Very High Energy Cosmic Gamma Rays Detected

China’s Large High Altitude Air Shower Observatory (LHAASO) has detected two photons with energies exceeding 1 peta-electron-volt (quadrillion electron-volts or PeV).  The photon at 1.4 PeV is the highest energy photon ever observed. The largest accelerator on Earth (LHC at CERN) can only accelerate particles to 0.01 PeV.

Aerial photograph of LHAASO

When a very high-energy particle strikes Earth’s atmosphere, it triggers a cascade of secondary particles. Ground-based detectors such as LHAASO record these air shower events and can then reconstruct the type, energy and trajectory of the primary particles.  Two of the photons detected from the Crab Nebular by LHAASO are the highest energy photons ever detected from the Crab Nebula: one at 0.88 PeV other at 1.1 PeV.

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Voyager 1 Spacecraft still talking to Earth after 40 years in Space and from 17 billion km away

The Voyager 1 spacecraft now at the immense distance of 18.5 billion kilometers (145 AU) from earth.  In 2017, thrusters were operated by NASA to adjust the orientation of the spacecraft; the signal from the spacecraft took 19 hours and 35 minutes to reach an antenna in Goldstone, California.

Voyager 2 launched on August 20, 1977, from Cape Canaveral, Florida aboard a Titan-Centaur rocket. On September 5, Voyager 1 launched, also from Cape Canaveral aboard a Titan-Centaur rocket.

The twin Voyager 1 and 2 spacecraft are exploring where nothing from Earth has flown before. Continuing on their more-than-39-year journey since their 1977 launches, they each are more that twice as far from Earth and the sun than Pluto.

Nuclear Power Plants Under Construction

As of March 2021, the World Nuclear Association lists 54 power reactors under construction where the first concrete for reactor has been poured.  Construction on five of these is currently suspended: Angra 3 (Brazil); Ohma 1 and Shimane 3 (Japan); Khmelnitski 3&4 (Ukraine) [World Nuclear Association 28 Mar 2021].

Of the remaining 49 power reactors under construction:

      • 1 is a 25 MWe small Pressurised Water Reactor (PWR) being built in Argentina,
      • 1 is a 211 MWe High Temperature Pebble Bed reactor (HTR-PM) being built in China,
      • 1 is a 500 MWe Fast Breeder Reactor (FBR) being built in India,
      • 2 are 600 MWe Fast Reactors (CFR-600) being built in China,
      • 3 are 700 MWe Pressurised Heavy Water Reactors (PHWR-700) being built in India,
      • 2 are 471 MWe pressurised water reactors (VVER-440) being built in Slovakia, and
      • 39 are larger pressurised water reactor between 1000 and 1720 MWe being built in 14 countries. 

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Natural Radioactivity and Background Radiation

Background radiation is a natural part of the environment. The largest source of background radiation exposure comes from the natural radioactivity in rocks and soil and the inhalation of naturally occurring radon that seeps from the ground into our buildings. We are also exposed to cosmic radiation and the natural radioactivity in food and in the body.

On average, Australians are exposed to about 1.5 mSv each year from natural sources, although for some the dose might be more than double that. On average, we also receive about 1.7 mSv per year from medical diagnoses and treatment. Continue reading “Natural Radioactivity and Background Radiation”

Black holes and neutron star collisions

The recent observations of gravitational waves from cosmic events opens a dramatic new window on the universe (first in 2015).  The first four events observed by gravitational waves were colliding black holes with masses between 7.5 and 35 solar masses. As black holes do not emit any radiation, there is no electromagnet radiation from the resultant black holes although the actual collision produces a gamma ray pulse which has been detected for one of the events. The amount of energy radiated away as gravitational energy from these black hole collisions is immense: between 1 and 3 solar masses of energy emitted in a short time of order or less than 100 seconds.

Even more interesting in terms of observations was the GW170817 event (published on 16 Oct 2017) which was caused by the collision of two neutron stars approximately 130 million years ago.  Continue reading “Black holes and neutron star collisions”

The Black Hole at the Centre of the Milky Way Galaxy

Recent observations by the W. M Keck Telescopes have provided clear evidence for the existence of a supermassive black hole at the centre of our Milky Way galaxy.  Because of dust, the galactic centre cannot be seen at visible, ultraviolet or soft x-rays wavelengths, but the W. M. Keck Telescopes have obtained incredible images of the stars and gas clouds at the centre of our Milky Way galaxy using infrared optics. Continue reading “The Black Hole at the Centre of the Milky Way Galaxy”