Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

NASA's Fermi shows that Tycho's star shines in gamma rays

14.12.2011
In early November 1572, observers on Earth witnessed the appearance of a "new star" in the constellation Cassiopeia, an event now recognized as the brightest naked-eye supernova in more than 400 years.

It's often called "Tycho's supernova" after the great Danish astronomer Tycho Brahe, who gained renown for his extensive study of the object. Now, years of data collected by NASA's Fermi Gamma-Ray Space Telescope reveal that the shattered star's remains shine in high-energy gamma rays.


Gamma-rays detected by Fermi's LAT show that the remnant of Tycho's supernova shines in the highest-energy form of light. This portrait of the shattered star includes gamma rays (magenta), X-rays (yellow, green, and blue), infrared (red) and optical data. Credit: (Credit: 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)

The detection gives astronomers another clue in understanding the origin of cosmic rays, subatomic particles -- mainly protons -- that move through space at nearly the speed of light. Exactly where and how these particles attain such incredible energies has been a long-standing mystery because charged particles speeding through the galaxy are easily deflected by interstellar magnetic fields. This makes it impossible to track cosmic rays back to their sources.

"Fortunately, high-energy gamma rays are produced when cosmic rays strike interstellar gas and starlight. These gamma rays come to Fermi straight from their sources," said Francesco Giordano at the University of Bari and the National Institute of Nuclear Physics in Italy. He is the lead author of a paper describing the findings in the Dec. 7 edition of The Astrophysical Journal Letters.

Better understanding the origins of cosmic rays is one of Fermi's key goals. Its Large Area Telescope (LAT) scans the entire sky every three hours, gradually building up an ever-deeper view of the gamma-ray sky. Because gamma rays are the most energetic and penetrating form of light, they serve as signposts for the particle acceleration that gives rise to cosmic rays.

"This detection gives us another piece of evidence supporting the notion that supernova remnants can accelerate cosmic rays," said co-author Stefan Funk, an astrophysicist at the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC), jointly located at SLAC National Accelerator Laboratory and Stanford University, Calif.

In 1949, physicist Enrico Fermi -- the satellite's namesake -- suggested that the highest-energy cosmic rays were accelerated in the magnetic fields of interstellar gas clouds. In the decades that followed, astronomers showed that supernova remnants may be the galaxy's best candidate sites for this process.

When a star explodes, it is transformed into a supernova remnant, a rapidly expanding shell of hot gas bounded by the blast's shockwave. Scientists expect that magnetic fields on either side of the shock front can trap particles between them in what amounts to a subatomic pingpong game.

"A supernova remnant's magnetic fields are very weak relative to Earth's, but they extend across a vast region, ultimately spanning thousands of light-years. They have a major influence on the course of charged particles," said co-author Melitta Naumann-Godo at Paris Diderot University and the Atomic Energy Commission in Saclay, France, who led the study with Giordano.

As they shuttle back and forth across the supernova shock, the charged particles gain energy with each traverse. Eventually they break out of their magnetic confinement, escaping the supernova remnant and freely roaming the galaxy.

The LAT's ongoing sky survey provides additional evidence favoring this scenario. Many younger remnants, like Tycho's, tend to produce more high-energy gamma rays than older remnants. "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 because the shockwaves and their tangled magnetic fields are stronger," Funk added. By contrast, older remnants with weaker shockwaves cannot retain the highest-energy particles, and the LAT does not detect gamma rays with corresponding energies.

The supernova of 1572 was one of the great watersheds in the history of astronomy. The star blazed forth at a time when the starry sky was regarded as a fixed and unchanging part of the universe. Tycho's candid account of his own discovery of the strange star gives a sense of how radical an event it was.

The supernova first appeared around Nov. 6, but poor weather kept it from Tycho until Nov. 11, when he noticed it during a walk before dinner. "When I had satisfied myself that no star of that kind had ever shone forth before, I was led into such perplexity by the unbelievability of the thing that I began to doubt the faith of my own eyes, and so, turning to the servants who were accompanying me, I asked them whether they too could see a certain extremely bright star…. They immediately replied with one voice that they saw it completely and that it was extremely bright," he recalled.

The supernova remained visible for 15 months and exhibited no movement in the heavens, indicating that it was located far beyond the sun, moon and planets. Modern astronomers estimate that the remnant lies between 9,000 and 11,000 light-years away.

After more than two and a half years of scanning the sky, LAT data clearly show that an unresolved region of GeV (billion electron volt) gamma-ray emission is associated with the remnant of Tycho's supernova. (For comparison, the energy of visible light is between about 2 and 3 electron volts.)

Keith Bechtol, a KIPAC graduate student who is also based at SLAC, was one of the first researchers to notice the potential link. "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. We thought it might be one of our best opportunities to identify a spectral signature indicating the presence of cosmic-ray protons," he said.

The science team's model of the emission is based on LAT observations, along with higher-energy TeV (trillion electron volt) gamma rays mapped by ground-based facilities and radio and X-ray data. The researchers conclude that a process called pion production best explains the emission. First, a proton traveling close to the speed of light strikes a slower-moving proton. This interaction creates an unstable particle -- a pion -- with only 14 percent of the proton's mass. In just 10 millionths of a billionth of a second, the pion decays into a pair of gamma rays.

If this interpretation is correct, then somewhere within the remnant, protons are being accelerated to near the speed of light, and then interacting with slower particles to produce gamma rays, the most extreme form of light. With such unbelievable goings-on in what's left of his "unbelievable" star, it's easy to imagine that Tycho Brahe himself might be pleased.

Francis Reddy | EurekAlert!
Further information:
http://www.nasa.gov

More articles from Physics and Astronomy:

nachricht New survey hints at exotic origin for the Cold Spot
26.04.2017 | Royal Astronomical Society

nachricht NASA's Fermi catches gamma-ray flashes from tropical storms
25.04.2017 | NASA/Goddard Space Flight Center

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Making lightweight construction suitable for series production

More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.

Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...

Im Focus: Wonder material? Novel nanotube structure strengthens thin films for flexible electronics

Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.

"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

7th International Conference on Crystalline Silicon Photovoltaics in Freiburg on April 3-5, 2017

03.04.2017 | Event News

 
Latest News

Link Discovered between Immune System, Brain Structure and Memory

26.04.2017 | Life Sciences

New survey hints at exotic origin for the Cold Spot

26.04.2017 | Physics and Astronomy

NASA examines newly formed Tropical Depression 3W in 3-D

26.04.2017 | Earth Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>