What's in a Jet from a Black Hole?

Originally posted at Forbes!

As far as we can tell, it’s mostly electrons, neutrons, and protons getting flung out into these jets. In the end, it turns out that the electrons are the key factor in making the jets so visible to our telescopes.

The jets themselves are interesting objects. Not every galaxy’s black hole produces a jet, even though all sizable galaxies have black holes. It seems that in order to produce this jet, the supermassive black hole in the very center of the galaxy has to be actively trying to gather new material into itself. Supermassive black holes are hilariously inefficient at growing larger, even when there’s material around for it to work with. Our Milky Way’s supermassive black hole isn’t growing at the moment because there’s no material nearby, but even if there were a lot more gas and dust very near the black hole, the black hole wouldn’t be able to grow very fast.

Part of the reason a black hole doesn’t grow very fast is that the material orbiting a black hole has to continue to lose energy to keep falling into the black hole, and that process of energy loss is driven by inefficient things like friction and heat. On top of all of this, there are probably crazy things happening with the magnetic fields within the rapidly rotating material around the black hole. Magnetic fields are a bit of a bugbear for studies of galaxies – we know that there are magnetic fields around, but we’re not quite sure how much of an effect they have on the galaxy, and they’re stupendously difficult to model correctly.

False-colour X-ray image of the giant elliptical active galaxy Centaurus A (NGC 5128) taken with the orbiting Chandra X-ray Observatory, featuring its 30,000 light-years long jet. Credit: NASA/SAO/R.Kraft et al.

False-colour X-ray image of the giant elliptical active galaxy Centaurus A (NGC 5128) taken with the orbiting Chandra X-ray Observatory, featuring its 30,000 light-years long jet. Credit: NASA/SAO/R.Kraft et al.

In the case of jets, we know that there must be strong magnetic fields, because we observe a type of glow that only happens if you have both very rapidly moving electrons and a magnetic field. It’s called synchrotron radiation, and its happens when you get a relativistic electron (which means that it’s moving at a significant fraction of the speed of light) caught in a twisting orbit around a magnetic field line. The electron moves in a helix around the magnetic field line, and emits light that we can observe with a wide range of different telescopes.

This VLA radio composite image shows the active galaxy 3C 348, also known as Hercules A. The VLA data, which record frequencies from 4-9 GHz, were taken in 2010-2011. Image Credit: R. Perley and W. Cotton (NRAO/AUI/NSF)

This VLA radio composite image shows the active galaxy 3C 348, also known as Hercules A. The VLA data, which record frequencies from 4-9 GHz, were taken in 2010-2011. Image Credit: R. Perley and W. Cotton (NRAO/AUI/NSF)

It’s usually this synchrotron radiation that we see in the images of jets coming from a supermassive black hole. If you’re looking at a radio image or an optical image, what you’re looking at is the glowing byproducts of nearly speed-of-light electrons bending under the influence of a magnetic field.

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If the Universe is Expanding, How Come Galaxies Collide?

The galaxies of this beautiful interacting pair bear some resemblance to musical notes on a stave. Long tidal tails sweep out from the two galaxies: gas and stars were stripped out and torn away from the outer regions of the galaxies. The presence of these tails is the unique signature of an interaction. ESO 69-6 is located in the constellation of Triangulum Australe, the Southern Triangle, about 650 million light-years away from Earth. Credit: NASA, ESA, the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration, and A. Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University)

The galaxies of this beautiful interacting pair bear some resemblance to musical notes on a stave. Long tidal tails sweep out from the two galaxies: gas and stars were stripped out and torn away from the outer regions of the galaxies. The presence of these tails is the unique signature of an interaction. ESO 69-6 is located in the constellation of Triangulum Australe, the Southern Triangle, about 650 million light-years away from Earth. Credit: NASA, ESA, the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration, and A. Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University)

Originally posted at Forbes!

Everything is expanding – and so this is a natural question to ask. How can everything be expanding away from every other thing, and yet still collide?

Part of the blame for this confusion lies with the sorts of diagrams and language we use to demonstrate the expansion of the universe. If I say “the space between every galaxy is expanding, so that each galaxy appears to drift away from every other galaxy”, that’s a good way to get you to imagine an expansion of space. It also means that I’m ignoring everything else that’s going on that might be complicating the situation, to make the expansion of space idea as clear as possible.

