Scientists Narrow Down Dark Matter's Mass

Physicists have set the most precise limit yet on the mass of dark matter, the mysterious and elusive stuff that is thought to make up 98 percent of all matter in the universe and nearly a quarter of its total mass.

The researchers used data from NASA's Fermi Gamma-ray Space Telescope to set parameters on the mass of dark matter particles by calculating the rate at which they appear to collide with their antimatter partners and annihilate each other in galaxies that orbit our own Milky Way.

Savvas Koushiappas, an assistant professor in the department of physics at Brown University, and graduate student Alex Geringer-Sameth found that dark matter particles must have a mass greater than 40 giga-electron volts (GeV) — approximately 42 times the mass of a proton.

"What we find is if a particle's mass is less than 40 GeV, then it cannot be the dark matter particle," Koushiappas said in a statement.

The details of the study will be published in the Dec. 1 issue of the journal Physical Review Letters.

Casting doubt on previous findings

The results throw into question recent findings from underground experiments that reported thepotential detection of dark matter, the researchers said.

These experiments claimed to have found dark matter particles with masses ranging from 7 to 12 GeV, which is significantly less than the limit determined by the new study. [Twisted Physics: 7 Mind-Blowing Findings]

Dark matter is invisible, and scientists have long tried in vain to directly detect the mysterious particles. But since dark matter has mass, its presence is inferred based on the gravitational pull it exerts on regular matter.

But it's more complicated than that. In the 1920s, astronomer Edwin Hubble discovered that the universe is not static, but is expanding. More than 70 years later, observations from the Hubble Space Telescope, which was named for the astronomer, found that the universe was expanding at a much more rapid pace than it was earlier.

Cosmologists think a mysterious force called dark energy is behind this puzzling acceleration. Dark energy, like dark matter, has not been directly detected, but it is thought to be the force pulling the cosmos apart at ever-increasing speeds.

"If, for the sake of argument, a dark matter particle's mass is less than 40 GeV, it means the amount of dark matter in the universe today would be so much that the universe would not be expanding at the accelerated rate we observe," Koushiappas said.

Our complicated universe

Dark energy is thought to make up 73 percent of the total mass and energy in the universe. Dark matter accounts for 23 percent, which leaves only 4 percent of the universe composed of the regular matter that can be seen, such as stars, planets, galaxies and people.

But because neither dark matter nor dark energy has been directly detected, they remain unproven concepts.

In at least one respect, dark matter is thought to behave like normal matter: When a dark matter particle meets its matching antimatter partner, they should destroy each other. Antimatter is a sibling to normal matter; an antimatter partner particle is thought to exist for each matter particle, with the same mass but opposite charge.

Scientists suspect that dark matter is made of particles called WIMPs ("weakly interacting massive particles"). When a WIMP and its anti-particle collide, they should annihilate one another.

To examine the mass of dark matter, Koushiappas and Geringer-Sameth essentially reversed the process of annihilation. The researchers observed seven dwarf galaxies that are thought to be full of dark matter because the motion of the stars within them cannot be fully explained by their mass alone.

Since these dwarf galaxies also contain much less hydrogen gas and other regular matter, they help paint a clearer picture of dark matter and its effects, Koushiappas said.

The physicists worked backward using data from the last three years that was collected by the Fermi telescope, which observes the universe in high-energy gamma-ray light. By measuring the number of light particles, called photons, in the galaxies, the scientists calculated backward to deduce how often particles called quarks are produced, which are products of the WIMP-anti-WIMP annihilation reaction.

This enabled the physicists to establish limits on the mass of dark matter particles and the rate at which they annihilate.

"This is a very exciting time in the dark matter search, because many experimental tools are finally catching up to long-standing theories about what dark matter actually is," Geringer-Sameth said in a statement. "We are starting to really put these theories to the test."

