New molecules around old stars

Jun 17, 2014
Herschel image of the Helix Nebula using the SPIRE instrument at wavelengths around 250 micrometres, superimposed on Hubble image of the nebula. The spectrum corresponds to the outer region of the Helix Nebula outlined on the SPIRE image. It identifies the OH+ molecular ion, which is needed for the formation of water. ESA’s Herschel space observatory is the first to detect this molecule in planetary nebulas – the product of dying Sun-like stars. Credit: Hubble image: NASA/ESA/C.R. O’Dell (Vanderbilt University), M. Meixner & P. McCullough (STScI); Herschel image: ESA/Herschel/SPIRE/MESS Consortium/M. Etxaluze et al.

(Phys.org) —Using ESA's Herschel space observatory, astronomers have discovered that a molecule vital for creating water exists in the burning embers of dying Sun-like stars.

When low- to middleweight stars like our Sun approach the end of their lives, they eventually become dense, white dwarf stars. In doing so, they cast off their outer layers of dust and gas into space, creating a kaleidoscope of intricate patterns known as planetary nebulas.

These actually have nothing to do with planets, but were named in the late 18th century by astronomer William Herschel, because they appeared as fuzzy circular objects through his telescope, somewhat like the planets in our Solar System.

Over two centuries later, planetary nebulas studied with William Herschel's namesake, the Herschel space observatory, have yielded a surprising discovery.

Like the dramatic supernova explosions of weightier stars, the death cries of the stars responsible for planetary nebulas also enrich the local interstellar environment with elements from which the next generations of stars are born.

While supernovas are capable of forging the heaviest elements, planetary nebulas contain a large proportion of the lighter 'elements of life' such as carbon, nitrogen, and oxygen, made by nuclear fusion in the parent star.

A star like the Sun steadily burns hydrogen in its core for billions of years. But once the fuel begins to run out, the swells into a red giant, becoming unstable and shedding its outer layers to form a .

The remaining core of the star eventually becomes a hot white dwarf pouring out ultraviolet radiation into its surroundings.

This intense radiation may destroy molecules that had previously been ejected by the star and that are bound up in the clumps or rings of material seen in the periphery of planetary nebulas.

The Ring Nebula at optical wavelengths as seen by the Hubble Space Telescope, with Herschel data acquired with SPIRE and PACS over a wavelength range of 51–672 micrometres for the region identified. The spectra have been cropped and the scales stretched in order to show the OH+ emission, a molecular ion important for the formation of water. ESA’s Herschel space observatory is the first to detect this molecule in planetary nebulas – the product of dying Sun-like stars. Credit: Hubble image: NASA/ESA/C. Robert O’Dell (Vanderbilt University) Herschel data: ESA/Herschel/PACS & SPIRE/ HerPlaNS survey/I. Aleman et al.

The harsh radiation was also assumed to restrict the formation of new molecules in those regions.

But in two separate studies using Herschel astronomers have discovered that a molecule vital to the formation of water seems to rather like this harsh environment, and perhaps even depends upon it to form. The molecule, known as OH+, is a positively charged combination of single oxygen and hydrogen atoms.

In one study, led by Dr Isabel Aleman of the University of Leiden, the Netherlands, 11 planetary nebulas were analysed and the molecule was found in just three.

What links the three is that they host the hottest stars, with temperatures exceeding 100 000ºC.

"We think that a critical clue is in the presence of the dense clumps of gas and dust, which are illuminated by UV and X-ray radiation emitted by the hot central star," says Dr Aleman.

"This high-energy radiation interacts with the clumps to trigger chemical reactions that leads to the formation of the molecules."

Meanwhile, another study, led by Dr Mireya Etxaluze of the Instituto de Ciencia de los Materiales de Madrid, Spain, focused on the Helix Nebula, one of the nearest planetary nebulas to our Solar System, at a distance of 700 light years.

The central star is about half the mass of our Sun, but has a far higher temperature of about 120 000ºC. The expelled shells of the star, which in optical images appear reminiscent of a human eye, are known to contain a rich variety of molecules.