In this case, what’s complicating the situation is our old friend gravity. If each galaxy in the universe were evenly spaced out – for instance, if they were all laid out as though they were points on a grid – then the simple description is also an accurate one. There wouldn’t be anything else going on. Each galaxy would continue to evolve in total isolation, slowly drifting farther away from anything else.

Numerical simulation of the density of matter when the universe was 4.7 billion years old. Galaxy formation follows the gravitational wells produced by dark matter, where hydrogen gas coalesces, and the first stars ignite. Image credit: V. Springel et al. 2005, Nature, 435, 629

Numerical simulation of the density of matter when the universe was 4.7 billion years old. Galaxy formation follows the gravitational wells produced by dark matter, where hydrogen gas coalesces, and the first stars ignite. Image credit: V. Springel et al. 2005, Nature, 435, 629

This isn’t what our universe looks like. Our universe looks much more cobwebby than gridlike, with big knots of galaxies, and little filaments of galaxies stretching away from each knot. The big knots are galaxy clusters, and can hold thousands of galaxies. Their smaller counterparts, galaxy groups, have a few galaxies in them. Our own galaxy is in a small group, with Andromeda, and a bunch of very small dwarf galaxies.

These clusters and groups are what happens when galaxies form close enough to each other that gravity can pull them together. If a galaxy is close enough to another galaxy, and not moving too fast, gravity will prevent them from ever truly separating again. These galaxies may spend many billions of years falling towards each other, and will generally miss each other on the first attempted collision, so will spend many more billions of years falling back together for a second, and then perhaps a third attempt. Our galaxy and Andromeda are in the first fall together stage, which will probably take about 3 billion more years before it’s hard to disentangle our two galaxies.

This system consists of a pair of galaxies, dubbed NGC 3690 (or Arp 299), which made a close pass some 700 million years ago. As a result of this interaction, the system underwent a fierce burst of star formation. In the last fifteen years or so six supernovae have popped off in the outer reaches of the galaxy, making this system a distinguished supernova factory. Credit: NASA, ESA, the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration, and A. Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University)

This system consists of a pair of galaxies, dubbed NGC 3690 (or Arp 299), which made a close pass some 700 million years ago. As a result of this interaction, the system underwent a fierce burst of star formation. In the last fifteen years or so six supernovae have popped off in the outer reaches of the galaxy, making this system a distinguished supernova factory. Credit: NASA, ESA, the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration, and A. Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University)

Fundamentally, the fact that we see galaxy collisions comes down to two things; galaxies didn’t form on a grid, and the force of expansion of our universe is less strong than the force of gravity for galaxies which are near each other. If the force of expansion were much, much stronger than it is, then even gravity might not be able to pull galaxies together, and each galaxy really would be an island universe, isolated for all time. Fortunately for us, gravity still reigns supreme as long as the conditions are right.

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Can We Find Out Where The Big Bang Started?

Is there a reason why we can’t extrapolate the expansion of the universe backwards to determine where it all started in the Big Bang? Thanks!
A representation of the evolution of the universe over 13.77 billion years. The far left depicts the earliest moment we can now probe, when a period of "inflation" produced a burst of exponential growth in the universe. (Size is depicted by the vertical extent of the grid in this graphic.) For the next several billion years, the expansion of the universe gradually slowed down as the matter in the universe pulled on itself via gravity. More recently, the expansion has begun to speed up again as the repulsive effects of dark energy have come to dominate the expansion of the universe. The afterglow light seen by WMAP was emitted about 375,000 years after inflation and has traversed the universe largely unimpeded since then. The conditions of earlier times are imprinted on this light; it also forms a backlight for later developments of the universe. Image credit: NASA / WMAP Science Team

A representation of the evolution of the universe over 13.77 billion years. The far left depicts the earliest moment we can now probe, when a period of "inflation" produced a burst of exponential growth in the universe. (Size is depicted by the vertical extent of the grid in this graphic.) For the next several billion years, the expansion of the universe gradually slowed down as the matter in the universe pulled on itself via gravity. More recently, the expansion has begun to speed up again as the repulsive effects of dark energy have come to dominate the expansion of the universe. The afterglow light seen by WMAP was emitted about 375,000 years after inflation and has traversed the universe largely unimpeded since then. The conditions of earlier times are imprinted on this light; it also forms a backlight for later developments of the universe. Image credit: NASA / WMAP Science Team

Originally posted at Forbes!

