Guests:This week, we welcome Andrew Helton and Ryan Hamilton, member of the SOFIA Telescope Team.
Andrew is the Instrument Scientist for the Faint Object infraRed CAmera for the SOFIA Telescope (FORCAST) dual channel, mid-infrared camera and spectrograph, one of the observatory’s facility-class science instruments.
Ryan is the Instrument Scientist for the upgraded High-resolution Airborne Wideband Camera (HAWC+) on board NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA).
We’ve had an abundance of news stories for the past few months, and not enough time to get to them all. So we’ve started a new system. Instead of adding all of the stories to the spreadsheet each week, 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!
We record the Weekly Space Hangout every Friday at 12:00 pm Pacific / 3:00 pm Eastern. You can watch us live on Google+, Universe Today, or the Universe Today YouTube page.
“Life exists because of supernovae,” said Steve Howell, project scientist for NASA’s Kepler and K2 missions at NASA’s Ames Research Center. “All heavy elements in the universe come from supernova explosions. For example, all the silver, nickel, and copper in the earth and even in our bodies came from the explosive death throes of stars.”
So a glimpse of a supernova explosion is of intense interest to astronomers. It’s a chance to study the creation and dispersal of the life-enabling elements themselves. A greater understanding of supernovae will lead to a greater understanding of the origins of life.
Stars are balancing acts. They are a struggle between the pressure to expand, created by the fusion in the star, and the gravitational urge to collapse, caused by their own enormous mass. When the core of a star runs out of fuel, the star collapses in on itself. Then there is a massive explosion, which we call a supernova. And only very large stars can become supernovae.
The brilliant flashes that accompany supernovae are called shock breakouts. These events last only about 20 minutes, an infinitesimal amount of time for an object that can shine for billions of years. But when Kepler captured two of these events in 2011, it was more than just luck.
Peter Garnavich is an astrophysics professor at the University of Notre Dame. He led an international team that analyzed the light from 500 galaxies, captured every 30 minutes over a period of 3 years by Kepler. They searched about 50 trillion stars, trying to catch one as it died as a supernova. Only a fraction of stars are large enough to explode as supernovae, so the team had their work cut out for them.
“In order to see something that happens on timescales of minutes, like a shock breakout, you want to have a camera continuously monitoring the sky,” said Garnavich. “You don’t know when a supernova is going to go off, and Kepler’s vigilance allowed us to be a witness as the explosion began.”
An artist’s concept of a shock breakout. Image: NASA Ames/STScl/G. Bacon
In 2011 Kepler caught two gigantic stars as they died their supernova death. Called KSN 2011a, and KSN 2011d, the two red super-giants were 300 times and 500 times the size of our Sun respectively. 2011a was 700 million light years from Earth, and 2011d was 1.2 billion light years away.
The intriguing part of the two supernovae is the difference between them; one had a visible shock breakout and one did not. This was puzzling, since in other respects, both supernovae behaved much like theory predicted they would. The team thinks that the smaller of the two, KSN 2011a, may have been surrounded by enough gas to mask the shock breakout.
The Kepler spacecraft is well-known for searching for and discovering extrasolar planets. But when some components on board Kepler failed in 2013, the mission was re-cast as the K2 Mission. “While Kepler cracked the door open on observing the development of these spectacular events, K2 will push it wide open, observing dozens more supernovae,” said Tom Barclay, senior research scientist and director of the Kepler and K2 guest observer office at Ames. “These results are a tantalizing preamble to what’s to come from K2!”
(For a brilliant and detailed look at the life-cycle of stars, I recommend “The Life and Death of Stars” by Kenneth R. Lang.)
There are a few places in the Universe that defy comprehension. And supernovae have got to be the most extreme places you can imagine. We’re talking about a star with potentially dozens of times the size and mass of our own Sun that violently dies in a faction of a second.
Faster than it take me to say the word supernova, a complete star collapses in on itself, creating a black hole, forming the denser elements in the Universe, and then exploding outward with the energy of millions or even billions of stars.
But not in all cases. In fact, supernovae come in different flavours, starting from different kinds of stars, ending up with different kinds of explosions, and producing different kinds of remnants.
There are two main types of supernovae, the Type I and the Type II. I know this sounds a little counter intuitive, but let’s start with the Type II first.
These are the supernovae produced when massive stars die. We’ve done a whole show about that process, so if you want to watch it now, you can click here.
Our eyes would never see the Crab Nebula as this Hubble image shows it. Image credit: NASA, ESA, J. Hester and A. Loll (Arizona State University)
But here’s the shorter version.
Stars, as you know, convert hydrogen into fusion at their core. This reaction releases energy in the form of photons, and this light pressure pushes against the force of gravity trying to pull the star in on itself.
