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Astronomy Without A Telescope – Home Made Quark-Gluon Soup

The most powerful operational heavy-ion collider in the world, the Relativistic Heavy Ion Collider (RHIC) recently recorded the highest ever temperature created in an Earth-based laboratory of 4 trillion Kelvin. Achieved at the almost speed of light collision of gold ions, this resulted in the temporary existence of quark-gluon soup – something first seen at about ten to the power of minus twelve of the first second after the big bang.

And sure, the Large Hadron Collider (LHC) may one day soon be the most powerful heavy-ion collider in the world (although it will spend most of its time investigating proton to proton collisions). And sure, maybe it’s going to generate a spectacular 574 TeV when it collides its first lead ions. But you have to win the game before you get the trophy.

To give credit where it’s due, the LHC is already the most powerful particle collider in the world – having achieved proton collision energies of 2.36 TeV in late 2009. And it should eventually achieve proton collision energies of 14 TeV, but that will come well after its scheduled maintenance shutdown in 2012, ahead of achieving its full design capabilities from 2013. It has already circulated a beam of lead ions – but we are yet to see an LHC heavy ion collision take place.

So, for the moment it’s still RHIC putting out all the fun stuff. In early March 2010, it produced the largest ever negatively charged nucleus – which is anti-matter, since you can only build matter nuclei from protons and/or neutrons which will only ever have a positive or a neutral charge.

This antimatter nucleus carried an anti-strange quark – which is crying out for a new name… mundane quark, conventional quark? And since the only matter nuclei containing strange quarks are hypernuclei, RHIC in fact created an antihypernucleus. Wonderful.

Then there’s the whole quark-gluon soup story. Early experiments at RHIC reveal that this superhot plasma behaves like a liquid with a very low viscosity— and may be what the universe was made of in its very early moments.  There was some expectation that melted protons and neutrons would be so hot that surely you would get a gas – but like the early universe, with everything condensed into a tiny volume, you get a super-heated liquid (i.e. soup).

An aerial view of the Relativistic Heavy Ion Collider (RHIC) in Upton, NY. The Alternating Gradient Synchrotron (AGS) built in the 1960s now works as a pre-accelerating injector for the larger RHIC.

The LHC hopes to deliver the Higgs, maybe a dark matter particle and certainly anti-matter and micro black holes by the nano-spoonful. And after that, there’s talk of building the Very Large Hadron Collider, which promises to be bigger, more powerful and more expensive.

But if that project doesn’t fly, we can still ramp up the existing colliders. Ramping up a particle collider is an issue of luminosity, where the desired outcome is a more concentrated and focused particle beam – with an increased energy density achieved by cramming more particles into a cross section of the beam you are sending around the particle accelerator. Both RHIC and the LHC have plans to undertake an upgrade to achieve an increase of their respective luminosities by up to a factor of 10. If successful, we can look forward to RHIC II and the Super Large Hadron Collider coming online sometime after 2020. Fun.

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Astronomy Without A Telescope – Gravity, Schmavity

The axiom that what goes up, must come down doesn’t apply to most places in the universe, which are largely empty space. For most places in the universe, what goes up, just goes up. On Earth, the tendency of upwardly-mobile objects to reverse course in mid-flight and return to the surface is, to say the least, remarkable.

It’s even more remarkable if you go along for the ride.

If you launch in a rocket you will be pushed back into your seat as long as your rockets fire. But as soon as you cut the engines you will experience weightlessness as you arc around and fall back down again, following a similar path that a cannon ball fired up from the Earth’s surface would take. And remarkably, you will continue to experience weightlessness all the way down – even though an external observer will observe your rocket steadily accelerating as it falls.

Now consider a similar chain of events out in the microgravity of space. Fire your rocket engines and you’ll be pushed back into your seat – but as soon as you switch them off, the rocket ship will coast at a constant velocity and you’ll be floating in free fall within it – just like you do when plummeting to your accelerated doom back on Earth.

