Herschel telescope 'fingerprints' colossal star

[junglelord]

I found that the satellite had significant voltage that fried one instrument to be the most interesting part of this article.

The death throes of the biggest star known to science have been observed by Europe's new space telescope, Herschel.

The observatory, launched in May, has subjected VY Canis Majoris, to a detailed spectroscopic analysis.

It has allowed Herschel to identify the different types of molecules and atoms that swirl away from the star which is 30-40 times as massive as our Sun.

VY Canis Majoris is some 4,500 light-years from Earth and it could be seen to explode as a supernova at any time.

It is colossal. If VY Canis Majoris were sited at the centre of our Solar System, its surface would extend to the orbit of Saturn.

The star, in the constellation Canis Major, has been recorded by astronomers for at least 200 years.

It is what is called a red hypergiant - a highly evolved object that is exhausting its nuclear fuel.

Its end days see it spew vast quantities of gas and dust into interstellar space, including elements such as carbon, oxygen and nitrogen - the raw materials that will go into the production of future planets, and, who knows, perhaps life elsewhere in the galaxy.

Herschel has trained the spectrometers in its Pacs and Spire instruments on the extensive cloud of material billowing away from the object.

Spectrometers capture and split light into its constituent wavelengths, creating a kind of "fingerprint" that will reveal information on the chemistry of a light source.

Pacs and Spire, for instance, detect copious amounts of carbon monoxide (CO) and water (H2O) in the vicinity of VY Canis Majoris.

"One of the most common molecules you see in this type of observation is carbon monoxide," explained Professor Matt Griffin, the Spire principal investigator from Cardiff University, UK.

"That's because carbon and oxygen are two of the most common materials produced in stars and they like to get together, so interstellar space is full of carbon monoxide. From our CO lines we can measure the temperature of the gas and by comparing them with other lines we can also measure density and optical depth and all kinds of other parameters.

"The other lines we're seeing in abundance in both Pacs and Spire spectra are water. Water is very important astrophysically because it is a diagnostic - it tells us a lot about the physical and chemical processes going on in a gas.


"And of course water cannot be seen from the Earth because there is so much of it in the atmosphere, its signal gets swamped; and that's why we have to go into space to do these kinds of observations."

Herschel studies like this should help to establish a detailed picture of the mass loss from stars and the complex chemistry occurring in their extended envelopes.

Scientists have models to describe what they think happens in stars like VY Canis Majoris and Herschel will give them some "ground truth" to constrain their ideas.

The European Space Agency's billion-euro Herschel observatory was sent into orbit on 14 May on an Ariane rocket. It has been positioned far from Earth to give it an unobstructed view of deep space.

The observatory works at longer wavelengths - in the far-infrared and sub-millimetre range (55 to 672 microns).

This means it can pick up details that are beyond the vision of other telescopes which operate in different parts of the electro-magnetic spectrum, such as Hubble which is tuned to see visible light and the near-infrared.

Herschel is demonstrating it has sensitivity and resolution beyond anything previously sent into space to work in its particular wavelengths.

Moreover, there are some parts of the electro-magnetic spectrum that Herschel will show scientists for the very first time.

The mission is now entering routine operations after completing commissioning and demonstration phases. However, its third instrument is currently down after experiencing a fault. Hifi experienced a damaging voltage peak in August

Engineers are expected to upload the software next month needed to reactivate the Heterodyne Instrument for the Far Infrared (HiFi).

The Dutch-led HiFi spectrometer has even better resolution than the Pacs and Spire instruments. A glimpse of its capability is demonstrated in a spectrograph of a comet released on Friday but taken before the shutdown.

The data on Comet Garradd shows up a strong water signal as is expected from an object composed of ice and dust.

Comets will be a key target for HiFi. It will be used to pick out the various chemical elements and molecules - some quite complex - that boil off these objects as they sweep in towards the Sun from the outer Solar System and heat up.

Some of the first science results from Herschel observations are expected in the coming weeks.

"Everything we have done so far, we've done extremely well," said Dr Göran Pilbratt, Herschel's project scientist.

"We have not been able to do everything we wanted because of HiFi, of course; but what we have released today and put on the [Esa website] for instance, you can judge for yourself. I think it is very impressive."

Jonathan.Amos-INTERNET@bbc.co.uk
http://news.bbc.co.uk/2/hi/science/nature/8382348.stm

[Biggins]

The voltage spike is suspected to be due to a radiation event on a memory area controlling a safety switch, causing said switch to trigger, causing a voltage spike on the DC-DC converter breaking it.
We still have the redundant side that is expected to be fully switched on in January with no loss of sensitivity.

I say 'we' since I am responsible for the operations of the instrument at the ESA control centre in Darmstadt, Germany.

Please also note that it is HIFI not HiFi (Heterodyne Instrument for the Far Infrared).

