The Earth Story

New Insights Into the Crab Nebula

Five observatories teamed up to spy on the Crab Nebula and the results are incredible. The VLA (radio) views are shown in red; Spitzer Space Telescope (infrared) in yellow; Hubble Space Telescope (visible) in green; XMM-Newton (ultraviolet) in blue; and Chandra X-ray Observatory (X-ray) in purple. The Crab Nebula is the remnant of a bright supernova explosion first spotted by the Chinese in 1054. Located 6,500 light-years from Earth, the Nebula is home to a super-dense neutron star. The stellar powerhouse -- known as a pulsar and seen as a bright dot in the center of the image -- emits pulsing lighthouse-like beams of radio waves and light as it rotates (or pulses) once every 33 milliseconds.

The super-dense star does more that put on a dazzling display of stellar strobe lights, it also gives the nebula it's intricate shape. A fast-moving blast of particles emanating from the pulsar, combines with material ejected by the supernova explosion and its progenitor star, to form the distinctive shape we know as the Crab Nebula.

This incredible new video starts by showing us a composite image of the Crab Nebula, created by combining data from five observatories spanning nearly the entire breadth of the electromagnetic spectrum: the Very Large Array, the Spitzer Space Telescope, the Hubble Space Telescope, the XMM-Newton Observatory, and the Chandra X-ray Observatory.

From the image, the video dissolves to the red-colored radio-light view illustrating how a neutron star’s fierce “wind” of charged particles energizes the nebula, ultimately causing it to emit the radio waves. Next we see the yellow-colored infrared image from Spitzer, which shows the glow of dust particles absorbing ultraviolet and visible light. Then we see through Hubble's eyes as the green-colored visible-light image offers a sharp view of hot filaments that permeate this nebula. Lastly, we see the blue-colored ultraviolet image and the purple-colored X-ray image, which highlight the effect of an energetic cloud of electrons driven by a rapidly rotating neutron star at the center of the nebula.

Image & Source Credit: Credits: NASA, ESA, J. DePasquale (STScI)

https://youtu.be/ZiGuh0yISao

Supernova blast debris found in ocean crust

As the old saying goes, we are all made of star stuff, and every element heavier than lithium has been baked into existence in a star, either during the evolution of its life cycle or during the spectacular death of larger stars known as supernovae. All sorts of elements and isotopes (atoms of the same element with more or less neutrons and hence a different atomic weight) are created, including iron 60, a rare isotope only formed in exploding stars.

Researchers examining cores drilled over decades from the sea floor have identified two iron 60 spikes in sediments, dated around 2.2 and 1.5 million years ago, a time when our early ancestors were wandering the African Rift Valley, and maybe gazing up at the new star that appeared in the daytime sky and is now shining as bright as a full moon at night. The explosions are estimated to have been relatively close, around 300 light years away (too far away to cause an extinction by radioactive blast, scientists estimate it need to be less than 30 light years away for that kind of disastrous event), and showered our planet with characteristic evidence of their occurrence. There may have been an effect on climate, lowering Earth's albedo by increasing cloud cover and while correlation is not causation, the timing is coincident with the cooling events at the beginning of the ice ages.

While the spike was first spotted in 1999, the team have been painstakingly analysing 120 samples from around the globe (Pacific, Atlantic and Indian Oceans), spanning an 11 million year span. They found a whole layer enriched in iron 60 between 3.2 and 1.7 million years ago, suggesting a series of explosions, along with the two spikes mentioned above. Evidence of a further supernova some 8 million years ago was also found, coinciding with a turnover in ecosystems in the Miocene.

A second paper in the same issue of Nature attempts to reconstruct the explosions, estimating that the closest involved a star of around nine solar masses meeting a violent demise, and the further one around eight. The timing was estimated using the age of the sediments (obtained from fossils) and the amount of decay of the iron 60, which has a short half life (the time it takes half the unstable atoms to decay into their stabler products) confirmed the dating. They trace as a possible source a cluster of ageing stars that was closer to us at the time than presently, and contains no more massive stars, suggesting that those who were going to explode already have.

The supernova remnant in the photo is some 160,000 light years away in our satellite galaxy, the Large Magellanic cloud, visible in the Southern hemisphere as a hazy unmoving smudge to the south of the plane of our galaxy (known as the Milky Way). The feature is now 23 light years across some 400 years after exploding, and expanding at 8,000km per second. The image is a combination of visible light and xray data (the greens and blues towards the centre, representing the radiation of tenuous gas heated to millions of degrees Celcius).

Loz

Image credit: X-ray: NASA/CXC/SAO/J.Hughes et al, Optical: NASA/ESA/Hubble Heritage Team.

http://bit.ly/1q6LSGq http://bit.ly/1VaZywS Information on the supernova in the photo: http://bit.ly/1oxkWi6 Original paper, free access: http://bit.ly/1NkiXno Second paper, free access: http://bit.ly/1WcMaYN

Why Are So Many American Barns Red?

If we start at the beginning then we need to talk about star birth. Not just any star, and not a living star; these stars (note the plural) have been dead for probably billions of years. But while they were living they did some pretty incredible things. Most importantly to our topic, they made iron.

When a star is born it's just a big ball of gas. There are some light elements floating in space that cluster together due to gravity, pulling each other in until they fuse, transforming hydrogen into the heavier element helium, for instance. These heavier elements are also floating around, but because of their weight they huddle a little closer (again due to gravity). As they do so, the temperature and the pressure inside the star continues to increase until they, too, fuse, forming an even heavier element. And the cycle continues.

This happens in all stars until a very specific threshold is reached. Stars don't create elements with more than 56 nucleons (or a total of protons and neutrons). Why? Because at this point there needs to be a net input of energy to create newer, heavier elements, energy which the sun just doesn't give. What is the most stable element with 56 nucleons? Iron. Stars produce more iron than anything else, and therefore iron is super abundant.

What on earth does all this star stuff have to do with red barn paint? Red paint is made from red ochre (Fe2O3), or anhydrous iron oxide. This is the stuff that makes the red paint red, thanks mainly to the way iron absorbs and reflects light. Because there is so much iron in the universe (and probably beyond) and therefore on earth, red ochre is extremely cheap, making the paint relatively cheap. And who wants to paint a cow barn with expensive paint?

In a delicious twist of fate, one of the more common adornments on American barns is the “barnstar”, considered a “lucky omen” similar to a horseshoe over a doorway.

Further reading: http://www.smithsonianmag.com/smart-news/barns-are-painted-red-because-of-the-physics-of-dying-stars-58185724/?no-ist

Picture credit: Dave Smith https://www.flickr.com/photos/skimerlin/

-Colter