From your frame of reference – and let’s say you’re blind-folded – you would have some difficulty distinguishing between the experience of following a rocket-blast-initiated parabolic trajectory in a gravity field versus a rocket-blast-initiated straight line trajectory out in the microgravity of space. Well OK, you’ll notice something when you hit the ground in the former case – but you get the idea.

So there is good reason to be cautious about referring to the force of gravity. It’s not like an invisible elastic band that will pull you back down as soon as you shut off your engines. If you were blindfolded, with your engines shut off, it would seem as if you were just coasting along in a straight line – although an external observer in a different frame of reference would see your ship turn about and then accelerate down to the ground.

So how do we account for the acceleration that you the pilot can’t feel?

An improvement on the standard two dimensional rubber sheet analogy for curved space-time - although it still lacks the contribution of the all-important time dimension.

Without a blindfold, you the pilot might find the experience of falling in a gravity field a bit like progressing through a slow motion movie – where each frame you move through is running at a slightly slower rate than the last one and where the spatial dimensions of each frame progressively shrink. As you move frame by frame – each time taking with you the initial conditions of the previous frame, your initially constant velocity becomes faster and faster, relative to each successive frame you move through – even though from your perspective you are maintaining a constant velocity.

So – no force of gravity, it’s just geometry.

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Eccentricity

When it comes to space, the word eccentricity nearly always refers to orbital eccentricity, or the eccentricity of the orbit of an astronomical body, like a planet, star, or moon. In turn, this relies on a mathematical description, or summary, of the body’s orbit, assuming Newtonian gravity (or something very close to it). Such orbits are approximately elliptical in shape, and a key parameter describing the ellipse is its eccentricity.

In simple terms, a circular orbit has an eccentricity of zero, and a parabolic or radial orbit an eccentricity of 1 (if the orbit is hyperbolic, its eccentricity is greater than 1); of course, if the eccentricity is 1 or greater, the ‘orbit’ is a bit of a misnomer!

In a planetary system with more than one planet (or for a planet with more than one moon, or a multiple star system other than a binary), orbits are only approximately elliptical, because each planet has a gravitational pull on every other one, and these accelerations produce non-elliptical orbits. And modeling orbits assuming the theory of general relativity describes gravity also leads to orbits which are only approximately elliptical (this is particular so for binary pulsars).

Nonetheless, orbits are nearly always summarized as ellipses, with eccentricity as one of the key orbital parameters. Why? Because this is very convenient, and because deviations from ellipses can be easily described by small perturbations.

The formula for eccentricity, in a two-body system under Newtonian gravity, is relatively easy to write, but, unfortunately, beyond the capabilities of the HTML coding of this webpage.

However, if you know the maximum distance of a body, from the center of mass – the apoapsis (apohelion, for solar system planets), ra – and the minimum such distance – the periapsis (perihelion), rp – then the eccentricity, e, of the orbit is just:

E = (ra – rp)/( ra+ rp)

Eccentricity of an Orbit (UCAR), Eccentricity of Earth’s Orbit (National Solar Observatory), and Equation of Time (University of Illinois) are websites with more on eccentricity.

Universe Today articles on eccentricity? Sure! For example: Measuring the Moon’s Eccentricity at Home, Buffy the Kuiper Belt Object, and Lake Asymmetry on Titan Explained.

Two Astronomy Cast episodes in which eccentricity is important are Neptune, and Earth; well worth listening to.

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Supermassive Black Holes Spinning Backwards Create Death Ray Jets?

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Why do some of the supermassive black holes in active galactic nuclei create back-to-back jets that can vaporize entire solar systems, while others have no jets at all?

Dan Evans, a postdoctoral researcher at MIT Kavli Institute for Astrophysics and Space Research (MKI) thinks he knows why; it’s because the jet-producing supermassive black holes are spinning backwards, relative to their accretion disks.

