Tag Archives: Fermi

Six New Millisecond Pulsars Discovered

Some of the most precise clocks in the universe are not clocks at all they are fastly-rotating pulsars, which can be more accurate than atomic clocks. They are so precise that they can be used to test the most sophisticated physics theories to a staggering precision, so astronomers are always looking for more of them.

And last week, using the Fermi Large Area Telescopes (LAT), an international team of astronomers wasable to discover six brand newmillisecond pulsars. The discovery was possible by following up the Fermi detection with radio observations at the Arecibotelescope in Puerto Rico.

Millisecond pulsars (MSP) are neutron stars that spin on their axis at an extremelyhigh velocity. Sometimes, pulsars have companion stars, and during their orbits the pulsar starts absorbing material from the companion, quite literally sucking the life out of them. Due to the conservation of angular momentum, the infalling material can give a boost to the pulsar that speeds it up, and it can end up rotating hundreds of times per second.

In a paper published online on Arxiv, the researchers detailed the rotational period of these objects, with the fastest spinning every 1.99 milliseconds and the slowest every 4.66 milliseconds.Although theyre all fast, there is much variation among the six objects. So the researchers divided them into three groups.

There were three MSPs categorized as black widows, where the pulsar has stolen almost all the mass from the companion, which is now just a degenerate mass object weighing less than 10 percentof the Suns mass. Two pulsars were redback,a term that describes pulsars eclipsed by the large outflows from the companion star. The last object has a more classical white dwarf companion.

Fermi has detected over 1,000 unidentified sources of gamma-rays, and the researchers think that some of those sources could be more MSPs. Of the 230 millisecond pulsars (MSPs) currently known in the Galactic disk, 30% have been discovered in previously unidentified sources of gamma rays detected by the Fermi LAT instrument the team noted in the paper.

While only around 10% of all known pulsars rotate at millisecond rates, MSPs make up half of all pulsars observed to emit gamma rays

Read more: http://www.iflscience.com/space/six-new-millisecond-pulsars-discovered

Most Convincing Evidence Yet For Dark Matter Detection

Scientists have been analyzing high-energy gamma rays originating from the center of the Milky Way and have presented the most convincing case so far that at least some of this may come from dark matter.

Dark matter is a type of matter that is thought to account for apparent effects due to mass where no mass can be observed. It behaves differently to normal matter, such as planets and stars, which only accounts for approximately 5% of the universe. It neither emits nor absorbs light or other forms of electromagnetic energy, so a simple definition is that it is matter that does not react to light. The total mass-energy of the known universe is estimated to contain approximately 27% dark matter.

Using data collected from NASA’s Fermi Gamma-ray Space Telescope, scientists from different institutions generated maps of the center of the galaxy. They found that some of the high-energy gamma rays could not be sufficiently explained by known sources. There are numerous known sources of gamma-rays in the center of the galaxy, such as supernova remnants, but it is also predicted to be rich in dark matter. Although scientists know dark matter exists, they are not entirely sure of what it is composed of. Weakly Interacting Massive Particles, or WIMPs, are a strong candidate. It is thought that collision of WIMPs may produce a quickly decaying particle, which could produce gamma rays detectable by Fermi.

Once they removed all the known sources of gamma rays from the Fermi observations, some emission was leftover. If dark matter particles with a particular mass are destroying each other, this would be a remarkable fit for the remaining emission. Despite this, the scientists err on the side of caution since alternative sources may still exist. Further sightings are also required to make this interpretation more convincing.

The Fermi scientists have also turned elsewhere in an attempt to detect dark matter by looking at dwarf galaxies orbiting the Milky Way. Dwarf galaxies are rich in dark matter and lack other types of gamma-ray sources present in the center of the Milky Way which make detection of dark matter problematic. On the flip side, their distance from us and the fact that the dark matter present is still considerably less than that in the center of the Milky Way means that the signals are weak. But according to Elliott Bloom, a member of the Fermi collaboration, “If we ultimately see a significant signal, it could be a very strong confirmation of the dark matter signal claimed in the galactic center.”

While at this stage the signal cannot be confirmed or refuted as dark matter, it represents an exciting step towards the detection of dark matter at the galactic center. 

Check out this YouTube video for an image of the Milky Way with the gamma-ray map from NASA’s Fermi superimposed on top. 

Credit: NASA Goddard; A. Mellinger, CMU; T. Linden, University of Chicago

Read more: http://www.iflscience.com/space/most-convincing-evidence-yet-dark-matter-detection