Tag Archives: interstellar medium

Buckyballs in space: how complex carbon molecules form in space

An artist’s conception showing spherical carbon molecules known as buckyballs coming out from a planetary nebula — material shed by a dying star. Researchers at the University of Arizona have now created these molecules under laboratory conditions thought to mimic those in their ‘natural’ habitat in space. NASA/JPL-Caltech

The mystery of how complex carbon molecules with a ‘soccer-ball’ type structure–nicknamed buckyballs–came to be found in interstellar space has puzzled scientists for some time.

But now, a team of researchers from the University of Arizona have proposed a potential formation mechanism for carbon-60 (C60)–a spherical molecule comprised of 60 carbon atoms in ring-like structures–in space.

The team discovered that silicon carbide dust left behind by dying stars then bombarded by high energy particles and extreme temperatures could shed silicates leaving behind pure carbon needed to create C60.

Their results are published in the journal Astrophysical Journal Letters.

The detection of buckyballs–named for their similarity to the dome-like architecture of Buckminister Fuller– and even larger C70 molecules a few years ago caused a rethink of the theory that such molecules could only be formed in the lab.

Additionally, and more importantly, the discovery overturned the idea that only light molecules–up to around 10 atoms–could be found scattered through interstellar space.

Another surprise emerged from the fact that the molecules detected were pure carbon.

In the lab, C60 is created by blasting together pure carbons sources such as graphite. This process should be almost impossible in the planetary nebulae that the interstellar C60 was found. This is because this environment– debris created in the violent death throes of stars–has about 10,000 hydrogen molecules for every carbon molecule.

“Any hydrogen should destroy fullerene synthesis,” says Jacob Bernal, an astrobiology and chemistry doctoral student and lead author of the paper. “If you have a box of balls, and for every 10,000 hydrogen balls you have one carbon, and you keep shaking them, how likely is it that you get 60 carbons to stick together?

“It’s very unlikely.”


Bernal and his team began investigating this conundrum with the aim of uncovering a potential C60 formation mechanism when they realised that the transmission electron microscope (TEM) located at the Kuiper Materials Imaging and Characterization Facility at the University of Arizona, was able to simulate the planetary nebula environment fairly well.

TEM’s 200,000-volt electron beam is able to probe matter down to 78 picometers in order to see individual atoms. The beam also operates in a vacuum with extremely low pressures. The incredibly low-pressure in TEM is very close to the pressure found in circumstellar environments. But this is more by luck than design.

“It’s not that we necessarily tailored the instrument to have these specific kinds of pressures,” explains study co-author Tom Zega, an associate professor in the Univerity of Arizona Lunar and Planetary Lab. “These instruments operate at those kinds of very low pressures not because we want them to be like stars, but because molecules of the atmosphere get in the way when you’re trying to do high-resolution imaging with electron microscopes.”

The team drafted the assistance of the U.S. Department of Energy’s Argonne National Lab, Chicago, which has a TEM capable of studying the radiation responses of materials. Placing silicon carbide–a common form of dust produced by stars– in the low-pressure environment of the TEM, the team in Chicago subjected it to temperatures up to 1,830 degrees Fahrenheit whilst bombarding it with high-energy xenon ions.

Tom Zega at the control panel of the 12-foot tall transmission electron microscope at the Kuiper Materials Imaging and Characterization Facility at the UArizona Lunar and Planetary Lab. The instrument revealed that buckyballs had formed in samples exposed to conditions thought to reflect those in planetary nebulae. Daniel Stolte/University Communications

Following this, the sample was returned to the University of Arizona so researchers could employ the higher resolution and better analytical capabilities of the TEM located there. The team’s hypothesis would be validated if they observed the silicon shedding and exposing pure carbon.

“Sure enough, the silicon came off, and you were left with layers of carbon in six-membered ring sets called graphite,” adds co-author Lucy Ziurys, Regents Professor of astronomy, chemistry and biochemistry. “And then when the grains had an uneven surface, five-membered and six-membered rings formed and made spherical structures matching the diameter of C60.

“So, we think we’re seeing C60.”

This work suggests that C60 is derived from the silicon carbide dust made by dying stars–hit by high temperatures, shockwaves and high energy particles. These violent conditions leech silicon from the surface and leaving carbon behind.

