Daily Archives: 27/04/2010

Crowdsourced x-ray binary observations pay off

The American Association of Variable Star Observers, which coordinates a global network of amateur astronomers who observe variability in stars on a variety of levels, is presently taking part in a scientific campaign. In coordination with the JACPOT collaboration, the AAVSO are making observations of x-ray binary stars.

X-ray binaries are pairs of objects – one very compact and high mass, of the order of white dwarfs, neutron stars and black holes, and the other big, gassy and able to feed that gas to the smaller one. As gas is ripped from what is normally a red or other type of giant star and collected by the compact companion, it forms an accretion disc as particles spiral down towards the companion’s surface. Charged particles spiraling always release energy and this can be in the form of x-rays if they are accelerated fast enough. In some cases, jets of particles also form and these too can emit energy, most normally as radio waves. The accretion of spinning matter by neutron stars in this way has been considered one of the ways of forming pulsars.

But it isn’t really known exactly how the formation of jets differs in the different types of binaries, especially the white dwarf ones whose companions are the least dense and compact of the three. To this end, a series of known binaries has been listed and the AAVSO have been asked to keep an eye on them. When it looks like one is setting off, then professional telescopes can be turned on them to confirm this and then begin to perform proper observations at different wavelengths.

In mid April, the AAVSO amateurs turned their eyes to the dwarf nova SS Cygni and on the 19th reported signs of an outburst. JACPOT then turned the Expanded Very Large Array telescope and the Very Long Baseline Array were turned to view it along with the Swift x-ray space telescope, Faulkes North, the FanCam IR Instrument, PAIRITEL and various other observers. The EVLA and the VLBA will continue their campaign to observe the development of the radio signal from the binary now the others have peeled off, having confirmed the event. The evolution of the signal will be crucial in determining its origin.

Further information, first results and any new results are all posted at this website at the AAVSO. This will not be their last such campaign, so I’d encourage all you skilled amateurs hoping to contribute and do some real science to join in. One place to start might be Citizen Sky, their online citizen science experiment.


Some spaceflight news

The shuttle mission STS-134 (Endeavour) has had its date of launch put back until November (from July 29th) so that some of the instruments it will be carrying to the International Space Station can have some extra time to be worked on (not so that the numbers, which refer to the order the missions were commissioned in, line up…). The instrument in question is the Alpha Magnetic Spectrometer, which will measure the composition of particles striking the station. The AMS is having its cryo-magnetic replaced by a permanent one in order for it to run longer with an eye on the extension to the life of the ISS that has recently been provided. This means that it will now follow STS-133 (Discovery), to be launched on September 16th and so it will become the new final ever shuttle launch. STS-132 (Atlantis) is still slated to launch on May 14th. A full launch manifest for the ISS missions, including automated transfers of cargo and Soyuz based crew launches, can be seen here.

On May 18th, the Japanese space agency, JAXA, is to launch two missions in one rocket. The first is Akatsuki (not the deadly crime gang), or PLANET-C, a Venus orbiter that will compliment the ESA Venus Express mission, presently gathering data from the second rock from the Sun. The second is Ikaros (not the big deadly laser satellite in the James Bond film Die Another Day). Ikaros is a hybrid engine designed to test a number of technologies in deep space. When the cylinder reaches orbit, it will open up and unfurl a 14 metre solar sail, thinner than a human hair but still incorporating solar panels. Particles from the Sun will then push the device along, which ground controllers angling the sail to alter velocity. Additionally, the electricity generated by the thin solar panels will be used to power an ion drive.

Three missions already in space are to celebrate milestones in their missions. The first is GIOVE-B. This mission contains a maser clock that provides the kind of accuracy that will be required of satellites in the Galileo network of navigation satellites, which is Europe’s version of the USA GPS system. The Galileo In Orbit Validation Experiment intended to prove the passive hydrogen maser clock was the best tool for the job and up to the task of coping in space for the required time. Two years to the day after its launch and more than 400 days since being switched on, things are going well. Meanwhile, as Spirit softly slumbers in the sand pits of Mars, she and sister rover Opportunity are about to pass the record set by Viking 1 for the longest duration experiment on Mars. Viking 1 ran for Six years and 116 days, a duration that will be passed by Spirit this week. But as the long in the tooth rover is presently snoozing, celebrations will have to hold off until she has been awoken after the Martian winter to make sure the old girl is still going. Meanwhile Opportunity, which arrived at the red planet a little later and is still running about and very much known to be alive, will also break the record in early May. Not bad for a couple of ninety-day rovers with solar panels rather than long lasting Viking style batteries.

