I later confirmed with Dr. Jon Morse that GLAST is being pushed back until at least the 6th or 7th of June. Upon further questioning Dr. Morse said the delay is because the close out operations for the Delta II rocket aren’t yet complete. Apparently the Air Force would like to see a more rigorous close out operation for this particular mission.

Scott

The long bursts are known (because we can seem them in the optical sometimes) to originate in the death of giant stars going not just supernova, but hypernova! The shorter bursts have been much more enigmatic, with only a handful (1 that I can find record of, but I leave room for more), being observed in wavelengths other than gamma-ray and X-ray. We had some ideas of causes: merging neutron stars, neutron stars with re-arranging magnetic fields (generally called soft-gamma ray repeaters, like SGR 1806-20), something not as powerful as exploding stars, but still pretty exotic. There is now reason to believe both the possibilities could be true.

In a pre-print posted on arXiv by Robert Chapman and collaborators, a statistical perspective is taken, and the question is asked, can all the short gamma-ray bursts observed be accounted for by just one of these populations, or does a combined model make the most sense?

Soft gamma-ray burst repeaters like SGR1806-20 are visible as far as 50 million parsecs away (for comparison, Andromeda Galaxy is 775 thousand parsecs away). In general, short gamma ray bursts can be correlated on the sky with galaxies as far away as 155 million parsecs.

In trying to sort out the cause of short gamma-ray bursts, this team combined models called luminosity functions describing the potential distributions of neutron star – neutron star binaries and and soft gamma-ray repeaters. They were able to reproduce the observed number of short gamma-ray bursts using a model that had the number of bursts coming from stars with rearranging magnetic fields becoming flat at a distance of about 200 million parsecs, and the number of bursts from neutron star – neutron star binaries increasing beyond 200 million parsecs.

Their attempt to fit observations using either just the soft gamma-ray bursts or neutron star – neutron star populations failed. No good fit could be found.

What is kind of neat about this is short gamma ray bursts always involve neutron stars, they just don’t always involve the same physical mechanism. Everything is tightly wound up in these little stars, and energy is just waiting to escape and light up our sky with gamma-rays.

“Once a parity is introduced in unparticle physics, under which unparticle provided in a hidden conformal
sector is odd while all Standard Model particles are even, unparticle can be a suitable candidate for the cold dark
matter (CDM) in the present universe through its coupling to the Standard Model Higgs doublet.”

No, I didn’t initially understand it either. (My first thought was actually, “All your base are belong to us.” )

But then I read the paper, and found that it was actually very cool. A few months ago, Harvard’s Howard Georgi (who was one of my favorites among the Harvard Faculty I used to work with), came out with a neat theory that in addition to the standard particles in the standard model of physics there is also a secondary particle regime which he called unparticles (see this article and this article). If this stuff exists, it will be detectable by the Large Hadron Collider (LHC) when it stars working at some point in (hopefully) the next 12 months.

And, in this new paper I read, by Tatsuru Kikuchi1, and Nobuchika Okada of The Graduate University for Advanced Studies in Japan, there are indications that if this unparticle stuff exists, it could be dark matter. Specifically, the predict that Higgs bosons (which the LHC will produce) can decay into two dark matter unparticles. They make specific predictions for various possible Higgs boson masses, and they are set to be proven right or wrong by the giant international experiment.

This is the kind of theory I like.

I am amazed at how much people can pull out of mathematics. This all started with Howard Georgi exploring the math a particle physics and finding a door through the equations into unparticles. Now, people are going through this door and exploring possible ways to redecorate our understanding of the universe. This isn’t something I have the ability to do. For me, math is a tool, and things like the quadratic equation have one purpose (like a tiny star wrench) while other equations like F=ma are giant adjustable wrenches that can be used as a hammer in a pinch. I know how to abuse tools (which may be why my husband tries to keep me out of his machine shop), but I don’t have it it me to build new tools that through there existence define a new way of building things. In opening the door to unparticles, Georgi was very much like the first person to make a screw and screw driver – because of the screw and screw driver, it was now possible to build new things, never before imagined.

And we’ll know soon enough if unparticles are real.

I can’t wait for the LHC to fire.