This image presents the Helix Nebula first at optical wavelengths, as seen by the Hubble Space Telescope, then by Herschel’s SPIRE instrument at wavelengths around 250 micrometres. A spectrum is shown for the region identified on the image, showing the clear signature of CO and OH+ emission in the clumpy outer regions of the planetary nebula. The molecular ion OH+ is needed for the formation of water, and ESA’s Herschel space observatory is the first to detect it in planetary nebulas – the product of dying Sun-like stars. Credit: Hubble image: NASA/ESA/C.R. O’Dell (Vanderbilt University), M. Meixner & P. McCullough (STScI); Herschel data: ESA/Herschel/SPIRE/MESS Consortium/M. Etxaluze et al.

Herschel mapped the presence of the crucial molecule across the Helix Nebula, and found it to be most abundant in locations where carbon monoxide molecules, previously ejected by the star, are most likely to be destroyed by the strong UV radiation.

Once oxygen atoms have been liberated from the carbon monoxide, they are available to make the oxygen–hydrogen molecules, further bolstering the hypothesis that the UV radiation may be promoting their creation.

The two studies are the first to identify in planetary nebulas this critical molecule needed for the formation of water, although it remains to be seen if the conditions would actually allow water formation to proceed.

"The proximity of the Helix Nebula means we have a natural laboratory on our cosmic doorstep to study in more detail the chemistry of these objects and their role in recycling molecules through the interstellar medium," says Dr Etxaluze.

"Herschel has traced water across the Universe, from star-forming clouds to the asteroid belt in our own Solar System," says Göran Pilbratt, ESA's Herschel project scientist.

"Now we have even found that stars like our Sun could contribute to the formation of water in the Universe, even as they are in their death throes."

Explore further: Image: The Cat's Eye Nebula (NGC 6543)

More information: "Herschel planetary nebula survey (HerPlaNS). First detection of OH+ in planetary nebulae," by I. Aleman et al., and "Herschel spectral-mapping of the Helix Nebula (NGC 7293): extended CO photodissociation and OH+ emission," by M. Etxaluze et al., are published in Astronomy & Astrophysics.

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no fate
1 / 5 (1) Jun 18, 2014
"This high-energy radiation interacts with the clumps to trigger chemical reactions that leads to the formation of the molecules."

This would almost pass as a valid assumption if the Ionization temperture for CO (app. 14ev) wasn't higher than that of OH+, O, and H. In other words, if the radiation breaks the bonds of CO, it ionizes the other elements required to make the molecule they found...
Uncle Ira
not rated yet Jun 18, 2014
"This high-energy radiation interacts with the clumps to trigger chemical reactions that leads to the formation of the molecules."

This would almost pass as a valid assumption if the Ionization temperture for CO (app. 14ev) wasn't higher than that of OH+, O, and H. In other words, if the radiation breaks the bonds of CO, it ionizes the other elements required to make the molecule they found...


Maybe it is only enough to break some of them and then they make the other stuffs when they join back together. Don't get mad at me, I'm not saying anything about gravity. I'm just making a guess that it wasn't enough radiators to break up the whole lot of them all and some was left over to make the new stuffs with parts of the stuffs that broke apart.
no fate
1 / 5 (1) Jun 18, 2014
Well uncle, radiation required to seperate atoms from molecules is an area of experimentation that has allowed a number of scientific breakthroughs...they are tested and confirmed data points. This is why we know that x number of UV photons will break molecular bonds and Ionize atoms. At this point it boils down to simple, useful math. You can check with the google for confirmation of Ionization temperatures. Look at it this way, if it is hot enough to melt lead, you can't use the melted lead to make a solid object with other ingredients that melt at a cooler temperature than the lead.

I told you in the other thread I won't get mad. A few times i have had my temperature up a bit on this forum, but there is never a serious enough conversation going on here to warrant getting mad about, life's too short.
Uncle Ira
not rated yet Jun 18, 2014
Well I said it was only a guess I was trying.

I sorta see what you are are saying, but I still think it has to do with how much radiators there is doing the breaking. Suppose the cloud has a bunch more CO things in it then there UV radiators, then some of the CO things would not get to being broken apart right? So if there aren't enough of them UV radiators to break them all, the left over ones can join up with the broken pieces. That is probably wrong I admit straight off, it is just me guessing maybe, it's not a theory I'm making no.

But let me tell you something about the heat that I do know good. You can stick your hand into the 450 degree oven (normal degrees not the kelvin things I don't use) and it be okay for a little bit even though all those air molecules are 450 normal degrees. But if you was to pick up the 450 normal degree pot in the oven, your hand not like that for even the little bit no.

That's what make me think of the not enough UV radiator thing.

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