plasma Archives

November 23, 2015February 23, 2017 by Fraser Cain

Why Do Red Dwarfs Live So Long?

While our Sun will only survive for about 5 billion more years, smaller, cooler red dwarfs can last for trillions of years. What’s the secret to their longevity?

You might say our Sun will last a long time. And sure, another 5 billion years or so of main sequence existence does sound pretty long lived. But that’s nothing compared to the least massive stars out there, the red dwarfs.

These tiny stars can have just 1/12th the mass of the Sun, but instead of living for a paltry duration, they can last for trillions of years. What’s the secret to their longevity? Is it Botox?

To understand why red dwarfs have such long lifespans, we’ll need to take a look at main sequence stars first, and see how they’re different. If you could peel back the Sun like a grapefruit, you’d see juicy layers inside.

In the core, immense pressure and temperature from the mass of all that starstuff bears down and fuses atoms of hydrogen into helium, releasing gamma radiation.

Outside the core is the radiative zone, not hot enough for fusion. Instead, photons of energy generated in the core are emitted and absorbed countless times, taking a random journey to the outermost layer of the star.

And outside the radiative zone is the convective zone, where superheated globs of hot plasma float up to the surface, where they release their heat into space.

Then they cool down enough to sink back through the Sun and pick up more heat. Over time, helium builds up in the core. Eventually, this core runs out of hydrogen and it dies. Even though the core is only a fraction of the total mass of hydrogen in the Sun, there’s no mechanism to mix it in.

A red dwarf is fundamentally different than a main sequence star like the Sun. Because it has less mass, it has a core, and a convective zone, but no radiative zone. This makes all the difference.

The convective zone connects directly to the core of the red dwarf, the helium byproduct created by fusion is spread throughout the star. This convection brings fresh hydrogen into the core of the star where it can continue the fusion process.

By perfectly using all its hydrogen, the lowest mass red dwarf could sip away at its hydrogen fuel for 10 trillion years.

One of the biggest surprises in modern astronomy is just how many of these low mass red dwarf worlds have planets. And some of the most Earthlike worlds ever seen have been found around red dwarf stars. Planets with roughly the mass of Earth, orbiting within their star’s habitable zone, where liquid water could be present.

One of the biggest problems with red dwarfs is that they can be extremely variable. For example, 40% of a red dwarf’s surface could be covered with sunspots, decreasing the amount of radiation it produces, changing the size of its habitable zone.

Other red dwarfs produce powerful stellar flares that could scour a newly forming world of life. DG Canes Venaticorum recently generated a flare 10,000 times more powerful than anything ever seen from the Sun. Any life caught in the blast would have a very bad day.

Fortunately, red dwarfs only put out these powerful flares in the first billion years or so of their lives. After that, they settle down and provide a nice cozy environment for trillions of years. Long enough for life to prosper we hope.

In the distant future, some superintelligent species may figure out how to properly mix the hydrogen back into the Sun, removing the helium, if they do, they’ll add billions of years to the Sun’s life.

It seems like such a shame for the Sun to die with all that usable hydrogen sitting just a radiative zone away from fusion.

Have you got any ideas on how we could mix up the hydrogen in the Sun and remove the helium? Post your wild ideas in the comments!

September 28, 2015February 24, 2017 by Fraser Cain

Can You Kill a Star With Iron?

Since the energy required to fuse iron is more than the energy that you get from doing it, could you use iron to kill a star like our sun?

A fan favorite was How Much Water Would it Take to Extinguish the Sun? Go ahead and watch it now if you like. Or… if you don’t have time to watch me set up the science, deliver a bunch of hilarious zingers and obscure sci-fi references, here’s the short version:

The Sun is not on fire, it’s a fusion reaction. Hydrogen mashes up to produce helium and energy. Lots and lots of energy. Water is mostly hydrogen, adding water would give more fuel and make it burn hotter. But some of you clever viewers proposed another way to kill the Sun. Kill it with iron!

Iron? That seems pretty specific. Why iron and not something else, like butter, donuts, or sitting on the couch playing video games – all the things working to kill me? Is iron poison to stars? An iron bar? Possibly iron bullets? Iron punches? Possibly from fashioning a suit and attacking it as some kind of Iron Man?