Here’s how it works: A supermassive black hole in the center of a galaxy eats something and emits a burst of light. Some of that light flies immediately to us on a straight line. That’s what our telescope catches first. Some of the light travels outward and interacts with surrounding clouds of material. Sometimes, the light will get absorbed by the clouds and will then be re-emitted in all directions – and some of this new light will now start traveling our way. Depending on the density, composition, temperature, and orbital velocities of the clouds, the light will interact in different ways and look different when it reaches us. Areas where the gas is cool and calm will emit narrow lines. Clouds that have high velocities emit broader lines.

Now, if we see that first blast of light followed by the appearance of broad lines followed by narrow line emission, that could mean the area emitting broad lines is closer in (the lights gets to the clouds first and then gets to us next), and the area emitting narrow lines is even farther out. The duration of time that we see light from the different regions also helps us understand how big they are. It will take a longer period of time for light from larger regions to finish getting to us. Think of it this way, imagine that you are looking at a hullahoop of material almost edge on. The initial burst of light its the entire ring at the same time, but the material nearest us has its light get to us first. Light from the backside of the hoop has to travel all the way across the hoop and then across space to us. The difference in time between when light from the near side and far side reach us (combined with the speed of light and the geometry of the galaxy), allows us to calculate the size of the hoop.

To make the measurements necessary to do these mapping projects, astronomers use spectroscopes on extremely large telescopes. Quasars aren’t found anywhere near our galaxy, and while they are some of the most luminous objects in the universe, they appear faint because they are far away. It takes large scopes to capture enough light from these distant objects to make out the lines used for echo mapping.

And large scopes have now been around long enough for scientists to have collected enough data over enough time to start producing initial maps of the distant galaxy cores.

This is one of those sets of of observations that is particularly exciting because it shows how far we, as astronomers, have come in the past decade or so. When I was an undergrad in the mid-nineties no one knew for certain what powered quasars. People talked about the angry monster in the center, and said it might, maybe, probably be a black hole. Today we have solid evidence of supermassive black holes in the center of many nearby galaxies and are using blackhole theories to map out distant galaxies.

The next person who says we’ve learned nothing new in the past (some number of) years is going to get directed toward a supermassive black hole

Image credit: NASA Education and Public Outreach at Sonoma State University – Aurore Simonnet

Astronomers in Switzerland and Washington, lead by A. Eigenbrod, observed Einstein’s Cross spectroscopically using the Very Large Telescopes in Chile. In a study spanning 2 years, they systematically mapped the structure of Q2337+0305 using microlensing. Here is what is happening: The light from the quasar bends through the intervening galaxy along different paths. Over time, stars in the galaxy will pass through these paths. When a star enters the light from the quasar, it magnifies the light (this is called microlensing). As the star passes in front of different parts of the quasar, those parts get their light amplified, while the other parts stay at a constant brightness. Over time, the star will move across different parts of the quasar, systematically amplifying new areas. By measuring what is amplified over time, as a star crosses, a map can be built.

This process can’t usually be used because different parts of the quasar naturally vary in brightness. Under normal circumstances it isn’t possible to determine if there is microlensing or if the quasar is fluctuating just because it can. In the unique case of Einstein’s Cross, observers will see the quasar’s natural variations in all four images while microlensing events will only appear in one image.

In looking at Einstein’s cross, Eigenbrod and his team specifically studied how different atomic lines, which come from regions of different densities and temperatures, varied over time. This allows detailed density maps to be built.

In their initial study, they saw significant variations in 2 of the 4 images in Einstein’s cross, and as they watch they expect to eventually see variations in the other images as well. The differences in microlensing in the four images is related to the distributions of orbits in the intervening galaxy, and its willingness to provide stars to orbit through each of the images of Q2337+0305. Over time, as more orbits have a chance to send stars across the images, more and more details maps can be built.

This is one of those really great cases of the universe providing some really neat built in tools, like Easter Eggs hidden among the stars.

Here’s the thing. At this stage in the game, even if we do someday find short comings in Einstein’s theories, we won’t be proving his theory wrong, we will be expanding on it. Just as we don’t say Newton’s theories as being wrong, we will not talk of Einstein as being wrong. Newton’s theories were incomplete, but they are correct within the realm of classical physics experiments. We already know Einstein’s theories break in quantum regimens, but they are correct in classical and relativistic regimens. One more theory (at least!) is needed, but all because something isn’t true all the time doesn’t mean it’s wrong.