Our Sun, doesn’t have the mass to support fusion reactions with elements beyond hydrogen or helium. So once all the helium is used up, the fusion reactions stop and the Sun becomes a white dwarf and starts cooling down.
But if you have a star with 8-25 times the mass of the Sun, it can fuse heavier elements at its core. When it runs out of hydrogen, it switches to helium, and then carbon, neon, etc, all the way up the periodic table of elements. When it reaches iron, however, the fusion reaction takes more energy than it produces.
The outer layers of the star collapses inward in a fraction of a second, and then detonates as a Type II supernova. You’re left with an incredibly dense neutron star as a remnant.
But if the original star had more than about 25 times the mass of the Sun, the same core collapse happens. But the force of the material falling inward collapses the core into a black hole.
Extremely massive stars with more than 100 times the mass of the Sun just explode without a trace. In fact, shortly after the Big Bang, there were stars with hundreds, and maybe even thousands of times the mass of the Sun made of pure hydrogen and helium. These monsters would have lived very short lives, detonating with an incomprehensible amount of energy. Artist’s impression of a supernova
Those are Type II. Type I are a little rarer, and are created when you have a very strange binary star situation.
One star in the pair is a white dwarf, the long dead remnant of a main sequence star like our Sun. The companion can be any other type of star, like a red giant, main sequence star, or even another white dwarf.
What matters is that they’re close enough that the white dwarf can steal matter from its partner, and build it up like a smothering blanket of potential explosiveness. When the stolen amount reaches 1.4 times the mass of the Sun, the white dwarf explodes as a supernova and completely vaporizes. In a Type Ia supernova, a white dwarf (left) draws matter from a companion star until its mass hits a limit which leads to collapse and then explosion. Credit: NASA
Because of this 1.4 ratio, astronomers use Type Ia supernovae as “standard candles” to measure distances in the Universe. Since they know how much energy it detonated with, astronomers can calculate the distance to the explosion.
There are probably other, even more rare events that can trigger supernovae, and even more powerful hypernovae and gamma ray bursts. These probably involve collisions between stars, white dwarfs and even neutron stars.
As you’ve probably heard, physicists use particle accelerators to create more massive elements on the Periodic Table. Elements like ununseptium and ununtrium. It takes tremendous energy to create these elements in the first place, and they only last for a fraction of a second.
But in supernovae, these elements would be created, and many others. And we know there are no stable elements further up the periodic table because they’re not here today. A supernova is a far better matter cruncher than any particle accelerator we could ever imagine.
Next time you hear a story about a supernova, listen carefully for what kind of supernova it was: Type I or Type II. How much mass did the star have? That’ll help your imagination wrap your brain around this amazing event.
A nebula is a truly wondrous thing to behold. Named after the Latin word for “cloud”, nebulae are not only massive clouds of dust, hydrogen and helium gas, and plasma; they are also often “stellar nurseries” – i.e. the place where stars are born. And for centuries, distant galaxies were often mistaken for these massive clouds.
Alas, such descriptions barely scratch the surface of what nebulae are and what there significance is. Between their formation process, their role in stellar and planetary formation, and their diversity, nebulae have provided humanity with endless intrigue and discovery.
Black holes are created when stars die catastrophically in a supernova. So what in the universe is a white hole?
It’s imagination day, and we’re going to talk about fantasy creatures. Like unicorns, but even rarer. Like leprechauns, but even more fantastical!
Today, we’re going to talk about white holes. Before we talk about white holes, let’s talk about black holes. And before we talk about Black Holes, what’s is this thing you have with holes exactly?
Black holes are places in the Universe where matter and energy are compacted so densely together that their escape velocity is greater than the speed of light. We’ve done at least a million videos on them, but if you still want more info, you can start here with our Black Hole playlist.
Fully describing a black hole requires a lot of fancy math, but these are real objects in our Universe. They were predicted by Einstein’s theory of relativity, and actually discovered over the last few decades.
Black holes are created when stars, much more massive than our Sun, die catastrophically in a supernova.
So then what’s a white hole?
White holes are created when astrophysicists mathematically explore the environment around black holes, but pretend there’s no mass within the event horizon. What happens when you have a black hole singularity with no mass?
White holes are completely theoretical mathematical concepts. In fact, if you do black hole mathematics for a living, I’m told, ignoring the mass of the singularity makes your life so much easier.
They’re not things that actually exist. It’s not like astronomers detected an unusual outburst of radiation and then developed hypothetical white hole models to explain them.
