares up again, and brightens in our sky.
Astronomers discovered that there’s a very specific relationship to the brightness and rate that this brightening happens. In other words, if you know how often a Mira variable flares up, you know how intrinsically bright it is. And if you know how bright it is, you can calculate how far away it is. Even in other galaxies.
That’s what Edwin Hubble did when he surveyed Mira variables in other galaxies. He discovered that most galaxies are actually speeding away from us in all directions, leading to the theory of the Big Bang.
Thanks to time, we understand that we life in an expanding Universe that originated from a single point, 13.8 billion years ago.
Let me give you another example: the discovery of gamma ray bursts. In the 1960s, the US launched a group of satellites as part of the Vela Mission. They had no astronomical purpose, they were designed to watch for the specific gamma ray signature from an unauthorized nuclear weapons test. But instead of nuclear explosions, they detected massive blasts of gamma radiation coming from deep space. These blasts only last for a few seconds and then fade away, leaving a faint afterglow that also fades.
Artist’s impression of a gamma-ray burst. Credit: ESO/A. Roquette
We now know that gamma ray bursts mark the deaths of the largest stars in the Universe, and the formations of new black holes. Other gamma ray bursts signal the collisions of exotic stellar remnants, like neutron stars and white dwarfs.
I can give you many more examples, where the dimension of time lead to a discovery in astronomy:
In 1930, Clyde Tombaugh compared pairs of photographic plates, switching back and forth over and over, looking for any object that moved position. This was how he discovered Pluto. In fact, this same technique is used by astronomers to find other dwarf planets, asteroids and comets to this day.
Astronomers return again and again to galaxies in the night sky, looking for any that have a new star in them. This is a tell tale sign of a supernova, the explosion of a star much more massive than our Sun. Some of these supernovae allowed astronomers to discover dark energy, that the expansion of the Universe is accelerating.
This is what time can help us discover.
Artist rendering of the LSST observatory (foreground) atop Cerro Pachón in Chile. Credit: Large Synoptic Survey Telescope Project Office.
Now, on to the Large Synoptic Survey Telescope. The observatory is currently under construction in north-central Chile, where many of the world’s most powerful telescopes are located.
Its main mirror is 8.4 meters across. Just for comparison, ESO’s Very Large Telescopes are 8.2 metres across. The Gemini Observatories are 8.1 metres across. The Keck Observatory is 10 metres wide. What I’m saying here, is that the LSST is plenty big.
But that’s not its most important feature. LSST is fast. When I say fast, I’m saying this in the astronomical sense, which means that it can gather a lot of light over a wide area on the sky in a very short amount of time. While Keck, for example, can focus incredibly deeply at a tiny spot in the sky, LSST gulps light across a huge region of the sky.
It’ll be able to see 3.5-degrees of the sky, every time it takes a picture. The Sun and the Moon are about 0.5-degrees across in the sky, so imagine a grid 7 moons across and 7 moons high.
Suzanne Jacoby with the LSST focal plane array scale model. The image of the moon (30 arcminutes) is placed there for scale of the Field of View. Credit: Large Synoptic Survey Telescope (CC-SA 4.0)
It’ll take a 15-second exposure every 20 seconds. In the amount of time you’ll spend watching this video, the LSST could have taken dozens of high resolution images of the sky.
In fact, it’ll completely image the available sky every few nights. And then petabytes of data will be released onto the internet, available for astronomers to pore over.
Want to find asteroids, just look through the LSST records. Want to know how fast the Universe is expanding, dig through the data. LSST is going to look everywhere and anywhere every couple of nights, and then provide this data to scientists to make discoveries.
Assuming the construction isn’t delayed, the Large Synoptic Survey Telescope should see first light in 2019. Shortly after that, it’ll be disgorging mountains of astronomical data onto the internet.
And shortly after that, I suspect, we’ll start to hear everything the Universe was doing when we weren’t watching before. Because now, thanks to LSST, we’ll be watching all the time.