Time for some stellar physics. Stars are massive balls of plasma. Mostly hydrogen and helium, and leftover salad from the Big Bang. Mass holds them together in a sphere, creating temperatures and pressures at their cores, where atoms of hydrogen are crushed together into helium, releasing energy. This energy, in the form of photons pushes outward. As they escape the star, this counteracts the force of gravity trying to pull it inward.

Over the course of billions of years, the star uses up the reserves of hydrogen, building up helium. If it’s massive enough, it will switch to helium when the hydrogen is gone. Then it can switch to oxygen, and then silicon, and all the way up the periodic table of elements.

The most massive stars in the Universe, the ones with at least 8 times the mass of the Sun, have enough temperature and pressure that they can fuse elements all the way up to iron, the 26th element on the Periodic Table. At that point, the energy required to fuse iron is more than the energy that you get from fusing iron, no matter how massive a star you are.

Massive Young Stellar Object HD200775 within the reflection nebula NGC7023.

In a fraction of a second, the core of the Sun shuts off. It’s no longer pushing outward with its light pressure, and so the outer layers collapse inward, creating a black hole and a supernova. It sure looks like the build up of iron in the core killed it.

Is it true then? Is iron the Achilles heel of stars? Not really. Iron is the byproduct of fusion within the most massive stars. Just like ash is the byproduct of combustion, or poop is the byproduct of human digestion.

It’s not poison, which stops or destroys processes within the human body. A better analogy might be fiber. Your body can’t get any nutritional value out of fiber, like grass. If all you had to eat was grass, you’d starve, but it’s not like the grass is poisoning you. As long as you got adequate nutrition, you could eat an immense amount of grass and not die. It’s about the food, not the grass.

The Sun already has plenty of iron; it’s 0.1% iron. That little nugget would work out to be 330 times the mass of the Earth. If you gave it much more iron, it would just give the Sun more mass, which would give it more gravity to raise the temperature and pressure at the core, which would help it do even more fusion.

This image shows iron debris in Tycho's supernova remnant. Credit: NASA/CXC/Chinese Academy of Sciences/F. Lu et al. — This image shows iron debris in Tycho’s supernova remnant. Credit: NASA/CXC/Chinese Academy of Sciences/F. Lu et al.

If you just poured iron into a star, it wouldn’t kill it. It would just make it more massive and then hotter and capable of supporting the fusion of heavier elements. As long as there’s still viable fuel at the core of the star, and adequate temperatures and pressures, it’ll continue fusing and releasing energy.

If you could swap out the hydrogen in the Sun with a core of iron, you would indeed kill it dead, or any star for that matter. It wouldn’t explode, though. Only if it was at least 8 times the mass of the Sun to begin with. Then would you have enough mass bearing down on the inert core to create a core collapse supernova.

In fact, since you’ve got the power to magically replace stellar cores, you would only need to replace the Sun’s core with carbon or oxygen to kill it. It actually doesn’t have enough mass to fuse even carbon. As soon as you replaced the Sun’s core, it would shut off fusion. It would immediately become a white dwarf, and begin slowly cooling down to the background temperature of the Universe.

Iron in bullet, bar, man or any other form isn’t poison to a star. It just happens to be an element that no star can use to generate energy from fusion. As long as there’s still viable fuel at the core of a star, and the pressure and temperature to bring them together, the star will continue to pump out energy.

What other exotic ways would you use to try and kill the Sun? Give us your suggestions in the comments below.

April 30, 2015December 23, 2015 by Jason Major

Watch an Enormous “Plasma Snake” Erupt from the Sun

SOHO LASCO C2 (top) and SDO AIA 304 (bottom) image of a solar filament detaching on April 28-29, 2015

Over the course of April 28–29 a gigantic filament, briefly suspended above the surface* of the Sun, broke off and created an enormous snakelike eruption of plasma that extended millions of miles out into space. The event was both powerful and beautiful, another demonstration of the incredible energy and activity of our home star…and it was all captured on camera by two of our finest Sun-watching spacecraft.

