Tag Archives: particles

Laser system

Physical constant is constant even in strong gravitational fields

An international team of physicists has shown that the mass ratio between protons and electrons is the same in weak and in very strong gravitational fields. Their study, which was partly funded by the FOM Foundation, is published online on 18 September 2014 in Physical Review Letters.


The idea that the laws of physics and its fundamental constants do not depend on local circumstances is called the equivalence principle. This principle is a cornerstone to Einstein’s theory of general relativity. To put the principle to the test, FOM physicists working at the LaserLaB at VU University Amsterdam determined whether one fundamental constant, the mass ratio between protons and electrons, depends on the strength of the gravitational field that the particles are in. Laser system

Laboratories on earth and in space 
The researchers compared the proton-electron mass ratio near the surface of a white dwarf star to the mass ratio in a laboratory on Earth. White dwarfs stars, which are in a late stage of their life cycle, have collapsed to less than one percent of their original size. The gravitational field at the surface of these stars is therefore much larger than that on earth, by a factor of 10,000. The physicists concluded that even these strong gravitational conditions, the proton-electron mass ratio is the same within a margin of 0.005 percent. In both cases, the proton mass is 1836.152672 times as big as the electron mass . 

Absorption spectra 
To reach their conclusion, the Dutch physicists collaborated with astronomers of the University of Leicester, the University of Cambridge and the Swinburne University of Technology in Melbourne. The team analysed absorption spectra of hydrogen molecules in white dwarf photospheres (the outer shell of a star from which light is radiated). The spectra were then compared to spectra obtained with a laser at LaserLaB in Amsterdam. 

Absorption spectra reveal which radiation frequencies are absorbed by a particle. A small deviation of the proton-electron mass ration would affect the structure of the molecule, and therefore the absorption spectrum as well. However, the comparison revealed that the spectra were very similar, which proves that the value of the proton-electron mass ratio is indeed independent of the strength of the gravitation field. 

Rock-solid 
FOM PhD student Julija Bagdonaite: “Previously, we confirmed the constancy of this fundamental constant on a cosmological time scale with the Very Large Telescope in Chile. Now we searched for a dependence on strong gravitational fields using the Hubble Space Telescope. Gradually we find that the fundamental constants seem to be rock-solid and eternal.”

Contact information Prof.dr. Wim Ubachs, LaserLaB VU University Amsterdam, +31 (0)20 598 79 48

Images The astronomical spectra were recorded with the Cosmic Origins Spectrograph (COS) aboard the Hubble Space Telescope. For a picture of the COS, please visit the NASA website.

Reference Limits on a Gravitational field Dependence of the Proton-to-Electron Mass Ratio from H2 in White Dwarf Stars, Physical Review Letters, 18 September 2014.
Paper on ArXiv.  

Source: FOM

The largest interstellar dust track found in the Stardust aerogel collectors was this 35 micron-long hole produced by a 3 picogram speck of dust that was probably traveling so fast that it vaporized upon impact. The other two likely interstellar dust grains were traveling more slowly and remained in
Image Credit: UC Berkeley/Andrew Westphal.

Stardust Team Reports Discovery of First Potential Interstellar Space Particles

Seven rare, microscopic interstellar dust particles that date to the beginnings of the solar system are among the samples collected by scientists who have been studying the payload from NASA’s Stardust spacecraft since its return to Earth in 2006. If confirmed, these particles would be the first samples of contemporary interstellar dust.

A team of scientists has been combing through the spacecraft’s aerogel and aluminum foil dust collectors since Stardust returned in 2006.The seven particles probably came from outside our solar system, perhaps created in a supernova explosion millions of years ago and altered by exposure to the extreme space environment.

The largest interstellar dust track found in the Stardust aerogel collectors was this 35 micron-long hole produced by a 3 picogram mote that was probably traveling so fast that it vaporized upon impact. The other two likely interstellar dust grains were traveling more slowly and remained intact after a soft landing in the aerogel. Image Credit: Andrew Westphal, UC Berkeley
The largest interstellar dust track found in the Stardust aerogel collectors was this 35 micron-long hole produced by a 3 picogram mote that was probably traveling so fast that it vaporized upon impact. The other two likely interstellar dust grains were traveling more slowly and remained intact after a soft landing in the aerogel.
Image Credit: Andrew Westphal, UC Berkeley

The research report appears in the Aug. 15 issue of the journal Science. Twelve other papers about the particles will appear next week in the journal Meteoritics & Planetary Science.

