When astronomers refer to the temperature of a star, they are talking about the temperature of the gases in the photosphere, and they express those temperatures on the Kelvin temperature scale. On this scale, zero degrees Kelvin (written 0 K) is absolute zero (2273.2°C or 2459.7°F), the temperature at which an object contains no thermal energy that can be extracted. Water freezes at 273 K and boils at 373 K (at sea-level atmospheric pressure). The Kelvin temperature scale is useful in astronomy because it is based on absolute zero and consequently is related directly to the motion of the particles in an object.
Now you can understand why a hot object glows, or to put it another way, why a hot object emits photons, bundles of electromagnetic energy. The hotter an object is, the more motion there is among its particles. The agitated particles, including electrons, collide with each other, and when electrons accelerate—change their motion—part of the energy is carried away as electromagnetic radiation. The radiation emitted by a heated object is called black-body radiation, a name translated from a German term that refers to the way a perfectly opaque object would behave. A perfectly opaque object would be both a perfectly efficient absorber and a perfectly efficient emitter of radiation. At room temperature, such a perfect absorber and emitter would look black, but at higher temperatures it would glow at wavelengths visible to a human eye. That explains why in astronomy and physics contexts you will see the term black-body referring to objects that glow brightly.
Black-body radiation is quite common. In fact, it is responsible for the light emitted by an incandescent light bulb. Electricity flowing through the filament of the bulb heats it to high temperature, and it glows. You can also recognize the light emitted by hot lava as black-body radiation. Many objects in the sky, including the sun and other stars, primarily emit black-body radiation because they are mostly opaque.
Gif credit: caucasianmale
In September 2012, hundreds of amateur and professional photographers had the rare opportunity to explore and photograph accelerators and detectors at particle physics laboratories around the world.
The top 39 photographs from the Photowalk, including the six winners of the jury and “people’s choice” competitions, are now viewable online.
“The worldwide opening of the physics laboratories for the Photowalk has been an excellent opportunity for showing the real places of physics research,” says Antonio Zoccoli, a member of the executive board at the Italian Institute for Nuclear Physics. “The Photowalk tells us that scientific research is a global enterprise, which brings together intelligence, resources and technologies from different countries toward a common goal.
The Large Hadron Collider
It’s super-massive and recently discovered something analogous to the Higgs-Boson, without which… nothing would *matter*. But in these detailed shots, even the $4 billion science-making uber-magnet can vogue it up a little for the cameras. Oh yes, LHC, yes, the cam-er-a loves you. Yeah baby.
One final shot I had to include, because this configuration of buttons actually exists:
— Richard Feynman
Image: Scientists assemble the endcap for the ATLAS experiment, one of the LHC’s two main experiments. Peter Ginter/CERN
Exploring the Universe with gamma rays
The last decade has witnessed the birth of a new field of astronomy – Very High Energy (VHE) gamma ray astronomy – expanding wavelength coverage of astronomical instruments by another 10 octaves towards the highest energy radiation. These gamma rays are produced when high energy cosmic rays bump into interstellar gas, creating a bunch of elementary particles. Unlike charged cosmic rays, the gamma rays travel on a straight path and point back to the point in the sky where they were produced. Apart from serving as tracers of cosmic rays, speculation is that some VHE 6.2 Exploring the Universe with gamma rays gamma rays may result from decays of relic particles with have survived since the Big Bang, such as the mysterious dark matter particles; detection of such gamma rays would give first hints towards the nature of dark matter.
Very High Energy gamma rays are absorbed in the Earth’s atmosphere, creating a cascade of secondary elementary particles, most of which never reach the ground. Satellite instruments such as AGILE and Fermi (the former GLAST), now in orbit, detect gamma-rays before they enter the atmosphere, but their size is too small to capture enough of the highest-energy gamma rays.
After long development, a ground-based detection technique pioneered by the American Whipple telescope and perfected by the European-led H.E.S.S. and MAGIC instruments has brought a break-through: Imaging Atmospheric Cherenkov telescopes. These telescopes collect and image the bluish light emitted by the particle cascades created by a VHE gamma ray in the atmosphere. Light from a single VHE gamma ray illuminates a “light pool” of about 150 m radius on the ground, hence a single telescope will detect gamma rays incident upon an area of a few 10000 m2, compared to the sub-m2 area of satellite detectors. Latest generation Cherenkov telescope systems use multiple telescopes to provide stereoscopic viewing of gamma-ray induced particle cascades, for improved determination of impact direction and energy of a gamma-ray.
VHE gamma-ray astronomy is becoming part of mainstream astronomy, with surveys of the Galaxy revealing dozens of VHE gamma-ray emitting cosmic-ray accelerators. Objects discovered include supernova remnants, binary systems, pulsars, stellar associations and different species of active galaxies, hosting super-massive black holes at their centres.
— Werner Heisenberg
Captured by Swiss photographer Fabian Oefner in his project Millefiori, the iron particles start to rearrange, forming black channels and separating the watercolours from the ferrofluid, creating these technicolour structures that look like psychedelic planets or trippy cells under a microscope.