Watch a video of the event below.

Made from data acquired by both NASA’s Solar Dynamics Observatory (SDO) and the joint ESA/NASA SOHO spacecraft, the video was compiled by astronomer and sungrazing comet specialist Karl Battams. It shows views of the huge filament before and after detaching from the Sun, and gives a sense of the enormous scale of the event.

At one point the plasma eruption spanned a distance over 33 times farther than the Moon is from Earth!

Filaments are long channels of solar material contained by magnetic fields that have risen up from within the Sun. They are relatively cooler than the visible face of the Sun behind them so they appear dark when silhouetted against it; when seen rising from the Sun’s limb they look bright and are called prominences.

When the magnetic field lines break apart, much of the material contained within the filaments gets flung out into space (a.k.a. a CME) while some gets pulled back down into the Sun. These events are fairly common but that doesn’t make them any less spectacular!

Also read: Watch the Sun Split Apart

This same particularly long filament has also been featured as the Astronomy Picture of the Day (APOD), in a photo captured on April 27 by Göran Strand.

For more solar news follow Karl Battams on Twitter.

Image credits: ESA/NASA/SOHO & SDO/NASA and the AIA science team.

*The Sun, being a mass of incandescent gas, doesn’t have a “surface” like rocky planets do so in this case we’re referring to its photosphere and chromosphere.

November 12, 2014December 23, 2015 by Bob King

Better than Bieber, Rosetta’s Comet Sings Strange, Seductive Song

Magnetic field lines bound up in the sun’s wind pile up and drape around a comet’s nucleus to shape the blue ion tail. Notice the oppositely-directed fields on the comet’s backside. The top set points away from the comet; the bottom set toward. In strong wind gusts, the two can be squeezed together and reconnect, releasing energy that snaps off a comet’s tail. Credit: Tufts University

Tune in to the song of Comet Churyumov-Gerasimenko

Scientists can’t figure exactly why yet, but Comet 67P/Churyumov-Gerasimenko has been singing since at least August. Listen to the video – what do you think? I hear a patter that sounds like frogs, purring and ping-pong balls. The song is being sung at a frequency of 40-50 millihertz, much lower than the 20 hertz – 20 kilohertz range of human hearing. Rosetta’s magnetometer experiment first clearly picked up the sounds in August, when the spacecraft drew to within 62 miles (100 km) of the comet. To make them audible Rosetta scientists increased their pitch 10,000 times.

The sounds are thought to be oscillations in the magnetic field around the comet. They were picked up by the Rosetta Plasma Consortium, a suite of five instruments on the spacecraft devoted to observing interactions between the solar plasma and the comet’s tenuous coma as well as the physical properties of the nucleus. A far cry from the stuff you donate at the local plasma center, plasma in physics is an ionized gas. Ionized means the atoms in the gas have lost or gained an electron through heating or collisions to become positively or negatively charged ions. Common forms of plasma include the electric glow of neon signs, lightning and of course the Sun itself.

Having lost their neutrality, electric and magnetic fields can now affect the motion of particles in the plasma. Likewise, moving electrified particles affect the very magnetic field controlling them.

Scientists think that neutral gas particles from vaporizing ice shot into the coma become ionized under the action of ultraviolet light from the Sun. While the exact mechanism that creates the curious oscillations is still unknown, it might have something to do with the electrified atoms or ions interacting with the magnetic fields bundled with the Sun’s everyday outpouring of plasma called the solar wind. It’s long been known that a comet’s electrified or ionized gases present an obstacle to the solar wind, causing it to drape around the nucleus and shape the streamlined blue-tinted ion or gas tail.

“This is exciting because it is completely new to us. We did not expect this, and we are still working to understand the physics of what is happening,” said Karl-Heinz Glassmeier, head of Space Physics and Space Sensorics at the Technical University of Braunschweig, Germany.

While 67P C-G’s song probably won’t make the Top 40, we might listen to it just as we would any other piece of music to learn what message is being communicated.

