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Milky Way's Super-efficient Particle Accelerators Caught in The Act

For Release: June 26, 2009


RCW 86
Credit: Optical: ESO/E. Helder; X-ray: NASA/CXC/Univ. of Utrecht/J.Vink et al.
Press Image and Caption

Thanks to a unique "ballistic study" that combines data from ESO's Very Large Telescope and NASA's Chandra X-ray Observatory, astronomers have now solved a long-standing mystery of the Milky Way's particle accelerators. They show in a paper published today on Science Express that cosmic rays from our galaxy are very efficiently accelerated in the remnants of exploded stars.

During the Apollo flights astronauts reported seeing odd flashes of light, visible even with their eyes closed. We have since learnt that the cause was cosmic rays - extremely energetic particles from outside the Solar System arriving at the Earth, and constantly bombarding its atmosphere. Once they reach Earth, they still have sufficient energy to cause glitches in electronic components.

Galactic cosmic rays come from sources inside our home galaxy, the Milky Way, and consist mostly of protons moving at close to the speed of light, the "ultimate speed limit" in the Universe. These protons have been accelerated to energies exceeding by far the energies that even CERN's Large Hadron Collider will be able to achieve.

"It has long been thought that the super-accelerators that produce these cosmic rays in the Milky Way are the expanding envelopes created by exploded stars, but our observations reveal the smoking gun that proves it", says Eveline Helder from the Astronomical Institute Utrecht of Utrecht University in the Netherlands, the first author of the new study.

"You could even say that we have now confirmed the calibre of the gun used to accelerate cosmic rays to their tremendous energies", adds collaborator Jacco Vink, also from the Astronomical Institute Utrecht.

For the first time Helder, Vink and colleagues have come up with a measurement that solves the long-standing astronomical quandary of whether or not stellar explosions produce enough accelerated particles to explain the number of cosmic rays that hit the Earth's atmosphere. The team's study indicates that they indeed do and it directly tells us how much energy is removed from the shocked gas in the stellar explosion and used to accelerate particles.

"When a star explodes in what we call a supernova a large part of the explosion energy is used for accelerating some particles up to extremely high energies", says Helder. "The energy that is used for particle acceleration is at the expense of heating the gas, which is therefore much colder than theory predicts".

The researchers looked at the remnant of a star that exploded in AD 185, as recorded by Chinese astronomers. The remnant, called RCW 86, is located about 8200 light-years away towards the constellation of Circinus (the Drawing Compass). It is probably the oldest record of the explosion of a star.

Using ESO's Very Large Telescope, the team measured the temperature of the gas right behind the shock wave created by the stellar explosion. They measured the speed of the shock wave as well, using images taken with NASA's X-ray Observatory Chandra three years apart. They found it to be moving at between 10 and 30 million km/h, between 1 and 3 percent the speed of light.

The temperature of the gas turned out to be 30 million degrees Celsius. This is quite hot compared to everyday standards, but much lower than expected, given the measured shock wave's velocity. This should have heated the gas up to at least half a billion degrees.

"The missing energy is what drives the cosmic rays", concludes Vink.

More information, including images and other multimedia, can be found at:

Visitor Comments (11)

This is the coolest site, keep so.

Posted by Mieng on Saturday, 10.10.09 @ 21:45pm

Good evening,
As far as I can see the space is more beautiful than our planet. Maybe one day the Earth will become as beautiful and peaceful as the space.
Goodbye and thank you for all you are doing for mankind.

Posted by simonetta maria angelica on Friday, 07.10.09 @ 15:11pm

I recently read about a supernova explosion from the death of a massive star and I'm extremely curious to how long it takes for these planets to form? Also, I read that the carbon emitted from these are the reason we have bones that among other things. This heavy element enriched gas will be incorporated into future generations of stars and planets. Without supernova the fiery death of massive stars there would be no carbon oxygen or other elements that make life possible ( big bang theory).

Posted by Allyson on Wednesday, 07.8.09 @ 14:52pm

Very cool results, excellent science. I'm curious about how it was determined that the supernova affected cosmic rays observed here on earth? If the shockwave travels between 1 and 3 percent of the speed of light and the explosion was first observed about 2250 years ago, it should have affected the cosmic rays here from about 1940 to 1980. Were cosmic ray observations being recorded with enough accuracy back then to form a reasonable correlation? Or is my math off.

Posted by David Guidos on Tuesday, 07.7.09 @ 11:01am

Oh my god, I was interested in astronomy and space researches in magazines and books which I could get here in Egypt what a difficulty. Now I am online with the very up-to-date well explained matter immediately from your and other telescopes sites. Thank you my friends and waiting for more revolutionary theories and views.

Posted by Salah abo elenin on Sunday, 07.5.09 @ 17:21pm

I take advance of this opportunity to give you my congratulations and tell you that my spirituality feel a firm ground when I realize about the creator of all this marvelous. God is unique, never the man could be able to understand all.

Posted by Edgar Samuel Ortiz Ch on Sunday, 07.5.09 @ 09:04am

That’s fabulous really scintillating.
Unfortunate part is that these type of seller facts remind us that how insignificant still we are when we talk about the exploration of this universe.

Posted by Sarwar Tipu on Friday, 07.3.09 @ 23:46pm

You provide an excellent service sharing information with the general public. We appreciate your efforts. Keep up the good work.

Posted by Doris Smart on Thursday, 07.2.09 @ 19:13pm

Thanks a lot Chandra, for helping us understanding more the cosmological phenomena and the mysteries of astrophysics. Best regards to all of you.

Posted by Angela on Thursday, 07.2.09 @ 11:36am

I am always interested in cosmological phenomena. Chandra is doing a fantastic job.
Thanks and congratulations. I am looking forward to new discoveries.

Posted by A M Qureshi on Thursday, 07.2.09 @ 09:18am

As a layman, I am a retired mechanical Engineer, your site helps in understanding the mysteries of astrophysics. To me without having to dwell deep into the theories I get an understanding of the stellar events. Thank you. May you keep progressing and my best wishes to your team.

Posted by AK Sharma on Wednesday, 07.1.09 @ 23:28pm