Nope – we can, in fact, trace the universe back to where it all started. Unfortunately, it rapidly gets complicated, because the answer is that it began where you are sitting. And also where I am sitting. And also where everyone else on the planet is sitting. And also at the center of our galaxy, and at the center of every other galaxy.

The idea here is that our current universe is expanding, so the universe must have been smaller in the past. So if you take every point in space that exists now, and trace it backwards, all those points get closer and closer together until they reach a mathematical and physical stopping point – a singularity. A singularity is an infinitesimally small point, which can contain quite a large amount of matter or energy – the centers of black holes are also singularities.

The singularity we reach if we trace back the whole universe must have contained all the energy that now exists in our universe, as either mass or light, or dark matter, or dark energy. But it also contained all the space – so all the points of space that we now see as very widely separated were present within that singularity. So the “where” of the Big Bang is, quite literally, everywhere.

We have quite a lot of evidence pointing us to this idea of a very tiny universe at the very beginning of our universe; one of the more important being the detection of the cosmic microwave background (or CMB for short). This background radiation is called “background” because our universe has a fundamental glow in the microwave that you can’t escape – any other observations you’re making at this wavelength will be in addition to the CMB.

Critically, the CMB is very precisely almost the exact same in every direction that we look, and even though this glow is the oldest light in the universe, and the universe was much, much smaller than it is now, you would still not expect it to be the exact same everywhere — unless the universe had been even smaller previously. The theory of the Big Bang produces this naturally, because in between all space being compressed into the singularity, and the production of the light we see as the CMB, there is predicted to be a period of super fast expansion — inflation. Or, if you’re tracing the universe backwards in time, the universe shrinks dramatically down.

The thing to keep in mind with the Big Bang and the expansion of the universe is that it wasn’t an “explosion” like a detonation here on earth, with a definite center, and the universe spooling outwards into a pre-existing space. The closest you can get while thinking of conventional explosions would be if you managed to really effectively explode a tiny object, and then asked “Where was this piece when the explosion happened?” It was at the center, with all the other scattered pieces. For our universe’s expansion, each of those pieces would have to be markers in space itself. Where did the universe’s big bang happen? It happened where the universe was small, and each fragment of our current universe was there to witness it.

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Why don't planets hit each other?

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Are We Missing Intelligent Life Because We're Looking Into The Past?

Scientists around the world say that they have found new planets thousands, millions or billions of light years away from Earth. Doesn’t that mean that the images those scientist receive are thousands or millions or billions of light years old? If intelligent life formed in one of those planets, and if they are also searching for new planets, then doesn’t it mean that those life forms will see only a rocky planet not habitable to life?
This artist’s impression shows the super-Earth 55 Cancri e in front of its parent star. Using observations made with the NASA/ESA Hubble Space Telescope and new analytic software scientists were able to analyse the composition of its atmosphere. It was the first time this was possible for a super-Earth. 55 Cancri e is about 40 light-years away and orbits a star slightly smaller, cooler and less bright than our Sun. As the planet is so close to its parent star, one year lasts only 18 hours and temperatures on the surface are thought to reach around 2000 degrees Celsius. Image credit: ESA/Hubble, M. Kornmesser

This artist’s impression shows the super-Earth 55 Cancri e in front of its parent star. Using observations made with the NASA/ESA Hubble Space Telescope and new analytic software scientists were able to analyse the composition of its atmosphere. It was the first time this was possible for a super-Earth. 55 Cancri e is about 40 light-years away and orbits a star slightly smaller, cooler and less bright than our Sun. As the planet is so close to its parent star, one year lasts only 18 hours and temperatures on the surface are thought to reach around 2000 degrees Celsius. Image credit: ESA/Hubble, M. Kornmesser

Originally posted at Forbes!

The search for planets outside our solar system has been expanding pretty rapidly recently with the data coming back from the Kepler mission, but nobody has managed to detect a planet quite as far away as a billion light years from Earth. Kepler can only detect Earth-like planets that are less distant than 3000 light years away from our solar system, in a very narrow region of our galaxy.