July 8, 2014December 23, 2015 by Elizabeth Howell

Voyager 1 Hears Sun Echoes Far Away, In Interstellar Space

Artist's concept of Voyager 1 in interstellar space. Credit: NASA/JPL-Caltech

Wow! Even from interstellar space, the plucky Voyager 1 can still listen in to activities from our Sun. Whenever the Sun has a large amount of activity, the waves of energy it sends out bashes into the charged gas particles or plasma surrounding the NASA spacecraft, which has been sailing away from Earth since 1977.

There have been three events so far from our Sun (which is in solar maximum), with each one confirming scientists’ findings that interstellar space is where the spacecraft is, NASA said.

“Normally, interstellar space is like a quiet lake,” stated Voyager project scientist Ed Stone of the California Institute of Technology. “But when our sun has a burst, it sends a shock wave outward that reaches Voyager about a year later. The wave causes the plasma surrounding the spacecraft to sing.”

“The tsunami wave rings the plasma like a bell,” added Stone. “While the plasma wave instrument lets us measure the frequency of this ringing, the cosmic ray instrument reveals what struck the bell — the shock wave from the Sun.”

The discovery of this wave front confirms the previous assertion that Voyager 1 is indeed in interstellar space, NASA added. Winds from the sun push against the plasma at the edge of interstellar space, making it denser (40 times denser than what was measured before Voyager reached the milestone in 2012, in fact.)

NASA’s announcement in 2013 that Voyager 1 is in interstellar space was accompanied by intense discussion about whether it is in or out of the Solar System (it still hasn’t reached the shell of the Oort Cloud that hosts comets, a milestone that won’t be possible for 300 years). Prior to the announcement, several scientific papers had also weighed in on Voyager 1’s status, with some saying it was interstellar space and some not.

Source: NASA

July 7, 2014March 1, 2017 by Fraser Cain

How Many Ways Can the Sun Kill You?

The Sun has a Swiss army knife of ways it can do you in, from radiation to solar flares. And when it dies, it’s taking you with it. What are the various ways the Sun can do you in?

There’s a terrifying ball of fire a short 150 million km away. Which, in galactic terms, is right on our doorstep. This super-heated ball of plasma-y death, has temperatures and pressures so high that atoms of hydrogen are crushed into helium.

We’ve told ourselves we’re a safe distance away, and generally understate the dangers of being gravitationally bound to a massive ongoing nuclear explosion which is catastrophically larger than anything we’ve ever managed to create here on Earth. We take its warmth and life-giving light for granted, and barely give it a second thought as we sunbathe, or laugh gregariously while frying eggs on sidewalks on days when it’s scorchingly hot out.

Have we been lulled into a false sense of security by an ancient and secret society of bananas crazy sun cultists? Instead of worshiping the giant BBQ death ball, should we be cowering in fear, waiting for the next great solar flare? So, how dangerous is that thing? What are all the ways the Sun could do us in? And how many of them does my insurance cover?

First, in 4.5 billion years nothing has managed to destroy our planet. In fact, life itself has existed for almost Earth’s entire history, and nothing has scoured the planet clear of all forms of life. So, don’t worry the most reasonable risk we face from the Sun in our lifetimes is from a solar flare – a sudden blast of brightness on the surface of the Sun.

These occur when the Sun’s magnetic field lines snap and reconfigure, releasing an enormous amount of energy. It’s the equivalent of hundreds of billions of tonnes of TNT and if we’re staring down the barrel of this blast, it’ll fire a stream of high energy particles right up our nose.

Fortunately, the Earth has evolved in a highly radioactive environment. We’re blasted by radiation from the Sun all the time. The Earth’s magnetic field lines channel the particles towards the poles, which is why we get to see the beautiful auroral displays.

We’re at little risk from flares from the Sun, but our technology isn’t so lucky. The increase of geomagnetic activity in our vicinity can overload electrical grids and take satellites offline. The most powerful geomagnetic storm in history, known as the Carrington Event in 1859, generated auroras as far south as Cuba. It didn’t cause any damage then, but it would cause a lot of damage to our fragile technology today.

For those of you now resting comfortably I say… Not so fast. This episode isn’t over yet. Our Sun is heating up, and its energy output is increasing.