Radio image of a typical DRAGN, showing the main features (Image credit:C. L. Carilli)

For two years, Evans has been comparing several dozen galaxies whose black holes host powerful jets (these galaxies are known as radio-loud active galactic nuclei, or AGN, and are often DRAGNs – double radio source associated with galactic nucleus) to those galaxies with supermassive black holes that do not eject jets. All black holes – those with and without jets – feature accretion disks, the clumps of dust and gas rotating just outside the event horizon. By examining the light reflected in the accretion disk of an AGN black hole, he concluded that jets may form right outside black holes that have a retrograde spin – or which spin in the opposite direction from their accretion disk. Although Evans and a colleague recently hypothesized that the gravitational effects of black hole spin may have something to do with why some have jets, Evans now has observational results to support the theory in a paper published in the Feb. 10 issue of the Astrophysical Journal.

Although Evans has suspected for nearly five years that retrograde black holes with jets are missing the innermost portion of their accretion disk, it wasn’t until last year that computational advances meant that he could analyze data collected between late 2007 and early 2008 by the Suzaku observatory, a Japanese satellite launched in 2005 with collaboration from NASA, to provide an example to support the theory. With these data, Evans and colleagues from the Harvard-Smithsonian Center for Astrophysics, Yale University, Keele University and the University of Hertfordshire in the United Kingdom analyzed the spectra of the active galactic nucleus with a pair of jets located about 800 million light years away in an AGN named 3C 33.

1477 MHz image of 3C 33 (Credit: Leahy & Perley (1991))

“It’s the first convincing galaxy of this type seen at this angle where the result is pretty robust,” said Patrick Ogle, an assistant research scientist at the California Institute of Technology, who studies AGN. Ogle believes Evans’s theory regarding retrograde spin is among the best explanations he has heard for why some AGN contain a supermassive black hole with a jet and others don’t.

Astrophysicists can see the signatures of x-ray emission from the inner regions of the accretion disk, which is located close to the edge of a black hole, as a result of a super hot atmospheric ring called a corona that lies above the disk and emits light (electromagnetic radiation) that an observatory like Suzaku can detect. In addition to this direct light, a fraction of light passes down from the corona onto the black hole’s accretion disk and is reflected from the disk’s surface, resulting in a spectral signature pattern called the Compton reflection hump, also detected by Suzaku.

But Evans’ team never found a Compton reflection hump in the x-ray emission given off by 3C 33, a finding the researchers believe provides crucial evidence that the accretion disk for a black hole with a jet is truncated, meaning it doesn’t extend as close to the center of the black hole with a jet as it does for a black hole that does not have a jet. The absence of this innermost portion of the disk means that nothing can reflect the light from the corona, which explains why observers only see a direct spectrum of x-ray light.

The researchers believe the absence may result from retrograde spin, which pushes out the orbit of the innermost portion of accretion material as a result of general relativity, or the gravitational pull between masses. This absence creates a gap between the disk and the center of the black hole that leads to the piling of magnetic fields that provide the force to fuel a jet.

While Ogle believes that the retrograde spin theory is a good explanation for Evans’ observations, he said it is far from being confirmed, and that it will take more examples with consistent results to convince the astrophysical community.

The field of research will expand considerably in August 2011 with the planned launch of NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR) satellite, which is 10 to 50 times more sensitive to spectra and the Compton reflection hump than current technology. NuSTAR will help researchers conduct a “giant census” of supermassive black holes that “will absolutely revolutionize the way we look at X-ray spectra of AGN,” Evans explained. He plans to spend another two years comparing black holes with and without jets, hoping to learn more about the properties of AGN. His goal over the next decade is to determine how the spin of a supermassive black hole evolves over time.

Sources: MITnews, Evans’ Astrophysical Journal paper (preprint is arXiv:1001.0588)

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Nuclear Fusion Power Closer to Reality Say Two Separate Teams

Nuclear Physics

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For years, scientists have been trying to replicate the type of nuclear fusion that occurs naturally in stars in laboratories here on Earth in order to develop a clean and almost limitless source of energy. This week, two different research teams report significant headway in achieving inertial fusion ignition—a strategy to heat and compress a fuel that might allow scientists to harness the intense energy of nuclear fusion. One team used a massive laser system to test the possibility of heating heavy hydrogen atoms to ignite. The second team used a giant levitating magnet to bring matter to extremely high densities — a necessary step for nuclear fusion.

