Special Guest:
This week’s special guest is Dr. Voula Saridakis, a professor at Lake Forest College in Illinois specializing in the history of science and astronomy, who runsthe History of Astronomy on Twitter at @histastro
We use a tool called Trello to submit and vote on stories we would like to see covered each week, and then Fraser will be selecting the stories from there. Here is the link to the Trello WSH page (http://bit.ly/WSHVote), which you can see without logging in. If you’d like to vote, just create a login and help us decide what to cover!
If you would like to join the Weekly Space Hangout Crew, visit their site here and sign up. They’re a great team who can help you join our online discussions!
If you would like to sign up for the AstronomyCast Solar Eclipse Escape, where you can meet Fraser and Pamela, plus WSH Crew and other fans, visit our site linked above and sign up!
We record the Weekly Space Hangout every Friday at 12:00 pm Pacific / 3:00 pm Eastern. You can watch us live on Universe Today, or the Universe Today YouTube page.
There are times when I really wish astronomers could take their advanced modern knowledge of the cosmos and then go back and rewrite all the terminology so that they make more sense. For example, dark matter and dark energy seem like they’re linked, and maybe they are, but really, they’re just mysteries.
Is dark matter actually matter, or just a different way that gravity works over long distances? Is dark energy really energy, or is it part of the expansion of space itself. Black holes are neither black, nor holes, but that doesn’t stop people from imagining them as dark tunnels to another Universe. Or the Big Bang, which makes you think of an explosion.
Another category that could really use a re-organizing is the term nova, and all the related objects that share that term: nova, supernova, hypernova, meganova, ultranova. Okay, I made those last couple up.
I guess if you go back to the basics, a nova is a star that momentarily brightens up. And a supernova is a star that momentarily brightens up… to death. But the underlying scenario is totally different.
In this artist’s conception, a supernova explosion is about to obliterate an orbiting Saturn-like planet. Credit: David A. Aguilar (CfA)
As we’ve mentioned in many articles already, a supernova commonly occurs when a massive star runs out of fuel in its core, implodes, and then detonates with an enormous explosion. There’s another kind of supernova, but we’ll get to that later.
A plain old regular nova, on the other hand, happens when a white dwarf – the dead remnant of a Sun-like star – absorbs a little too much material from a binary companion. This borrowed hydrogen undergoes fusion, which causes it to brighten up significantly, pumping up to 100,000 times more energy off into space.
Imagine a situation where you’ve got two main sequence stars like our Sun orbiting one another in a tight binary system. Over the course of billions of years, one of the stars runs out of fuel in its core, expands as a red giant, and then contracts back down into a white dwarf. It’s dead.
Some time later, the second star dies, and it expands as a red giant. So now you’ve got a red dwarf and a white dwarf in this binary system, orbiting around and around each other, and material is streaming off the red giant and onto the smaller white dwarf.
Illustration of a white dwarf feeding off its companion star Credit: ESO / M. Kornmesser
This material piles up on the surface of the white dwarf forming a cosy blanket of stolen hydrogen. When the surface temperature reaches 20 million kelvin, the hydrogen begins to fuse, as if it was the core of a star. Metaphorically speaking, its skin catches fire. No, wait, even better. Its skin catches fire and then blasts off into space.
Over the course of a few months, the star brightens significantly in the sky. Sometimes a star that required a telescope before suddenly becomes visible with the unaided eye. And then it slowly fades again, back to its original brightness.
Some stars do this on a regular basis, brightening a few times a century. Others must clearly be on a longer cycle, we’ve only seen them do it once.
Astronomers think there are about 40 novae a year across the Milky Way, and we often see them in other galaxies.
Tycho Brahe: He lived like a sage and died like a fool. He also created his own cosmological model, the Tychonic system.
The term “nova” was first coined by the Danish astronomer Tycho Brahe in 1572, when he observed a supernova with his telescope. He called it the “nova stella”, or new star, and the name stuck. Other astronomers used the term to describe any star that brightened up in the sky, before they even really understood the causes.