Example: They sky, as I write this, is not blue. That said, when I say the sky is blue, I am not making a stupid statement – I’m just making a statement that is only true in certain regimens of sunlight and weather.

Einstein’s not wrong.

Got it? Good.

Now, that you know my state of mind, imagine my reaction to the current press being given to this latest claim that relativity had been falsified in the classic regimen (note – the paper is not accepted to any peer reviewed journal). So you’ve seen the coverage in New Scientist, you’ve seen the hubbub on Slashdot. But what does it all mean?

That’s actually a very good question.

If you read the paper, 2 things should stand out: there is no statement of uncertainty, and no data results are stated – they just state rather vaguely: “The measured time delay in both reflection and transmission of the digital pulse is about 100 ps.” Can someone please define about 100ps for me? (ps = picosecond = 10^-12 seconds)

So here is what I understand of their experiment: They took two prisms and shot laser light through them. When the two prisms were touching, the laser light passed straight through both and hit a detector. What they don’t say, but I’m assuming, is the light was pulsed, and they measured the time from some part of the departing pulse to some part of the arriving-at-the-detector pulse. (This is how pretty much all experiments of this type are done.) After sending everything through with the prisms touching, they then pulled the prisms apart. In this new situation, as the light traveled through the first prism and hit the surface between the first prism and the air gap between the two prisms, some of the light went through the prism into the air and some of the light internally reflected back. The reflected light went out the base of the first prism and hit a detector, and the transmitted light went through the air, entered the second prism and then hit a different detector.

Since the two prisms are the same size, and the detectors are the same distance from the detectors, the light that is internally reflected should travel a shorter distance (goes in, reflects, bounces out) than the transmitted light (goes in, goes through air, bounces out). The extra travel distance is the size of the air gap. Their claim is photons traveling both paths hit the detectors at the same time.

Here is where it would be nice to see data, and here is why. First off, I’d like to know, does the travel time stay unchanged as the prism spacing increases? This is really important. There is an effect called the Goos-Haanchen shift (hat tip to Jack Glassman for explaining this one to me) that causes a photon that is reflecting to partially pass through the surface and get laterally shifted. The best way I know how to think of this weirdness is like this: imagine throwing a shoe at a chainlink fence at an angle. If the shoe is rotating and the laces are untied, the heel of the shoe may hit the fence, and the shoe may pivot about the heel until the toe hits, and then fly off at a new angle. While it’s hitting, the laces may fly through the fence. Exactly what happens is going to depend on the size of the chainlink and the size of the shoe. This isn’t a perfect analogy, but it is hard to explain wave packets.

So, there could be weird effects that allow the photon interacting with the surface and the photon passing through the air to both get delayed, and in a table of spacing versus travel time, both paths could have the same travel time, while the travel time increases as the air gap increases. Without seeing a data table I can’t know.

And then there is the little matter of error. They are using light with a frequency of 9.15 GHz ~10GHz. This means there are ~10^-10 seconds between wavepeaks if you are watching a wave go by. Now, they mention that the transmission time of the digital pulse is about 100 ps = 100 * 10^-12 seconds = 10 ^-10 seconds. This means there travel time and the spacing between wave peaks in a continuous wave is suspiciously the same. I want to see that explained and that coincidence designed out of the experiment.

And, what is the resolution they are measuring with anyway? When they say about 100ps, do they mean plus or minus 10 ps or plus or minus 100 ps?

And what about the light pulse size? And how are they measuring time? The shape of a pulse of light as it passes through these different systems can change, and unless they are doing this a single photon at a time, we have no way of knowing if the changes in the pulse shape are effecting things. There is a great analogy over on Cosmic Log that explains it this way: You have a train leaving Boston for New York with 99 cars. As the train leaves the station you start a timer as its middle car, number 50, passes the end of the platform. Now, image that as the train travels, rather than stopping for passengers, it just dropped the last car, and then the next to last car, etc, until only 5 cars remain. If you then stop your travel time clock as the new middle car passes the end of the NY platform – car number 3 – it will appear that the train mysteriously sped up, especially when compared to a train that kept all 99 of its cars (whose clock had to keep going for the extra amount of time it took those extra 47 cars to pass). So, the size of the train, and the size of the light packet, matters when you are triggering on the midpoint.

We don’t know what these folks are triggering on.