These big molecules are dispersed because dying stars eject their material into the interstellar medium – the spaces in between stars – thus accounting for their presence outside of planetary nebulae.

Buckyballs are very stable to radiation, allowing them to survive for billions of years if shielded from the harsh environment of space.

“The conditions in the universe where we would expect complex things to be destroyed are actually the conditions that create them,” says Bernal, also adding that the implications of the findings are endless.

“If this mechanism is forming C60, it’s probably forming all kinds of carbon nanostructures,” Ziurys concludes. “And if you read the chemical literature, these are all thought to be synthetic materials only made in the lab, and yet, interstellar space seems to be making them naturally.”

Original research: “Formation of Interstellar C60 from Silicon Carbide Circumstellar Grains,” The Astrophysical Journal Letters, 2019.

Voyager at the edge of the final frontier. Spacecraft expected to exit solar system earlier than thought

It’s remarkably impressive how a spacecraft built and launched in the late 70’s is not only still functional, but well on its way of becoming the first man-made object to leave our solar system. After 35 years, new data shows that this plucky probe may soon cross the undulating boundary between the edge of our solar system and interstellar space.

Artist impression of the Voyager-1 spacecraft, and its partner, Voyager-2, as they’re approaching the edge of the Sun’s protective bubble, separating them from interstellar flight. (c) NASA/JPL-Caltech

The boundary of the solar system has been settled by scientists as the place where the solar wind fizzles out completely – this called the  heliopause. Currently, Voyager-1 is still in the heliosheath where the sun’s solar wind is significantly slowed by the pressure of interstellar gas, but not quite minimal yet. Tantalizing signs now have it that Voyager I, now some 11 billion miles from home, is right near this cosmic milestone for humanity.  Voyager-1′s sister probe, Voyager-2, is currently lagging behind about 2 billion miles

“It’s not that clear because there’s no signpost telling you that you’re now leaving the solar system, but the evidence is mounting that we’re getting really close,” says Arik Posner, a Voyager program scientist at NASA’s headquarters in Washington, D.C.

Voyager’s initial mission in the late 70’s was that of taking first close-up pictures of Jupiter, Saturn, Uranus and Neptune, but apparently it went on going, and it has been for decades now. NASA engineers at the time were apparently invested with some sort of scientific foresight, when they decided to equip the spacecraft with a nuclear power source. Each Voyager is powered by three large radioisotope thermoelectric generators (RTGs), each containing 24 pressed plutonium-238 oxide spheres. The heat released by the decay of the radioactive material is converted into electricity using an array of thermocouples, initially granting around 470 watts of power. The power output of the RTGs does decline over time, though, but the RTGs will continue to support some of its operations through about 2025, more than enough to exit the solar system and transmit data back of what really lies beyond.

“When the Voyagers launched in 1977, the space age was all of 20 years old,” said Mr. Stone. “Many of us on the team dreamed of reaching interstellar space, but we really had no way of knowing how long a journey it would be — or if these two vehicles that we invested so much time and energy in would operate long enough to reach it.”

via NPR

 

Our solar system seems to be inside a “bubble” of interstellar medium.

Our solar system appears to exist inside a “bubble”, inside a network of cavities inside the interstellar medium, which was probably created by massive star explosions millions billions of years ago. Interstellar medium (ISM) is a term coined for the matter that exists in galaxies, between solar systems. This matter includes gas in ionic, atomic, and molecular form, dust, and cosmic rays, smoothly filling the gaps between the intergalactic matter.

ISM is extremely important and intensely studied by astrophysicists because of the intermediary role it plays, somewhere between stellar and galactic scales; also, dense ISM is the birthplace of stars and molecular clouds. The interplay between ISM and stars also represents the rate at which a galaxy depletes its gaseous content, thus the lifespan of active star formation.

Currently, the sun is passing through a Local Interstellar Cloud (LIC), shown in violet, located in a low density “hole”, called the Local Bubble, shown in black. Understanding this makes a shy, but important step towards understanding the birth and development of our solar system, in an intergalactic context. For example phosphorus, a crucial element which is essential for the formation of DNA is extremely rare in our solar system, and it’s quite possible that it was alltogether absent in the early phases of the Earth.

Picture and article source.