During a nova event, only about 5% of the material gathered on the white dwarf is actually consumed in the flash of fusion. Some is blasted off into space, and some of the byproducts of fusion pile up on its surface.
Tycho’s Supernova Remnant. Credit: Spitzer, Chandra and Calar Alto Telescopes.
Over millions of years, the white dwarf can collect enough material that carbon fusion can occur. At 1.4 times the mass of the Sun, a runaway fusion reaction overtakes the entire white dwarf star, releasing enough energy to detonate it in a matter of seconds.
If a regular nova is a quick flare-up of fusion on the surface of a white dwarf star, then this event is a super nova, where the entire star explodes from a runaway fusion reaction.
You might have guessed, this is known as a Type 1a supernova, and astronomers use these explosions as a way to measure distance in the Universe, because they always explode with the same amount of energy.
Hmm, I guess the terminology isn’t so bad after all: nova is a flare up, and a supernova is a catastrophic flare up to death… that works.
Now you know. A nova occurs when a dead star steals material from a binary companion, and undergoes a momentary return to the good old days of fusion. A Type Ia supernova is that final explosion when a white dwarf has gathered its last meal.
We usually record Astronomy Cast as a live Google+ Hangout on Air every Friday at 1:30 pm Pacific / 4:30 pm Eastern. You can watch here on Universe Today or from the Astronomy Cast Google+ page.
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.
We use a tool called Trello to submit and vote on stories we would like to see covered each week, and then Fraser will be selecting the stories from there. Here is the link to the Trello WSH page (http://bit.ly/WSHVote), which you can see without logging in. If you’d like to vote, just create a login and help us decide what to cover!
If you would like to join the Weekly Space Hangout Crew, visit their site here and sign up. They’re a great team who can help you join our online discussions!
If you would like to sign up for the AstronomyCast Solar Eclipse Escape, where you can meet Fraser and Pamela, plus WSH Crew and other fans, visit our site linked above and sign up!
We record the Weekly Space Hangout every Friday at 12:00 pm Pacific / 3:00 pm Eastern. You can watch us live on Universe Today, or the Universe Today YouTube page.
It turns out that nature figured out how to use electricity long before humans did. Lightning storms are common across the Earth, and even the Solar System. What causes this electricity in the sky, and how can science use it?
We usually record Astronomy Cast as a live Google+ Hangout on Air every Friday at 1:30 pm Pacific / 4:30 pm Eastern. You can watch here on Universe Today or from the Astronomy Cast Google+ page.
I seem like a pretty calm and collected guy, but if you want to see me go on an epic rant, all you have to do is ask me some variation on the question: “why should we bother exploring space when we’ve got problems to fix here on Earth.”
I see this question all the time. All the time, in forums, comments on videos, and from people in audiences.
I think the question is ridiculous on many levels, and I’ve got a bunch of reasons why, but allow me to explain them here.
Before I do, however, I want you to understand that I believe that we human beings are indeed messing up the environment. We’re wiping out species faster than any natural disaster in the history of planet Earth. We’re performing a dangerous experiment on the climate of the planet, increasing temperatures worldwide, with devastating consequences, for both ecosystems and human civilization.
Credit: USFS Gila National Forest (CC BY-SA 2.0)
Unless we get this under control, and there’s no reason to believe we will, we’re going to raise temperatures to levels unseen in millions of years.
There are islands of plastic garbage in the oceans, collected into huge toxic rafts by the currents. Colonies of bees are dying through pesticides and habitat loss.
We’re even polluting the space around the Earth with debris that might tear apart future space missions.
I believe the science, and the science says we’re making a mess.
The first thing is that this whole question is a false dilemma fallacy. Why do we have to choose between space exploration and saving the planet? Why can’t we do both?
NASA’s Orion spacecraft. Credit: NASA
The world spent nearly $750 billion on cigarettes in 2014. NASA’s total budget is less than $20 billion, and Elon Musk thinks he can start sending colonists to Mars for less than $10 billion.
How about the whole world stops smoking, and we spend $20 billion on colonizing Mars and the other $730 billion on renewable fuels and cleaning up our negative impact on the environment, reducing poverty and giving people access to clean water?