As it uses up the hydrogen in its core, this region of the Sun contracts a little, and the Sun increases in temperature to balance things out. Over the next few hundred million years, temperatures on Earth will rise and rise. Within a billion years, the surface of the planet will be an inhospitable oven.

Mercury seen by Mariner 10. Image credit: NASA — The Earth will one day be as dry and baked as Mercury. Image credit: NASA

Eventually the oceans will boil and the hydrogen will be blown out of the atmosphere by the Sun’s solar wind. Even though the Sun will remain in its main sequence phase for another 4 billion years after that, any life will need to be living underground.

Of course, as we’ve discussed in previous episodes, the Sun’s final act of destruction will happen when it runs out of hydrogen fuel in its core. The core will contract and the Sun will puff up into a red giant, consuming the orbits of Mercury, Venus and possibly the Earth. And even if it doesn’t consume the Earth, it’ll hit our planet with so much heat and radiation that it’ll finally get around to scouring any life off the surface.

So, like your fanatical sun cultist friends. Don’t worry about the Sun. It might make sense to keep some spare batteries around for the times when solar flares knock out the lights for a few days, but the Sun is remarkably safe and stable. We’ve got billions of years of warm light and heat from our star. But after that, it might make sense to shop for a new home.

So what do you think? Where do you think we should move when the temperature of the Sun heats up?

June 16, 2014December 23, 2015 by Jason Major

Watch the Rise and Fall of a Towering Inferno on the Sun

A solar prominence imaged on May 27, 2014. Earth and Moon are shown to scale at the bottom. (NASA/SDO)

Caught on camera by NASA’s Solar Dynamics Observatory, a prominence blazes hundreds of thousands of miles out from the Sun’s surface (i.e., photosphere) on May 27, 2014. The image above, seen in extreme ultraviolet wavelengths, shows a brief snapshot of the event with the column of solar plasma stretching nearly as far as the distance between Earth and the Moon.

Watch a video of the event below:

The video covers a span of about two hours.

Although it might look fiery in these images, a prominence isn’t flame — it’s powered by rising magnetic fields trapping and carrying the Sun’s superheated material up into the corona. And while this may not have been a unique or unusual event — or even particularly long-lived — it’s still an impressive reminder of the immense scale and energy of our home star!

Credit: NASA/SDO

May 22, 2013December 23, 2015 by Tammy Plotner

Ain’t Misbehavin’ – Turbulence, Solar Flares and Magnetism

In this image, the Solar Dynamics Observatory (SDO) captured an X1.2 class solar flare, peaking on May 15, 2013. Credit: NASA/SDO

What’s more fun than something that misbehaves? When it comes to solar dynamics, we know a lot, but there are many things we don’t yet understand. For example, when a particle filled solar flare lashes out from the Sun, its magnetic field lines can do some pretty unexpected things – like split apart and then rapidly reconnect. According to the flux-freezing theorem, these magnetic lines should simply “flow away in lock-step” with the particles. They should stay intact, but they don’t. It’s not just a simple rule they break… it’s a law of physics.

What can explain it? In a paper published in the May 23 issue of “Nature”, an interdisciplinary research team led by a Johns Hopkins mathematical physicist may just have found a plausible explanation. According to the group, the underlying factor is turbulence – the “same sort of violent disorder that can jostle a passenger jet when it occurs in the atmosphere” – or the one your brother leaves behind after he’s eaten baked beans. By employing a well-organized and logically constructed computer modeling technique, the researchers were able to simulate what happens when magnetic field lines meet up with turbulence in a solar flare. Armed with this information, they were then able to state their case.

“The flux-freezing theorem often explains things beautifully,” said Gregory Eyink, a Department of Applied Mathematics and Statistics professor who was lead author of the “Nature” study. “But in other instances, it fails miserably. We wanted to figure out why this failure occurs.”