“These are the most challenging objects we will ever have in the lab for study, and it is a triumph that we have made as much progress in their analysis as we have,” said Michael Zolensky, curator of the Stardust laboratory at NASA’s Johnson Space Center in Houston and coauthor of the Science paper.

Stardust was launched in 1999 and returned to Earth on Jan. 15, 2006, at the Utah Test and Training Range, 80 miles west of Salt Lake City. The Stardust Sample Return Canister was transported to a curatorial facility at Johnson where the Stardust collectors remain preserved and protected for scientific study.

Inside the canister, a tennis racket-like sample collector tray captured the particles in silica aerogel as the spacecraft flew within 149 miles of a comet in January 2004. An opposite side of the tray holds interstellar dust particles captured by the spacecraft during its seven-year, three-billion-mile journey.

Scientists caution that additional tests must be done before they can say definitively that these are pieces of debris from interstellar space. But if they are, the particles could help explain the origin and evolution of interstellar dust.

The particles are much more diverse in terms of chemical composition and structure than scientists expected. The smaller particles differ greatly from the larger ones and appear to have varying histories. Many of the larger particles have been described as having a fluffy structure, similar to a snowflake.

The largest interstellar dust track found in the Stardust aerogel collectors was this 35 micron-long hole produced by a 3 picogram speck of dust that was probably traveling so fast that it vaporized upon impact. The other two likely interstellar dust grains were traveling more slowly and remained in Image Credit: UC Berkeley/Andrew Westphal.
The largest interstellar dust track found in the Stardust aerogel collectors was this 35 micron-long hole produced by a 3 picogram speck of dust that was probably traveling so fast that it vaporized upon impact. The other two likely interstellar dust grains were traveling more slowly and remained in
Image Credit: UC Berkeley/Andrew Westphal.

Two particles, each only about two microns (thousandths of a millimeter) in diameter, were isolated after their tracks were discovered by a group of citizen scientists. These volunteers, who call themselves “Dusters,” scanned more than a million images as part of a University of California, Berkeley, citizen-science project, which proved critical to finding these needles in a haystack.

A third track, following the direction of the wind during flight, was left by a particle that apparently was moving so fast — more than 10 miles per second (15 kilometers per second) — that it vaporized. Volunteers identified tracks left by another 29 particles that were determined to have been kicked out of the spacecraft into the collectors.

Four of the particles reported in Science were found in aluminum foils between tiles on the collector tray. Although the foils were not originally planned as dust collection surfaces, an international team led by physicist Rhonda Stroud of the Naval Research Laboratory searched the foils and identified four pits lined with material composed of elements that fit the profile of interstellar dust particles.

Three of these four particles, just a few tenths of a micron across, contained sulfur compounds, which some astronomers have argued do not occur in interstellar dust. A preliminary examination team plans to continue analysis of the remaining 95 percent of the foils to possibly find enough particles to understand the variety and origins of interstellar dust.

Supernovas, red giants and other evolved stars produce interstellar dust and generate heavy elements like carbon, nitrogen and oxygen necessary for life. Two particles, dubbed Orion and Hylabrook, will undergo further tests to determine their oxygen isotope quantities, which could provide even stronger evidence for their extrasolar origin.

Scientists at Johnson have scanned half the panels at various depths and turned these scans into movies, which were then posted online, where the Dusters could access the footage to search for particle tracks.

Once several Dusters tag a likely track, Andrew Westphal, lead author of the Science article, and his team verify the identifications. In the one million frames scanned so far, each a half-millimeter square, Dusters have found 69 tracks, while Westphal has found two. Thirty-one of these were extracted along with surrounding aerogel by scientists at Johnson and shipped to UC Berkeley to be analyzed.

NASA’s Jet Propulsion Laboratory, Pasadena, California, manages the Stardust mission for NASA’s Science Mission Directorate, Washington. Lockheed Martin Space Systems, Denver, developed and operated the spacecraft.