If aliens were heading towards the Earth, would we see them coming?
Classic sci fi trope time. The air force detects a fleet of alien spacecraft out past Jupiter, leaving enough time to panic and demonstrate what awful monsters we truly are before they come ring our bell.
Is that how this would work?
Imagine a pivotal scene in your favorite alien mega disaster movie. Like the one where the gigantic alien ships appear over London, Washington, Tokyo, and Paris and shoots its light-explody ray, obliterating a montage of iconic buildings. Demonstrating how our landmark construction technology is nothing against their superior firepower.
What could we do? We’re merely meat muppets with pitiful silicon based technology. How could we ever hope to detect these aliens with their stealth spacecraft and 3rd stage guild navigators? If we’re going to do this, I’m going to make up some rules. If you don’t like my rules, go get your own show and then you can have your own rules.
Alternately, as some of you are clearly aware, you can rail against the Guide To Space in the comments below. Dune reference notwithstanding, I’m going to assume that aliens live in our Universe and obey the laws of physics as we understand them. And I know you’re going to say, what if they use physics we haven’t discovered yet?
Then just pause this video and get that out of your system. You can make that your first decree against the state right in the comments below. As I was saying, physical aliens, physical universe. We’ll discuss the metaphysical aliens in a magic universe in a future video. The ones that have crystals and can heal your liver through the power of song.
A basic rule of the Universe is that you can’t go faster than the speed of light. So I’m going to have any aliens trying to attack us traveling at sublight speeds.
So, we’ll say they’ve got access to a giant mountain of power. They can afford to travel at 10% the speed of light, which means before they get to us, they have to slow down. At this speed, deceleration is expensive. We’d see the energy signature from their brakes long before they even reached Earth.
Let’s say they’re passing the orbit of the dwarf planet Pluto, which is 4 light-hours away. Since they’re travelling at 10% the speed of light, we’d have about 40 hours to scramble jet fighters, get those tanks out onto the streets and round up Will Smith, Jeff Goldblum and Bruce Willis to hide behind.
A composite image with Chandra data (purple) showing a “point-like source” beside the remains of a supernova, suggesting a companion star may have survived the explosion. Credit: X-ray: NASA/CXC/SAO/F.Seward et al; Optical: NOAO/CTIO/MCELS, DSS
Would we even notice? Maybe, or maybe not. A growing trend in astronomy is scanning the sky on a regular basis, looking for changes. Changes like supernova explosions, asteroids and comets zipping past, and pulsating variable stars.
One of the most exciting new observatories under construction is the Large Synoptic Survey Telescope in Chile. Once it begins regular operations in 2022, this array of telescopes will photograph the entire sky in fairly high resolution every few nights.
Computers will process the torrent of data coming from the observatory and search for anything that changes. What if they engage their cloak?
Actually (push glasses up your nose) the laws of physics say that the aliens can’t hide the waste heat from whatever space drive they’re using. We’re actually pretty good at detecting heat with our infrared telescopes.
A space drive decelerating a city-sized alien spacecraft from a significant portion of the speed of light would shed a mountain of heat, and that’s all heat we might detect.
Astronomers have been searching for alien civilizations by looking for waste heat generated by Dyson spheres encapsulating entire stars or even all the stars in a galaxy. Nothing’s turned up yet. Which I for one, find a little suspicious.
Freemon Dyson theorized that eventually, a civilization would be able to build a megastructure around its star to capture all its energy. Credit: SentientDevelopments.com
If you’re from an alien race who’s planning to invade. Cover your ears. If aliens wanted to catch us off guard, they can use one of the oldest tricks in the aerial combat book, known as the Dicta Boelcke. They can fly at us using the Sun as camouflage. A rather large portion of the sky is completely obscured by that glowing ball of fiery plasma. It worked in WW1, and it’ll still work now.