I want data. I want it now. (Strangely the Veruca Salt, “I want it now” song just popped into my head, but instead of a golden ticket (which I would accept if you offered it) the voice in my head wanted golden data).

Give it to me. I don’t care how. I want data, and I want it now

So, the moral – don’t believe a paper that isn’t peer reviewed, that uses the adjective about in front of any of their key results without stating error bars, and that presents no actual data while claiming to be an experimental result.

Be skeptical. The truth is out there, but I think we may need to do some more looking to find it.

In a trio of spin related press releases, scientists described how to measure spin, the consequences spin has on how black holes merge, and results on a test to check if our understanding is wrong.

Measuring Spin: To measure the spin of the black hole, scientists start from the knowledge that Black Hole magnetic fields couple with accretion disks, and the inner accretion disk and the rotation of the black hole are also coupled via other, far more complex physics. By looking at spectra of accretion disks in active galaxies, it is possible to get at the disks’ rotation rates. According to soon-to-be Dr. Laura Brenneman (University of Maryland), they used the iron lines in disk spectra to measure disk rotation rates. To do this, they had to model how doppler effects broaden the line, and how relativistic effects alternatively enhance the blue and spread the red. They had to integrate across the entire width of the accretion disk to develop a model for the aggregate line profile as a function of spin rate. Applying this dissertation making profile to actual data, they found that super massive black holes spin at a variety of rates.

With this info, they looked at how spins effect black hole mergers. If two black holes try to merge with spins that are pointed north pole to north pole with the axis in the plane of the merger, than there is a ~10% or more probability that one of black holes will get ejected during the merger. The thing is, we never see these ejected black holes, so some mechanism must/should/could exist to torque the black holes such that they don’t have this ejection causing alignment. If instead, the black holes merged with their north poles both aligned perpendicular to their shrinking orbits with the N poles pointed in the same direction, then black holes wouldn’t be ejected. In looking for a way to get the black holes to align, Drs. Christopher Reynolds and Tamara Boganovic (University of Maryland), explained that it is possible for the fluid dynamic (drag / friction/ etc) and gravitational torques from the disk formed during the merger to flip the black holes and their disks, such that everything aligns in the same way, with all disks (the two accretion disks and the disk formed during the galaxy merger) all align with the black holes aligned perpendicular to the disk. Using advanced computer models, they demonstrated that the time scales to rotate the disks into a non-flinging alignment are short and should prevent all black holes in gas-rich galaxy-galaxy mergers from escaping. Problems solved.

Problem solved, sorta.

In gas poor mergers, there won’t be a central disk of gas and dust formed during the merger, so there won’t be anything to torque the disks. So, free ranging super massive black holes may be able to happen in 10% of the specifically aligned gas poor galaxy mergers (in other words, it might happen in very rare events).

Looking for ejections: Not one (or two) to trust theory, Drs. Erin Bronning (Observatoire de Paris) and Greg Shields (University of Texas) searched through 2600 Sloan spectra of mergers looking for signatures of a black hole being ejected. No ejected super massive black holes were found. Theory 1, Observations 0

Next on the agenda: The Sun and its Danger Zone (the Chromosphere).

Not being a good humorist, I will not try to fill in the blanks. I will simply work to explain how two such very different objects can announce their formation via the same physical process.

Astrophysical jets are a by product of magnetic fields, and magnetic fields are generally a by product of charged particles moving. For instance, if you wrap a bunch of wire into a loop, and connect it to a battery, the current through the loop (the charges moving though the loop) will turn your loop of wire into a magnet strong enough to deflect a compass needle, and maybe even to make a small engine.

In astrophysical situations, charged particles (for instance, ionized atoms), move in different situations and create their own magnetic fields. For instance, in accretion disks, lots of particles are confined to orbits in a flat pancake of material, and these orbital paths act (in a college physics without calculus, cows are spheres, approximation) like the current in your coiled wire.

If you use a compass to explore the direction of the magnetic field associated with a coil, you’ll find that the N-S axis goes though the center of the loop perpendicular to the loop. This is the same orientation as astrophysical magnetic fields.

