David Kirkpatrick

October 29, 2009

Einstein-1, physicist detractors-0

I’ll let this release speak, so to speak, for itself:

Gamma-ray photon race ends in dead heat; Einstein wins this round

IMAGE: In this illustration, one photon (purple) carries a million times the energy of another (yellow). Some theorists predict travel delays for higher-energy photons, which interact more strongly with the proposed…

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Racing across the universe for the last 7.3 billion years, two gamma-ray photons arrived at NASA’s orbiting Fermi Gamma-ray Space Telescope within nine-tenths of a second of one another. The dead-heat finish may stoke the fires of debate among physicists over Einstein’s special theory of relativity because one of the photons possessed a million times more energy than the other.

For Einstein’s theory, that’s no problem. In his vision of the structure of space and time, unified as space-time, all forms of electromagnetic radiation – gamma rays, radio waves, infrared, visible light and X-rays – are reckoned to travel through the vacuum of space at the same speed, no matter how energetic. But in some of the new theories of gravity, space-time is considered to have a “shifting, frothy structure” when viewed at a scale trillions of times smaller than an electron. Some of those models predict that such a foamy texture ought to slow down the higher-energy gamma-ray photon relative to the lower energy one. Clearly, it did not.

Even in the world of high-energy particle physics, where a minute deviation can sometimes make a massive difference, nine-tenths of a second spread over more than 7 billion years is so small that the difference is likely due to the detailed processes of the gamma-ray burst rather than confirming any modification of Einstein’s ideas.

“This measurement eliminates any approach to a new theory of gravity that predicts a strong energy-dependent change in the speed of light,” said Peter Michelson, professor of physics at Stanford University and principal investigator for Fermi’s Large Area Telescope (LAT), which detected the gamma-ray photons on May 10. “To one part in 100 million billion, these two photons traveled at the same speed. Einstein still rules.”

Michelson is one of the authors of a paper that details the research, published online Oct. 28 by Nature.

Physicists have yearned for years to develop a unifying theory of how the universe works. But no one has been able to come up with one that brings all four of the fundamental forces in the universe into one tent. The Standard Model of particle physics, which was well developed by the end of the 1970s, is considered to have succeeded in unifying three of the four: electromagnetism; the “strong force” (which holds nuclei together inside atoms); and the “weak force” (which is responsible for radioactive decay, among other things.) But in the Standard Model, gravity has always been the odd man out, never quite fitting in. Though a host of theories have been advanced, none has been shown successful.

But by the same token, Einstein’s theories of relativity also fail to unify the four forces.

“Physicists would like to replace Einstein’s vision of gravity – as expressed in his relativity theories – with something that handles all fundamental forces,” Michelson said. “There are many ideas, but few ways to test them.”

The two photons provided rare experimental evidence about the structure of space-time. Whether the evidence will prove sufficient to settle any debates remains to be seen.

The photons were launched on their pan-galactic marathon during a short gamma-ray burst, an outpouring of radiation likely generated by the collision of two neutron stars, the densest known objects in the universe.

A neutron star is created when a massive star collapses in on itself in an explosion called a supernova. The neutron star forms in the core as matter is compressed to the point where it is typically about 10 miles in diameter, yet contains more mass than our sun. When two such dense objects collide, the energy released in a gamma-ray burst can be millions of times brighter than the entire Milky Way, albeit only briefly. The burst (designated GRB 090510) that sent the two photons on their way lasted 2.1 seconds.

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NASA’s Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership, developed in collaboration with the U.S. Department of Energy, along with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.

March 11, 2009

NASA’s Fermi Telescope and the gamma-ray sky

Cool and interesting release from NASA on its Fermi Telescope and mapping gamma rays.

The release from today:

NASA’s Fermi Telescope Reveals Best-Ever View of the Gamma-Ray Sky

GREENBELT, Md., March 11 /PRNewswire-USNewswire/ — A new map combining nearly three months of data from NASA’s Fermi Gamma-ray Space Telescope is giving astronomers an unprecedented look at the high-energy cosmos. To Fermi’s eyes, the universe is ablaze with gamma rays from sources ranging from within the solar system to galaxies billions of light-years away.

(Logo: http://www.newscom.com/cgi-bin/prnh/20081007/38461LOGO)

“Fermi has given us a deeper and better-resolved view of the gamma-ray sky than any previous space mission,” said Peter Michelson, the lead scientist for the spacecraft’s Large Area Telescope (LAT) at Stanford University, Calif. “We’re watching flares from supermassive black holes in distant galaxies and seeing pulsars, high-mass binary systems, and even a globular cluster in our own.”

A paper describing the 205 brightest sources the LAT sees has been submitted to The Astrophysical Journal Supplement. “This is the mission’s first major science product, and it’s a big step toward producing our first source catalog later this year,” said David Thompson, a Fermi deputy project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md.

The LAT scans the entire sky every three hours when operating in survey mode, which is occupying most of the telescope’s observing time during Fermi’s first year of operations. These snapshots let scientists monitor rapidly changing sources.

The all-sky image released today shows us how the cosmos would look if our eyes could detect radiation 150 million times more energetic than visible light. The view merges LAT observations spanning 87 days, from August 4 to October 30, 2008.

The map includes one object familiar to everyone: the sun. “Because the sun appears to move against the background sky, it produces a faint arc across the upper right of the map,” Michelson explained. During the next few years, as solar activity increases, scientists expect the sun to produce growing numbers of high-energy flares. “No other instrument will be able to observe solar flares in the LAT’s energy range,” he said.

To better show individual sources, the new map was processed to suppress emissions from gas in the plane of our galaxy, the Milky Way. As a way of underscoring the variety of the objects the LAT is seeing, the Fermi team created a “top ten” list comprising five sources within the Milky Way and five beyond our galaxy.

The top sources within our galaxy include the sun; a star system known as LSI +61 303, which pairs a massive normal star with a superdense neutron star; PSR J1836+5925, which is one of many new pulsars, a type of spinning neutron star that emits gamma-ray beams; and the globular cluster 47 Tucanae, a sphere of ancient stars 15,000 light-years away.

Top extragalactic sources include NGC 1275, a galaxy that lies 225 million light-years away and is known for intense radio emissions; the dramatically flaring active galaxies 3C 454.3 and PKS 1502+106, both more than 6 billion light-years away; and PKS 0727-115, which is thought to be a type of active galaxy called a quasar.

The Fermi top ten also includes two sources — one within the Milky Way plane and one beyond it — that researchers have yet to identify. More than 30 of the brightest gamma-ray sources have no obvious counterparts at other wavelengths. “That’s good news. It means we’re seeing new objects,” Michelson said. “It also means that we have lots of work to do.”

NASA’s Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership mission, developed in collaboration with the U.S. Department of Energy and important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden, and the U.S.

For images related to this release and the top ten LAT sources, please visit:

http://www.nasa.gov/mission_pages/GLAST/news/gammaray_best.html

For more information about the Fermi Gamma-ray Space Telescope, please visit:

http://www.nasa.gov/fermi

Photo:  http://www.newscom.com/cgi-bin/prnh/20081007/38461LOGO
AP Archive:  http://photoarchive.ap.org/
PRN Photo Desk photodesk@prnewswire.com
Source: NASA
   

Web Site:  http://www.nasa.gov/