White Hole. Image Credit: universe-review.ca
As my good friend and sometimes Guide to Space contributor, Dr. Brian Koberlein says, “If you start with five cupcakes and start giving them away, you eventually run out. At that point you can’t give away any more. In this case you can’t count down past zero. Sure, you can hand out slips of paper with “I O U ONE cupcake.” written on them, but it would be ridiculous to use the existence of negative numbers to claim that “negative cupcakes” exist and can be handed out to people.”
Now if white holes did exist, which they probably don’t, they would behave like reverse black holes – just like the math predicts. Instead of pulling material inward, a white hole would blast material out into space like some kind of white chocolate fountain. So generous, these white holes and their chocolate.
One of the other implications of white hole math, is that they only theoretically exist as long as there isn’t a single speck of matter within the event horizon. As soon as single atom of hydrogen drifted into the region, the whole thing would collapse. Even if white holes were created back at the beginning of the Universe, they would have collapsed long ago, since our Universe is already filled with stray matter.
That said, there are a few physicists out there who think white holes might be more than theoretical. Hal Haggard and Carlo Rovelli of Aix-Marseille University in France are working to explain what happens within black holes using a branch of theoretical physics called loop quantum gravity.
Artistic view of a radiating black hole. Credit: NASA
In theory, a black hole singularity would compress down until the smallest possible size predicted by physics. Then it would rebound as a white hole. But because of the severe time dilation effect around a black hole, this event would take billions of years for even the lowest mass ones to finally get around to popping.
If there were microscopic black holes created after the Big Bang, they might get around to decaying and exploding as white holes any day now. Except, according to Stephen Hawking, they would have already evaporated.
Another interesting idea put forth by physicists, is that a white hole might explain the Big Bang, since this is another situation where a tremendous amount of matter and energy spontaneously appeared.
In all likelihood, white holes are just fancy math. And since fancy math rarely survives contact with reality, white holes are probably just imaginary.
What other highly theoretical theories in space and physics would you like us to investigate? Tell us in the comments below.
When a massive star reaches the end of its life, it can explode as a supernova. How quickly does this process happen?
Our Sun will die a slow sad death, billions of years from now when it runs out of magic sunjuice. Sure, it’ll be a dramatic red giant for a bit, but then it’ll settle down as a white dwarf. Build a picket fence, relax on the porch with some refreshing sunjuice lemonade. Gently drifting into its twilight years, and slowly cooling down until it becomes the background temperature of the Universe.
If our Sun had less mass, it would suffer an even slower fate. So then, unsurprisingly, if it had more mass it would die more quickly. In fact, stars with several times the mass of our Sun will die as a supernova, exploding in an instant. Often we talk about things that take billions of years to happen on the Guide to Space. So what about a supernova? Any guesses on how fast that happens?
There are actually several different kinds of supernovae out there, and they have different mechanisms and different durations. But I’m going to focus on a core collapse supernova, the “regular unleaded” of supernovae. Stars between 8 and about 50 times the mass of the Sun exhaust the hydrogen fuel in their cores quickly, in few short million years.
Just like our Sun, they convert hydrogen into helium through fusion, releasing a tremendous amounts of energy which pushes against the star’s gravity trying to collapse in on itself. Once the massive star runs out of hydrogen in its core, it switches to helium, then carbon, then neon, all the way up the periodic table of elements until it reaches iron. The problem is that iron doesn’t produce energy through the fusion process, so there’s nothing holding back the mass of the star from collapsing inward.
… and boom, supernova.
The outer edges of the core collapse inward at 70,000 meters per second, about 23% the speed of light. In just a quarter of a second, infalling material bounces off the iron core of the star, creating a shockwave of matter propagating outward. This shockwave can take a couple of hours to reach the surface.
SN 1987A, an example of a Type II-P Supernova
As the wave passes through, it creates exotic new elements the original star could never form in its core. And this is where we get all get rich. All gold, silver, platinum, uranium and anything higher than iron on the periodic table of elements are created here. A supernova will then take a few months to reach its brightest point, potentially putting out as much energy as the rest of its galaxy combined.
Supernova 1987A, named to commemorate the induction of the first woman into the Rock and Roll Hall of Fame, the amazing Aretha Franklin. Well, actually, that’s not true, it was the first supernova we saw in 1987. But we should really name supernovae after things like that. Still, 1987A went off relatively nearby, and took 85 days to reach its peak brightness. Slowly declining over the next 2 years. Powerful telescopes like the Hubble Space Telescope can still see the shockwave expanding in space, decades later.
Evolution of a Type Ia supernova. Credit: NASA/CXC/M. Weiss
Our “regular flavor” core collapse supernova is just one type of exploding star. The type 1a supernovae are created when a white dwarf star sucks material off a binary partner like a gigantic parasitic twin, until it reaches 1.4 times the mass of the Sun, and then it explodes. In just a few days, these supernovae peak and fade much more rapidly than our core collapse friends.