The Lunar Rover Lunokhod 1, which rambled around the surface of the Moon for ten months alongside sister rover 2 in the early seventies, has been rediscovered. The rover, along with other lunar missions including the Apollo missions, took retroreflectors with it to the surface of the Moon, the intention being that lasers on the Earth could be bounced off them once operations ceased. It was tried after Lunokhod 1 first shut down, but no return signal was detected. It has been tried intermittently since, but again, no cigar. Now LRO data have identified the position of the rover to be significantly far from the assumed position. With the new coordinates, a laser was fired and a bullseye hit. The reflections from 1 are five times as strong as those from 2, which is significant in studies of lunar dust, which tends to gather on these reflectors over time.

Another mission still producing science after its primary objectives were long completed is Cassini, which is nearing the end of its first mission extension, Equinox. Cassini plans to turn itself into a gravity probe as it flies to within 100km of the surface of the moon Enceladus. Using precise telemetry to determine by how much the probe is being pulled one way and another, the ground crew hope to probe the gravitational field of the body. As different compositions have different densities, masses and hence gravitational effects, the data may help rule in and out such hypotheses as the size and composition (salty or not) of subsurface water beneath the tiger stripes that fire water particles into orbit around Saturn and whether or not subsurface materials at the south pole are heated and caused to rise in a lava-lamp like way to create the strange heat signatures and repaving in that region. This event will occur sometime tomorrow.

On Universe Today, part eleven of the 13 things that saved Apollo 13 series to celebrate 40 years since Apollo 13 has been published and it is – the 1969 movie Marooned. This movie features a situation where three men are stuck in an Apollo like spacecraft with failing batteries. One of the ground crew watched the movie and ruminated on how he would solve the problems just hours before he was disturbed by the news that this was exactly how his next several days were going to go…

The Herschel Infrared Space Telescope will be showing off its wares at a press conference on the 6th of May. Details of the schedule and how to register to be there are here. The theme will be Revealing the Hidden Side of Star Formation, and the location the European Space Research and Technology Centre (ESTEC), Noordwijk, The Netherlands.

Finally, and at the other end of the scale, a brainstorming session to develop technologies and methods for space missions, StarTiger, has come up with a method for observing the parts of the solar corona closest to the disc of the Sun. The problem is most spacecraft have coronographs blocking out the Sun’s light that are too big to see the closest bits just above the solar surface, meanwhile visible and filtered light observations see the solar disc outshine the corona massively. The end result of six months huddled together in a laboratory in France under the auspices of the Space Technology Advancements by Resourceful, Targeted and Innovative Groups of Experts and Researchers program is a series of technologies, software, requisite mathematical models and a completed demonstration model of a space mission that would see two spacecraft flying in perfect formation, 150 metres apart with one blotting out the Sun for the other, controlled with millimetre precision.

High mass distributions in galaxies in the spotlight

Two surveys of mass in the vicinity of galaxies have produced surprising but theoreticaly supported results. The first is to do with the distribution of massive stars within a galaxy and the second, the dark matter halo around it.

In the first survey, presented at the National Astronomy Meeting, 2010 and then in Astronomy Now’s article, a series of galaxies were observed and supernovae within them recorded. Supernovae are the death calls of the most massive stars. As massive stars are short lived, supernova rates are good ways of estimating rates of star formation in the galaxy’s recent history. As the supernova outshine anything else the galaxy will have to offer, they’re also easier to spot than say the emerging smaller stars that were thought to make up the bulk of new star birth.

Stacey Habergham of Liverpool John Moores University and colleagues examined the supernovae in 140 galaxies, amounting to 178 explosions, using the Liverpool Robotic Telescope and the Isaac Newton Telescope in the Canary Islands. They divided the galaxies into two classes – those that showed tidal disruption due to probable interactions with others and those that didn’t – and also divided the supernovae into two categories – Type 1 b/c, which are metal rich with little hydrogen, indicative of the most massive stars and Type II’s, which have hydrogen and are likely to be the end of less massive (but still, very massive) stars.

The result of marking the positions of the two supernova types onto the two galaxy types was the suggestion that in tidally disrupted galaxies, the more massive stars ended their lives more clustered to the centre than the evenly distributed less massive stars. In undisturbed galaxies, both types were more evenly distributed.

The analysis suggests that when galaxies merge, the result is starburst with an emphasis on larger stars, happening at the point of interaction. The deaths of these stars creates high metallicity gas that then gets pushed to the centre of the galaxy where it can give rise to the kinds of stars that undergo Type 1b/c supernovae.

The team now plans to perform infrared observations to better record the disturbances the galaxies are showing and also spectroscopic campaigns to find the metallicity of the remaining gas and dust around the galaxies’ bodies.

One facility that may be able to help her with that is the Large Binocular Telescope in Arizona, which has twin 8 metre mirrors operating together in the infrared. It is to be joined by the LBT near infrared spectroscopic Utility with Camera and Integral Field unit for Extragalactic Research (LUCIFER – are we really that low on acronyms?).