Okay, aliens you can listen in again. Everyone else might want to mute the next part, as it’s not terribly reassuring. Astronomers often discover asteroids skimming by the Earth just after they’ve just gone past. That’s because they hurl at us from the Sun, just like clever aliens.
To spot those asteroids, we’ll need to deploy a space-based sky survey that can watch the heavens from a different perspective than Earth. Plans for this kind of mission are actually in the works.
Even with our rudimentary technology, we’d actually stand a pretty good chance of noticing the alien attack vessels before they actually arrived at centre of Sector 001. It’ll get better with automated observatories and space-based sky surveys.
Of course, there’s little we can do if we did know the aliens were coming. We’d be best to start with some kind of deterrent, contaminate all our fresh water, load our livestock up on antibiotics and cover our cities in toxic smog to deter the harvesting of our citizens.
Do you think we’d stand a chance against an alien invasion? Tell us how we’d do in the comments below.
Artist rendering of the LSST observatory (foreground) atop Cerro Pachón in Chile. Credit: Large Synoptic Survey Telescope Project Office.
The world’s largest-ever digital camera has received the green light to move forward with development. The 3,200-megapixel camera for the Large Synoptic Survey Telescope (LSST) will snap the widest, deepest and fastest views of the night sky ever observed, providing unprecedented details of the Universe. Astronomers say the LSST will help uncover some of the biggest mysteries in astronomy.
The SLAC National Accelerator Laboratory announced this week they have received key “Critical Decision 2” approval from the Department of Energy.
“This important decision endorses the camera fabrication budget that we proposed,” said LSST Director Steven Kahn. “Together with the construction funding we received from the National Science Foundation in August, it is now clear that LSST will have the support it needs to be completed on schedule.”
A rendering of the LSST Camera with a cut away to show the inner workings. Credit: LSST.
Set to begin science operations in 2022, the LSST will create an unprecedented archive of astronomical data that will track billions of remote galaxies, helping researchers study galaxy formation. It will rapidly scan the sky, charting objects that change or move: from exploding supernovae to potentially hazardous near-Earth asteroids and create high resolution time-lapse videos of these objects and a 3-D map of the Universe. It will also help us better understand mysterious dark matter and dark energy, which make up 95 percent of the Universe
The camera itself will be the size of a small car and weigh more than 3 tons. It will be able to take up to 800 panoramic images each night and can cover the sky twice each week. Researchers say it will have the ability to reach faint objects twenty times faster than currently possible over the entire visible sky. Scientists anticipate LSST will generate 6 million gigabytes of data per year.
The unique LSST M1/M3 mirror surfaces being carefully polished. Credit: E. Acosta / LSST Corporation.
The telescope will have an 8.4-meter-diameter primary mirror that has an integrated 5-meter-diameter tertiary mirror. This mirror has already been fabricated at the University of Arizona’s Mirror Lab. The outer ring serves as the first mirror, and is called M1. Another more steeply curved mirror, M3, is carved out of the center. It has a 3-degree field of view.
LSST will be taking digital images of the entire visible southern sky every few nights from atop the Cerro Pachón mountain in Chile.
Cerro Pachon is already home to the Gemini South 8-meter telescope and the SOAR 4.1-meter telescope. This graphic also shows LSST’s future site. Credit: C. Claver, NOAO/LSST
Amateur and armchair astronomers will be happy to know that data from the LSST will be shared publicly and become available quickly via the internet. Researchers involved are planning to involve the public, including students, by using portals like Google Sky or World Wide Telescope, as well as developing research projects that can be done by students in classroom settings, and the public at home and at settings like science museums. They also hope to utilize citizen science projects like Cosmoquest and Galaxy Zoo.
With the latest approval from the DOE, the LSST team can now move forward with the development of the camera. There will be a “Critical Decision 3” review process next summer, which will be the last requirement before actual fabrication of the camera can begin. Components of the camera will be built by an international collaboration of labs and universities.