So, how long does a supernova take to explode? A few million years for the star to die, less than a quarter of a second for its core to collapse, a few hours for the shockwave to reach the surface of the star, a few months to brighten, and then just few years to fade away.
Which star would you like to explode? Tell us in the comments below.
Thanks for watching! Never miss an episode by clicking subscribe. Our Patreon community is the reason these shows happen. We’d like to thank David Hall and the rest of the members who support us in making great space and astronomy content. Members get advance access to episodes, extras, contests, and other shenanigans with Jay, myself and the rest of the team. Want to get in on the action? Click here.
Hubble image of the Crab Nebula supernova remnant captured with the Wide Field and Planetary Camera 2. Credit: NASA, ESA, J. Hester and A. Loll (Arizona State University)
“The nitrogen in our DNA, the calcium in our teeth, the iron in our blood, the carbon in our apple pies were made in the interiors of collapsing stars,” Carl Sagan famously said in his 1980 series Cosmos. “We are made of starstuff.”
And even today, observations with NASA’s airborne SOFIA observatory are supporting this statement. Measurements taken of the dusty leftovers from an ancient supernova located near the center our galaxy – aka SNR Sagittarius A East – show enough “starstuff” to build our entire planet many thousands of times over.
“Our observations reveal a particular cloud produced by a supernova explosion 10,000 years ago contains enough dust to make 7,000 Earths,” said research leader Ryan Lau of Cornell University in Ithaca, New York – the same school, by the way, where Carl Sagan taught astronomy and space science.
Composite image of SNR Sgr A East showing infrared SOFIA data outlined in white against X-ray and radio observations. (NASA/CXO/Herschel/VLA/Lau et al.)
While it’s long been known that supernovae expel enormous amounts of stellar material into space, it wasn’t understood if clouds of large-scale dust could withstand the immense shockwave forces of the explosion.
These observations, made with the joint NASA/DLR-developed Faint Object InfraRed Camera for the SOFIA Telescope (FORCAST) instrument, provide key “missing-link” evidence that dust clouds do in fact survive intact, spreading outward into interstellar space to seed the formation of new systems.
Interstellar dust plays a vital role in the evolution of galaxies and the formation of new stars and protoplanetary discs – the orbiting “pancakes” of material around stars from which planets (and eventually everything on them) form.
The findings may also answer the question of why young galaxies observed in the distant universe possess so much dust; it’s likely the result of frequent supernova explosions from massive early-generation stars.
“We have begun to contemplate our origins: starstuff pondering the stars; organized assemblages of ten billion billion billion atoms considering the evolution of atoms; tracing the long journey by which, here at least, consciousness arose.”
Tauris argues that a lopsided supernova explosion may be the source of certain hypervelocity stars (image credit: IsiacDaGraca).
Hypervelocity stars have been observed traversing the Galaxy at extreme velocities (700 km/s), but the mechanisms that give rise to such phenomena are still debated. Astronomer Thomas M. Tauris argues that lopsided supernova explosions can eject lower-mass Solar stars from the Galaxy at speeds up to 1280 km/s. “[This mechanism] can account for the majority (if not all) of the detected G/K-dwarf hypervelocity candidates,” he said.
Several mechanisms have been proposed as the source for hypervelocity stars, and the hypotheses can vary as a function of stellar type. A simplified summary of the hypothesis Tauris favors begins with a higher-mass star in a tight binary system, which finally undergoes a core-collapse supernova explosion. The close proximity of the stars in the system partly ensures that the orbital velocities are exceedingly large. The binary system is disrupted by the supernova explosion, which is lopsided (asymmetric) and imparts a significant kick to the emerging neutron star. The remnants of supernovae with massive progenitors are neutron stars or potentially a more exotic object (i.e., black hole).
Conversely, Tauris noted that the aforementioned binary origin cannot easily explain the observed velocities of all higher-mass hypervelocity stars, namely the B-stars, which are often linked to an ejection mechanism from a binary interaction with the supermassive black hole at the Milky Way’s center. Others have proposed that interactions between multiple stars near the centers of star clusters can give rise to certain hypervelocity candidates.
There are several potential compact objects (neutron stars) which feature extreme velocities, such as B2011+38, B2224+65, IGR J11014-6103, and B1508+55, with the latter possibly exhibiting a velocity of 1100 km/s. However, Tauris ends by noting that, “a firm identification of a hypervelocity star being ejected from a binary via a supernova is still missing, although a candidate exists (HD 271791) that’s being debated.”