Americans spend $27 billion on takeout pizza. Don’t get me wrong, pizza’s great, but I’d be willing to forego pizza if it meant a vibrant and healthy industry of space exploration.
Gambling, lawn care, hood ornaments, weapons of war. Humans spend a lot of money on a lot of things that could be redirected towards both space exploration and reducing our environmental impact.
Number two, it might turn out that space exploration is the best way to save the Earth. I totally agree with Blue Origin’s Jeff Bezos when he says that we already know that Earth is the best place in the Solar System. Let’s keep it that way.
Mars might be a fascinating place to visit and an adventure to colonize, but I want to swim in rivers, climb mountains, walk in forests, watch birds, sail in the ocean.
But the way we’re using up the natural environment will take away from all that. As Bezos says, we should move all the heavy industry off Earth and up into space. Use solar collectors to gather power, mine asteroids for their raw materials. Keep Earth as pristine as possible.
Asteroid mining concept. Credit: NASA/Denise Watt
We won’t know how to do that unless we actually go into space and learn how to survive and run that industry, from space.
Number three, it might be that we’ve already crossed the point of no return. There’s a great science fiction story by Spider Robinson called “In the Olden Days”. It’s about how modern society turned its back on technology, and lost the ability to ever recover.
Humanity used up the entire technology ladder that nature put in front of us; the chunks of iron just sitting on the ground, the oil bubbling out of the Earth, the coal that was easily accessible. Now it takes an offshore drilling rig to get at the oil.
These resources took the Earth millions and even billions of years to accumulate for us to use, and transcend. When the cockroaches evolve intelligence and opposable thumbs, they won’t have those easily accessible resources to jumpstart their own space exploration program.
Number four, as Elon Musk says, we have to protect the cradle of consciousness. Until we find proof otherwise, we have to assume that the Earth is the only place in the Universe that evolved intelligent life.
And until the alien overlords show up and say, “don’t worry humans, we’ve got this,” we have to assume that the responsibility for seeding the life with intelligence rests on us. And we’re one asteroid strike or nuclear apocalypse away from snuffing that out.
I don’t entirely agree that Mars is the best place to do it, but we should at least have another party going on somewhere.
NASA astronaut Ed White during a spacewalk June 3, 1965. In his hand, the Gemini 4 astronaut carries a Hand Held Self Maneuvering Unit (HHSMU) to help him maneuver in microgravity. Credit: NASA
And number five, it’ll be fun. Humans need adventure. We need great challenges to push us to become the best versions of ourselves. We climb mountains because they’re there.
Ask anyone who’s built their own house or tried their hand at homesteading. It’s a tremendous amount of work, but it’s also rewarding in ways that buying stuff just isn’t.
The next time someone uses that argument on you, I hope this gives you some ammunition.
Phew, now I’ll get off my soapbox. Next week, I’m sure we’ll return to poop jokes, obscure science fiction references with a smattering of space science.
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.
We are now using a tool called Trello to submit and vote on stories we would like to see covered each week, and then Fraser will be selecting the stories from there. Here is the link to the Trello WSH page (http://bit.ly/WSHVote), which you can see without logging in. If you’d like to vote, just create a login and help us decide what to cover!
If you would like to join the Weekly Space Hangout Crew, visit their site here and sign up. They’re a great team who can help you join our online discussions!
If you would like to sign up for the AstronomyCast Solar Eclipse Escape, where you can meet Fraser and Pamela, plus WSH Crew and other fans, visit our site linked above and sign up!
We record the Weekly Space Hangout every Friday at 12:00 pm Pacific / 3:00 pm Eastern. You can watch us live on Universe Today, or the Universe Today YouTube page.
As Hurricane Matthew reminded us, cyclonic storms are a force to be reckoned with. What causes these storms, and how can they form across the Solar System.
We usually record Astronomy Cast as a live Google+ Hangout on Air every Friday at 1:30 pm Pacific / 4:30 pm Eastern. You can watch here on Universe Today or from the Astronomy Cast Google+ page.
