Astronomy Now Home
Home Magazine Resources Store

On Sale Now!



The October 2014 issue of Astronomy Now is on sale! Order direct from our store (free 1st class post & to UK addresses). The Astronomy Now iPad/iPhone editions are now available worldwide on the App Store.



Top Stories



Earthshine used to test life detection method
...By imagining the Earth as an exoplanet, scientists observing our planet's reflected light on the Moon with ESO's Very Large Telescope have demonstrated a way to detect life on other worlds...
  READ MORE

Solid buckyballs discovered in space
...Astronomers using NASA’s Spitzer Space Telescope have detected a particular type of molecule, given the nickname “buckyball”, in a solid form for the first time...
  READ MORE

Steamy water-world gets the Hubble treatment
...Hubble Space Telescope observations of a 7 Earth-mass planet find an unusual water-rich world swathed in a thick, steamy atmosphere...
  READ MORE








Tycho’s star lives on
in gamma rays

DR EMILY BALDWIN
ASTRONOMY NOW
Posted: 14 December 2011


Bookmark and Share

Using the Fermi Gamma-Ray Space Telescope, astronomers have found that the shattered remains of the 1572 supernova event known as ‘Tycho’s supernova’ live on in high-energy gamma rays, providing vital insight into the generation of cosmic rays.

Tycho’s supernova is named after the Danish astronomer Tycho Brahe, who studied the exploded stellar remains extensively when the bright ‘star’ appeared in the skies in 1572. Now, after several years of data collection using the space-based Fermi satellite’s Large Area Telescope (LAT), astronomers have detected high energy gamma rays emanating from the supernova, providing clues into the origin of cosmic rays – subatomic particles that move through space at nearly the speed of light. Where and how cosmic rays gain their high energies is much debated; their sources are not readily identifiable since their paths are easily deflected by stellar magnetic fields. Clues can be found by studying high-energy gamma rays, however, which can be produced when cosmic rays strike interstellar gas and starlight.

“This detection gives us another piece of evidence supporting the notion that supernova remnants can accelerate cosmic rays,” says Stefan Funk of the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) and a co-author on the paper describing the results in the 7 December edition of The Astrophysical Journal Letters.


Gamma-rays detected by Fermi's LAT show that the remnant of Tycho's supernova shines brightly in gamma rays (magenta). This image also shows data in X-rays (yellow, green, and blue), infrared (red) and optical data. Image: Gamma ray, NASA/DOE/Fermi LAT Collaboration; X-ray, NASA/CXC/SAO; Infrared, NASA/JPL-Caltech; Optical, MPIA, Calar Alto, O. Krause et al. and DSS.

A supernova explosion marks the death of a massive star once its fuel supply has been exhausted, and its remnants form a rapidly expanding shell of hot gas bounded by a shock wave created in the blast. Magnetic fields either side of the shock front are thought to be able to trap particles between them, and they gain energy as they ‘ping-pong’ back and forth across the shock front. Eventually they break out of the remnant and perhaps collide with an onlooking space satellite’s detectors, such as Fermi’s LAT, which revealed a region of billion electron volt gamma-ray emission in Tycho’s supernova remnant (for comparison, the energy of visible light is 2-3 electron volts).

“We knew that Tycho’s supernova remnant could be an important find for Fermi because this object has been so extensively studied in other parts of the electromagnetic spectrum,” says Keith Bechtol, a KIPAC graduate student and one of the first researchers to notice the potential link. “We thought it might be one of our best opportunities to identify a spectral signature indicating the presence of cosmic-ray protons.”

The team’s interpretation of the LAT observations – combined with additional data from ground-based facilities and with radio and X-ray data – imply that a process called pion production best explains the high energy emission. In this process, a proton traveling close to the speed of light strikes a slower-moving proton, creating an unstable, lower-mass particle called a pion, which almost immediately decays into a pair of gamma rays. Applied to Tycho’s star, somewhere within the remnant, protons are being rapidly accelerated and then interacting with slower particles to produce gamma rays.

"The gamma-ray energies reflect the energies of the accelerated particles that produce them, and we expect more cosmic rays to be accelerated to higher energies in younger objects [like Tycho’s supernova remnant] because the shockwaves and their tangled magnetic fields are stronger," adds Funk.

The Planets
From tiny Mercury to distant Neptune and Pluto, The Planets profiles each of the Solar System's members in depth, featuring the latest imagery from space missions. The tallest mountains, the deepest canyons, the strongest winds, raging atmospheric storms, terrain studded with craters and vast worlds of ice are just some of the sights you'll see on this 100-page tour of the planets.
 GET YOUR COPY

Hubble Reborn
Hubble Reborn takes the reader on a journey through the Universe with spectacular full-colour pictures of galaxies, nebulae, planets and stars as seen through Hubble's eyes, along the way telling the dramatic story of the space telescope, including interviews with key scientists and astronauts.
 GET YOUR COPY

3D Universe
Witness the most awesome sights of the Universe as they were meant to be seen in this 100-page extravaganza of planets, galaxies and star-scapes, all in 3D!
 GET YOUR COPY


HOME | NEWS ARCHIVE | MAGAZINE | SOLAR SYSTEM | SKY CHART | RESOURCES | STORE | SPACEFLIGHT NOW

© 2014 Pole Star Publications Ltd.