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Is Phobos-Grunt Dead? Troubled Russian Probe Still Unresponsive

The European Space Agency announced today (Dec. 2) that it will stop trying to contact the beleaguered Russian Phobos-Grunt spacecraft, which has been stuck in the wrong orbit for almost a month now.
Russia's Phobos-Grunt probe launched Nov. 8 on a mission to collect and return samples from Mars' moon Phobos. But the spacecraft's thrusters malfunctioned shortly after launch, leaving it stuck in a low orbit around Earth rather than on a course for the Red Planet.
A signal from Phobos-Grunt was picked up last week by a European tracking station located in Australia, and since then, the European Space Agency (ESA) has been helping Russia's Federal Space Agency with efforts to rescue the troubled probe.
However, all subsequent attempts to call Phobos-Grunt have failed to make contact, and ESA announced today that it will cease trying.
"In consultation and agreement with Phobos-Grunt mission managers, ESA engineers will end tracking support today," agency officials said in a statement. "Efforts in the past week to send commands to and receive data from the Russian Mars mission via ESA ground stations have not succeeded; no response has been seen from the satellite." [Photos: Russia's Mars Moon Mission]
The agency had attempted to send instructions to the spacecraft to boost its orbit, but officials reported that these commands went unanswered.
Russian officials were unable to decipher the information that was received from ESA's Australian ground station from the probe. While some data received by a Russian station in Baikonour, Kazakhstan reportedly indicated the spacecraft's radio equipment was operational, efforts to regain contact with Phobos-Grunt have failed.
Ultimately, ESA engineers say they have not completely given up hope for Phobos-Grunt. While the chances to save the marooned spacecraft appear to be dwindling, agency officials maintained their willingness to help if needed.
"ESA teams remain available to assist the Phobos-Grunt mission if indicated by any change in situation," officials said in an update posted on ESA's website.
Yet, time is quickly running out to save the $165 million mission, and Russian officials remain tight-lipped about the status of their rescue efforts. The window of opportunity for the probe to reach the Martian moon has closed already, since the journey requires Earth and Mars to be properly aligned.
If control cannot be regained of the spacecraft, scientists have predicted that Phobos-Grunt could fall back to Earth as a piece of space debris sometime in mid-January.
The ambitious Russian mission was designed to study Phobos and return rocks from the Martian moon to Earth in 2014. Phobos-Grunt is the 19th spacecraft Russia has launched toward Mars since 1960. To date, none has achieved full mission success.

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Two Elements Named: Livermorium and Flerovium

Chemistry's periodic table can now welcome livermorium and flerovium, two newly named elements, which were announced Thursday (Dec. 1) by the International Union of Pure and Applied Chemistry. The new names will undergo a five-month public comment period before the official paperwork gets processed and they show up on the table.
Three other new elements just recently finished this process, filling in the 110, 111 and 112 spots.
All five of these elements are so large and unstable they can be made only in the lab, and they fall apart into other elements very quickly. Not much is known about these elements, since they aren't stable enough to do experiments on and are not found in nature. They are called "super heavy," or Transuranium, elements.
The newly named elements fit in the 114 and 116 spots, down in the lower-right corner of the periodic table, and were officially accepted to the periodic table back in June. They originally were synthesized more than 10 years ago, after which repeat experiments led to their confirmation.
Elements 113, 115, 117 and 118 have also been synthesized at Russia's Joint Institute for Nuclear Research, located in Dubna, Russia (about two hours drive from Moscow), but their creation hasn't been confirmed by the International Union yet. Once they have been confirmed, they will also have to go through the naming and public-commenting periods.
Both livermorium and flerovium were also synthesized at the same Russian lab, where Russian researchers were working with American researchers from the Lawrence Livermore National Laboratory in California.
Element 114, previously known as ununquadium, has been named flerovium (Fl), after the Russian institute's Flerov Laboratory of Nuclear Reactions founder, which similarly is named in honor of Georgiy Flerov (1913-1990), a Russian physicist. Flerov's work and his writings to Joseph Stalin led to the development of the USSR's atomic bomb project.
The researchers got their first glimpse at flerovium after firing calcium ions at a plutonium target.
Element 116, which was temporarily named ununhexium, almost ended up with the name moscovium in honor of the region (called an oblast, similar to a province or state) of Moscow, where the research labs are located. In the end, it seems the American researchers won out and the team settled on the name livermorium (Lv), after the national labs and the city of Livermore in which they are located. Livermorium was first observed in 2000, when the scientists created it by mashing together calcium and curium.
"Proposing these names for the elements honors not only the individual contributions of scientists from these laboratories to the fields of nuclear science, heavy-element research, and super-heavy-element research, but also the phenomenal cooperation and collaboration that has occurred between scientists at these two locations," Bill Goldstein, associate director of Lawrence Livermore National Labs' Physical and Life Sciences Directorate, said in a statement.
The names for the next batch of super-heavy atoms is still up for grabs, perhaps moscovium will make a comeback.

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