Unlike nuclear fission, which tears apart atoms to release energy and highly radioactive by-products, fusion involves putting immense pressure, or “squeezing” two heavy hydrogen atoms, called deuterium and tritium together so they fuse. This produces harmless helium and vast amounts of energy.

Recent experiments at the National Ignition Facility in Livermore, California used a massive laser system the size of three football fields. Siegfried Glenzer and his team aimed 192 intense laser beams at a small capsule—the size needed to store a mixture of deuterium and tritium, which upon implosion, can trigger burning fusion plasmas and an outpouring of usable energy. The researchers heated the capsule to 3.3 million Kelvin, and in doing so, paved the way for the next big step: igniting and imploding a fuel-filled capsule.

In a second report released earlier this week, researchers used a Levitated Dipole Experiment, or LDX, and suspended a giant donut-shaped magnet weighing about a half a ton in midair using an electromagnetic field. The researchers used the magnet to control the motion of an extremely hot gas of charged particles, called a plasma, contained within its outer chamber.

The donut magnet creates a turbulence called “pinching” that causes the plasma to condense, instead of spreading out, which usually happens with turbulence. This is the first time the “pinching” has been created in a laboratory. It has been seen in plasma in the magnetic fields of Earth and Jupiter.
A much bigger ma LDX would have to be built to reach the density levels needed for fusion, the scientists said.

Paper: Symmetric Inertial Confinement Fusion Implosions at Ultra-High Laser Energies

Sources: Science Magazine, LiveScience

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Niels Bohr

Niels Bohr

[/caption]Niels Bohr was a Nobel Prize winner. He was born Niels Henrik David Bohr on October 7, 1855, in Copenhagen. His home atmosphere growing up aided his intellect and skill in physics, since he was the son of a university professor. Niels Bohr enrolled at the University of Copenhagen. At first he began to study mathematics and philosophy, but after he won a prize for examining the property of surface tension, he switched to studying physics. While there, he got both his Master’s and doctorate degrees in physics.

 In 1911, in Cambridge, England, he studied with the man who had discovered the atom a decade and a half earlier. Soon after, he discovered, along with colleagues, the structure of the atom He created the Bohr atomic model in 1913, which says that electrons travel around the nucleus in a discrete orbit. He said that electrons traveled in set orbits around the nucleus. The electrons moved between these set orbits depending on whether they gained or lost energy. The Bohr model was a revision of the Rutherford model of the atom. In 1922, Niels Bohr was awarded the Nobel Prize in Physics for his work regarding the structure of atoms. He was only 37 when he won the Nobel Prize.

In 1920, Copenhagen University formed the Institute for Theoretical Physics for Bohr to head. He was in charge of the institute until his death. Following him, one of his sons who was a physicist, Aage Bohr, took over the institute. Niehls Bohr continued to study the structure of the atom’s nuclei (the Bohr atom)while he was in charge of the Institute, creating the liquid drop model of the nucleus.

He also lectured at Victoria University. In 1916, he was given the job of Professor of Theoretical Physics at Copenhagen University. He continued working in Copenhagen the rest of his life, except for when he left during the war. During World War II, Bohr fled Copenhagen and moved to Sweden and also spent time in England and America. While in the United States, he worked on the Manhattan Project. For security measures, he assumed the name Nicholas Baker while he was working on Manhattan Project. Bohr was in favor of sharing nuclear knowledge with the scientific community which was very much opposed by world leaders, such as Winston Churchill. Bohr continued to advocate sharing nuclear technology.

In addition to Bohr’s other contributions and extensive writings, he had a chemical element, Bohrium, named after him. One of Bohr’s sons, Aage Bohr, shared the Nobel Peace Prize in Physics with two others. Niels Bohr died in 1962 as a result of a stroke.

Universe Today has articles on Bohr’s atomic model and the Bohr model.

For more information, check out a biography of Niels Bohr and Niels Bohr.

Astronomy Cast has an episode on inside the atom.