Just what is the flux-freezing theorem? Maybe you’ve heard of Hannes Alfvén. He was a Swedish electrical engineer, plasma physicist and winner of the 1970 Nobel Prize in Physics for his work on magnetohydrodynamics (MHD). He’s the man responsible for explaining what we now know as Alfvén waves – a low-frequency travelling oscillation of the ions and the magnetic field in plasma. Well, some 70 years ago, he came up with the thought that magnetic lines of force sail along a locomotive fluid similar to snippets of thread flowing along a stream. It should be impossible for them to break and then join again. However, solar physicists have discovered this just isn’t the case when it comes to activity within a particularly violent solar flare. In their observations, they have determined that the magnetic field lines within these flares can stretch to the breaking point and then reconnect in a surprisingly quick amount of time – as little as 15 minutes. When this happens, it expels a copious amount of energy which, in turn, powers the flare.

“But the flux-freezing principle of modern plasma physics implies that this process in the solar corona should take a million years!” Eyink animatedly states. “A big problem in astrophysics is that no one could explain why flux-freezing works in some cases but not others.”

Of course, there has always been speculation that turbulence may have been the root source of the enigmatic behavior. Time for investigation? You bet. Eyink then joined forces – and minds – with other experts in astrophysics, mechanical engineering, data management and computer science, based at Johns Hopkins and other institutions. “By necessity, this was a highly collaborative effort,” Eyink said. “Everyone was contributing their expertise. No one person could have accomplished this.”

Gregory Eyink, professor of applied mathematics and statistics at Johns Hopkins. Photo by Nat Creamer.

The next step was to create a computer simulation – a simulation which could duplicate the plasma state of solar flare activity and all the nuances the charged particles undergo during different conditions. “Our answer was very surprising,” stated Eyink. “Magnetic flux-freezing no longer holds true when the plasma becomes turbulent. Most physicists expected that flux-freezing would play an even larger role as the plasma became more highly conducting and more turbulent, but, as a matter of fact, it breaks down completely. In an even greater surprise, we found that the motion of the magnetic field lines becomes completely random. I do not mean ‘chaotic,’ but instead as unpredictable as quantum mechanics. Rather than flowing in an orderly, deterministic fashion, the magnetic field lines instead spread out like a roiling plume of smoke.”

Of course, other solar experts feel there may be alternative answers for this rule-breaking activity within solar flares, but as Eyink says, “I think we made a pretty compelling case that turbulence alone can account for field-line breaking.”

What is most exciting is the collaborative effort of the team members from such widely varied disciplines. It was a group effort which aided Eyink to come up with this new theory on the solar flare riddle. “We used ground-breaking new database methods, like those employed in the Sloan Digital Sky Survey, combined with high-performance computing techniques and original mathematical developments,” he said. “The work required a perfect marriage of physics, mathematics and computer science to develop a fundamentally new approach to performing research with very large datasets.”

In conclusion, Eyink noted this type of research work may very well give us a better understanding of solar flares and coronal mass ejections. As we know, this type of dangerous “space weather” can be harmful to astronauts, disrupt communications satellites, and even be responsible for the shut-down of electrical power grids on Earth. And you know what that means… no satellite TV and no power to watch it by. But, that’s O.K.

“I don’t stay out late. Don’t care to go. I’m home about eight… Just me and my radio. Ain’t misbehavin’.. Savin’ my love for you.”

Original Story Source: Johns Hopkins University News Release.

February 22, 2013December 23, 2015 by Jason Major

Bright Jets Blast Out from a Newborn Star

A young star is spotted firing jets of material out into space (ESA/Hubble & NASA. Acknowledgement: Gilles Chapdelaine)

Like very young humans, very young stars also tend to make a big mess out of the stuff around them — except in the case of stars it’s not crayon on the walls and Legos on the floor (ouch!) but rather huge blasts of superheated material that are launched from their poles far out into space.

The image above, acquired by the Hubble Space Telescope, shows one of these young stars caught in the act.

HL Tau is a relatively newborn star, formed “only” within the past several hundred thousand years. During that time it has scooped up vast amounts of gas and dust from the area around itself, forming a disc of hot, accelerated material that surrounds it. While most of this material eventually falls into the star, increasing its mass, some of it gets caught up in the star’s complex, rotating magnetic fields and is thrown out into space as high-speed jets.