Our galaxy is about 50,000 light years from center to edge (so about 100,000 light years across), and the next nearest large galaxy is Andromeda, sitting about two and a half million light years away from us. While our current observations of the Milky Way lead us to believe that there’s a planet around pretty much every star in our galaxy, we haven’t been able to survey that much of our own galaxy, let alone the stars in Andromeda, which would be exponentially more difficult to observe. The furthest solid detection of an exoplanet is still only about 21,000 light years away.

But you’re absolutely correct - our images of exoplanets are just as out of date as they are distant from us, and we won’t ever be able to get around that limitation unless we can go visiting them so that the light-delay isn't so severe. A planet that we see at 10,000 light years distant from us will be an image that has traveled for 10,000 years.

In this rare image taken on July 19, 2013, the wide-angle camera on NASA's Cassini spacecraft has captured Saturn's rings and our planet Earth and its moon in the same frame. It is only one footprint in a mosaic of 33 footprints covering the entire Saturn ring system (including Saturn itself). At each footprint, images were taken in different spectral filters for a total of 323 images: some were taken for scientific purposes and some to produce a natural color mosaic. This is the only wide-angle footprint that has the Earth-moon system in it. Image credit: NASA/JPL-Caltech/Space Science Institute

In this rare image taken on July 19, 2013, the wide-angle camera on NASA's Cassini spacecraft has captured Saturn's rings and our planet Earth and its moon in the same frame. It is only one footprint in a mosaic of 33 footprints covering the entire Saturn ring system (including Saturn itself). At each footprint, images were taken in different spectral filters for a total of 323 images: some were taken for scientific purposes and some to produce a natural color mosaic. This is the only wide-angle footprint that has the Earth-moon system in it. Image credit: NASA/JPL-Caltech/Space Science Institute

On a geological timescale, 10,000 years is just a blip of time - the Earth was pretty much in the same shape as it is now, though we humans had made fewer changes to its surface. On a human timescale, 10,000 years has made a big difference. 10,000 years puts us back into the Neolithic era - the end of the Stone Age, around the time when pottery was developing, and we were beginning to cultivate plants for agriculture. So an intelligent civilization, 10,000 light years distant, that is just now looking for other life in the Universe would spy our Earth as a rocky planet with an atmosphere, far enough away from our sun that water could exist in our atmosphere, and if they managed to examine our atmosphere, they would notice that it is mostly nitrogen, with some oxygen and carbon dioxide in it as well, and that it contains water vapor. They would not be able to tell that there are creatures on that planet that are 10,000 years away from developing the internet, neurosurgery, and machines able to detect tiny distortions in space itself.

This kind of time delay is one of the reasons that scientists get extra excited when they find a nearby rocky planet that might be able to have liquid water on its surface - if the planet is close to us, then the time delay isn’t as bad as a more distant planet. (It is also much easier to observe these nearby planets in any degree of detail - the farther away you are from the Earth, the harder these measurements get.) We only managed to detect the contents of the atmosphere of a slightly-bigger-than-Earth planet for the first time a few days ago — unfortunately that planet is totally devoid of water, having an atmosphere of mostly hydrogen and helium, with some hydrogen cyanide thrown in for extra poisonous flavor. This planet is only 60 light years away, so our image of it is only out of date as far as 1976— this particular planet won’t have evolved into a friendlier, life-hosting planet in such a short time.

But let’s say a super-intelligent civilization out there has built an impossibly large telescope, and has the power (and the time) to detect planets orbiting stars in a distant galaxy, and they pointed it at our Earth. If they happened to be 2.5 billion light years distant, our planet’s atmosphere would be in the middle of a dramatic change. 2.5 billion years ago, our planet was in the middle of the Oxygen Catastrophe - the earliest photosynthetic bacteria were dumping oxygen into the atmosphere faster than it could be absorbed, and oxygen was slowly building up. As oxygen was a toxic byproduct to the single-celled life which had been living in a delightfully oxygen-free environment, they would have to adapt or die off. Observations of our planet from that distance would be able only to tell the observer that our planet existed, it has water in its atmosphere, and how rapidly we travel around our star, but not so much as a hint to our space-exploring future.

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