Source:
Nobel Prize

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Atomic Mass Unit

Faraday's Constant

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Believe it or not, there are actually several atomic mass units … however, the one that’s standard – throughout chemistry, physics, biology, etc – is the unified atomic mass unit (symbol u). It is defined as 1/12 (one-twelfth) of the mass of an isolated carbon-12 atom, in its ground state, at rest. You’ll still sometime see the symbol amu – which stands for atomic mass unit – but that’s actually two, slightly different, units (and each is different from the unified atomic mass unit!) … these older units are defined in terms of oxygen (1/16th of an isolated oxygen-16 atom, and 1/16th of an ‘average’ oxygen atom).

As it’s a unit of mass, the atomic mass unit (u) should also have a value, in kilograms, right? It does … 1.660 538 782(83) x 10-27 kg. How was this conversion worked out? After all, the kilogram is defined in terms of a bar of platinum-iridium alloy, sitting in a vault in Paris! First, it is important to recognize that the unified atomic mass unit is not an SI unit, but one that is accepted for use with the SI. Second, the kilogram and unified atomic mass unit are related via a primary SI unit, the mole, which is defined as “the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon 12“. Do you remember how many atoms there are in a mole of an element? Avogadro’s number! So, work out the Avogadro constant, and the conversion factor follows by a simple calculation …

The Dalton (symbol D, or Da) is the same as the unified atomic mass unit … why have two units then?!? In microbiology and biochemistry, many molecules have hundreds, or thousands, of constituent atoms, so it’s convenient to state their masses in terms of ‘thousands of unified atomic mass units’. That’s far too big a mouthful, so convention is to use kDa (kilodaltons).

Find out more on the (unified) atomic mass unit, from the Argonne National Laboratory, from the International Union of Pure and Applied Chemistry, and from the National Institute of Standards and Technology (NIST).

Learning to Breathe Mars Air and Mini-Detector Could Find Life on Mars or Anthrax at the Airport are two Universe Today articles relevant to the atomic mass unit.

Energy Levels and Spectra and Inside the Atom are two Astronomy Cast episodes related to the atomic mass unit.

Sources:
Wikipedia
Newton Ask a Scientist
Wise Geek

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Physicists Tie Beam of Light into Knots

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Imagine taking a beam of light and tying it in knots like a piece of string. Hard to fathom? Well, a group of physicists from the UK have achieved this remarkable feat, and they say understanding how to control light in this way has important implications for laser technology used in wide a range of industries.

“In a light beam, the flow of light through space is similar to water flowing in a river,” said Dr. Mark Dennis from the University of Bristol and lead author of a paper published in Nature Physics this week. “Although it often flows in a straight line – out of a torch, laser pointer, etc – light can also flow in whirls and eddies, forming lines in space called ‘optical vortices.’ Along these lines, or optical vortices, the intensity of the light is zero (black). The light all around us is filled with these dark lines, even though we can’t see them.”

Optical vortices can be created with holograms which direct the flow of light. In this work, the team designed holograms using knot theory – a branch of abstract mathematics inspired by knots that occur in shoelaces and rope. Using these specially designed holograms they were able to create knots in optical vortices.

This new research demonstrates a physical application for a branch of mathematics previously considered completely abstract.

“The sophisticated hologram design required for the experimental demonstration of the knotted light shows advanced optical control, which undoubtedly can be used in future laser devices,” said Miles Padgett from Glasgow University, who led the experiments

“The study of knotted vortices was initiated by Lord Kelvin back in 1867 in his quest for an explanation of atoms,” addeds Dennis, who began to study knotted optical vortices with Professor Sir Michael Berry at Bristol University in 2000. “This work opens a new chapter in that history.”

Paper: Isolated optical vortex knots by Mark R. Dennis, Robert P. King, Barry Jack, Kevin O’Holleran and Miles J. Padgett. Nature Physics, published online 17 January 2010.

Source: University of Bristol

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What is Absolute Temperature?

If you measure temperature relative to absolute zero, the temperature is an absolute temperature; absolute zero is 0.

The most widely used absolute temperature scale is the Kelvin, symbolized with a capital K, which uses Celsius-scaled degrees (there’s another one, the Rankine, which is related to the Fahrenheit scale). We write temperatures in kelvins without the degree symbol; absolute zero is 0 K.