So where do jets come in? Well, as some of my students demonstrated for me, that coil can get things moving if it wants to! If you take large diameter wire and wrap it around small diameter PVC pipe, you can build something called a Coil Gun. I’d recommend something like 50 ft of 10 gauge insulated wire around a 3/4-inch PVC. This worked really well for some of my students (see Video). Now find yourself the largest power source you can that is Direct Current (I used the portable battery for jump starting cars that was in my trunk, my students daisy chained drill batteries). Drop a magnet into the PVC and flick the connection on and off (you want to create a burst of magnetic field). If all goes well, the magnets will get flung out one end of the PVC or the other (it all depends on which way is the fields North, and which way is the magnet’s North.

So, the accretion disk acts like your coil and material trying to get into the center can gets flung out by the magnetic field just like your magnet got flung out. To first approximation.

To make your coil gun more dangerous, you need only increase the current (bigger battery, or preferably a bank of capacitors you can charge in parallel and discharge in series) and increase the number of coils. By maximizing both these things you can create a fairly good weapon.

The universe can do the same thing by increasing the size of the disk and increasing the orbital velocities of the charged particles. Small, slow disk = Small sad jets. Large, high velocity disk = jets to be feared.

Today’s press feed offered both the scenarios in two separate stories. Astronomers lead by Emma Whelan used the Very Large Telescope in Chile to image a very low mass brown dwarf with small jets. This object, named 2MASS1207-3932, is about 24 Jupiter masses and has a 5 Jupiter mass companion (I say companion because I don’t know if their formation resembled that of two binary stars or a planet and star, so I have no idea would nouns to use). This little almost-a-star’s jets are about 1 billion kilometers long and the material in the jets is moving at a few kilometres per second (a speed man-made rockets can attain). This is only the second brown dwarf found to have jets, it is the smallest star found to have jets. The fact that such tiny failed stars have jets while forming raises the possibility that gas giant planets may also go through a phase of having jets during their formation.

On the other end of the size scale, astronomers lead by Hans Krimm have used the Swift satellite to figure out that long duration gamma-ray bursts (those associated with a special class of supernovae) have continued X-Ray flare activity for several minutes to hours after the initial gamma ray burst. The physical picture of the event looks something like this: A giant star runs out of material to fuse into heavy elements (namely Iron in the core), and when the fusion shuts off, there is no longer sufficient radiation pressure (pressure from the light created in the nuclear reactions) to support the out layers of the star. The star had been rotating, and when the outer layers – now unsupported – collapse inward, they collapse somewhat into a disk. Magnetic fields channel some of the material in this collapsing disk out in jets. The whole process is short lived, but it sputters out rather then cleanly coming to an end. Initially, when the disk would have the most food to offer the forming forming black hole that is where the star’s core used to be, the jets are emitting in a few seconds as much energy as the Sun will emit in its entire lifetime. When this jet material hits shells of ejected material, gamma rays are given off. The jets in this case are moving at near light speed! This initial gamma ray burst will general last a few 10s of seconds to in rare cases a few hundreds of seconds. Over the subsequent several minutes or hours, additional X-ray flares may also be observed. By studying the X-ray flares associated with GRB 060714, Krimm and his team determined they were likely caused by subsequent infall of material and associated emission as the star’s material continues to build the black hole.

In both cases the jets were related to formation of a new object, and the physics in both situations was similar. The differences come out of the details. As with almost everything in astronomy, it all comes down to the mass. Small objects have small jets, and giant objects have dangerous jets. And luckily, none of these jets are pointed at us.

Balancing stars against gravitational collapse is actually a process that is much more simple than many people think. When a star forms, the pressure and density in the center causes nuclear reactions to occur. These reactions release energy, partially in the form of photons, and the photons exert a pressure on the outer layers of the star. The light pressure pushes outward with the same force that the gravity presses inward. As long as nuclear reactions are occurring in the star’s center, the star doesn’t collapse. When stars die, their nuclear reactions stop and without the pressure from the light they collapse. If a star is similar to the Sun, it becomes a white dwarf, and the force of the electrons repelling one another supports the star. If a star is more massive, the electrons and protons in the stars atoms get crushed together and become neutrons, and the star is supported by the neutrons pushing against each other. If the star is even more massive, there is nothing left to support the star against gravitational collapse and it becomes a black hole.

So, for every force, their is an opposing force, and in black holes, well, inside the BH, we have no idea what is happening, but whatever it is, it kicks in after the material has collapsed small enough that we can get close enough to the center of mass that bad things can happen. Spaghetification anyone?