Astro Bob blog: Gamma rays in thunderstorms? Say it ain't so!Scientists have discovered brief gamma ray flashes in thunderstorms that might pose a concern for air travelers. See the latest closeup photo of one of the biggest stars in the sky.
By: Bob King, Duluth News Tribune
Gamma rays in thunderstorms? Say it ain't so!
Lightning over Toulouse, France. Credit: Sebastien D'arco
TGF -- a new abbreviation of Thank God it's Friday? No actually. TGFs are terrestrial gamma ray flashes and the most powerful, newly-discovered form of energy on Earth. They're produced in thunderstorms and were discovered by accident by the orbiting Fermi Gamma-ray telescope used to study black holes and dark matter.
The blasts are extremely short -- only one or two milliseconds long -- but they occur near the tops of thunderclouds and may pose a threat to airline travelers. If one occurred near a plane, passengers would be exposed to 400 chest X-rays worth of radiation. The chances of getting a charge like that are very small because pilots typically avoid flying through thunderstorms because of their other destructive effects like fierce winds, hail and lightning.
The electromagnetic spectrum includes every kind of light from radio waves, which can be as large as buildings to small waves of visible light (the rainbow) to minute but energy-acked gamma rays. Like X-rays, gamma rays are invisible but can cause damage to our cells if we're exposed to high levels. Illustration: NASA
Scientists still don't know if the TGFs aim their energy upward from the cloudtops (safe for airplanes) or if they also travel downward (not so safe). It's a whole new field of study and a great example of how a new instrument like the Fermi telescope, intented to study objects far away, led to unanticipated discoveries much closer to home. If you'd like to read more about TGFs, please click HERE.
Betelgeuse in Orion is one of biggest, brightest stars around which is why it was the first star ever to have its size measured. The huge red supergiant star is 600 times bigger than the sun and radiates about 100,000 times more energy. If you were to put Betelgeuse in the sun's place, it would cover nearly the entire sky -- 300 degrees worth! We'd actually be orbiting inside the star -- a very bad place for a planet to be.
Recently, an international team of astronomers combined images from three separate telescopes in Arizona in a technique called interferometry to produce a single, super-high resolution image of the star released last month (at left). The photo shows two hot spots each about the size of Earth-sun distance or 93 million miles. They're huge bubbles of hot gas welling up from below the star's surface like bubbles in boiling water or in piping hot oatmeal. When a gas or liquid is heated, it expands, becomes buoyant and rises. When it reaches a cooler region, the material releases its heat and sinks back down only to be reheated and rise again. This cyclic rising and sinking is called convection.
We see convection at work in our own sun as it transports energy from the interior of the star to the surface. Stars create energy inside their cores through the fusion of hydrogen into helium, essentially a controlled thermonuclear bomb. From there, the energy radiates outward until it reaches the convective zone.
A sunspot in a sea of solar granules or convective cells boiling up on the sun's surface. Credit: NASA
In the sun, that zone is about 2/3 of the way from the core to the surface. Large columns and bubbles of starstuff (mostly hydrogen) rise to the surface in the convective zone, dump some of their heat and light, cool and sink back down again to be reheated. We see these bubbles as small granules through a properly filtered telescope. They look like rice grains and each is about the size of the state of Texas. Granules come and go in a matter of minutes.
The convection bubbles on Betelgeuse are enormous compared to those on the sun, but it's awesome to look at another star so far away and find the same process at work there as in the sun and even in that pot of morning oatmeal.
Betelgeuse (BET-l-jooz) is easy to find just to the upper left of Orion's three belt stars. This map shows the sky as you face south around 8 o'clock. Created with Stellarium