A second survey of relevance to galactic scale mass distributions was performed by the Subaru telescope in Hawaii. Masamune Oguri of the National Astronomical Observatory of Japan and an international team used the process known as gravitational lensing to measure the clumping of mass between the telescope’s aperture and a galaxy cluster.

Gravitational lensing is the effect of space-time bending more near to the surface of a higher mass object than a lower mass one. Light travelling past finds its direction altered, sending it away from the centre of mass, with the displacement greater the closer to the mass it travels. Eddington used this effect to provide some experimental proof of the predictions of General Relativity in 1919 and the effect has been going strong ever since, becoming a new branch of astronomy.

The survey’s results have been analysed and show that dark matter, the component of the Universe’s matter-like stuff that cannot be directly seen with ordinary telescopes due to its low level of interactivity with other matter or light in any way other than gravitationally, clumps in cigar shaped formations. This is consistent with the idea of Dark Matter being composed of cold WIMPs – Weakly Interacting Massive Particles – ie just another type of particle that ignores the electromagnetic force, doesn’t exert pressure on ordinary matter, but does have gravitational influence. The term cold in this case refers to the velocity of motion of the particles. Hot would imply near light speed particles like neutrinos, cold refers to relatively slow particles. In this case, the bulge is the response of the Dark Matter cloud to its own spinning. The exact shape is determined by the temperature of the Dark Matter and its interactions with the matter component of the region, allowing more determinations to be made and compared with other observations.

Another science based program to watch tonight

(or later via iPlayer)

The Story of Science – Proof, Power and Passion is to be broadcast on BBC2 at 9pm tonight, the first of six parts. Tonight’s episode centres on how it came to be understood that the Earth is not the centre of the Universe.

Further details on the program and related links are available via its website.

#SciVote roundup for today

…well, yesterday really.

It has been quite an active day in the world of science policy promotion. Professor Brian Cox, who tweets here, has a new column in the Sun, which he’ll use to promote science.

The Lib Dems have been promoting their science credentials in answers to questions put to them by the Guardian. Their answers are analysed here. Jon Butterworth has posted his own big question to the parties, pointing towards the STFC debacle and asking why it hasn’t been sorted out three years later (we weren’t even in a recession then). Of course if you want to ask such a question, then there are a number of ways to do this. The party leaders are famously taking part in televised debates and questions for the final one of these debates (Thursday on the BBC) can be submitted here. The same three party leaders will be taking part in a ‘digital debate’ hosted by youtube and facebook. Questions are submitted in advance and voted on, with the top two in each category going through to the leaders for answers. In this case, a question has been prepared and clicking here (plus signing in to your youtube and facebook accounts) will allow you to view it and then vote for it.

But what about answers? How many supporters of science are there in parliament? How many are there likely to be after the election? The Times has looked at each constituency in turn and tried to predict the outcome based on the present opinion polls and it doesn’t look good, with supporters of science leaving the commons outweighing those coming in.

Stricken JAXA probe to attempt touchdown

The Japanese spacecraft Hayabusa has not had the best of all lives. It was destined to have a quick spin around the near solar system, visiting asteroid Itokawa, collecting some dust and rock samples trailing in its wake and then return back home, dropping off the samples canister and cremating in the upper atmosphere.

But no. Apparently, once the probe was at the asteroid, it decided it might like to stay. One by one each of the four ion engines that do most of the work propelling the spacecraft shut down. The chemical propellant that powers the shorter lasting but much more powerful normal thrusters leaked into space. The reaction wheels that correct the probe’s direction from any perturbations closed down, leaving just one operational.

In 2007, the probe’s departure from the asteroid was postponed until this year. When the last of the ion engines shut down last November, it looked like the probe would get its wish – it sent back lots of pictures of the asteroid, but no actual bits. In fact, due to the failure of the collection systems, it isn’t even known whether or not a single pebble was netted. Then things started to turn.

Engineers on the ground were able to rig up a system that allowed two of the ion engines to negotiate enough working components to function as one. The lack of a strong chemical thruster simply meant corrections and alterations for the trajectory would be over a longer timescale. The existence of just the one reaction wheel meant… well… fingers crossed.

The probe has now left the asteroid three years late and is headed back to Earth orbit. Due to the length of the extension of stay, it is not known whether the batteries in the samples canister still function (they are needed to deploy a parachute in order to avoid a repeat of another space dust collection mission, which went splat, as well as activate a navigation beacon so it can be found – even if it goes splat). The probe will therefore arrive at Earth, turn over to bask the canister in the rays of the Sun to warm it, then push the thing into the atmosphere before launching onwards to its own fiery death.

The canister is expected to attempt a landing at the Woomera Test Facility, Australia on June 13th at 11pm local time.

…and I guess this would be a suitable article to mention that part 10 of Universe Today’s 13 things that saved Apollo 13 is up and it is Duct Tape.