As these jets plow thorough surrounding interstellar space they ram into nearby clouds of molecular gas, ionizing the material within them and causing them to glow brightly. These “shocks” are known as Herbig-Haro objects, after researchers George Herbig and Guillermo Haro who each discovered them independently in the early 1950s.

Detail of HH 151's jet — Detail of HH 151’s jet

In this Hubble image HH 151 is visible as a multiple-lobed cone of material fired away from HL Tau, with the leftover glows from previous outbursts dimly illuminating the rest of the scene.

The material within these jets can reach speeds of several hundred to a thousand kilometers a second. They can last anywhere from a few years to a few thousand years.

HH 151 is embedded within the larger star-forming region LDN 1551, located about 450 light-years away in the constellation Taurus. LDN 1551 is a stellar nursery full of dust, dark nebulae, newborn stars… and Herbig-Haro objects like HH 151.

(Hey, if baby stars are going to make a mess at least they can do it in the nursery.)

December 4, 2012December 23, 2015 by Jason Major

Black Hole Jets Might Be Molded by Magnetism

Visible-light Hubble image of the jet emitted by the 3-billion-solar-mass black hole at the heart of galaxy M87 (Feb. 1998) Credit: NASA/ESA and John Biretta (STScI/JHU)

Even though black holes — by their definition and very nature — are the ultimate hoarders of the Universe, gathering and gobbling up matter and energy to the extent that not even light can escape their gravitational grip, they also often exhibit the odd behavior of flinging vast amounts of material away from them as well, in the form of jets that erupt hundreds of thousands — if not millions — of light-years out into space. These jets contain superheated plasma that didn’t make it past the black hole’s event horizon, but rather got “spun up” by its powerful gravity and intense rotation and ended up getting shot outwards as if from an enormous cosmic cannon.

The exact mechanisms of how this all works aren’t precisely known as black holes are notoriously tricky to observe, and one of the more perplexing aspects of the jetting behavior is why they always seem to be aligned with the rotational axis of the actively feeding black hole, as well as perpendicular to the accompanying accretion disk. Now, new research using advanced 3D computer models is supporting the idea that it’s the black holes’ ramped-up rotation rate combined with plasma’s magnetism that’s responsible for shaping the jets.

In a recent paper published in the journal Science, assistant professor at the University of Maryland Jonathan McKinney, Kavli Institute director Roger Blandford and Princeton University’s Alexander Tchekhovskoy report their findings made using computer simulations of the complex physics found in the vicinity of a feeding supermassive black hole. These GRMHD — which stands for General Relativistic Magnetohydrodynamic — computer sims follow the interactions of literally millions of particles under the influence of general relativity and the physics of relativistic magnetized plasmas… basically, the really super-hot stuff that’s found within a black hole’s accretion disk.

What McKinney et al. found in their simulations was that no matter how they initially oriented the black hole’s jets, they always eventually ended up aligned with the rotational axis of the black hole itself — exactly what’s been found in real-world observations. The team found that this is caused by the magnetic field lines generated by the plasma getting twisted by the intense rotation of the black hole, thus gathering the plasma into narrow, focused jets aiming away from its spin axes — often at both poles.

At farther distances the influence of the black hole’s spin weakens and thus the jets may then begin to break apart or deviate from their initial paths — again, what has been seen in many observations.

This “magneto-spin alignment” mechanism, as the team calls it, appears to be most prevalent with active supermassive black holes whose accretion disk is more thick than thin — the result of having either a very high or very low rate of in-falling matter. This is the case with the giant elliptical galaxy M87, seen above, which exhibits a brilliant jet created by a 3-billion-solar-mass black hole at its center, as well as the much less massive 4-million-solar-mass SMBH at the center of our own galaxy, Sgr A*.

Using these findings, future predictions can be better made concerning the behavior of accelerated matter falling into the heart of our galaxy.

Read more on the Kavli Institute’s news release here.

Inset image: Snapshot of a simulated black hole system. (McKinney et al.) Source: The Kavli Institute for Particle Astrophysics and Cosmology (KIPAC)