[jjohnson]

This looks like good scientific investigation to me, from the perspective that it is sensitive instrumentation well done. The trouble-shooting of the cause of the switch failure is excellent and there's a backup which will be used to further the HIFI instrument's work. The astronomical assumptions that the comet is a dirty snowball, in effect, can and should still be questioned (that's still a hypothesis, let's remember - no one's been there with a scoop.) Whether or not the blue giant star is fixing to become a supernova in our lifetime may or may not play out as expected. The radiant flux in our direction, if it were to go nova, would be about 5x10^-8 of the value one light year from the nova (1LY / 4500LY^2) or 1.53x10^-17 that at a point 1 AU from the nova. We'll see -so to speak - or not

EU thought, of course, is that stellar evolution does not concern itself with supernovas coming from exploding old stars and the rebound shock wave from a gravity collapse as internal pressure support ceases, instead assigning the energy output to the breakdown of an exceptionally highly charged electromagnetic sheath (double layer) in which the energy is stored as in a capacitor. This is analogous to common events in the Sun's lower corona, per Peratt, where beta = the gas pressure divided by the magnetic pressure:

Higher up in the corona where the density is so small that the magnetic pressure dominates, we have a low-beta plasma, and the magnetic field must take on a force-free character (Gold 1964) as it slowly evolves. This magnetohydrodynamic process (MHD) is possible since the timescale for the "wind-up" is days or weeks, while the field adjustment at any stage takes place with the Alfvén speed Eq.(2.19), leading to timescales of the order of seconds.

Imagine that at the scale of cosmic conditions around a large star, rather than locally in its corona, that over a rather longer period the double sheath protecting the local parsecs-in-diameter Birkeland current becomes highly charged by the continuing huge electron flux (plasma motion). The magnetic energy stored in a circuit is proportional to the square of the amperage. If the pressure in this ultra-low beta plasma becomes high enough to require a "field adjustment", then it occurs at the Alfvén speed, which probably scales up to minutes or possibly hours. If I grasp this correctly, the observed energy release is not initiated by the star; it impacts the star. The star is the last to know what just happened! This may also be the reason that a flood of neutrinos is the first tell-tale that a supernova-like-event is about to proceed, as "the release energy ...is mainly used for accelerating charged particles [mostly relativistic beams at galactic scales], with a small percent released in the generation of noise. Secondary effects associated with the particle acceleration include localized heating and radiation" Peratt, 5.6.3.

Peratt describes cosmic radiation (primarily high energy proton) production at the scale of a solar flare, which gives us an idea of what may happen at the larger scale: "Just after a solar gamma ray impulsive burst, indicating the onset of a strong (1B) flare, neutrons with energies at least as high as 6x10^8 GeV were detected at the Earth... In Section 5.6.2 we found that a double layer in a solar filament carrying the current I = 3x10^11 amps can sustain a maximum potential drop of about 9x10^10 Volts. This means that such a layer is capable of accelerating particles to energies that correspond to the highest solar cosmic ray particles observed." This is in a solar current filament of length perhaps 10^8 m. Scale this up to a light year filament radius and estimate what is going on.

I was wondering what could creates the neutrino burst at the onset until I read Peratt's sentence above about a strong neutron flux reaching the earth from a solar release. These fresh new neutrons may be close to relativistic - have a velocity an appreciable fraction the speed of light. This means that they may not have yet had time to decay into a proton, an electron, and a neutrino in the inevitably short lifetime of a free neutron, crossing space from sun to Earth quickly enough. To observers more than about 15 light minutes away from a double layer collapse, it seems logical that all of the neutrons would have had time to decay and provide a flood of neutrinos accompanied by the protons and electrons. The lifetime of the neutrons might be extended by their relativistic motion (their clocks run slower) but still, it would be short, likely a lot less than hours, before all have decayed.

Neutrinos are even more "neutral" than the other two species, so the rate of extinction through encounters with electromagnetic and gravity fields, recombination (neutralization) of the electrons and protons, with each other and other en route charged particles, would be higher for electrons and protons than for the slippery neutrinos. The neutrinos only interact with other matter via the weak force, not E/M or gravity, so they continue for thousands or millions of light years virtually unextinguished by the column of space from the collapse to the observer on Earth, losing their brothers along the way. Since solar flares seem to have a preflare phase of maybe 10 minutes (Peratt) with slow optical and EU and soft X ray brightening, followed by the explosive or impulsive phase of about 1 minute, followed by a rise to maximum brightness during the 5 to 15 minute flash phase. The neutron production is in the fast impulsive phase so naturally (by my logic anyway) the neutrinos precede the maximum brightness when we can first "see" the bright dot appear in a galaxy far off. Local nova observations should be able to parse out and time these various events with much finer precision, and might corroborate one model or another better than today's ideas of what's going on. A closer event might theoretically be able to stir the sluggish LIGOs into action, too, although I think that all the necessary energy is there already, stored in the double layers, and there is no net loss of mass-to-energy conversion that would wiggle the ol' LIGO (Little In; Garbage Out) pens at all.

An interesting experiment to set up would be to" arrange for" a supernova to occur a short time after the star's visual occultation by the Sun, and see if the preceding neutrinos are bent by the Sun's gravity field like the (optical) light appears to be. They shouldn't be. Good luck in arranging that which is unpredictable and unmanageable.

Thoughts on this topic welcome (conclusions about what really happens, from Herschel's fine scientific observations).