Another name for absolute temperature is thermodynamic temperature. Why? Because absolute temperate is directly related to thermodynamics; in fact it is the Zeroth Law of Thermodynamics that leads to a (formal) definition of (thermodynamic) temperature.

Roughly speaking, the temperature of an object (or similar, like the gas in a balloon) measures the kinetic energy of the particles (atoms, molecules, etc) of the matter it’s made up of … in an average sense, and macroscopically. Note that blobs of matter have far more energy than just the kinetic energy of the atoms in the blob – there’s the energy that holds the atoms together in molecules (if there are any), the binding energy of the nuclei (unless the blog is pure hydrogen, with no deuterium), and so on; none of these energies are counted in the blob’s temperature.

You might think that at absolute zero a substance would be in its lowest possible energy state, especially if it is a pure compound (or isotopically pure element). Well, it isn’t quite that simple … leaving aside zero point energy (something quite counter-intuitive, from quantum mechanics), there’s the fact that many solids have several different, stable crystal structures (even at 0 K), but only one with minimal energy. Then there’s helium, which is a liquid at 0 K (the solid phase of a substance has a lower energy than the corresponding liquid phase), unless under pressure.

The Kelvin is one of the International System of Units (SI) base units (there are seven of these), and is defined with reference to the triple point of water (“The kelvin, unit of thermodynamic temperature, is the fraction 1/273.16 of the thermodynamic temperature of the triple point of water” is the 1967/8 definition; the current one – adopted in 2005 – expands on this to take account of isotropic variations).

Why is it called the Kelvin? Because William Thompson – Lord Kelvin – was the first to describe an absolute temperature scale, in a paper he wrote in 1848; he also estimated absolute zero was -273o C.

Project Skymath has a nice introduction to absolute temperature.

Some Universe Today material you may find interesting: Absolute Zero, Coldest Temperature Ever Created, and Planck First Light.

Sources: Wikipedia, Hyperphysics

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Quintessence

Quintessence is one idea – hypothesis – of what dark energy is (remember that dark energy is the shorthand expression of the apparent acceleration of the expansion of the universe … or the form of mass-energy which causes this observed acceleration, in cosmological models built with Einstein’s theory of general relativity).

The word quintessence means fifth essence, and is kinda cute … remember Earth, Water, Fire, and Air, the ‘four essences’ of the Ancient Greeks? Well, in modern cosmology, there are also four essences: normal matter, radiation (photons), cold dark matter, and neutrinos (which are hot dark matter!).

Quintessence covers a range of hypotheses (or models); the main difference between quintessence as a (possible) explanation for dark energy and the cosmological constant Λ (which harks back to Einstein and the early years of the 20th century) is that quintessence varies with time (albeit slooowly), and can also vary with location (space). One version of quintessence is phantom energy, in which the energy density increases with time, and leads to a Big Rip end of the universe.

Quintessence, as a scalar field, is not the least bit unusual in physics (the Newtonian gravitational potential field is one example, of a real scalar field; the Higgs field of the Standard Model of particle physics is an example of a complex scalar field); however, it has some difficulties in common with the cosmological constant (in a nutshell, how can it be so small).

Can quintessence be observed; or, rather, can quintessence be distinguished from a cosmological constant? In astronomy, yes … by finding a way to observed (and measure) the acceleration of the universe at widely different times (quintessence and Λ predict different results). Another way might be to observe variations in the fundamental constants (e.g. the fine structure constant) or violations of Einstein’s equivalence principle.

One project seeking to measure the acceleration of the universe more accurately was ESSENCE (“Equation of State: SupErNovae trace Cosmic Expansion”).

In 1999, CERN Courier published a nice summary of cosmology as it was understood then, a year after the discovery of dark energy The quintessence of cosmology (it’s well worth a read, though a lot has happened in the past decade).

Universe Today articles? Yep! For example Will the Universe Expand Forever?, More Evidence for Dark Energy, and Hubble Helps Measure the Pace of Dark Energy.

Astronomy Cast episodes relevant to quintessence include What is the universe expanding into?, and A Universe of Dark Energy.

Source: NASA